Early Results from an Imaging Interferometer Prototype Operating in the Sagnac Configuration

Recent advances in Earth remote sensing imagers have being attempted with the launch of the first Fourier Transform Hyperspectral Imager placed on board of U.S. Department of Defence. From the analysis of alternative optical layouts for a stationary interferometer, we have developed a laboratory imaging interferometer operating in the Sagnac configuration. This instrument does not employ any moving part to optically scan the instrument field-of-view, and acquires the image of the observed target modulated from a staring interference pattern of vertical fringes. Despite of traditional Michelson-like interferometers, the intensity autocorrelation functions are generated by moving the concerned scene with respect to the imaging device. In this paper we present some laboratory measurements obtained by this new stationary imaging interferometer. In order to calibrate the instrument response and to determine its spectral resolution, we have executed a set of measurements illuminating a planar double diffuser with a red HeNe laser. The dependence of the optical-path-differences on the source spectral content has been assessed observing a 600W halogen lamp with interference filters having 10nm of bandwidth. In order to retrieve at-sensor radiance spectrum a calibration procedure of the acquired data has been implemented, which also takes into account dark signal subtraction, instrument spatial response compensation, geometrical and radiation distortion correction, DC-offset subtraction, and inverse cosine transform. Some hints are given about the use of such an instrument on board of airborne platforms for remote sensing of the Earth.