## 3 Results
### Evaluations of the Corrected BNU-1 Images  
The spectral information of several typical ground objects was collected at four ground locations which are near Zhongshan Station, East Antarctica in December 2019 (Figure 11). The land cover information and acquisition time of spectral information are shown in Table 2. A total of 40 spectral signatures from three typical surfaces, including snow, lichen, and rock, were observed. The spectral signatures are compared with the observations of the corrected BNU-1 image. Landsat-8 OLI imagery is also used for ground verification due to it having comparable spectral wavelength range at RGB bands and panchromatic bands as BNU-1 imagery. Two images are used to calculate the corresponding radiance at the ground locations. One is the BNU-1 image acquired on 13 December 2019. The other is the Landsat-8 OLI image acquired on 12 December 2019. Both images are chosen since their acquisition time is the closest to the ground spectrum collection time in the field. Figure 11: Four ground field locations in East Antarctica. The red box in (**a**) shows the location of the ground fields in Antarctica. The black box in (**a**) shows the spatial region where the 10,000 random point pairs were generated for further assessment. (**b,c**) shows four ground field locations in East Antarctica superimposed on top of true color composite images (**a**) Landsat-8 OLI acquired on 12 December 2019 and (**b**) the corrected BNU-1 acquired on 13 December 2019. Figure 10: Comparisons of the original and corrected BNU-1 images. The images shown in (**a,d**) are acquired on 6 June 2020 (orbit number: 200020455). The images shown in (**b,e**) are acquired on 5 July 2020 (orbit number: 200021032). The images shown in (**c,f**) are acquired on 6 June 2020 (orbit number: 200020458). The evaluations of spectral radiance from original, corrected BNU-1 image and Landsat8 OLI image by using ground observations are shown in Table 3. Compared to the uncorrected images, the spectral radiances of the corrected images remain unchanged in the panchromatic band. The spectral radiances of green (B2) and red (B3) bands are slightly increased, with a general increase of 1-20 \(W/\mathrm{m}^{2}/\upmu\mathrm{m}/\mathrm{sr}\). The most significant increase is detected in the blue (B1) band, with an increase of 20-70 \(W/\mathrm{m}^{2}/\upmu\mathrm{m}/\mathrm{sr}\). The radiances are most increased on high-reflectance surfaces, such as ice, while they increase less on surfaces with low reflectance, such as rock and lichen. In comparison with the Landsat8 OLI image of the same band, the uncorrected BNU-1 image had slightly higher spectral radiances of low-reflectance surfaces in the green and red bands, such as rocks and lichens, while the radiance in the blue band is much lower than the OLI image. This result indicates that the spectral radiances of uncorrected BNU-1 image have a significant deviation in the blue band. After correction, the radiances of the corrected BNU-1 image in the blue band are consistent with the red and green bands, both being higher than the OLI image. On high-reflectance snow surfaces, the radiances of the uncorrected image in the blue, red, and green bands are significantly lower than the OLI image, while the radiances of the corrected BNU-1 image are close to the OLI image. All the above results indicate that the corrected BNU-1 image has better consistency with the OLI image than the uncorrected one. Compared with the ground radiance measurements, the radiances of corrected BNU-1 image are consistent across all bands with OLI and closely matched with the ground observations on the high-reflectance snow surface. On the low-reflectance surfaces, the corrected BNU-1 image and OLI image are both significantly higher than ground measurements. The underestimation of radiances in the BNU-1 and OLI images may be due to the difference in spatial scale between satellite remote sensing images and ground observations.