New 3-5 μ wavelength range hyperspectral imager for ground and airborne use based on a single-element interferometer

Spectral imagers rely mainly on two techniques for collection of spectral information: gratings and interferometers. The former type needs cooling of the optics to avoid background signals which significantly limit the dynamic range of the measurement. The latter type, in its present commercial configurations, is not suitable for pushbroom operation in an airborne situation. A recent spectral imager configuration based on a shearing interferometer has been shown to be suitable for pushbroom operation without the need for cooling the optics. In this paper we describe the planned implementation of such a spectral imager for the 3-5 μ range, where the interferometer is a specially designed single prism. The advantages of this interferometer configuration are: i) compact optics, ii) high S/N ratio in the 3-5 μ range with small optical collection diameter, and iii) enhanced mechanical stability. The instrument yields a spectrum for 320x240 pixels of the image with a spectral resolution of better than 50 cm-1. The spectrum is calibrated in units of Watt/(steradian.cm2.cm-1). If used in an airborne pushbroom mode it provides a swath width of 240 pixels in a ~6.9 degree transverse field of view. If used in a horizon scanning configuration, it has a vertical field of ~6.9° and a horizontal field up to 300 degrees. The IFOV is 0.5 milliradians. In this paper the major instrument design considerations are presented. The instrument is being constructed and we will give more details on actual performance and examples of measurement results in a future paper, as we gain more experience. An 8-12 μ range version is also planned for the near future.