Performance and polarization response of slit homogenizers for the GeoCarb mission

Abstract. The observing strategy of the Geostationary Carbon Observatory (GeoCarb), which is a “step and stare” approach, can lead to distortions in instrument spectral response function (ISRF) when there are gradients brightness across field view. These induce errors retrieved trace gases. In order minimize these errors, GeoCarb design was modified include “slit homogenizer” whose purpose scramble pattern incoming light effectively remove ISRF caused by variations illumination slit. As risk reduction, procured six different homogenizers had them tested for performance benchtop optical system. major finding that homogenizer depends strongly on polarization light, with sensitivity growing as wavelength. width substantially smaller vertically polarized (orthogonal slit length) compared horizontally (parallel length), throughput accordingly reduced. effects due gold coating high incidence angles present design, verified using polarization-dependent model generalized from previous modeling work. results recommend controlling entering similar implementation polarizer, depolarizer, or scrambler other instruments attempting mitigate scene non-uniformity effects, well robust characterization all key subsystems.