A comparison with traditional soil moisture monitoring methods shows that the remote sensing method has great superiority. This paper presents a review of the remote sensing methods currently used both in China and abroad for monitoring soil moisture, which include the reflectivity method, the vegetation index method, the surface temperature, temperature-vegetation index method, the crop water stress index method, the thermal inertia method and the microwave method, with a detailed comparative description of the advantages and disadvantages of these methods. Based on summarizing researches on remote sensing monitoring methods for soil water, this paper evaluated the focal points, difficulties and development trend of this research field. It is held that the thermal inertia method and the vegetation temperature index method are relatively mature methods for soil moisture monitoring. With the wide application of geographic information system, the microwave remote sensing will become the key research direction in this field because of its unique advantages.
Taking Beijing as the study area, the authors developed a method of soil moisture inversion by using Radar data and optical remote sensing images in the vegetation-covered area. Firstly, NDWI was extracted by using homochronous optical images, and then water-cloud model was used to eliminate the contribution of backscattering coefficients caused by the vegetation. Secondly, HH and HV backscattering coefficients were employed to construct the soil moisture inversion model in consideration of surface roughness based on backscattering database built by AIEM model and Oh model. Then the simulating data were used to validate the accuracy of this model. The result shows that the RMSE and relative error of HH is 0.044 and 15.5%, and the RMSE and relative error of HV is 0.057 and 20.3% respectively. It is proved that the result of using HH backscattering coefficient is much better than that of using HH backscattering coefficient.
This paper proposes a method for extracting linear object based on Freeman chain code and Hough transform with the purpose of extracting linear object effectively. After the original image is enhanced and filtered, a method based on the gray-level uniformization is used for region segmentation of image. Then the approach of Freeman chain code is carried out. Finally, the parallel linear structure is detected when Hough transform is used for the data of the chain code. The experiment results show that the proposed algorithm can extract the parallel linear structure of the image effectively, as evidenced by the fact that it showed high efficiency and high accuracy when it was applied to network target recognition in the ZY-3 satellite images.
A new approach to the fusion of multifocus images based on wavelet transform is proposed to solve the problem that some parts of the images are blurred because of the different focus points. The images are firstly decomposed by using wavelet transform, and then the low and high frequency coefficients are fused by using different fusion strategies: the low frequency coefficient is fused with a rule weighted average of energy, while the high frequency coefficient is processed with the regional grads. After that the fused image is obtained by inverse wavelet transform. Experiments prove that the fused image obtained by the method has a better subjective visual effect and objective evaluation criteria, thus attaining a better result than other traditional fusion methods.
Taking into consideration the needs of the remote sensing monitoring and application with Chinese resource satellite in west highland lakes, the authors carried out research on water extraction method by using ZY-1 02C satellite images. The two traditional spectral indexes i.e., the normalized difference vegetation index(NDVI)and the normalized differential water index(NDWI), were used to extract the water bodies in Longyangxia reservoir and, by combining these two kinds of water extraction method, a decision tree water extraction method was presented in this paper. Taking the manual interpretation of the water region as the reference,the authors used the overall area of the water extraction results, the detail extraction and the rate of error extraction results to make statistic and comparative analysis. The experimental results show that the NDVI method is susceptible to the influence of thin cloud, but is less affected by snow and terrain. Under the imaging conditions of snow,thin cloud and mountain shadows,the NDWI method is subject to different degrees of impact. In spite of the fact that it is susceptible to mountain terrain effects such as shadows,the method of the decision tree can effectively eliminate the interference of climate conditions such as snow and thin cloud.
Impervious surface plays an important role in monitoring urban sprawl and understanding human activities. Linear spectral mixture analysis (LSMA) is commonly used to estimate impervious surface due to its simple structure and clear physical meaning. However, previous researches found that LSMA seemed to overestimate slightly impervious surface fraction in less developed areas (0-20%) but underestimate it in the central business district (CBD) (over 80%). To tackle this problem, the authors developed impervious surface of Fujin Town in Heilongjiang Province from the Landsat Thematic Mapper (TM) image by using LSMA model under different constrained conditions and end-members. The results indicated that three end-members (high albedo, soil, and vegetation) semi-constrained LSMA provided a fine performance with a RMSE of 16.71%. Moreover, the paddy field in impervious surface fraction image was removed by using land surface temperature and vegetation coverage data.
A method for extracting building boundaries using airborne LiDAR point cloud data and imageries is proposed in this paper. Firstly, an α-shape algorithm is used to extract the rough outline of buildings from point clouds. Then building edge line segments are extracted from the registered images by an straight line segments extraction algorithm based on line region support. By using voting mechanism and point-to-line distance, the true boundaries of the buildings are obtained. Finally, a new method for refinement of a building outline is put forward, in which the extracted edge information is utilized to correct the rough outline extracted by the point cloud image, and the revised outline is processed by Douglas - Peucker algorithm to remove redundant nodes. the force intersect method is employed to restore the corner of the building, and finally the accurate outside contour polygons of the building is obtained. The effectiveness of the proposed method has been verified by experiments.
Traditional geological mapping methods usually cannot conduct mapping for the whole study area and takes little account to the situation that a variety of features has symbiotic combination in one pixel, which makes it difficult to reflect the complex geological distribution characteristics. Since the unmixing accuracy of the linear model cannot meet actual application need, the secondary scattering model was used to the unmixing of hyperspectral data. On such a basis, this paper proposed k (k ≥ 2) class mapping rules based on the unmixing result. The Nevada Cuprite AVIRIS data were used in the experiment, and actual mapping results obtained by Clark et al. were taken as the reference. The comparison results have shown that mapping results based on the secondary scattering mixture model are closer to actual ground feature distribution than those based on the linear model and, in comparison with the results from one class mapping rule, the results using k (k ≥ 2) class mapping rules have richer details and are closer to the results obtained by Clark et al.
In optical image registration, the polynomial regression model generally supposes that the reference control points (RCPs) used as the coefficient matrix is error-free. However, the actual RCPs often inevitably contain errors and RCPs residual errors between different images are not the same. The general least squares method (LS) only considers the error in the observation vector whereas the total least squares method (TLS) takes the errors of both the observation vector and the coefficient matrix into account and assumes that they have the same residual error. In view of this situation, this paper introduces a more reasonable weighted total least squares method (WTLS) for polynomial regression coefficients estimation. Experiments show that the WTLS can estimate the parameters better and significantly improve the image registration accuracy.
As we all know,GPS has brought great convenience to surveying and mapping work. Its horizontal accuracy has reached sub-millimeter. However, due to the influences of such factors as the effects of ionosphere,multipath effect,GDOP(geometric dilution of precision) and height of antenna,the vertical deformation measurements from GPS are seldomly used by precision survey workers. Based on the reasonable layout of deformation monitoring network of Shuping landslide in the Three Gorges Reservoir Area,the authors obtained a large number of leveling and GPS data from long-term monitoring,and used leveling data as the reference to analyze the height precision of single-frequency static GPS in landslide vertical deformation monitoring. The results show that the vertical deformation monitoring precision of single-frequency static GPS is ± 2cm, that the deformation monitoring accuracy should be greater than 1/5 of deformation in the measurement period according to the monitoring code of landslide, and that single frequency static GPS is suitable for the landslide whose vertical deformation is above 10 cm in its monitoring period. For the Shuping landslide,GPS measurement can provide good monitoring data in the second to third period whose vertical deformation is up to 30 cm,but it is unsuitable for other monitoring periods in slow state.
How to obtain suitable threshold to distinguish radiation fog,clear sky surface and clouds is the focus of the study of fog detection. The Santa Barbara DISORT atmospheric radiative transfer(SBDART)model can simulate the fog top brightness temperature. In this paper,the authors obtained the brightness temperature difference(BTD)between MODIS B20 and MODIS B31 bands based on the model and applied it to the detection of radiation fog at night. The data used for feasibility test were from EOS MODIS satellite in the North China Plain on November 25, 2007,and ground validation data were from the National Satellite Meteorological Center. The varification results show that the accuracy of using the model to monitor the night time radiation fog (POD)is 78.3%,the false alarm rate (FAR)is 21.7%, the reliability index(CSI)is 0.643,and the Kappa factor is 0.730. To further validate the stability of the method,the authors selected the sequence of eight satellite images in northern China for the time series analysis. The results show that the mean value of reliability index is 0.744,suggesting that the proposed method can serve as the foundation of night time fog forecasting and parameter inversion.
The spatial resolution of hyperspectral data is generally very low,the mixed pixels are extensively distributed, and hence fuzzy classification is commonly used in the mixed pixel analysis. As the accuracy of fuzzy classification is often limited by the feature dimensions and fuzzy samples selection,the random forest (RF) algorithm is put forward in this paper to select features and obtain fuzzy samples; in the low-dimensional feature space, fuzzy samples are used to make fuzzy classification. Fuzzy classification and RF are merged by using two-step classification,following the principle of unanimity assumption. Using different samples,different experimental areas and different partition optimization situations,the authors conducted three comparative experiments, and the results show that the method proposed in this paper solves the limitation of fuzzy classification and improves its accuracy. It is also proved that the classification accuracy of the method is robust for the original sample.
In consideration of the features of remarkable difference in the gray-scale of the remote sensing image with multi-scales,this paper presents an image registration method with improved Hausdorff distance based on scale-invariant to solve the registration of multi-source remote sensing images. According to the method,the scale-invariant features of multi-scale images were firstly extracted by using the feature extraction method based on scale-invariant feature transform(SIFT),and then the Hausdorff distance was used as the fitness function to seek for geometric image transformation parameters with the help of genetic algorithm(GA). At last,the image to be registered was re-sampled by using the transformation parameters and matched with the references image. The experimental results show that,compared with the traditional method of Hausdorff distance,the new method has higher registration accuracy and stability, and is more suitable for image registration.
Rapid and accurate access to the oil spill information is of great significance for dynamic monitoring, conservation and sustainable use of the oceans. HJ-1 is a new satellite platform designed for ecological environmental pollutions and disasters. However, the multispectral image obtained from HJ-CCD has insufficient spectral bands, and the accuracy of acquiring the oil spill coverage only by spectral information is low. In this paper, the oil spill that occurred in the Gulf of Mexico was selected as the research object. Based on the spectral analysis of different features, the authors chose the right texture structure factors and extracted the texture characteristics which affect oil spill identification by gray co-occurrence matrix. A decision tree model combining spectral characteristics with texture characteristics was established to extract the oil spill on the sea surface. A comparative analysis by using the result of maximum likelihood supervision classification method was performed, and the results show that, in comparison with the maximum likelihood classification method, the decision tree method could improve the user's accuracy and the producer's accuracy of oil spill extraction by 11.85% and 4.28% respectively.
For the purpose of better predicting the soil organic matter content in the study area, the soil near the tailings dam of the Dexing copper mine was chosen as the study object. Using the ASD device in the laboratory, the authors measured 68 groups of soil samples and, by studying soil reflectance spectral characteristics, took the logarithmic differential transformation of the selected reflectance spectra as the dependent variable of the soil organic matter prediction model. The correlation analysis of soil organic matter and soil spectra showed that the first derivative of logarithm of 402 nm and 2 312 nm wavelength reflectance was the best. Finally, from the multiple regression analysis and fuzzy mathematics, two models of organic matter content prediction were established. The results demonstrate that the research method based on fuzzy mathematics is better than multiple linear regressions, with the correlation coefficient up to 89.3% and the error relatively smaller. Studies have shown that using ground measured spectra to predict soil organic matter content has such advantages as short cycle and low cost.
The application of the Radar remote sensing data to landslide investigation is of great importance, especially in cloudy and rainy areas. The high-performance airborne synthetic aperture Radar system(HASARS) developed by Institute of Electronics,Chinese Academy of Sciences,is the first home-made system characterized by multi-band and multi-mode,which has the capability of interferometric survey of X band and double antennas as well as polarimetric observation of P band. In this paper, the accuracies of landslide information extraction from polarimetric SAR data using different polarization combinations were investigated to evaluate the technology, methodology and implementation ideas of the landslide applications with the HASARS, and the focuses included two aspects: the methods of information extraction and the ways to select the feature. The results show that, based on Bayes decision theory and using the samples of landslide and non-landslide in the image to analyze and make decision, the method of feature selection could make classification of polarimetric SAR image satisfactorily. Based on the results of feature selection, the authors extracted the landslide regions from SAR images with supervised classification methods, with their accuracies higher than 90%. The airborne SAR system, with high spatial resolution, high precision DEM production and P band polarimetric observations, can obtain the thematic information of landslide surface more flexibly and precisely, and hence it has a broad prospect in the landslide disaster relief applications.