We describe an in-scene technique for accurate wavelength calibration of our airborne MAHI (Mid-infrared Airborne Hyperspectral Imager) sensor using modelled atmospheric spectral features. MAHI operates in the 3.3 to 5.4 μm region with a spectral sampling of 3.3 nm. The new technique significantly improves the accuracy over a lab technique using plastic film spectral features. We demonstrate the technique’s performance against: poorly known spectral response function; error in the initial wavelength grid guess; and deviation of the measured pixel spectra from the reference atmospheric spectrum. Performance of the new calibration technique for a recent airborne campaign in the Los Angeles area is demonstrated.
The Mako airborne longwave-infrared hyperspectral sensor is a whiskbroom imager operating in the 7.6-13.2 μm region with 44-nm spectral sampling and <30 mK noise-equivalent differential temperature (NEDT). It has undergone progressive development since its inaugural flights in 2010 and is capable of acquiring 112° swaths with an areal rate of 33 km2 min-1 at 2-m ground sampling distance. The sensor performance envelope allows for a number of operational modes that can be deployed against a variety of acquisition scenarios. Its suitability for environmental remote sensing applications is illustrated with reference to a number of representative case studies drawn from several years of airborne collections within the Los Angeles Basin and beyond.
The Aerospace Corporation’s sensitive Mako thermal infrared imaging spectrometer, which operates between 7.6 and 13.2 microns at a spectral sampling of 44 nm, and flies in a DeHavilland DHC-6 Twin Otter, has undergone significant changes over the past year that have greatly increased its performance. A comprehensive overhaul of its electronics has enabled frame rates up to 3255 Hz and noise reductions bringing it close to background-limited. A replacement diffraction grating whose peak efficiency was tuned to shorter wavelength, coupled with new AR coatings on certain key optics, has improved the performance at the short wavelength end by a factor of 3, resulting in better sensitivity for methane detection, for example. The faster frame rate has expanded the variety of different scan schemes that are possible, including multi-look scans in which even sizeable target areas can be scanned multiple times during a single overpass. Off-nadir scanning to ±56.4° degrees has also been demonstrated, providing an area scan rate of 33 km2/minute for a 2-meter ground sampling distance (GSD) at nadir. The sensor achieves a Noise Equivalent Spectral Radiance (NESR) of better than 0.6 microflicks (μf, 10-6 W/sr/cm2/μm) in each of the 128 spectral channels for a typical airborne dataset in which 4 frames are co-added. An additional improvement is the integration of a new commercial 3D stabilization mount which is significantly better at compensating for aircraft motions and thereby maintains scan performance under quite turbulent flying conditions. The new sensor performance and capabilities are illustrated.
A sensitive, ground-based thermal imaging spectrometer was deployed at the Army's Dugway Proving Ground to
remotely monitor explosively released chemical-warfare-agent-simulant clouds from stand-off ranges of a few
kilometers. The sensor has 128 spectral bands covering the 7.6 to 13.5 micron region. The measured cloud spectra
clearly showed scattering of high-elevation-angle sky radiance by liquid aerosols or dust in the clouds: we present
arguments that show why the scattering is most likely due to dust. This observation has significant implications for early
detection of dust-laden chemical clouds. On one hand, detection algorithms must properly account for the scattered
radiation component, which would include out-of-scene radiation components as well as a dust signature; on the other
hand, this scattering gives rise to an enhanced "delta-T" for detection by a ground-based sensor.
A new airborne thermal infrared imaging spectrometer, "Mako", with 128 bands in the thermal infrared covering 7.8 to
13.4 microns, has recently completed its engineering flight trials. Results from these flights, which occurred in
September 2010 and included two science flights, are presented. The new sensor flies in a Twin Otter aircraft and
operates in a whiskbroom mode, giving it the ability to scan to ±40° around nadir. The sensor package is supported on a
commercial 3-axis-stabilized mount which greatly reduces aircraft-induced pointing jitter. The internal optics and focal
plane array are operated near liquid helium temperatures, which in conjunction with a fast f/1.25 spectrometer enables
low noise performance despite the sensor's small (0.55 mrad) pixel size and the high frame rate needed to cover large
whisk angles. Besides the large-area-coverage scan mode (20 km2 per minute at 2-meter GSD from 12,500 ft. AGL), the
sensor features a scan mirror pitch capability that enables both a high-sensitivity mode (longer integration times using
frame summing, covering a smaller spatial region) and a multiple-look mode (multiple looks at a smaller region in a
single aircraft overpass, for discriminating plume motion, for example).
The Dyson spectrometer form is capable of providing high throughput, excellent image quality, low spatial and spectral
distortions, and high tolerance to fabrication and alignment errors in a compact format with modest demands for weight,
volume, and cooling resources. These characteristics make it attractive for hyperspectral imaging from a space-based
platform. After a brief discussion of history and basic principles, we present two examples of Dyson spectrometers being
developed for airborne applications. We conclude with a concept for an earth science instrument soon to begin
development under the Instrument Incubator Program of NASA's Earth Science Technology Office.
A novel thermal-band imager is proposed for space-based Earth science measurement applications such as rock
identification and volcano monitoring. The instrument, MAGI-L (Mineral and Gas Identifier - LEO), would also enable
detection of gases from natural and anthropogenic sources. Its higher spectral resolution, compared to ASTER-type
sensors, will improve discrimination of rock types, greatly expand the gas-detection capability, and result in more
accurate land-surface temperatures. The optical design for MAGI-L will incorporate a novel compact Dyson
spectrometer. Data from SEBASS have been used to examine the trade-offs between spectral resolution, spectral range,
and instrument sensitivity for the proposed sensor.
The domain and technology of mobile robotic space exploration are fast moving from brief visits to benign Mars surface regions to more challenging terrain and sustained exploration. Further, the overall venue and concept of space robotic exploration are expanding-“from flatland to 3D”-from the surface, to sub-surface and aerial theatres on disparate large and small planetary bodies, including Mars, Venus, Titan, Europa, and small asteroids. These new space robotic system developments are being facilitated by concurrent, synergistic advances in software and hardware technologies for robotic mobility, particularly as regard on-board system autonomy and novel thermo-mechanical design. We outline these directions of emerging mobile science mission interest and technology enablement, including illustrative work at JPL on terrain-adaptive and multi-robot cooperative rover systems, aerobotic mobility, and subsurface ice explorers.
Steven Watson, N. Olson, R. Dalley, W. Bone, Robert Kroutil, Kenneth Herr, Jeff Hall, G. Schere, M. Polak, Thomas Wilkerson, Dennis Bodrero, R. Borys, D. Lowenthal
Tethered and free-flying manned hot air balloons have been demonstrated as platforms for various atmospheric measurements and remote sensing tasks. We have been performing experiments in these areas since the winter of 1993. These platforms are extremely inexpensive to operate, do not cause disturbances such as prop wash and high airspeeds, and have substantial payload lifting and altitude capabilities. The equipment operated and tested on the balloons included FTIR spectrometers, multi-spectral imaging spectrometer, PM10 Beta attenuation monitor, mid- and far-infrared cameras, a radiometer, video recording equipment, ozone meter, condensation nuclei counter, aerodynamic particle sizer with associated computer equipment, a tethersonde and a 2.9 kW portable generator providing power to the equipment. Carbon monoxide and ozone concentration data and particle concentrations and size distributions were collected as functions of altitude in a wintertime inversion layer at Logan, Utah and summertime conditions in Salt Lake City, Utah and surrounding areas. Various FTIR spectrometers have been flown to characterize chemical plumes emitted from a simulated industrial stack. We also flew the balloon into diesel and fog oil smokes generated by U.S. Army and U.S. Air Force turbine generators to obtain particle size distributions.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.