The primary payload on a small-satellite, the Air Force Research Laboratory's MightySat II.1, is a spatially modulated Fourier Transform Hyperspectral Imager (FTHSI) designed for terrain classification. The heart of this instrument is a solid block Sagnac interferometer with 85cm-1 spectral resolution over the 475nm to 1050nm bands and 30m spatial resolution. Coupled with this hyperspectral imager is a Quad-C40 card, used for on-orbit processing. The satellite was launched on 19 July 2000 into a 575km, 97.8 degree inclination, sun-synchronous orbit. The hyperspectral imager collected its first data set on 1 August 2000, and has been in continuous operation since that time. To the best of our knowledge, the MightySat II.1 sensor is the first true hyperspectral imager to be successfully operated in space. The paper will describe the satellite and instrument, pre-launch calibration results, on-orbit performance, and the calibration process used to characterize the sensor. We will also present data on the projected lifetime of the sensor along with samples of the types of data being collected.
Including polarization signatures of material samples in passive sensing may enhance target detection capabilities. To obtain more information on this potential improvement, a simulation is being developed to aid in interpreting IR polarization measurements in a complex environment. The simulation accounts for the background, or incident illumination, and the scattering and emission from the target into the sensor. MODTRAN, in combination with a dipole approximation to singly scattered radiance, is used to polarimetrically model the background, or sky conditions. The scattering and emission from rough surfaces are calculated using an energy conserving polarimetric Torrance and Sparrow BRDF model. The simulation can be used to examine the surface properties of materials in a laboratory environment, to investigate IR polarization signatures in the field, or a complex environment, and to predict trends in LWIR polarization data. In this paper we discuss the simulation architecture, the process for determining and roughness as a function of wavelength, which involves making polarization measurements of flat glass plates at various angles and temperatures in the laboratory at Kirtland AF Base, and the comparison of the simulation with field dat taken at Elgin Air Force Base. The later process entails using the extrapolated index of refraction and surface roughness, and a polarimetric incident sky dome generated by MODTRAN. We also present some parametric studies in which the sky condition, the sky temperature and the sensor declination angle were all varied.
The primary payload on a small-satellite, MightySat II.1, is a spatially modulated Fourier transform hyperspectral imager designed for terrain classification. This imager is the first hyperspectral imager to be successfully operated from space. As part of its year long mission, images have been taken of the Earth's limb and the moon. Analysis of the limb data have shown the presence of large scale structure in the limb while the moon imagery is being used to determine the suitability of using the moon as a vicarious calibration source. The paper briefly describes the satellite and hyperspectral instrument and presents examples of the limb and moon observations and data.
The emitted polarization signature of materials is of interest for use in discriminating targets from cluttered backgrounds. In addition, spectrally varying polarization signatures might be used for material identification or to separate target and environment radiance contributions. A spectrally filtered LWIR Imaging Polarimeter (LIP) has been constructed and used in the lab and in the field to make signature measurements of controlled targets. In addition, a full-stokes FTIR Polarization Spectrometer (FSP) has been constructed for higher spectral resolution measurements of materials. This paper will discuss the instruments, calibration methods, general operation, and results characterizing the emitted polarization properties of materials as a function of wavelength.
The effect of atmospheric phase perturbations on the diffractive and coherent properties of the uplink and downlink paths of an active imaging illumination beam has been studied in some detail. Similarly, the scattering and depolarization induced by water and ice cloud particles in the path of coherent laser illumination is currently an area of much production research. In contrast, the effect of cloud particles on the diffractive properties of a laser illumination beam has not received as much attention due primarily to the daunting mathematics of the physical mode. This paper seeks to address some of the mathematical issues associated with modeling the interaction of a coherent illumination beam with a cloud of ice particles. The simulation constructs a 3D model of a cirrus cloud consisting of randomly oriented hexagonal ice crystals in the shape of plates, columns, and bullet rosettes. The size, shape, and vertical distribution of the crystals are modeled after measured particles concentrations and distributions. An illumination pattern, in the form of grid of rays, is traced through the cloud, and the properties of the exiting wavefronts are analyzed.