A triple-etalon imaging interferometer for Earth and planetary remote sensing

A space-borne, high spectral resolution interferometer is being developed under the NASA Earth Science Technology Office Instrument Incubator Program. The instrument includes three vacuum or air spaced Fabry- Perot etalons, each of them tunable by piezoelectric adjustment of the etalon gaps. Together with imaging optics and a two dimensional array detector, the instrument acquires a 2-D, high-spectral resolution image of a scene when the etalons are tuned in resonance. By stepping all three etalons together, each pixel scans a spectrum with resolution on the order of 0.05~cm-1. Combination of three etalons with appropriately selected free spectral ranges improves rejection of out-of-band light, so that the interferometer can achieve good performance in the presence of a strong continuum background. This instrument concept could be applied to any remote sensing application requiring near-simultaneous acquisition of very high resolution spectra over a two dimensional scene. We are currently developing a prototype of a system for global observation of cloud parameters from geosynchronous orbit. The Geostationary Imaging Fabry-Perot Spectrometer (GIFS) would derive cloud top pressure, optical depth, and cloud fraction from the pressure- broadened line shape of O2 absorption lines near 690~nm. Other potential applications include mapping of trace gas concentrations or chlorophyll fluorescence. Though current work centers on applications in the visible and near infrared using CCD detectors, the concept could be extended to the infrared with, for example, 2-D HgCdTe array detectors. We will describe the measurement concept and instrument design, and discuss the performance expected in the cloud sensing application. We will also overview the GIFS development status and laboratory and aircraft test plans.