With the fast development and wide application of remote sensing technology, remote sensing images with higher quality are needed. However, it is difficult to directly acquire high-resolution, multispectral remote sensing images. To obtain high-quality images by integrating the information from different imaging sensors, pansharpening technology emerged. Pansharpening is an effective method used to obtain multispectral images with high spatial resolution. Many scholars have studied this method and obtained fruitful achievements. In recent years, deep learning theory has developed rapidly and has been widely applied in pansharpening. This study aims to systematically introduce the progress in pansharpening and promote its development. To this end, this study first introduced the traditional, classical pansharpening methods, followed by commonly used remote sensing satellites. Then, this study elaborated on the pansharpening methods based on deep learning from the perspective of supervised learning, unsupervised learning, and semi-supervised learning. After that, it described and analyzed loss functions. To demonstrate the superiority of the pansharpening methods based on deep learning and analyze the effects of loss functions, this study conducted remote sensing image fusion experiments. Finally, this study presented the future prospects of the pansharpening methods based on deep learning.
Water color represents the most intuitive visible perception of the color of water bodies that is jointly affected by substances such as suspended particulate matter, chlorophyll, and soluble organic matter. Water color is a water environmental parameter with a long history and plays a critical role in research on the ecosystem of inland and nearshore water bodies. With the progress made in colorimetric research, as well as hyperspectral imaging and satellite remote sensing techniques, the colorimetric method of water color has developed. This study systematically reviewed the colorimetric research progress of inland and nearshore water bodies and elaborated on the theories and practical applications of the colorimetric method from the angles of apparent optical properties (AOP) and inherent optical properties (IOP). Moreover, it presented the colorimetric processing method of satellite remote sensing data. The colorimetric method is a technical method for the quantitative expression of water color. It is also an important branch of water color research and an extension and supplement to the study of water color components, with a broad application prospect. To further improve the application of the colorimetric methods in inland and nearshore water bodies, it is necessary to enhance the construction of bio-optical datasets of water bodies in the future. Moreover, colorimetric studies should be conducted in two dimensions, namely AOP and IOP, and it is necessary to intensify research on domestic satellite-based colorimetric methods and increase the types of relevant water color products.
With the trend towards the precise and digital planting management of orchards, apple cultivation relies more heavily on the planting management supporting technologies of orchards. In recent years, continuous breakthroughs made in spatial resolution and revisiting frequency have made remote sensing technology a major supporting technology for the precise planting management of apple orchards. However, there is an absence of reviews of the application status and prospect of this technology in the planting management of orchards. Based on the analysis of primary applications of remote sensing technology in the precise planting management of apple orchards, this study classified the applications into three major categories, namely the surveys of basic orchard information, inversions of orchard parameters, and the planting management support of orchards. Furthermore, this study reviewed the methods and performance of the applications of remote sensing technology in various fields and explored the application potential. Finally, it identified three types of problems with current research and application of remote sensing technology, namely insufficient studies on mechanisms and in some application fields, low-degree integration of multiple technologies, and the lack of large-scale application models. In addition, this study proposed four hot research and application topics in the future, namely models used to simulate the growth mechanisms of apple trees, the integrated support system for the planting management of apple trees, the single-tree monitoring based on satellite data, and the diversified services of remote sensing-based monitoring products.
The remote sensing-based feature extraction of opencast mining areas is a hot topic in research on the monitoring of mining activities. However, there is a lack of systematic reviews and summaries of relevant studies. Therefore, this study first defined the features of an opencast mining area, divided the feature extraction into single- and multi-feature extractions according to feature types, and briefly described the differences between the feature extraction of opencast mining areas and general surface feature extraction and land use classification. Then, this study briefly summarized the sources and data processing platforms of remote sensing images available in relevant studies. Subsequently, this study divided the remote sensing-based methods for the feature extraction of opencast mining areas into three categories, namely visual interpretation, traditional feature-based approach, and deep learning. Then, it summarized the research status of these methods and analyzed their advantages, disadvantages, and applicability. Finally, this study proposed the future research direction of the remote sensing-based feature extraction of opencast mining areas, holding that the future developmental trend is to further promote the intelligent, fine-scale, and robust feature extraction of mining areas by effectively utilizing multi-source and multi-temporal data, networks with a stronger feature extraction capacity, and methods for the optimization of complex scenes. The results of this study can be used as a reference for the study and application of remote sensing-based feature extraction of opencast mining areas.
As an essential branch of surveying and mapping science, underwater topographic surveys are closely related to human operations in oceans and lakes. For underwater topography detection in shallow-water areas, conventional acoustic methods face the hull stranding risk, and passive optical methods have low survey accuracy. The airborne laser sounding is a novel means for bathymetric surveys in shallow-water areas, and its application in offshore areas can fill the gap of underwater topography data in shallow-water areas. This study presents a brief introduction to the composition and principle of the airborne laser sounding system, followed by a description of laser sounding data acquisition. Furthermore, this study highlights the critical processing technologies for airborne laser sounding data, including waveform data processing, error correction, and point cloud data processing. Finally, this study summarizes the technical difficulties and developmental trends of airborne laser sounding.
Mangrove forests are periodically inundated by tidal water. This characteristic opens up an opportunity but also poses a challenge for the information extraction of mangrove forests using remote sensing technology. To explore the contribution of the red-edge band of GF-6 satellite data in information extraction of mangrove forests under the condition of random tides, this study investigated the southeastern Dongzhaigang area-the largest mangrove forest area in Hainan Province and obtained standard samples using the GF-2 satellite data. The reflectance spectral curves of typical surface features were constructed based on the standard samples and the GF-6 satellite data. Then, a baseline was established based on the bands strongly absorbed by vegetation, and the intertidal mangrove forest index (IMFI) applicable to the GF-6 satellite data was defined using the average reflectance of bands above the baseline. Meanwhile, the red-edge normalized difference vegetation index (RENDVI) was also established. The two indices were compared with commonly used indices, such as the normalized difference vegetation index (NDVI) and the normalized difference water index (NDWI), using box-whisker plots. Then, using the decision tree model constructed based on IMFI and RENDVI, information on typical mangrove forest in the study area were extracted. The precision of the extraction results was verified through comparison with visual interpretation results of the samples extracted from the GF-2 satellite data. The results show that: ① Because mangrove forests are periodically inundated by tidal water, the reflectance spectral curves of intertidal mangrove forests were relatively scattered between the standard spectral curves of water bodies and mangrove forests; ② IMFI and RENDVI can reflect the differences in the reflectance spectra of the red-edge and near-infrared bands and thus effectively separated the intertidal mangrove forests, mangrove forests, and water bodies; ③ The decision tree model constructed based on IMFI and RENDVI can effectively extract the distribution information of the mangrove forests, with an overall accuracy of 0.95 and a Kappa coefficient of 0.90. The introduction of the red-edge band plays an important role in the information extraction of mangrove forests and has great potential for application. This study can be used as a reference for the ecological applications of red-edge data from domestic satellites.
Targeting the subtropical climate characteristics of the Guangdong-Hong Kong-Macao Greater Bay Area, this study acquired the images of the experimental area from the TerraSAR-X Radar remote sensing satellite. Given the varying scale of the surface feature targets in the Radar satellite observation scenes, this study proposed an ENet convolution spatial pyramid pooling module (ENet-CSPP) model for surface feature classification. Since ordinary convolution can more effectively maintain domain information than atrous convolution, this study proposed a multi-scale feature fusion module based on convolution spatial pyramid pooling. Since there were a few training samples in the SAR remote sensing image dataset, this study combined the multi-scale feature fusion module with the lightweight convolutional neural network. The encoder of the ENet-CSPP network consisted of an improved ENet network and the convolution spatial pyramid pooling module. The decoder output surface feature classification images after the fusion of deep and shallow features. The quantitative comparison experiments were conducted on the GDUT-Nansha dataset. The ENet-CSPP model outperformed other models in three performance indices, namely pixel accuracy, average pixel accuracy, and mean intersection over union. This result indicates that the multi-scale lightweight model effectively improved the accuracy of surface feature classification.
Multi-scale segmentation is a key step in the information extraction of high-resolution remote sensing images. However, the evaluation of segmentation quality and the quantification of segmentation errors are still challenging. Based on boundary strength information, this study developed an unsupervised segmentation evaluation method of selecting the optimal scale parameter and elevating the local segmentation quality for multi-scale remote sensing image segmentation. Segmentation errors include over-segmentation and under-segmentation. This study modeled the two types of errors using normalized boundary gradient characteristics. The gradient information of patch edges was considered in the estimation of over-segmentation errors, while the intra-patch gradients were employed for the assessment of under-segmentation errors. To validate the proposed method, this study conducted an experiment on the evaluation of multi-scale segmentation results using two scenes of high-resolution remote sensing images. The segmentation evaluation results of the method coincided perfectly with the actual segmentation effects. The results indicate that the method proposed in this study can effectively reflect over- and under-segmentation errors.
Net ecosystem productivity (NEP) represents the carbon sequestration capacity of a regional ecosystem. Based on the Google Earth Engine (GEE) platform, this study analyzed the temporal and spatial variations in the NEP of the Three-River Headwaters Region (TRHR) from 2001 to 2020 based on the Moderate Resolution Imaging Spectrometer (MODIS) and meteorological data and revealed their relationships with climate factors. The results are as follows: ① The TRHR had an important carbon sink function, with carbon sink areas accounting for 99.89%; The carbon source areas in the TRHR were primarily distributed in the northwest, accounting for only 0.11%. The NEP of the TRHR decreased gradually from the southeast to the northwest and differed significantly among different ecological areas; ② The NEP of the TRHR showed an upward trend overall in the past 20 years, with an annual increasing rate of 1.13 gC/(m2·a), indicating huge carbon sequestration potential; ③ The area of zones whose NEP showed an upward trend accounted for 95.05% of the total area. Ecological engineering construction significantly improved the NEP of vegetation. As a result, the carbon sink function gradually increased and was highly stable; ④ The TRHR had an annual average NEP of 120.93 gC/(m2·a), and the NEP was positively correlated with the annual precipitation but negatively correlated with average annual temperature and annual solar radiation. The warm, humid climate and the ecological engineering construction contributed to the carbon sink function of vegetation in the TRHR. This is of great significance for improving the carbon sink value of the terrestrial ecosystem and achieving the peak carbon dioxide emissions and carbon neutrality of China.
A rational land use plan is of great significance for avoiding high carbon emissions. The simulations of land use optimization from the perspective of low-carbon economy are conducive to the development of green economy and the scientific allocation of land resources. Taking Beijing as an example, this study incorporated the points of interest (POI) into the BP-ANN algorithm module of the FLUS model and verified the simulation accuracy of the improved model through comparison using the land use data of 2010 and 2020. On this basis, by coupling the Markov method and the order preference by similarity ideal solution (TOPSIS) method, this study simulated and analyzed the structure and spatial layout of land quantity in the study area in 2030 under the natural evolution scenario and the low-carbon economy scenario. The results show that: ① Compared with those of the original FLUS model, the Kappa coefficient and the overall accuracy of the improved model by incorporating POI data increased by 4.85% and 3.42%, respectively. These results indicate that the improved model had higher simulation accuracy. ② The simulation results verified that, under the natural evolution scenario, the carbon emission and the land for construction would increase by 7.70% and 7.68%, respectively, and the areas of farmland and grassland would continue to decline. ③ Under the low-carbon economy scenario, the carbon emissions would be reduced by 198.49×104 t, the continuous expansion trend of construction land would be curbed, the occupation of grassland in low mountainous areas would be mitigated, and the area of forest land in the north would increase significantly. The results show that the simulation accuracy of the land use model would change with urban development elements and that the incorporation of POI data helped to provide more effective decision support for land planning. The low-carbon economy-oriented land structure adjustment and spatial layout optimization can be used as a reference for the rational use, planning, and layout of regional lands.
The current dead tree detection primarily relies on manual field surveys and, thus, is limited by forest topography, suffers a low detection efficiency, and is dangerous. Given these problems, this study proposed a YOLOv4-tiny dead tree detection algorithm based on the attention mechanism and spatial pyramid pooling (SPP) and improved the original detection model. First, the SPP structure was introduced after the Backbone part of the model to combine local and global features and enrich the feature representation capability of the model. Then, the original activation function LeakyReLU in the model was replaced with ELU, which made the activation function saturate unilaterally, thus improving the convergence and robustness of the model. Finally, the attention mechanism ECANet was introduced into the model to enhance the capacity of the network to learn important information in images, thus improving the performance of the network. The images of trees in a mountain forest of a scenic area in southern Liaoning were collected using an unmanned aerial vehicle (UAV). Then, dead trees in these images were detected using different models. The detection results show that the improved algorithm had a detection accuracy of 93.25%, which was improved by 9.58%, 12.57%, 10.54%, and 4.87% than that of the YOLOv4-tiny, YOLOv4, and SSD algorithms and an algorithm stated in literature , respectively, and achieved the effective detection of dead trees.
Nearshore monitoring covers natural environments and human activities. High-accuracy identification of nearshore monitoring targets significantly influences the healthy development of the marine economy, the ecological protection of marine environments, and the prevention and mitigation of marine disasters. The nearshore monitoring targets feature multiple types, diverse sizes, and uncertainty. The existing identification models suffer low accuracy, low efficiency, and severe omission of small targets. This study proposed an identification model (Re-YOLOX) for nearshore monitoring targets by improving YOLOX using a learnable image resizer model (the Resizer model). First, the model training was intensified using the Resizer model to improve the feature learning and expression abilities and the recall rate of the Re-YOLOX model. Then, the feature pyramid fusion structure of the YOLOX algorithm was improved to reduce the omission of small targets in the identification. With the nearshore video data from UAV monitoring as the data set and cars, ships, and piles as monitoring targets, this study compared the Re-YOLOX model with other models, including CenterNet, Faster R-CNN, YOLOv3, and YOLOX. The results show that the Re-YOLOX model yielded a mean average precision of 94.23%, a mean recall of 91.99%, and a mean F1 score of 89.67%, all of which were higher than those of the other models. In summary, the Re-YOLOX model can improve the target identification accuracy while ensuring target identification efficiency, thus providing technical support for managing nearshore seas.
Given the land surface types and atmospheric features of the Heihe River basin, this study calculated the surface emissivity of the study area using the ASTER Global Emissivity Database and the vegetation cover method (VCM) and estimated the atmospheric water vapor content using the improved multilayer feed-forward neural network (MFNN). Moreover, by establishing the coefficient lookup table of input parameter groups, this study developed an ASTER data-based split-window algorithm for the remote sensing inversion of land surface temperature. To validate the applicability and accuracy of the split-window algorithm, this study elevated the algorithm using the measured site data on the land surface temperature of the Heihe River basin in 2019 and MODIS instruments. Compared with the site data, the results of the split-window algorithm had root mean square errors of 1.81~3.01 K. In the cross-validation using the MODIS instruments, the split-window algorithm had relatively small errors and deviations, with root mean square errors of 1.11~1.75 K. Overall, the accuracy of the land surface temperature obtained from the inversion using the split-window algorithm can meet the needs of meteorological and climatological studies. Moreover, the development philosophy of the split-window algorithm can be used as a reference for similar thermal infrared sensors.
The rapid detection of soil salinity using remote sensing technology can scientifically guide the soil salinization control and the rational development of oasis agriculture. Based on 95 soil samples from the oasis of the Weigan-Kuqa River delta, this study established four soil salinity estimation models of multiple linear regression, partial least squares regression (PLSR), support vector machine regression (SVR), and random forest regression using the spectral index, band reflectance, and the measured soil salinity. Then, it conducted the remote sensing inversion for the spatial distribution pattern of the soil salinity in the study area using the optimal estimation results. The results are as follows: ① Nine spectral factors that were significantly related to soil salinity were screened using the all-subsets regression method, with correlation coefficients of all above 0.5 (P < 0.01). Among them, the correlation coefficient between salinity index SI-T and the soil salinity was the highest (0.648); ② The comparison of estimation precision show that the fitting effect of the four inversion models was in the order of random forest regression > SVR > PLSR > multiple linear regression. Among these models, the random forest model had the best fitting precision. Its training and validation sets had coefficients of determination(R2) of 0.870 and 0.766, respectively, with relative percent deviation (RPD) of 2.792 and 2.105, respectively, both of which were greater than 2. These results indicate that the random forest model had a good inversion effect and stable estimation capacity; ③ According to the inversion results of the random forest model, grade I and II zones account for 41.62% and are distributed in the cultivated land area inside the oasis; grade III, IV, and V zones account for 56.41% and are primarily distributed in the desert and the desert-oasis ecotones. Therefore, compared with conventional statistical models, the random forest modeling method can yield significantly better estimation effects in the inversion of soil salinity. This study can be used as a reference for the monitoring of soil salinization in oases in arid areas.
The Hadamengou gold deposit in Baotou City, Inner Mongolia is an important large gold deposit in the Wulashan-Daqingshan metallogenic belt, with great prospecting potential. To give full play to remote sensing technology in geological prospecting, this study extracted the mineralization alteration information of the Hadamengou gold deposit from remote sensing data of different satellites. Based on the spectral characteristics of alteration minerals in the mining area, this study proposed a comprehensive processing method that extracted iron staining information from the Landsat8 OLI and WorldView-3 data, hydroxyl information from the ASTER and WorldView-3 data, and carbonation information from the ASTER data through principal component analysis. As a result, two alteration zones were delineated based on the distribution patterns of alteration anomalies and the geological map analysis of the mining area. By combining the study results of the ore-controlling structures, it is believed that the metallogenic hydrothermal processes of the Hadamengou gold deposit were closely related to structures. This study can provide a reference for the prospecting for the same type of gold deposits in the Wulashan-Daqingshan metallogenic belt and can guide the peripheral prospecting of the Hadamengou gold deposit.
Earthquake-induced landslides are unnegligible secondary earthquake disasters and tend to cause severe casualties and property loss. Remote sensing identification of earthquake-induced landslides is an important means of the investigation and assessment of post-earthquake disasters. With GF-1 remote sensing images as a data source, this study identified the earthquake-induced landslides in the Xiongmaohai area in Jiuzhaigou using the object-oriented classification method. Specifically, the rule set for hierarchical identification of earthquake-induced landslides was constructed based on multi-scale segmentation and multi-conditional threshold classification. The aim is to fully utilize the features of ground objects, reduce the mixing of ground objects with similar spectra, and improve the identification precision of landslides. The identification results show that about 2.18 km2 of landslide area was extracted near the Xiongmaohai scenic spot, with a general identification accuracy of up to 98.11%. Therefore, the method proposed in this study can quickly identify earthquake-induced landslides, with high identification accuracy and applicable identification rules, and, thus, can be used as a reference and basis for the emergency investigation and rapid loss assessment of post-earthquake disasters.
High-resolution meteorological data serve as an important data basis for fine-scale meteorological services. Using the hourly 2-meter air temperature grid data from January 2020 to March 2021 and the terrain factors such as altitude, longitude, and latitude, this study aimed to enhance the resolution of 2-meter air temperature grid data with a resolution of 1 km to 100 m through downscaling based on four machine learning methods, namely LightGBM (LGB), XGBoost (XGB), gradient boosting tree (GBT), and random forest (RF). Then, this study conducted the weighted fusion of downscaling results of different models. Finally, the downscaling results of different models were compared with the bilinear interpolation results, and the results are as follows. The results of each downscaling model were relatively consistent with the observational data. Compared with the bilinear interpolation results, the results of the LGB, XGB, and RF models had similar spatial structures but were more detailed. All downscaling models yielded the same spatio-temporal distribution characteristics of errors. Compared with the bilinear interpolation results, the data of the LGB, XGB, and GBT models showed significantly higher precision, and their root mean square errors (RMSEs) decreased by 5.2%, 4.1%, and 4.6%, respectively. Meanwhile, the RMSE after weighted fusion decreased by 5.9%, which was higher than that of any single machine learning model. The downscaling results of the LGB, XGB, and GBT models were improved to a certain degree compared with the bilinear interpolation results under different terrain conditions, especially in high-altitude areas (above 600 m). The correlation coefficients of results of the LGB, XGB, and BGT models and model based on weighted fusion increased by 0.45%, 0.40%, 0.63%, and 0.66%, respectively, and their RMSEs decreased by 9.1%, 8.0%, 12.7%, and 13.1%, respectively. These results indicate that the downscaling model based on the weighted fusion of different machine learning methods can both improve spatial resolution and maintain data precision and, thus, is suitable for downscaling research on 2-meter air temperature data in the study area. This study can be used as a reference for developing high-resolution data products.
Aiming at the problems of poor extraction effect and slow extraction speed of traditional road extraction methods in the information extraction of roads from high-resolution remote sensing images, this study proposed a new information extraction model based on improved Deeplabv3+. In the new model, the combination of the MobileNetv2 backbone feature extraction network with the Dice Loss function effectively balanced the contradiction between the precision and speed of road information extraction from high-resolution remote sensing images. As a result, high extraction precision was achieved while meeting timeliness requirements by reducing model parameters. The experimental results based on the open-source road information extraction dataset show that: ① The road information extraction model proposed in this study was feasible for high-resolution remote sensing images, with overall accuracy of up to 98.71%; ② In terms of the information extraction speed, the new model had an average frame number of 120.05 and parameter amount of only 5.81 M. Therefore, the new model was more lightweight lighter than original models, meeting the timeliness requirements. Therefore, the model proposed in this study meets the timeliness requirements by greatly reducing the parameter amount while ensuring high extraction accuracy. This study provides a new philosophy and method for improving the accuracy and speed of road information extraction from high-resolution images.
The continuous monitoring of the dynamic changes in coastlines is crucial to ascertaining the change patterns and evolution characteristics of coastlines. Long-time-series coastline datasets allow for the detailed description of the dynamic changes in coastlines from the spatio-temporal dimensions and further reflect the effects of human activities and natural factors on coastal areas. Therefore, they are conducive to the scientific management and sustainable development of the spatial resources in coastal wetlands. Based on the Google Earth Engine (GEE), this study analyzed the change in the coastline of Hangzhou Bay during 1990—2019 based on long-time-series Landsat TM/ETM+/OLI images. Using the pixel-level modified normalized difference water index (MNDWI) time series reconstruction technology, this study achieved the automatic information extraction of long-time-series coastlines and the analysis of spatio-temporal changes by combining the Otsu algorithm threshold segmentation and the Digital Shoreline Analysis System. The results show that the total coastline length of Hangzhou Bay increased by about 20.69 km during 1990—2019, corresponding to an increase in the land area by about 764.81 km2, with an average annual increase rate of 0.35%. In addition, the average end point rate (EPR) and linear regression rate (LRR) of the coastline were 110.07 m/a and 119.06 m/a, respectively. The analysis of the spatio-temporal evolution of the coastline in Hangzhou Bay over 30 years will provide a basis for the sustainable development and comprehensive management of resources along the coastline in Hangzhou Bay.
With 14 types of multi-feature information, such as spectrum, index, and texture, of remote sensing images from satellite Sentinel-2 as input and using the Bayesian optimization algorithm, this study designed the BO-XGBoost method used to automatically obtain the optimal hyperparameter combination. This method was successfully applied to the information extraction of cyanobacteria in Yangcheng Lake in 2021. The results show that: ① The optimal hyperparameter combination was obtained using the Bayesian optimization algorithm, and then the BO-XGBoost cyanobacteria classification model was established through obtaining. The training results performed well on the test and training sets, with an accuracy rate of up to 96.07%; ② The BO-XGBoost method was applied to the images used in the sample set. The comparison between the cyanobacteria identification results and the manual interpretation results shows that the two methods yielded roughly the same spatial distribution of cyanobacteria, with a lowest intersection over union (IoU) of 41.31%; ③ To evaluate the applicability of the BO-XGBoost method in other periods, images of other periods were selected for the information extraction of cyanobacteria. As a result, both BO-XGBoost and manual interpretation also yielded roughly the same spatial distribution of cyanobacteria, with a lowest IoU of 43.85%.
Conventional information extraction methods for aquacultural ponds frequently yield blurred boundaries and low accuracy due to the effect of different objects with the same spectrum in complex geographical environments of offshore and coastal areas. This study proposed a method for extracting information on coastal aquacultural ponds from remote sensing images based on the U2-Net deep learning model. First, an appropriate band combination method was selected to distinguish aquacultural ponds from other surface features through preprocessing of remote sensing images. Samples were then prepared through visual interpretation. Subsequently, the U2-Net model was trained, and information on coastal aquacultural ponds extracted. Finally, the scopes of aquacultural ponds were determined using the local optimum method. The experimental results show that the method proposed in this study yielded the average overall accuracy of 95.50%, with the average Kappa coefficient, recall, and F-value of 0.91, 91.45%, and 91.01%, respectively. Furthermore, 19 ponds were extracted, with a total area of 9.79 km2. The average accuracies of the number and area of aquacultural ponds were 94.06% and 93.18%, respectively. The method proposed in this study allows for quick and accurate mapping of coastal aquacultural ponds, thus providing technical support for marine resource management and sustainable development.
Since the availability of global runoff data decrease year by year, the inversion algorithms, as substitutes for the river discharge measured at hydrological stations, have become increasingly important. With the continuous development of satellite remote sensing technology, the methods for estimating river discharge have increased in number. This study systematically summarized the remote sensing-based inversion methods for river discharge, as well as the inversion methods for hydraulic remote sensing elements that are closely related to the estimation of river discharge and the progress made in them. Moreover, this study reviewed the methods, principles, and application status of two types of algorithms based on hydrological models and empirical regression equations and summarized the applicable conditions and shortcomings of different methods. Finally, this study predicted the worldwide development trends of the river discharge inversion based on the satellite remote sensing technology, including ① actively developing the advanced data assimilation technology for satellite remote sensing data; ② integrating new sensor products; ③ optimizing and innovating algorithms.
To achieve accurate remote sensing scene classification, this study proposed a classification algorithm based on DenseNet feature hashing. First, dimension reduction was conducted for high-level semantic features output by a DenseNet through a fully connected layer. Then, normalized feature vectors were generated as the input of the classification layer using an activation function, and an end-to-end classification network was formed. Using the trained network as a feature extractor, the features of the activation layer of test data were mapped into binary hash codes. Finally, the remote sensing scene classification was conducted using support vector machine. The new algorithm was validated on public data sets UC Merced, WHU, and NWPU-RESISC45, and its classification effect was compared with that of multiple algorithms at three levels, namely the conventional local feature descriptor, transfer learning, and depth feature coding. The experimental results are as follows. The new algorithm had significantly higher classification accuracy than conventional algorithms based on mid- and low-level semantic features. Compared with the algorithm based on transfer learning, the proposed algorithm has fine-scale DenseNet feature mapping and accumulates elements used to determine core categories of images and, thus, is more suitable for the feature distribution of remote sensing images. Compared with the depth feature coding algorithm, the new algorithm has a simple feature structure, high classification accuracy, and strong transferability and extensibility and, thus, can meet the classification requirements of different remote sensing scenarios.
With the vigorous development and in-depth application of civilian and commercial satellites, the space-based remote sensing application demands of different users become increasingly complex. However, the current space-based remote sensing services face problems such as single application mode, weak pertinence, and insufficient flexibility. Based on the analysis of the major application demands of various remote sensing users, this study proposed a space-based remote sensing application service mode based on cloud + terminals. This mode covers eight subcategories in three categories, whose characteristics and application process were analyzed and formulated individually. Last, this study presented the potential applications under two typical scenarios, namely single-person independent application and multi-person collaborative application. The results of this study will lay a foundation for the development, construction, and optimization of various space-based remote sensing ground systems and further improve the space-based remote sensing service capabilities for different users, different application demands, and different application scenarios.
Accurate and efficient quality inspection and database updates of cadastral data are essential for natural resource management. The current cadastral data management faces problems such as the low efficiency of quality inspection and updates, difficulty in meeting the demand for dynamic supervision, and small application scopes of relevant methods. To solve these problems, this study proposed a method framework based on spatio-temporal knowledge graphs. Moreover, with cadastral data and remote sensing images as data sources, this study constructed a spatio-temporal knowledge graph targeting the quality inspection and update workflow of cadastral data by designing conceptual and data layers and inference rules. Finally, experiments on the method proposed in this study were conducted using seven parcels of land in Changsha. As a result, the common errors in the process of quality inspection and updates were solved, and the method proposed in this study was proven to be more efficient than common methods.
Xiong’an New Area is a national new area. It has a low groundwater level and close water exchange between the zone of aeration and the saturated zone, with the upward recharge of groundwater increasing the water content in soil. On this basis, with remote sensing images as the data source, this study carried out object-oriented land classification for the study area, extracted the vegetation information by mask, and further extracted the soil moisture information of the vegetation area using the temperature vegetation dryness index (TVDI). Then, by combining the geological and geomorphic characteristics of the palaeochannels in the area, as well as visual interpretation, this study identified the palaeochannels in the study area and verified them in the field. Finally, it reconstructed the paleodrainage system of the study area. The results are as follows: ① The method proposed in this study can effectively extract information on the paleodrainage system in the study area; ② The distribution of the current surface water bodies in the study area is quite different from that of the paleodrainage system; ③ The comparison between the land classification results and the paleodrainage system interpretation results shows that the paleodrainage system was mostly distributed in present construction land, which is present as rural residential areas in remote sensing images. 50 m, 100 m, and 200 m buffer zones were set in the paleodrainage system areas, and then a intersection analysis was made for the buffer zones and the land classification results. The results show that the proportion of construction land in the buffer zones is significantly higher than that of construction land in the whole region. This result indicates that there exists a certain correlation between the distribution of the paleodrainage system and villages.
The Zhada earth forest, located in Zhada and Pulan Counties, Tibet, is composed primarily of weakly consolidated to semi-consolidated clastics s of the Tuolin and Xiangzi formations. This area forms a unique geological landscape consisting of peaks and ravines due to the long-term erosion by rivers and rain. To further explore the tourism resources in the Zhada earth forest distribution area and fully reveal the scientific and aesthetic values of the study area, this study carried out the geological interpretation of the study area mainly based on the GF-1 satellite remote sensing images, with the interpretation focusing on the Xiangzi and Tuolin formations constituting the earth forest landscape, as well as ophiolites and tectonic melanges reflecting plate subduction. Based on the interpretation results and the 3D interpretation environment of the Aerial Geophysical Remote Sensing Multivariate Data Processing and Product Display Platform, this study extracted information on typical geological landscapes in the study area, including earth forests, various rocks, and fault structures. The remote sensing technology helped delineate the distribution range of the earth forest more accurately. The 3D display platform enabled the more vivid display of the geological relics that represented the dramatic changes in the regional evolution history, such as earth forests, oceanic crust remnants, and unconformities. The application of modern information technology can provide strong support for the landscape planning of the Zhada Earth Forest National Geopark.
The inconsistency of multi-source geographic data in scale, geometric position, and attribute cause difficult data fusion and update. This study proposed a fusion and update method for geographic data based on geometric and attribute matching. First, the candidate set was acquired using the generalized Voronoi diagram, thus effectively improving the acquisition efficiency and reducing the impact of unrelated targets on the candidate set. Then, the matching analysis of point, line, and plane data was made using key techniques such as geometric and attribute matching. Finally, based on the matching results, the incremental data were extracted from the reference geographic information data, followed by fusion and update of target data. The experimental results show that the method proposed in this study can efficiently identify and extract incremental data and serves as a reference for the innovative exploration into the update mode of monitoring data.
In 2020, a flood disaster occurred throughout Anhui Province due to the persistent heavy rainfall during the super-long plum rain period. To quickly and accurately extract the flood inundation ranges and provide scientific support for flood prevention and disaster relief, this study selected the pre-disaster and mid-disaster Sentinel-1A/SAR data of the Chaohu Lake and Huaihe River basin in Anhui Province. After rapid data preprocessing, this study extracted information about water bodies in the plains and mountainous areas using the Sentinel-1 dual-polarized water index (SDWI) method and topographic factors. Then, it established a monitoring process for flooded areas. Using this process, this study extracted the flood inundation ranges of the Chaohu Lake and Huaihe River basins on July 27, 2020 using the pre-disaster and mid-disaster synthetic aperture Radar (SAR) data. The results are as follows. The SDWI was superior to the backscattering coefficient in the extraction of information about water bodies. The Chaohu basin had a flood inundation area of 524.8 km2 on July 27, and the Baishitian River subbasin was the most severely inundated, followed by the Xihe River subbasin. In the flood flowing and storage areas of the Huaihe River basin within Anhui Province, the flood inundation area of four cities along the Huaihe River basin decreased in the order of Huainan City, Fuyang City, Lu’an City, and Bengbu City. The results of this study show that the Sentinel-1A-based monitoring process of flood inundation areas established using SDWI and topographic factors has high accuracy, applicability, and timeliness for plains and mountainous areas and is convenient for the timely monitoring of flood disasters in these areas.
The forest area of Tibet ranks among the top in China, and the forest resources in Tibet play an important role in water conservation and ecological service. Therefore, it is of great significance to assess the assets of forest natural resources in this region. However, existing products and statistical data related to forest cover fail to meet the demands for the assessment of forest natural resource assets in this region, and it is necessary to explore a fine-scale forest classification method suitable for this region. Based on the cloud computing platform Google Earth Engine (GEE), this study constructed the temporal, spatial, spectral, and auxiliary feature sets of the forest coverage in Motuo County using the Landsat8 remote sensing images of 2015 and 2020, as well as field survey data, and the basic geographic data. Then, it conducted forest classification using the random forest (RF) and classification and regression tree (CART) algorithms. As indicated by the accuracy evaluation of the assessment results obtained using the two algorithms, the forest classification results of 2015 and 2020 obtained using the RF algorithm had relatively high accuracy, with overall classification accuracy of 0.88 and 0.87, respectively and Kappa coefficients of both greater than 0.8. The analyses of the areal and spatio-temporal characteristics of forest classification results show that: ① Motuo County had a total forest area of 34 000 km2 in 2015, with a forest cover rate of up to 84.63%, which was 2% less than that in 2020; ② The forest resources in Motuo County are dominated by broadleaved forests, which are mainly distributed in Yarlung Zangbo Grand Canyon and low-altitude areas and accounted for 72.27% and 75.37% of the total forest area in 2015 and 2020, respectively. Coniferous forests accounted for 25.96% and 23.19% of the total forest area in 2015 and 2020, respectively and are concentrated in high-altitude areas, such as the Namcha Barwa and Gyala Peri peaks. This study determined the spatio-temporal distribution of the forests in Motuo County in 2015 and 2020 by developing a spatio-temporal-spectral classification method. It can provide a reference method for calculating specific forest cover indices SDGs and fill the gap of forest data of small zones. The obtained monitoring data will provide data support for the natural asset assessment and ecological function evaluation in Motuo County.
The Axi mining area in Xinjiang has a complex geographical environment. The long-term exploitation of mineral resources has caused severe ground subsidence and deformation in the mining area, as well as safety hazards of mining and production and the destruction of the surrounding ecological environment. This study aims to further investigate and analyze the spatial-temporal variation characteristics of the ground subsidence and the patterns of surface deformation in the Axi mining area. To this end, this study first calculated the land subsidence using the small baseline subset-interferometric synthetic aperture Radar (SBAS-InSAR) technique based on the 127 scenes descending Sentinel-1A images acquired from February 9, 2017 to April 25, 2021. Then, it compared the subsidence monitoring results obtained using the InSAR technique with the leveling results for verification. Finally, this study analyzed the spatial-temporal variation characteristics of land subsidence in the Axi mining area in recent five years and investigated the driving factors for the land subsidence. The results show that the surface deformation of the Axi mining area showed a roughly stable trend and significant local subsidence throughout the monitoring period. The main factors affecting the ground subsidence included mineral exploitation, geological structure, precipitation, and the impoundment of open-pit mines. This study will provide a scientific basis for ground subsidence monitoring and the future proper exploitation of underground minerals in the Axi mining area.
The soil roughness of cultivated land is an important element affecting the monitoring of agricultural information, such as soil moisture, microwave remote sensing observation, and plant growth. Soil roughness is generally interpreted according to field photos. However, such interpretation suffers some shortcomings such as low efficiency and anthropogenic effects on processing results. UAV low-altitude remote sensing is sensitive to surface relief. To explore the precision of the soil roughness determined using UAV data, this study employed UAV photogrammetry to photograph the surface and then compared the photogrammetry results with the data obtained using a gauging plate for soil roughness. The results show that the close-range photogrammetry had mean absolute errors of mainly 0.4~1.2 cm, a mean relative error of 6.16%, and a root mean square error of 0.40 cm. Therefore, UAV-based point cloud photogrammetry could be effectively applied to the measurement of surface roughness, and a smaller sampling area is associated with more accurate soil roughness.
Accurate information about land use/land cover (LULC) can provide significant guidance for regional spatial planning and sustainable development. However, conventional methods for remote sensing image classification are challenging due to complex surface morphologies, diverse surface feature types, and nonlinear features of remote sensing images. Therefore, they fail to fully utilize the rich information in remote sensing images. This study developed a random forest-based classification method for remote sensing images to extract LULC information by integrating indices and principal components. First, the images covering the study area were selected to determine cloud cover and conduct median synthesis of images, obtaining interannual remote sensing images. Then, various calculated indices and the extracted principal components were integrated into the band stacks of remote sensing images. Furthermore, classifiers were constructed using different machine-learning algorithms. Finally, based on a confusion matrix, the classification results were evaluated using overall accuracy and the Kappa coefficient. The experimental results of the Hangzhouwan area show that the decision support based on vegetation, water, building indices, and principal components can improve the classification accuracy, yielding overall accuracy and Kappa coefficient of 91.42% and 0.894 2, respectively, which were higher than those of conventional methods such as random forest, classification and regression tree, and support vector machine. The method for remote sensing image classification proposed in this study, which integrates indices and principal components, can obtain high-accuracy land use classification results by accurately extracting land cover features in remote sensing images. This study will provide method support for fine-scale surface classification.
On September 5, 2022, a Ms 6.8 earthquake occurred in Luding County, Ganzi Prefecture, Sichuan Province, inducing numerous landslides. This study collected the pre- and post-earthquake images from the GF-2 and GF-6 satellites, as well as the DEM data of Luding. Then, using the object-oriented method, the stepwise optimization multi-scale segmentation method, and the nearest neighbor classification method, this study extracted the landslide information according to the spectrum, thematic index, geometric texture, and topographic features of the objects in the experimental area. The overall identification accuracy of pre- and post-earthquake landslides was 92.3% and 95.4%, respectively. The comprehensive analysis of the distribution of pre- and post-earthquake landslide landslides shows that 23.91 km2 of new landslides were induced by the earthquake. This study summarized the distribution characteristics of post-earthquake landslides through the spatial statistical analysis of seven topographic factors. The results are as follows: ① The post-earthquake landslides were mainly affected by the Xianshuihe fault zone, and they show a banded distribution along rivers and a lamellar, dense distribution along the hillsides and valleys near the fault zone; ② Compared with the historical landslides, the new landslides have a relatively stable elevation range and a large slope range. Moreover, there is a significantly negative correlation between the area of the post-earthquake landslides and the surface roughness.
Conventional processing methods for remote sensing data are inefficient and time-consuming. Using the object-oriented classification method this study extracted the distribution of mangrove forests of 2000, 2010, and 2020 in the Shankou Mangrove Nature Reserve in Guangxi based on the GEE cloud platform and Landsat TM/OLI remote sensing data. Then, this study monitored the spatio-temporal variations in mangrove forests in the study area in combination with the landscape analysis method and revealed their driving factors. The results are as follows: ① During 2000—2020, the mangrove forests in the study area increased by about 63 hm2, including a significant increase of about 40 hm2 during 2010—2020; ② Compared with other land use types, the mangrove forests showed the most intense conversion with spartina alterniflora areas and mudflats, with 152 hm2 of spartina alterniflora areas and mudflats being converted to mangrove forests and 122 hm2 of mangrove forests being converted to spartina alterniflora areas over the 20 years; ③ During 2000—2020, the mangrove landscape in the study area showed decreased fragmentation, increased patch aggregation, continuously expanded landscape dominance, and landward migration of the mangrove forest centroid; ④ Among the factors affecting the area of mangrove forests in the nature reserve, the control of invasive vegetation and moderate aquaculture can increase the area of mangrove forests, while climate changes and invasive vegetation had adverse effects on the growth of mangrove forests. The results of this study will provide a method reference and data basis for the conservation and management of mangrove wetlands in Shankou, Guangxi.
Monitoring the spatio-temporal dynamic changes in macroalgae aquaculture is crucial to its environmental management. However, few studies have been reported on the comparative monitoring of different macroalgae species. Based on images of the Sentinel-2 satellite and using the normalized difference vegetation index (NDVI) and the support vector machine (SVM), this study monitored the dynamic characteristics of both the Porphyra aquaculture area in the sea area of southern Wendeng District, Weihai City, Shandong Province and the kelp aquaculture area in the sea area of southern Rongcheng City, Weihai City. The results show that: ① The Porphyra aquaculture in Wendeng District was first captured in the satellite images of 2016, which is the same as the first year of Porphyra aquaculture in this city; the extraction method used in this study performed well in extracting the information about both the Porphyra and the kelp aquaculture areas overall, with the overall accuracy of 84% and above; ② During 2017—2021, the Porphyra aquaculture area monitored through remote sensing increased year by year and showed a trend far away from the shore; ③ The Porphyra and kelp aquaculture areas monitored both showed seasonal variations (high in winter and low in summer) of cold-water macroalgae aquaculture, but the minimum and maximum values of the Porphyra aquaculture area appeared 1~2 months earlier than those of the kelp aquaculture area. Compared with statistical yearbooks, satellite remote sensing can provide more accurate spatio-temporal information on macroalgae aquaculture. This study can be used as a reference in terms of monitoring technology and data for the management of macroalgae aquaculture in coastal areas of northern China.
With the large-scale exploitation and utilization of coal resources, the geological environmental problems of coal mines have been increasingly severe, thus restricting social and economic development. This study aims to ascertain the disaster status of the collapse of the mined-out areas in Anhui Province, analyze the changing trend of the collapse areas, and summarize the countermeasures and methods for the collapse areas. With 2016—2017 remote sensing images of Anhui Province obtained from domestic GF satellites as an information source, this study conducted the processing, interpretation, and analysis of the remote sensing images and field surveys using the 3S technology (the collective term of remote sensing, global position system, and geographical information system). The results are as follows: ① The total area of the collapse areas in 2017 was 396.62 km2, accounting for 0.28% of the land area of the province; ② The growth rate of the area and quantity of collapse areas decreased compared with those in previous years; ③ A set of countermeasures and four treatment methods were proposed. As revealed by the results, the 3S technology-based remote sensing monitoring of the mine environment in Anhui Province can be used to produce high-quality data and extract relevant data information macroscopically, efficiently, and accurately, thus greatly improving the treatment efficiency of mine geological disasters. This study will provide technical support for the restoration, treatment, and sustainable development of the collapse areas of coal mines in the future.
Areas with power transmission lines have been frequently struck by flood disasters in recent years. Therefore, forecasting the water table depths in these areas is critical to the safety of these areas. This study forecasted the water table depth using remote sensing satellite products and observed meteorological and hydrological data. Based on the meteorological and hydrological data, this study forecast the daily and monthly water table depths using the long short-term memory (LSTM), gated recurrent unit (GRU), long short-term memory-seq2seq (LSTM-S2S), and feedforward neural network (FFNN) models. The results indicate that the LSTM-S2S and FFNN models delivered the best and the worst performances, respectively. Meanwhile, the LSTM, GRU, and LSTM-S2S models performed well in forecasting both daily and monthly water table depths, with their forecasts of daily water table depths having a higher coefficient of determination (R2) and a Nash-Sutcliffe efficiency coefficient (NSE) than those of monthly water table depths. Therefore, the method presented in this study can be used to forecast the future daily and monthly water table depths in areas with power transmission lines.
Currently, the high-quality fusion of SAR and optical images is a hot research topic. However, the significant radiation difference and weak gray correlation between SAR and optical images greatly reduce the fusion quality. In this regard, this study proposed a SAR and optical remote sensing image fusion algorithm that coupled non-local self-similarity and divergence. First, images were decomposed in the frequency domain. Then, the non-local directional entropy and divergence were used as characteristic parameters to guide the fusion of low- and high-frequency components, respectively. Finally, the fusion components were reconstructed to obtain fusion images with clear structural features and rich spectral information. The comparative experiments verified the effectiveness of the proposed algorithm in fusing SAR with optical images and its superiority in maintaining structural features and reducing spectral distortion.
With the rapid socio-economic development and the increasing demand for natural resources in China, the protection of natural reserves is facing increasing difficulties. The remote sensing-based research on monitoring the disturbance and the restoration of mangrove forests through time series analysis is still in its initial stage. Moreover, time series algorithms are highly complex. Based on the LandTrendr time segmentation algorithm of Google Earth Engine (GEE) and the Landsat image time-series data, this study investigated the disturbance to mangrove forests in the Dongzhaigang Mangrove Nature Reserve during 1990—2020. The results are as follows: ① A total of 42.39 hm2 of mangrove forests were disturbed during 1990—2020, among which the largest disturbance area of 12.78 hm2 occurred in 2014; ② During 1990—2020, minor, moderate, and severe disturbances accounted for 65.39%, 30.78%, and 3.83%, respectively; ③ The overall identification accuracy of the pixels of mangrove forests subject to changes was 89.50%, and the overall detection accuracy of years witnessing disturbance was 88%, with a Kappa coefficient of 0.79. This study analyzed the years and areas of the disturbance to mangrove forests in the Dongzhaigang Mangrove Nature Reserve over 30 years based on LandTrendr. Moreover, this study analyzed the disturbance factors according to the actual situation and concluded that human activities are the main disturbance factor, followed by natural factors, such as diseases, pests, and extreme weather events. This study will provide a scientific basis and a decision reference for the management of the mangrove forest reserve.
Rocky desertification is the primary eco-environmental problem in Karst mountainous areas in southwestern China. Scientific measures must be formulated to comprehensively promote the prevention and control of rocky desertification. Remote sensing technology, which enjoys the advantages of rapid positioning, wide coverage, and economic efficiency, has become an important technical method for investigating the spatial distribution of regional rocky desertification. Therefore, this study extracted three key indices used to characterize rocky desertification information (i.e., vegetation coverage, bedrock exposure rate, and soil coverage) of the study area using the pixel unmixing method based on GF-5 hyperspectral data and the spectral index method based on Landsat8 multispectral data. The results show that information on vegetation coverage can be accurately extracted from the two types of satellite remote sensing data. However, Landsat8 multispectral data are difficult to distinguish information about exposed bedrocks from that of bare soil due to their band setting and spectral resolution. By contrast, GF-5 hyperspectral data enable the direct and effective extraction of bedrock exposure rate and soil coverage, as well as the accurate identification of mineral components such as calcite and dolomite in exposed bedrocks. The results of this study can provide a scientific and effective technical and theoretical basis for the evaluation, classification, and comprehensive control of rocky desertification.
This study aims to explore the optimal remote sensing salinization detection index (SDI) model for the inversion of soil salinization in the Alar reclamation area. Based on Landsat8 OLI remote sensing images and field measured data, this study built the remote sensing SDI models using the salinity index (SI), the normalized difference vegetation index (NDVI), the modified soil adjusted vegetation index (MSAVI), and the surface albedo. Then, using these models, this study extracted the soil salinization information on the Alar reclamation area and verified the model precision. Finally, this study determined the optimal remote sensing-based SDI model through comparative analysis. The results are as follows. The four types of remote sensing-based SDI models SDI1 (SI-NDVI), SDI2 (SI-MSAVI), SDI3 (SI-Albedo), and SDI4 (Albedo-MSAVI)had general classification precision of 83.45%, 69.78%, 53.23%, and 71.94%, respectively. Model SDI1 was the most suitable for the inversion of the degree of soil salinization in the Alar reclamation area. Models SDI2 and SDI4 can be utilized as a reference for soil salinization monitoring of the Alar reclamation area. As revealed by the inversion results of the SDI model, the reclamation area is dominated by non-saline and lightly saline soils, with heavily saline soil and saline soil primarily distributed in the northeast and southeast. Model SDI1 established based on SI and NDVI has high accuracy in extracting the soil salinization information of the Alar reclamation area and can be used as the remote sensing-based SDI model for the inversion of soil salinization in reclamation areas. This study can provide an effective technical reference for the control and prevention of soil salinization.
Urbanization has decreased the area of ecological land and deteriorated ecological environment in Zhanjiang City. Therefore, it is significant to quickly, comprehensively, and accurately monitor the changes the ecological environment quality in this city. Based on the Landsat images in 2000, 2005, 2009, 2015, and 2020, this study constructed the improved remote sensing ecological index (IRSEI) using six indicators, namely greenness (NDVI), humidity (WET), dryness (NDBSI), heatiness (LST), land use (LUI), and population distribution (POP). Using IRSEI, this study quantitatively analyzed the changes in the ecological environment quality in Zhanjiang during 2000—2020. The results are as follows: ① The mean IRSEI values of 2000, 2005, 2009, 2015, and 2020 are 0.18, 0.18, 0.35, 0.42, and 0.38, respectively, showing a first increasing and then decreasing trend. ② According to the difference processing on IRSEIs during 2000—2020, the proportions of ecological environment areas with significant improvement (dominant), improvement, no change, deterioration, and significant deterioration in the study area are 78.95%, 8.70%, 8.01%, 1.35%, and 2.99%, respectively. ③ The IRSEI can effectively reflect the poor urban environment along the coastal zone during 2000—2020, specifically manifested as a low IRSEI value of building land along the coastal zone. The results of this study can provide a theoretical and scientific basis for Zhanjiang’s ecological environment protection.
Coastal zones are the world’s most populated areas, with their ecosystems being strongly influenced by human activities. Tidal flats, shorelines, and aquacultural water bodies are critical elements in monitoring the health of coastal zone ecosystems. However, the dynamic changes in the waterlines between land and sea areas caused by tidal effects make it challenging to detect tidal flats and shorelines using the remote sensing technology. By integrating Landsat4/5/7/8 and Sentinel-2A/B satellite remote sensing images, this study conducted seven phases (1989—2021) of monitoring of tidal flats, shorelines, and aquacultural water bodies along coastal zones in China mainland. By taking advantage of the high frequency of multi-source satellite observations, this study identified tidal flats, shorelines, and aquacultural water bodies by detecting the waterlines at different tidal levels. The results are as follows: ① Seawater of different colors requires different combinations of water body indices. For clear or low-turbidity seawater, this study selected the modified normalized difference water index (mNDWI) and the normalized difference water index (NDWI) to detect the waterlines at high and low tidal levels, respectively. This improved the reliability of tidal flat detection, with the detected tidal flat area being 122% larger than that detected only using the mNDWI. For high-turbidity seawater (in Zhejiang, Jiangsu, and Shanghai), this study selected mNDWI to detect the waterlines at high and low tidal levels, avoiding misidentifying high-turbidity seawater as tidal flats using NDWI. Besides, this study selected NDWI to detect aquacultural water bodies. ② During 1989—2021, coastal zones in China mainland changed significantly, as evidenced by rapidly decreased tidal flats and increased aquacultural water bodies and shorelines. The decreased rate of tidal flats and the increased rates of shorelines and aquacultural water bodies along the coastal zones averaged 46.2%, 34.4%, and 149.3%, respectively. Correspondingly, the tidal flat area decreased by 7 173.2 km2, while the the shoreline length and aquacultural water body area increased by 5 320.5 km and 9 046.5 km2, respectively. Provinces or cities in northern China suffered more tidal flat losses than those in southern China. Based on the average decrease rate of tidal flats during 1989—2021, tidal flats in Liaoning, Hebei and Tianjin, and Shandong will disappear within 27 a, 10 a, and 22 a, respectively. ③ The area changes between tidal flats and aquacultural water bodies are highly negatively correlated, indicating that the expansion of aquacultural water bodies is a critical driving factor for the decrease in tidal flats.
Myrica rubra is a specialty crop in Zhejiang Province. Its cultivation area in Zhejiang ranks first in China. This study aims to comprehensively investigate and analyze the suitability of Myrica rubra planting in Zhejiang and better serve the Myrica rubra planting by scientifically using modern meteorological observation data. Based on the distributed simulation of climate factors, this study introduced the influencing factors related to soil and terrain and determined the weights of these factors through the analytic hierarchy process (AHP). Then, in combination with the suitability grade indices of various influencing factors, this study divided Zhejiang into regions suitable, fairly suitable, and unsuitable for Myrica rubra planting. The results are as follows: Regions with a suitable climate occupy most of Zhejiang, indicating superior climate resources; Zhejiang Province enjoys excellent soil conditions and roughly varies between regions fairly suitable and suitable for Myrica rubra planting regarding soil conditions; The terrain varies greatly and is a key factor in the suitability of precise Myrica rubra planting. The regions with suitable terrains have altitudes of 250~450 m and slopes of 5°~25°; Except for northern Zhejiang and the boundary between Shaoxing and Ningbo cities, Zhejiang is suitable or fairly suitable for Myrica rubra planting. This study achieved the spatial simulation of meteorological factors, thus providing data support for the development and improvement of the Myrica rubra planting layout in Zhejiang and being of great practical significance for improving the yield and quality of Myrica rubra.
In view of the drastic changes in the ocean-atmosphere environment, the accurate and efficient identification of coral reef substrate information is essential for the dynamic monitoring of coral reefs. Based on the Landsat8 satellite data of the Yongle Atoll in the Xisha Islands of four periods during 2013—2021, this study proposed a decision tree classification model using spectral and texture indices according to the spectral and texture differences between different substrates. Then, the coral information was extracted using object-oriented and pixel-based classification methods. In addition, the changes in the substrate of the Yongle Atoll were quantitatively analyzed. The results are as follows: ① The results of the object-oriented classification are superior to those of pixel-based classification overall. Moreover, the decision tree classification results yielded Kappa coefficients of 0.63~0.68, with classification accuracy about 7~10 percentage points higher than that of conventional supervised classification; ② Coral thickets are mostly distributed in the central, weakly-hydrodynamic parts of islands and reefs. The corals in the Yinyu Reef and the Jinyin Island exhibit a planar distribution pattern, while those in other islands and reefs mostly show a zonal distribution pattern; ③ The areas of coral thickets and sandbanks in the Yongle Atoll changed significantly overall. Although the total area of coral thickets increased by 1.689 km2, the coral thickets in the Shiyu, Jinqing, Quanfu, and Shanhu islands and the Lingyang reef were severely degraded, with areas decreasing by 0.107~0.892 km2. This study verified that the substrate index established using medium spatial resolution images is reliable and can be applied to remote sensing information extraction of corals. Therefore, this study will provide technical support for the investigation and scientific management of coral reef resources.
Landscape indices are quantitative indices used to reflect the composition and spatial configuration of a landscape ecological structure. Current landscape index systems are generally constructed based on the characterization of 2D spatial characteristics, thus their evaluation results fail to accurately reflect the pattern and composition of a real 3D landscape system. Accordingly, there is an urgent need to develop an index system used to describe the 3D landscape characteristics of islands and a whole-process evaluation method. With Tianheng Island in Shandong Province as a case study and based on the point clouds of unmanned aerial vehicle (UAV) tilt photogrammetry, as well as the classification and processing of point clouds using the deep learning method, this study constructed six basic 3D landscape indices covering type and landscape scales to quantitatively describe the 3D landscape features of the island. Moreover, this study established the building landscape indices to evaluate the impacts of the construction activities of human beings on the island ecosystem. The results are as follows: ① As revealed by the analysis of basic 3D landscape indices, the buildings on Tianheng Island are characterized by small 3D volumes and dense spatial distribution. Furthermore, tall vegetation exhibits high isolation, regularity, and spatial aggregation, while low vegetation exhibits high diversity, compactness, and connectivity; ② Due to the difference in dimension, 3D landscape indices contain more spatial information than 2D landscape indices and are greatly affected by terrain undulation; ③ In the case of the same landscape type, the landscape shape index (TLSI) is more sensitive to the change in height (sensitivity index: 7.480). In the case of the same landscape index, the building type changes more greatly than vegetation with irregular spatial characteristics (sensitivity index: 5.861) and is influenced by the design characteristics of buildings; ④ Tianheng Island has a 3D building index (TBI) of 0.523, which increases with an increase in the density and complexity of buildings. Compared with building density and spatial congestion indices, TBI can better reflect the influence of artificial structures on the 3D landscape pattern of the island. This study aims to provide methodological support and a case study for the construction of 3D landscape indices based on modern surveying and mapping technology, as well as the planning of 3D spatial landscapes and the development of their management and evaluation system.
Ecological carrying capacity is an important indicator used to measure the stability of an ecosystem. The spatial-temporal change analysis of the ecological carrying capacity can help understand the changing trend of a regional ecological environment and serve as a comprehensive reference for the evaluation of ecological management and restoration, research on the overall sustainable development of an environment, and the optimization of land resources. Targeting the arid and semi-arid regions at the northeastern margin of the Ulan Buh Desert, this study constructed a comprehensive index evaluation system of ecological carrying capacity based on the actual ecological conditions of the regions and Landsat remote sensing images as the data source. Then, this study determined the spatial-temporal distribution and evolution pattern of regional ecological carrying capacity and made a driver analysis of the change in the ecological carrying capacity from the angles of rainfall, temperature, and land use changes. The results show that the ecological carrying capacity of the northeastern margin of the Ulan Buh Desert showed a first decreasing and then increasing trend from 1990 to 2020. The irrigated areas north of the Yellow River continued to expand to the desertification areas in the southwest. As a result, the percentage of the area with relatively high ecological carrying capacity increased greatly, while the area with high ecological carrying capacity decreased. The change in the ecological carrying capacity of the irrigated areas was mainly affected by land development and utilization, followed by temperature and rainfall. In contrast, the ecological carrying capacity of the desertification areas south of the Yellow River was mainly at a moderate level, which was shifted to a low level in large areas before 2010 and was restored to a moderate level in 2020. The change in the ecological carrying capacity of the desertification areas was greatly affected by temperature, followed by rainfall and changes in shrub and grass vegetation cover.
The Five-hundred-meter Aperture Spherical radio Telescope (FAST), also known as Tianyan (meaning the Eye of the Sky), has attracted worldwide attention and is the largest single-dish radio telescope in the world. The joint observations of FAST and several more FAST-type radio telescopes allow detection sensitivity and resolution to be further improved and the research fields to be expanded. Therefore, Chinese radio astronomy scientists have the expectation of building more FAST-type radio telescopes in China, which should be achieved based on the preceding research on depressions as the sites of FAST-type radio telescopes. Presently, the shared digital elevation model (DEM) data enjoy intercontinental coverage and different ground resolutions. The development of computer processing technology has greatly enhanced the processing and analysis capacities of DEM data and continuously innovated the processing technologies. Moreover, relevant analyses and expressions can be simulated. Therefore, based on a comparative analysis of the structural scales of the projects of the Arecibo radio telescope and the FAST, as well as the morphological characteristics of karst depressions, this study proposed the conditions of ideal depressions as the sites of FAST-type radio telescopes. Moreover, by analyzing the resolution and data quality of shared DEM data on the Internet, it is concluded that areas with ASTER_GDEMV3 data with a resolution of 30 m are suitable as sites of large radio telescopes in provincial-level regions. In search of large-scale depressions in Guizhou Province, this study developed special modules for quantitative analyses, such as extracting the characteristic parameters of depressions and the fitting of filling, excavation, and superimposed sections, based on the ArcGIS platform and summarized the key steps to organize and apply the major tools of ArcGIS in the special modules. The results of this study determined key technology in search of large Karst depressions in provincial-level regions. Furthermore, this study proposed several issues that are noteworthy in the application.
The one-class classification (OCC) of land use in image interpretation is a hot research topic of remote sensing. Many novel algorithms of OCC were introduced and developed. The maximum entropy model (MaxEnt)-the most promising OCC algorithm as evaluated-is widely used in the OCC study of land use. However, it is unclear about the applicability of these algorithms (including MaxEnt) in multi-class classification (MCC) of land use. Thus, this study established a procedure for MaxEnt-based land-use MCC in remote sensing image interpretation and applied the procedure to the land-use MCC of the Yunyan River basin. The overall classification effect of MaxEnt and the performance of MaxEnt in the prediction of various land were evaluated using overall classification accuracy, Kappa coefficient, sensitivity, and specificity. Moreover, the Kappa coefficient was also used to evaluate the consistency between MaxEnt and random forest (RF), maximum likelihood classification (MLC), and support vector machine (SVM) in the prediction of land use maps. The results are as follows: ① MaxEnt showed the best classification effect, with overall classification accuracy of 84% and a Kappa coefficient of 0.8; ② MaxEnt showed no worst performance in any land type, and even performed the best in some land types; ③ MaxEnt showed high classification consistency with RF and SVM, and the consistency evaluation of the land use maps obtained using the three algorithms yielded Kappa coefficients of greater than 0.6; ④ Compared with the other the three algorithms, MLC yielded a significantly different land use map, with a Kappa coefficient of less than 0.4. This result indicates that MLC is not applicable to the interpretation of land use of the study area. The procedure established in this study only depends on the occurrence probability of land use rather than the threshold selected. As a result, the OCC algorithms represented by MaxEnt have great potential for application to the land-use MCC in remote sensing image interpretation. In addition, the introduction of parallel computing into large-scale land use interpretation will help improve the efficiency of solving MCC problems using MaxEnt.