Abstract:
Changes in the vegetation index can reflect variations in vegetation cover and growth in the region to some extent. Monitoring the changes in vegetation index time-series data plays a significant role in local agricultural management. However,existing methods for vegetation index time-series data reconstruction face challenges such as a single data source input and low spatial resolution of reconstruction results. In response to this,this paper proposes a reconstruction method for vegetation index time-series data that integrates the satellite data standardization method and the crop reference curve method. Consequently,it reconstructed vegetation index time-series data with high spatiotemporal resolution for winter wheat in the study area in 2021,including normalized differential vegetation index (NDVI) and enhanced vegetation index (EVI). The results show that after reflectance normalization,the coefficient of determination (R
2) for GF-1 satellite and VIIRS surface reflectance data in red,green,infrared,and near infrared bands generally increased by 0.05%,with a few exceeding 0.1%. The root mean square error (RMSE) was reduced,with the majority decreasing by 0.01. In contrast,the relative root mean square error (rRMSE) showed a reduction of about 2%. Most data from the GF-6 satellites exhibited an increase of about 0.12 in
R2,a decrease of 0.03 in
RMSE,and a general decline in
rRMSE ranging from 3% to 4%. In contrast,the data from the Sentinel-2 satellite show an overall increase of about 0.05 in
R2,as well as a decrease of around 0.001 and 2% in
RMSE and
rRMSE,respectively. The accuracy assessment results for the reconstructed high-resolution vegetation index time-series data indicate that the NDVI time-series reconstruction results presented high
R2 values in the validation period,with five validation images reaching 0.49 and above. The
RMSE was less than 0.1 in all validation periods,while the relative error (RE) was less than 15% in most cases,with only one validation image reaching 18%. Similarly,the EVI time-series reconstruction results also exhibited high
R2 values,with five validation images above 0.44. Both
RMSE and
rRMSE values were less than 0.15 and 20%,respectively.