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

A prototype for 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, very narrow band image of a scene. By stepping all three etalons together, each pixel scans a spectrum with resolution on the order of 0.0025~nm. 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 very high resolution spectra acquired over a two dimensional scene. The curent instrument is a prototype 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 report on the status of the testing and calibration of the instrument. We will also describe plans for upcoming aircraft flight tests in early 2008. GIFS will be flown on a NASA P3 acquiring cloud parameter measurements, while a Langley King Air flying in formation observes the same clouds with lidar (HRLS) and an O2 atmospheric band spectrometer (LAABS) for validation.