Toward scene-based retrieval of spectral response functions for hyperspectral imagers using Fraunhofer features

Abstract

Initial steps are proposed and tested in the development of a method for retrieving and (or) refining instrument spectral characteristics for dispersive hyperspectral imagers such as the Airborne Visible / Infrared Imaging Spectrometer (AVIRIS), Compact Airborne Spectrographic Imager (casi), HyMap, Hyperion, and compact high-resolution imaging spectrometer (CHRIS) based on data acquired by the instrument in operation using statistical spectrum matching with moderate-resolution transmittance code (MODTRAN) modelled instrument results in the vicinity of reference Fraunhofer feature windows. Until now, such scene-based retrieval has focused primarily on refining spectral band-centre shifts while assuming that spectral response function (SRF) parameters remain static. In particular, most methods assume that the SRF is of a Gaussian shape. As a consequence of recent investigations showing that scene-based discernment of SRF shape should be feasible given current typical instrument performance, this paper explores algorithmic components deemed necessary for the development of a look-up table (LUT) based retrieval method for obtaining SRF parameters on a band-by-band basis, even in the presence of minor band-centre or bandwidth deviations from nominal instrument specifications. The proposed method employing these components is appropriate for dispersive hyperspectral imagers but not for others, for example Fourier transform hyperspectral imagers. In experiments using nominal implementations of the proposed components, reference spectra match expected LUT spectra in nearly all cases, even when band-centre and bandwidth deviations are considered. This holds true for all three modelled instruments and nearly all of the six selected Fraunhofer windows. Expected signal-to-noise requirements are in many cases challenging, yet feasible using signal-enhancement techniques such as along-track averaging.