Vicarious calibration of airborne hyperspectral sensors in operational environments

A reflectance-based vicarious calibration (RBVC) method has been used to correct the radiometric coefficients for hyperspectral data obtained with the Probe 1 sensor over the Raglan region of northern Quebec, and to perform a radiance renormalisation for compact airborne spectrographic imager (casi) data obtained over Goose Bay, Labrador. It relies on the simultaneous acquisition of ground-based reflectance spectra for at least one calibration site within the hyperspectral flight line. The RBVC method yields a new set of radiometric coefficients that convert the hyperspectral data from digital numbers (DNs) to radiances, and that are applicable to flight lines taken under different conditions. For both the Raglan and the Goose Bay projects, the calibration site was a gravel airstrip, and ground-based reflectance measurements were made with a GER3700 field spectrometer using a Spectralon panel for reference. This represents a novel use of the RBVC method for validation and correction of the sensorʹs radiometric calibration at the time of data acquisition, applied in an operational setting that lacks a large, bright and homogeneous calibration target and well-characterized atmospheric conditions. Analysis of the errors involved in correcting the radiometric coefficients yielded a total relative error (averaged over wavelength) of 3.9–5.6% on the final reflectance spectra.