Spectral calibration of imaging spectrometers by atmospheric absorption feature matching

Abstract

A procedure has been developed to measure the band centres and bandwidths for imaging spectrometers using data acquired by the sensor in flight. This is done for each across-track pixel, thus allowing the measurement of the instrument's slit curvature or spectral "smile." The procedure uses spectral features present in the at-sensor radiance that are common to all pixels in the scene. These are principally atmospheric absorption lines. The band-centre and bandwidth determinations are made by correlating the sensor-measured radiance with a modelled radiance, the latter calculated using MODTRAN 4.2. Measurements have been made for a number of instruments, including the Airborne Visible / Infrared Imaging Spectrometer (AVIRIS), shortwave infrared full spectrum imager (SFSI), Compact Airborne Spectrographic Imager (casi), compact high-resolution imaging spectrometer (CHRIS), and Hyperion. The measurements on AVIRIS data were performed as a test of the procedure; since AVIRIS is a whisk-broom scanner, it is expected to be free of spectral smile. SFSI and casi are airborne pushbroom instruments, and CHRIS and Hyperion are satellite pushbroom sensors all exhibiting, to varying degrees, spectral smile. Measurements of Hyperion were made using three different datasets to check for temporal variations.