Forward calculation for interferometers: method and validation

摘要

An approach to approximating the instrument response for an unapodized interferometer is presented. The approach comprises functions that are local enough in frequency space (no more than five wave numbers) that one can use the Planck function at a single frequency to calculate the radiance at a given frequency and atmospheric pressure level, and it is well behaved (transmittances change monotonically from 1.0 to 0.0), so existing transmittance calculation procedures can be used. It is faster than calculating radiances at a high resolution, doing a Fourier transform, and then doing a second transform, and it produces brightness temperatures that agree with exact values to better than the 0.01 K that is due to errors in the approximation. The approach is accurate enough and fast enough to be used for calculating unapodized radiances from an interferometer. It also can be used to calculate transmittances as well as radiances. (C) 1998 Optical Society of America. [References: 10]