Development of target detection algorithms and simulation models for present and future multispectral and hyperspectral sensor systems requires accurate characterization of the reflectance and thermal emission of natural and man-made materials. Fourier transform spectrometry is one method for obtaining relatively high spectral resolution, in-situ measurements of surface reflectance. This paper discusses the performance characteristics of the SOC-400T FTIR and its application to field measurements. The SOC-400T is a relatively small and portable FTIR reflectometer that was designed to measure the directional reflectance and calculate the directional thermal emittance of surfaces in the spectral range from 2 to 25 ημm. The SOC-400T uses a silicone carbide glowbar to illuminate samples. This permits accurate results to be obtained in the MWIR. We recently deployed this instrument to the field to perform measurements on various materials of interest to the military. Prior to the deployment, the instrument was evaluated to assess its performance under true field operating conditions. This paper specifically examines noise characteristics, warmup time, transients induced by reorientation of the sensor, spurious detector artifacts, and sensitivity to vibration. We also address the practical issue associated with positioning, stabilizing, and calibrating the instrument for field measurements of irregular or arbitrarily oriented surfaces.
Several of the leading atmospheric compensation algorithms for LWIR hyperspectral data require the detection and exclusion low-emissivity objects from the analysis. In this paper, nine different methods for detection of low-emissivity objects are presented. In testing, it was found that the algorithms proposed suffered from temperature sensitivities. Further testing was accomplished without filtering to test the performance of Scaled and Unscaled ISAC under a range of environmental and system parameters. Detection performance is quantified directly in terms of probability of detection vs. probability of false alarm and in terms of atmospheric state parameters.
This paper has two objectives: (1) to assess the performance of atmospheric correction techniques for VIS-SWIR
hyperspectral data, and (2) to evaluate the ability to identify a variety of materials in five major backgrounds. Data from the HYDICE sensor obtained under alpine, desert, forest, jungle, and littoral conditions were evaluated. In addition to comparing retrieved reflectance spectra from ground truth, the impact of various atmospheric correction techniques on material identification was assessed.
Estimates have been made of wavelength calibration and instrument line shape (ILS) for the SEBASS hyperspectral sensor. FASCODE estimates of at-sensor radiance were made, convolved with gaussian or triangular ILS functions of various widths, had slight wavelength shifts introduced and were downsampled to SEBASS wavelengths. The downsampled FASCODE estimates were compared to measured data for 21 atmospheric absorption features between 8-13 um. The combination of ILS width and wavelength shift providing the best match was recorded. The technique was sensitive to wavelength calibration, but relatively insensitive to ILS width. Results demonstrated that SEBASS wavelength calibration was within +/- 0.5 channel widths.
This paper presents an overview of the latest version of a MODTRAN4-based atmospheric correction (or "compensation") algorithm developed by Spectral Sciences, Inc. and the Air Force Research Laboratory for spectral imaging sensors. New upgrades to the algorithm include automated aerosol retrieval, cloud masking, and speed improvements. In addition, MODTRAN4 has been updated to correct recently discovered errors in the HITRAN-96 water line parameters. Reflectance spectra retrieved from AVIRIS data are compared with "ground truth" measurements, and good agreement is found.
The performance of a variety of atmospheric correction algorithms applied to VIS-SWIR hyperspectral data are assessed quantitatively. Data from HYDICE obtained under desert, forest, tropical, and alpine conditions were tested. In addition to comparing retrieved reflectance spectra from ground truth, performance is assessed in terms of the impact of various atmospheric correction techniques on material identification.
Algorithms have been developed for estimating temperature and emissivity of terrestrial targets from airborne LWIR hyperspectral radiance data. This report documents a performance comparison of these algorithms. Data collected at the Department of Energy's Atmospheric Radiation Measurement Site by the Spatially-Enhanced Broadband Array Spectrograph System (SEBASS) was used. SEBASS is a 128-band hyperspectral instrument covering a wavelength range of 7.3 to 13.6 micrometers. Spectra of natural and man-made objects were processed by Thermal Log Residual, Alpha Log Residual, Normalized Emissivity, Inverse Wave, Graybody, EOS/ASTER, N- Temperature, and Max-Min Difference methods. Temperature and emissivity estimates are compared to ground truth measurements. Sample results and performance statistics are presented.
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