Calibration of CRISM/MRO apparent wavelengths using synthetic data

The Compact Reconnaissance Instrument Spectrometer for Mars (CRISM) is a hyperspectral imager that is affected by optical distortions onto its spatial-spectral detector matrix that is also non-uniform in responsivity. In particular, central wavelength of the spectral response varies along the spatial dimension of the array, thus giving rise to artifacts in the data. An accurate knowledge of the point spread function (PSF) of each individual detector of the matrix is fundamental to correct for these effects. In this work, CRISM images from the poles of Mars are noticed to suffer from wavelength shifts that do not agree with pre-launch calibration data. The source of this instrumental anomaly is identified as a faulty flat fielding in the CRISM data pipeline and a method that is based on synthetic spectra is introduced for wavelength calibration. In the experiments, a polar CRISM image is calibrated by estimating its apparent wavelengths. Results are finally compared with the same test image after undergoing a prototype calibration that does not present the wavelength anomaly.