PRACTICAL EXAMPLE OF THE CORRECTION OF FOURIER-TRANSFORM SPECTRA FOR DETECTOR NONLINEARITY

HgCdTe photoconductive detectors can display a nonlinear response when illuminated. In interferometric applications, this behavior must be a ccounted for in the data transformation process to avoid erros in the measurement of the spectral distribution of the incident radiation. A model for the distortion of the interferogram is proposed and applied to solar observations made by the Atmospheric Trace Molecule Spectrosc opy (ATMOS) Fourier-transform spectrometer during orbital sunrise and sunset from the Space Shuttle. Empirical estimation of the dc current level is necessary for this instrument, and satisfactory nonlinearity correction is obtained for several of the primary ATMOS optical filter s. For ATMOS broadband optical filters that cover more than one half t he alias bandwidth, the model is inadequate because of the presence of antialising electronic filters within the instrument, and it is neces sary to resort to estimation and subtraction of the residual baseline offset. In either case the remaining baseline offsets are typically sm aller than 1%, which is satisfactory, although offset remains a signif icant systematic source of error in the estimation of the abundance of telluric and solar constituents from the spectra.