Far-field diffraction and focal plane misalignment effects on simulated GIFTS data from the IHOP field program

Abstract

The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) and the Hyperspectral Environmental Suite (HES) instruments are geostationary infrared spectrometers. Geostationary orbit provides observations with very good time resolution, but also increases the effect of diffraction. There can be significant differences in emitted radiances due to clouds and changes in surface characteristics. High, thick clouds in particular are much cooler than clear areas. Diffraction causes radiation that originates from cloudy areas outside of the detector field of view to contaminate the clear pixels. GIFTS will also have two detector arrays on different focal planes, which may not be perfectly aligned. This can cause spatial misalignment between the data for the two spectral regions. High spatial resolution numerical models run at the University of Wisconsin - Cooperative Institute for Meteorological Satellite Studies (UW-CIMSS) provide data for examining the diffraction and misalignment effects. The model data represents a variable cloud case during the IHOP field experiment at 1.3-km resolution. This paper outlines the production of high spatial resolution simulated data, characterization of the far field diffraction effects on radiances, and analysis of misalignment effects on temperature and moisture profile retrievals.