Fig. 1. Schematic diagram of UAV observation scheme

Fig. 2. Surface reflectance spectra of different sites at different times. (a) Surface reflectance spectra of XCDH_W at different times on August 11, 2019; (b) surface reflectance spectra of SHDBAN at different times on August 13, 2019; (c) spectral comparison among XCDH_W, SHDBAN and DHANG at same time or adjacent time; (d) Comparison of reflectance spectra among XCDH_W, SHDBAN, DHANG, YCZG, DAZH_E and DAZH_W

Fig. 3. Surface reflectance spectra at different scales. (a) Comparison between surface reflectance spectra measured by SVC and spectra of MCD43 reflectance product at XCDH_W and SHDBAN; (b) comparison between surface reflectance spectra measured by UAV and SVC at XCDH_W and SHDBANC

Fig. 4. Schematic diagram of spectral angle

Fig. 5. Sensitivity analysis of surface reflectance with four parameters. (a) Surface reflectance varying with A; (b) surface reflectance varying with β; (c) surface reflectance varying with α; (d) surface reflectance varying with B

Fig. 6. Comparison between measured and simulated reflectance spectra of calibration sites. (a) ALSH, WHAI_W, BDJL; (b) YCZG, XCDH_W, DAZH_W, DAZH_E;(c) MQIN, DHUANG, SHDBAN

Fig. 7. Relative deviation of reflectance of top of atmosphere for different MERSI channels based on two different surface reflectance spectra

Table 1. Latitude and longitude information of 10 calibration sites

Table 2. Relative deviation of reflectance between SVC and MODIS observationsunit: %

Table 3. Spectral angle, RMSE and R of reflectance spectra observed by SVC and UAV

Table 4. Spectral model parameters and statistical factors for different sites

Table 5. Observational geometry and atmospheric parameters of SHDBAN and XCDH_W