Long-slit polarization-insensitive imaging spectrometer for wide-swath hyperspectral remote sensing from a geostationary orbit.

To improve the swath width and quantitative accuracy of hyperspectral payloads on a geostationary orbit, a long-slit polarization-insensitive imaging spectrometer is designed and demonstrated in this paper. For the wide swath, several long-slit spectrometers with the same specification have been designed and compared. The result shows that the Wynne-Offner spectrometer has advantages in increasing slit length and reducing volume, and it is suitable for being spliced for ultra-wide swath. To solve the problem of inaccurate radiation measuring caused by the polarization of imaging spectrometers, the requirement for linear polarization sensitivity (LPS) is theoretically analyzed and assessed. As diffraction grating is the main polarization-sensitive element in an imaging spectrometer, we propose to increase the apical angle of the grating groove to reduce its LPS and compensate its residual polarization by specially polarized optical films coated on lens surfaces, thus the polarization-insensitive system is achieved. At last, a VNIR spectrometer with superior spatial and spectral performance is developed, and its slit is 61.44 mm long. The maximum LPS of this system is reduced from 10.0% to 2.3% (test 2.5%) after the depolarization design, which greatly reduces the uncertainty of the measuring radiation caused by polarization. The developed imaging spectrometer can play a role in quantitative hyperspectral remote sensing, especially in wide-swath applications on geostationary orbit.