JPSS-1 CrIS Measurement Noise Covariance Characterization at Full Spectral Resolution

The Crosstrack Infrared Sounder (CrIS) flight module 2 is scheduled for launch into orbit in 2017 on-board the JPSS-1 satellite. CrIS is an IR Fourier Transform Spectrometer that acquires interferograms measuring the spectral radiance from 650 to 2550 cm-1 (3.9 to 15.4 micron) separated into three frequency bands, namely the LWIR (650-1095 cm-1), the MWIR (1210-1750 cm-1), and the SWIR (2155-2550 cm-1). CrIS detectors form a 3 by 3 grid array (one center, 4 sides and 4 corners) for each bands for a total of 27 detectors. During the TVAC testing, the scan scenario data set acquired data at full spectral resolution (0.625 cm-1 spectral resolution for all 3 bands) configured with the normal operational mode. Using the SDR algorithm, the spectral radiance of the external calibration target or ECT , a high emissivity black body, was calculated. The ECT radiance measurements were decomposed using the principal component analysis tool. The data set was reconstructed by removing the first singular value. From this reconstructed data set, the measurement noise full covariance matrix was calculated for unapodized data. The noise equivalent radiance differential (NEdN) shows an increase as function of the off-axis position of the detector affecting mostly the SWIR band. The corner detectors have higher noise than the side detectors and the center detector has the least. This feature is due to the nature of the inverse self-apodization function. The covariance matrix shows strong correlated noise (up to -0.5 correlation factor) for off-diagonal terms mostly in the SWIR band for the off-axis detectors. By applying the Hamming apodization to the data set, the NEdN and the correlated noise are greatly reduced. The noise measurement covariance matrix is important as it is used by the retrieval algorithm in order to calculate the atmospheric profiles.