Radiometric properties of the NS001 Thematic Mapper Simulator aircraft multispectral scanner

Abstract

The radiometry of the NS001 Thematic Mapper Simulator reflective channels was examined based on laboratory tests conducted between 1987 and 1989. Principal emphasis was on absolute calibration. The NS001 data are calibrated in-flight by reference to the NS001 internal integrating sphere source. Apparent instabilities in this source or its monitoring circuitry, which are not fully understood, are the principal limiting factors in the absolute calibration of NS001 data. Uncertainties due solely to this behavior may reach 25% in 1987, though more typically are expected to be less than 15%. Other identified error sources at the 1–2% level for typical signals include dark current drift along the scan line, hysteresislike sensitivity changes along the scan line, random noise, scan-speed-induced and nonlinearity. Channel 7 (2.08-2.35 μm) shows a number of peculiarities that are hysteresislike including a change in the apparent dark current drift along scan with scene brightness and a drop in sensitivity in scanning across a bright target of an estimated 8% over the total 100° scan angle. Polarization sensitivity of the NS001 was such that for typical atmospheric conditions errors in Channel 1 (.45–.52 μm) radiances would be up to ±10% and vary with scan angle; this progressively decreases with increasing wavelength.