Fig. 1. VNIR-SWIR reflection spectra of Kaolinite, Halloysite and Montmorillonite. (a) Typical spectral curve; (b) local enlarged drawing of the selected area in Fig. 1(a)

Fig. 2. VNIR-SWIR reflection spectra of HEDs. (a) Spectral curve of HEDs from different regions; (b) local enlarged drawing of the selected area in Fig. 2(a)

Fig. 3. Diagram of the partitioned diffraction gratings

Fig. 4. Imaging diagram of Rowland circles on meridional image locations

Fig. 5. Steps to calculate the initial structure

Fig. 6. Optical layout of the designed optical system

Fig. 7. Spot diagram of designed optical system

Fig. 8. Curve of the smile versus the normalized field of view

Fig. 9. Curve of the keystone versus the normalized field of view

Fig. 10. Diffraction efficiency of gratings in VNIR band. (a) Diffraction efficiency at different blaze angles; (b) combined diffraction efficiency with different area ratios

Fig. 11. Diffraction efficiency of gratings in SWIR band

Fig. 12. Partitioned grating and the prototype of the designed optical system. (a) Partitioned grating; (b) prototype of the designed optical system

Fig. 13. Photo of the spectrum performance measurement device for the VNIR band

Fig. 14. Spectral image and intensity distribution curves in the VNIR band

Fig. 15. Photo of the spectrum performance measurement device for the SWIR band

Fig. 16. Spectral image and intensity distribution curves at 1900 nm