Detection and Correction of Spectral Shift Effects for the Airborne Prism Experiment

Abstract

Shifts of center wavelengths (CWLs) and related changes of full-widths at half-maximums (FWHMs) occur during in-flight data acquisitions of push-broom imaging spectrometers such as the airborne prism experiment (APEX). Combined with the spectrally changing properties of the dichroic coating that acts as a beam splitter between the visible and near infrared (VNIR) as well as the short-wave infrared (SWIR) channels, these shifts affect both the spectral and radiometric accuracies of the spectrometer data, and hence the accuracy of higher level products. In this paper, two independent standards, i.e., atmospheric absorption features as well as features of the standard reference material filter built in the APEX in-flight characterization facility, are used in a complementary way to improve in-flight spectral calibration. The CWL shift and FWHM change for each detector element are simultaneously detected by using spectrum-matching and surface fitting techniques under constraints from pregenerated shift realizations. Subsequently, the APEX spectroradiometric response model is improved in the aspect of spectral resolution by using performance parameters of optics and detector modules. The radiometric gain and offset for each detector element are corrected according to the detected CWLs and FWHMs, as well as the improved APEX response model. Compared with the spectral and radiometric parameters acquired during laboratory calibration, the detected CWLs and FWHMs promote the accuracy of the atmospheric feature positions in the SWIR channel by 10 nm, whereas the corrected gains and offsets reduce the radiance deviation in the spectral regions 375–550 nm and 950–1080 nm both by 70% on average.