## 4 Results
### Geolocation Accuracy of the BNU-1 L1B Product  
The verification points used to evaluate the geolocation errors of the BNU-1 L1B product for the Sample Images A, B, C, and D are shown in Figure 10a. We compared the coordinates of verification points in the BNU-1 L1A/L1B images with those in the corresponding MODIS images in Figure 10b, c. The verification points extracted from the BNU-1 L1A product (green dots) are distributed on one side of the 1:1 line (black diagonal line), which means that geolocation errors exist in the BNU-1 L1A product, while the verification points extracted from the BNU-1 L1B product (red dots) are almost scattered on the 1:1 line. We fitted the linear relationships between the coordinates of the verification points from BNU-1 L1A/BUN-1 L1B and the MODIS image. The regression coefficients, intercepts, and determined coefficients of the relationship fitted by the BNU-1 L1B product are significantly better than those fitted by BNU-1 L1A. The coordinates of the points from the BNU-1 L1B product show great consistency with the coordinates from the MODIS images. The geolocation accuracy of the BNU-1 L1B images was improved significantly. After geometric correction, the average geolocation error was reduced from 10,480.31 m to 301.14 m (Table 1).  
We obtained the image mosaics of the Amery Ice Shelf and Victoria Land in Antarctica and northern Greenland in the panchromatic band of BNU-1 (Figure 11). Mismatches in the coastlines were found in the image mosaics from the BNU-1 L1A product. However, the coastlines in the image mosaics from the BNU-1 L1B product are consistent with the existing coastline dataset [25]. Even though the junction of adjacent images in the image mosaic from the BNU-1 L1B product has greatly improved coherence compared to the BNU-1 L1A product, the BNU-1 L1B product still has an average geolocation error of \(\sim\)300 m. For example, the discontinuous waters at the junction are found in Victoria Land (obvious mismatches in the yellow circle in Figure 11a) from the BNU-1 L1A product, while the mosaic from the BNU-1 L1B product has consistent waters at the junction regions (slight mismatches in the green circle in Figure 11a).  
Figure 9: BNU-1 image after geometric correction of the BNU-1 L1A image using the CPs extracted from the original image (**a**) and Scheme 2 (**b**). The corrected image with 50% transparency is superimposed on the corresponding MODIS image in (**b**).  
Figure 10: Spatial distribution of the verification points for accuracy evaluation of BNU-1 L1B Sample Images A, B, C, and D (**a**); and the coordinates comparison of the verification points of BNU-1 L1A/L1B Sample Image A, B, D, and E and their corresponding MODIS images, in X-direction (**b**) and Y-direction (**c**), respectively. [PERSON] and red dots represent the verification points on the BNU-1 L1A image and the BNU-1 L1B image, respectively. The black diagonal line in the sub-figures represents that the coordinates of points in the BNU-1 image are almost equal to those in the corresponding MODIS image. The two small graphs in each sub-graph are the enlarged version of the orange and blue rectangular areas on the black diagonal line.  
Figure 11: Mosaic of the panchromatic band images of some BNU-1 L1A/L1B Sample images: (**a**) Antarctica; (**b**) Greenland. The blue lines represent the existing coastline dataset.