John Lewis Hinrichs

Three years of operation of AHI: the University of Hawaii's Airborne Hyperspectral Imager

The AHI sensor consists of a long-wave infrared pushbroom hyperspectral imager and a boresighted 3-color visible high resolution CCD linescan camera. The system used a background suppression system to achieve good noise characteristics (less than 1(mu) fl NESR). Work with AHI has shown the utility of the long-wave infrared a variety of applications. The AHI system has been used successfully in the detection of buried land mines using infrared absorption features of disturbed soil. Recently, the AHI has been used to examine the feasibility active and passive hyperspectral imaging under outdoor and laboratory conditions at three ranges. In addition, the AHI was flown over a coral reef ecosystem on the Hawaiian island of Molokai to study fresh water intrusion into coral reef ecosystems. Theoretical calculations have been done propose extensions to the AHI design in order to produce an instrument with a higher signal to noise ratio.

A compact Fourier transform imaging spectrometer employing a variable gap Fabry-Perot interferometer

Fourier transform spectroscopy is a widely employed method for obtaining visible and infrared spectral imagery, with applications ranging from the desktop to remote sensing. Most fielded Fourier transform spectrometers (FTS) employ the Michelson interferometer and measure the spectrum encoded in a time-varying signal imposed by the source spectrum interaction with the interferometer. A second, less widely used form of FTS is the spatial FTS, where the spectrum is encoded in a pattern sampled by a detector array. Recently we described using a Fabry-Perot interferometer, with a deliberately wedged gap geometry and engineered surface reflectivities, to produce an imaging spatial FTS. The Fabry-Perot interferometer can be much lighter and more compact than a conventional interferometer configuration, thereby making them suitable for portable and handheld applications. This approach is suitable for use over many spectral regimes of interest, including visible and infrared regions. Primary efforts to date have focused on development and demonstration of long wave infrared (LWIR) spectral imagers. The LWIR version of the miniaturized Fabry-Perot has been shown to be effective for various applications including spectral imaging-based chemical detection. The compact LWIR spectral imager employs uncooled optics and a microbolometer camera; a handheld version is envisioned for future development. Recent advancements associated with the spatial Fourier Transform imaging spectrometer system are described.

LWIR hyperspectral micro-imager for detection of trace explosive particles

Chemical micro-imaging is a powerful tool for the detection and identification of analytes of interest against a cluttered background (i.e. trace explosive particles left behind in a fingerprint). While a variety of groups have demonstrated the efficacy of Raman instruments for these applications, point by point or line by line acquisition of a targeted field of view (FOV) is a time consuming process if it is to be accomplished with useful spatial resolutions. Spectrum Photonics has developed and demonstrated a prototype system utilizing long wave infrared hyperspectral microscopy, which enables the simultaneous collection of LWIR reflectance spectra from 8-14 μm in a 30 x 7 mm FOV with 30 μm spatial resolution in 30 s. An overview of the uncooled Sagnac-based LWIR HSM system will be given, emphasizing the benefits of this approach. Laboratory Hyperspectral data collected from custom mixtures and fingerprint residues is shown, focusing on the ability of the LWIR chemical micro-imager to detect chemicals of interest out of a cluttered background.

Incorporation of portable infrared spectral imaging into planetary geological field work: Analog studies at Kīlauea Volcano, Hawaii and Potrillo Volcanic Field, New Mexico

During geological work for future planetary missions, portable/hand-held infrared spectral imaging instruments have the potential to significantly benefit science objectives. We assess how ground-based infrared spectral imaging can be incorporated into geological field work in a planetary setting through a series of field campaigns at two analog sites: Kīlauea Volcano, Hawaii, and Potrillo Volcanic Field, New Mexico. For this study, we utilize thermal infrared emission spectroscopy (8–13 μm) because this wavelength range is sensitive to major silicate spectral features and covers the terrestrial atmospheric window; however, our conclusions are applicable to other forms of infrared imaging (e.g., near-infrared reflectance spectroscopy). We demonstrate the ways in which spectral imaging could potentially enhance the science return and/or efficiency of traditional geological field work. Benefits include the following: documentation of major compositional variations within scenes, the ability to detect visually subtle and/or concealed variability in (sub) units, and the ability to characterize remote and/or inaccessible outcrops. These advantages could help field workers rapidly document sample context and develop strategic work plans. Furthermore, ground-based imaging provides a critical link between orbital/aerial imaging scales and sampling scales. Last, infrared spectral imaging data may be combined with in situ measurement techniques, such as X-ray fluorescence, as well as other ground-based remote sensing techniques, such as LIDAR (Light Detection And Ranging), to maximize geological understanding of the work area. Plain Language Summary Future missions to planetary objects are expected to have increasingly more human and rover components in surface exploration. To aid the explorers in conducting scientific tasks, portable instruments will likely be invaluable. Currently, knowledge of instrument suitability and most effective incorporation strategies are not sufficiently developed. As one of the first steps in this development process, we assess the fundamental capabilities of portable imaging technique in providing critical information for geological field work on planetary surfaces. Portable imaging, operating in the thermal infrared (8–13 μm), captured crucial data regarding rock/mineral types at field sites analogous to planetary settings. Value brought forth by portable infrared imaging is substantial, and this technique has the potential to benefit effective geological field work, which may lead to maximizing scientific return from missions. This finding and accompanying analyses presented here serve as a foundation for further development of instruments and mission strategies.

A long-wave infrared hyperspectral sensor for Shadow class UAVs

The University of Hawaii has developed a concept to ruggedize an existing thermal infrared hyperspectral system for use in the NASA SIERRA UAV. The Hawaii Institute of Geophysics and Planetology has developed a suite of instruments that acquire high spectral resolution thermal infrared image data with low mass and power consumption by combining microbolometers with stationary interferometers, allowing us to achieve hyperspectral resolution (20 wavenumbers between 8 and 14 micrometers), with signal to noise ratios as high as 1500:1. Several similar instruments have been developed and flown by our research group. One recent iteration, developed under NASA EPSCoR funding and designed for inclusion on a microsatellite (Thermal Hyperspectral Imager; THI), has a mass of 11 kg. Making THI ready for deployment on the SIERRA will involve incorporating improvements made in building nine thermal interferometric hyperspectral systems for commercial and government sponsors as part of HIGP’s wider program. This includes: a) hardening the system for operation in the SIERRA environment, b) compact design for the calibration system, c) reconfiguring software for autonomous operation, d) incorporating HIGP-developed detectors with increased responsiveness at the 8 micron end of the TIR range, and e) an improved interferometer to increase SNR for imaging at the SIERRA’s air speed. UAVs provide a unique platform for science investigations that the proposed instrument, UAVTHI, will be well placed to facilitate (e.g. very high temporal resolution measurements of temporally dynamic phenomena, such as wildfires and volcanic ash clouds). Its spectral range is suited to measuring gas plumes, including sulfur dioxide and carbon dioxide, which exhibit absorption features in the 8 to 14 micron range.

A compact LWIR hyperspectral system employing a microbolometer array and a variable gap Fabry-Perot interferometer employed as a Fourier transform spectrometer

A prototype long wave infrared Fourier transform spectral imaging system using a wedged Fabry-Perot interferometer and a microbolometer array was designed and built. The instrument can be used at both short (cm) and long standoff ranges (infinity focus). Signal to noise ratios are in the several hundred range for 30 C targets. The sensor is compact, fitting in a volume about 12 x12 x 4 inches.