A unifying theme throughout the ESE science objectives is the identification of regions with large temporal and spatial gradients. Severe storm formation occurs in the boundary regions between airmasses with very different temperatures, pressures, water content, aerosol loading. Severe storm tracking and forecasting utilizes the discontinuities in observed fields and gradient fields to diagnose and forecast the formation, evolution, and motion of severe storms. In a similar fashion, heat islands, super-regional pollution, and rain shower formation are each the result of temporal and spatial gradients present in the atmosphere. Diagnosing and forecasting these events requires an ability to map atmospheric gradients and discontinuities in real-time on micro to meso-scales in the atmosphere (0.5 - 500 km). A new measurement concept, the Imaging Fourier Transform Spectrometer (IFTS) is capable of demonstrating a class of autonomous event identification, monitoring and tracking sensors. In order to provide this capability a sensor with the ability to combine high spatial resolution (0.5 - 1 km) imaging with high spectral resolution (0.25 cm - 1 across the mid infrared 3 -10 microns) in time intervals of a few seconds is required. An electronically programmable infrared camera that combines a large-format focal plane array with a Fourier transform spectrometer can deliver this capability. It also builds on currently fielded airborne demonstration systems and an instrument concept in development for the Next Generation Space Telescope (NGST). The IFTS concept is revolutionary in several aspects. It can produce 2 - 10 fold increase in spatial resolution, 2 fold increases in spectral resolution, and 30 fold increases in temporal resolution. In combination the measurement concept would require a 100 - 600 fold increase in telemetry bandwidth without a new approach to imaging. IFTS breaks this paradigm with a new approach to hyperspectral imaging. Severe storm forecasting requires gradient fields (i.e., first and second derivatives of atmospheric observations). Hence, this measurement concept for IFTS is enabled by four innovations: (1) directly observe the derivative fields, (2) Nyquist sample the image plane to enable full utilization of the telescope performance, (3) have multi-channel detection of gradient regions, and (4) provide an autonomous targeting and tracking system that identifies, subsets, and follows regions with significant discontinuities (i.e., regions where severe storms, toxic pollution, heat islands, or rain/thunderstorms will form).
Under the sponsorship of the DARPA Hyperspectral Mine Detection program, a series of both non-imaging and imaging experiments have been conducted to explore the physical basis of buried object detection in the visible through thermal infrared. Initially, non-imaging experiments were performed at several geographic locations. Potential spectral observables for detection of buried mines in the thermal portion of the infrared were found through these measurements. Following these measurements with point spectrometers, a series of hyperspectral imaging measurements was conducted during the summer of 1995 using the SMIFTS instrument from the University of Hawaii and the LIFTIRS instrument from Lawrence Livermore National Laboratory. The SMIFTS instrument (spatially modulated imaging Fourier transform spectrometer) acquires hyperspectral image cubes in the short-wave and mid-wave infrared and LIFTIRS (Livermore imaging Fourier transform infrared spectrometer) acquires hyperspectral image cubes in the long-wave infrared. Both instruments were optimized through calibration to maximize their signal to noise ratio and remove residual sensor pattern. The experiments were designed to both explore further the physics of disturbed soil detection in the infrared and acquire image data to support the development of detection algorithms. These experiments were supported by extensive ground truth, physical sampling and laboratory analysis. Promising detection observables have been found in the long-wave infrared portion of the spectrum. These spectral signatures have been seen in all geographical locations and are supported by geological theory. Data taken by the hyperspectral imaging sensors have been directly input to detection algorithms to demonstrate mine detection techniques. In this paper, both the non-imaging and imaging measurements made to date will be summarized.
In this article, recent characterization measurements made with LIFTIRS, the Livermore imaging Fourier transform infrared spectrometer, are presented. A discussion is also presented of the relative merits of the various alternative designs for imaging spectrometers.
In this article, recent measurements made with LIFTIRS, the Livermore Imaging Fourier Transform Infrared Spectrometer, are presented. The experience gained with this instrument has produced a variety of insights into the tradeoffs between signal to noise ratio (SNR), spectral resolution, and temporal resolution for time multiplexed Fourier transform imaging spectrometers. This experience has also clarified the practical advantages and disadvantages of Fourier transform hyperspectral imaging spectrometers regarding adaptation to varying measurement requirements on SNR versus spectral resolution, spatial resolution, and temporal resolution.
Lawrence Livermore National Laboratory is currently operating a hyperspectral imager, the Livermore Imaging Fourier Transform Infrared Spectrometer. This instrument is capable of operating throughout the infrared spectrum from 3 to 12.5 micrometers with controllable spectral resolution. In this presentation we report on its operating characteristics, current capabilities, data throughput, and calibration issues.
We are developing an imaging Fourier transform spectrometer for chemical effluent monitoring. The system consists of a 2D IR imaging array in the focal plane of a Michelson interferometer. Individual images are coordinated with the positioning of a moving mirror in the Michelson interferometer. A 3D data cube with two spatial dimensions and one interferogram dimension is then Fourier transformed to produce a hyperspectral data cube with one spectral dimension and two spatial dimensions. The spectral range of the instrument is determined by the choice of optical components and the spectral range of the focal plane array. Measurements in the near UV, visible, near IR, and mid-IR ranges are possible with the existing instrument. Gaseous effluent monitoring and identification measurements will be primarily in the `fingerprint' region of the spectrum, ((lambda) equals 8 to 12 micrometers ). Initial measurements of effluent using this imaging interferometer in the mid-IR will be presented.
We have conducted experiments to demonstrate the enhanced detectability of buried land mines using sensor fusion techniques. Multiple sensors, including visible imagery, IR imagery, and ground penetrating radar, have been used to acquire data on a number of buried mines and mine surrogates. We present this data along with a discussion of our application of sensor fusion techniques for this particular detection problem. We describe our data fusion architecture and discuss the some relevant results of these classification methods.
The operating principles of an Imaging Fourier Transform Spectrometer (IFTS) are discussed. The advantages and disadvantages of such instruments with respect to alternative imaging spectrometers are discussed. The primary advantages of the IFTS are the capacity to acquire more than an order of magnitude more spectral channels than alternative systems with more than an order of magnitude greater etendue than for alternative systems. The primary disadvantage of IFTS, or FTS is general, is the sensitivity to temporal fluctuations, either random or periodic. Data from the IRIFTS (ir IFTS) prototype instrument, sensitive in the infrared, are presented having a spectral sensitivity of 0.01 absorbance units per pixel, a spectral resolution of 6 cm-1 over the range 0 to 7899 cm-1, and a spatial resolution of 2.5 mr.
This paper discusses recent progress in LLNL's high resolution XUV spectroscopy efforts with x-ray laser plasmas. We describe the instrumentation used, and we present preliminary time-resolved data on the spectral profiles of several XUV (extreme ultraviolet) lines from Ne- like Se and Ne-like Y x-ray lasers which have been obtained with instrumental resolutions ((lambda) /(Delta) (lambda) ) of approximately 10,000. The Se data indicates that the 206.4 angstroms J equals 2 - 1 laser line narrows below the expected 400 eV Doppler width (35 m angstroms) when amplified through approximately 6 gain lengths, while the Y data shows no evidence of the J equals 0 - 1 laser predicted to be nearly resonant with the J equals 2 - 1 laser at 154.9 angstroms.
The spatial coherence of a neon-like selenium x-ray laser operating at 206 and 210 angstroms has been measured using a technique based on partially coherent x-ray diffraction. The time integrated spatial coherence of the selenium x-ray laser was determined to be equal to that of a quasi-monochromatic spatially incoherent disk source whose diameter is comparable to the line focus of the visible light laser pumping the x-ray laser. The spatial coherence was improved by narrowing the line focus width. Laboratory x-ray lasers have been available for six years as potential tools for research. Their basic characteristics such as output energy, pulselength, linewidth, and divergence have been measured. Knowledge of these characteristics has resulted in x-ray lasers being used in some preliminary applications experiments including photo-ionization physics, contact microscopy of cells, and holography. Future applications of x-ray lasers, such as nonlinear x-ray optics and holographic microscopy of biological microstructures, require a detailed knowledge of the spatial coherence. This paper presents the first measurement of the spatial coherence of an x-ray laser.