Thermal Infrared Field Spectrometer Measurements (Feb. 2002)

Thermal infrared field spectrometer measurements differ fundamentally from laboratory, airborne, and satellite spectrometer measurements. We research textural, viewing geometry, proximity, and downwelling radiance effects as seen from the different viewing perspectives, with a focus on solid phase targets, and develop measurement protocols and instrumentation for hyperspectral field measurements. This improves the ability to identify materials, confidence in the result, and data fusion from the different perspectives. The results aid material identification using thermal infrared hyperspectral data from hand-carried instruments, manned and unmanned vehicles and rovers, and fusion with data from airborne (including UAV), and satellite thermal infrared hyperspectral measurements.

Here we describe some instrumentation and field measurements undertaken for this research. We will make the data freely available. If you are interested in receiving the data, please contact Laurel Kirkland,, 281-486-2112. We will also make our follow-on measurements freely available, and please forward any suggestions for targets or field sites.

This fundamental research into applied remote identification is used to advance work both in Mars research, and also is applied to defense against chemical warfare and terrorist attack. The Aerospace Corporation and the Lunar and Planetary Institute funded these data collects. NASA research programs provide no funding for any of the data collects, reduction, analysis, or distribution, and no member of our group is a member of any NASA instrument team. The Aerospace Corporation owns all the equipment used here.

For these tests, we used a Block Engineering Model 100 (M100) Fourier Transform infrared interferometer (FTIR) mounted on a van platform. It measures the scene using a precisely controlled mirror that raster scans in two dimensions. The viewing angles are automatically recorded with the data. The M100 covers the 7.5-13.5 Ám spectral range at 4 cm-1 spectral resolution (apodized) in 1024 channels. We raster scanned most images 20 degrees horizontally by 10 degrees vertically, in 0.25 degree steps, to produce images 80 pixels wide by 40 pixels high. A few images are 20 by 15 degrees, and so are 80 by 60 pixels. The instrument field of view is 0.5 degrees (8.7 milliradians).

Calibration measurements include blackbody targets measured at two temperatures above ambient, and a third at ambient temperature, and water ice. The data sets were recorded under clear sky conditions, during mid-morning to mid-afternoon. Ambient temperature was automatically recorded with the data throughout the collect.

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Surveillance Technologies Department van (The Aerospace Corporation).

Surveillance Technologies Department van (The Aerospace Corporation).

Scan head. The M100 is in the lower section of the scan head box, and the raster scanning mirror is in the middle of the upper section. The two plates outboard of the mirror are blackbody targets, and an additional blackbody target behind the mirror is not visible. An infrared camera in on the left and a visible camera is on the right. The scan head is positioned for the desired region of scan, and then the raster scanning mirror builds the image.

Inside the van. The scan head mount is in the center. The instrument is raised on the mount through the roof opening. We view spectra real-time on the computer at the left. The visible and infrared camera output are also viewed real-time on the displays above the computer, and the output is recorded.

Setting up. Some of the targets are in the foreground. The larger targets are the diffuse aluminum target (lower left) and the painted, non-diffuse aluminum target (lower right).

Eric Keim (left) and Jess Valero (The Aerospace Corporation). Eric manages The Aerospace Corporation's airborne SEBASS instrument, but we let him watch, anyway. Jess Valero manages the field instrumention, hardware and target set-ups.

Real-time viewing. This shows a completed image displayed on the screen, which Ken Herr is pointing to. Darker is colder, and the darkest blocks are the aluminum targets. The matching visible image of the targets is displayed in the upper right screen.

The Mars 2003 rover plans to carry a thermal infrared spectrometer called Mini-TES. It measures the ~5-25 Ám spectral range at ~20 cm-1 spectral resolution (unapodized) and ~10 cm-1 spectral sampling, and has a KBr beamsplitter. It can raster scan images in two dimensions, like our field spectrometers. The field of view is selectable as 20 or 8 milliradians.

In part we release our field spectrometer data to provide NASA researchers with the only publicly available data set measured in a manner similar to the Mini-TES. Open access to our data allows the NASA community to research issues of importance before the Mars flight.

We measured targets with a range of textures, including a painted, non-diffuse aluminum target; a diffuse aluminum target; a non-diffuse aluminum target; an aluminized mylar target; a mirror positioned to direct the field of view approximately toward zenith; particulate materials with a range of overall emissivity (salt, gravel, cement, quartz sand, kitty litter); water ice; and a target with putty-like consistency that started smooth and we periodically put pits into it, in order to study the hohlraum (cavity) effect.

We tilted the targets to study viewing geometry effects, and we measured about 25 images. We also measured the targets in the open and next to a building with a large garage door that was open for some collects and closed for others. Below is the general set-up (targets not drawn to scale). Not all targets were in all images, and the field notes to match the data will give details. The target dimensions are given in inches.

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Targets in an open area.

Targets next to the building. Rear are targets tilted here, but are flat in other images.

Hohlraum (cavity effect) target. The target started with no pits, and we added pits between raster scanning the hyperspectral images. The pits do not pierce the back of the material.

Supporting laboratory data
We will place hemispherical reflectance data of all the target materials here.

Laboratory FTIR set-up, with Paul Adams (The Aerospace Corporation). Click image for larger picture.

Laboratory FTIR, showing the hemispherical attachment. Click image for larger picture.

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