Imaging spatial heterodyne spectroscopy (ISHS) was invented by Roesler and Harlander and applied to the far UV. It also has advantages for remote sensing applications in the visible and IR bands. We have designed, assembled, and ground-tested a new instrument designed for eventual airborne or spaceborne deployment for imaging spectroscopy at ultraspectral resolution. IRISHS is a true, imaging, Fourier transform spectrometer (FTS) with a fully open square field of view, where the third dimension required to assemble data cubes is acquired by scanning the FOV linearly over the scene. Spatially displayed fringes are difference with a spatial frequency determined by a pair of diffraction gratings, giving easily sampled fringe patterns. The current system operates between 8 and 12.5 microns in six sub-bands and employs a 256 X 256 pixel focal plane array. In comparison to dispersive imaging spectrometers with equivalent resolution, ISHS has: 1) much larger etendue in a small package; 2) full-field imaging for ease in image reconstruction; 3) approximately the same signal-to-noise ratio in equivalent observing scenarios, expect in the case where the entire dispersive spectrometer is cryogenically cooled. In comparison to conventional FTS, ISHS has: 1) no moving parts during data collection; 2) pushbroom imaging, 3) approximately the same S/N for equivalent conditions, 4) much lower data rate.
We present the Infrared Imaging Spatial Heterodyne Spectrometer (IRISHS) experiment. IRISHS is a new hyperspectral imaging spectrometer for remote sensing being developed by Los Alamos National Laboratory for use in identifying and assaying gases in the atmosphere when viewed against the Earth's background. The prototype instrument, which can operate between 8 and 11.5 micrometers (although the current IR camera operates from 8 - 9.5 micrometers), will be described. Imaging spatial heterodyne spectrometer technology is discussed in four companion papers also presented at this symposium.
The hemispherical optimized net radiometer (HONER) is an instrument under development at the Los Alamos National Laboratory as part of the Atmospheric Radiation measurements/Unmanned Aerospace Vehicles (ARM/UAV) program. HONER is a radiometer which will either measure directly the difference between the total upwelling and downwelling fluxes or the individual fluxes and will provide a means of measuring the atmospheric radiative flux divergence. Unlike existing instruments which only measure the upwelling and downwelling fluxes separately, HONER will achieve an optical difference by chopping the two fluxes alternately onto a common pyroelectric detector. HONER will provide data resolved into the two relevant spectral bands; one covering the solar dominated region from less than 0.4 micrometer to approximately 4 micrometers and the other covering the region from approximately 4 micrometers to greater than 50 micrometers, dominated by thermal radiation. The means of separating the spectral regions guarantees seamless summation to calculate the total flux. The fields-of-view are near-hemispherical, upward and downward. The instrument can be converted, in flight, from the differential mode to absolute mode, measuring the upwelling and downwelling fluxes separately and simultaneously. The instrument also features continuous calibration from on-board sources. We describe the basic design and operation of the sensor head and the on-board reference sources as well as the means of the initial deployment on a UAV. This instrument can also be used in ground-based, space, or other airborne applications.
We have developed a mathematical model of a technique in which a pyramidal arrangement of wavelength-selective optical detectors can be used to determine the identity (wavelength), intensity, and direction of arrival of laser irradiation. The advantages of this technique are that only unobtrusive, skin-like structures are required and that the large collection areas provide high sensitivity. The disadvantage is that the angular resolution (approximately 5 degrees in a 60 degree field of view) is less than that which can be achieved using methods requiring thicker structures. The detector elements are large-area, polyvinylidine fluoride, pyroelectric devices with wavelength selective coatings. We situated four identical arrays of these elements on the top and sides of a frustrated, three-sided prism. Because only the relative orientations are significant, we are able to use selected regions on the surface of an existing structure in an application of this work. Our efforts included developing the mathematical description of the system and, using coated detectors whose performance was experimentally verified, modeling the response to in-channel, monochromatic radiation. Although we limited our model to a simple, two-channel system, the concept and algorithm can easily be extended to a system of any reasonable number of nonoverlapping channels.