Kenneth C. Herr

First use of an airborne thermal infrared hyperspectral scanner for compositional mapping

In May 1999, the airborne thermal infrared hyperspectral imaging system, Spatially Enhanced Broadband Array Spectrograph System (SEBASS), was flown over Mormon Mesa, NV, to provide the first test of such a system for geological mapping. Several types of carbonate deposits were identified using the 11.25-μm band. However, massive calcrete outcrops exhibited weak spectral contrast, which was confirmed by field and laboratory measurements. Because the weathered calcrete surface appeared relatively smooth in hand specimen, this weak spectral contrast was unexpected. Here we show that microscopic roughness not readily apparent to the eye has introduced both a cavity effect and volume scattering to reduce spectral contrast. The macroroughness of crevices and cobbles may also have a significant cavity effect. The diminished spectral contrast is important because it places higher signal-to-noise ratio (SNR) requirements for spectroscopic detection and identification. This effect should be factored into instrumentation planning and interpretations, especially interpretations without benefit of ground truth. SEBASS had the required high SNR and spectral resolution to allow us to demonstrate for the first time the ability of an airborne hyperspectral thermal infrared scanner to detect and identify spectrally subtle materials.

A Rapid-Scan Infrared Spectrometer; Flash Photolytic Detection of Chloroformic Acid and of CF 2

A rapid-scan infrared spectrometer has been constructed and successfully applied to the study of short-lived intermediates produced by flash photolysis. A zinc-doped germanium semiconductor detector and a high-speed rotating Littrow mirror permit scan rates of 1000 cm−1/100 μsee through the region 5000–650 cm−1. Two transient species, chloroformic acid and CF2, have been identified, and lough estimates of their lifetimes have been obtained, 50–70 μsec and about 2.5 msec, respectively. This is the first spectroscopic detection of chloroformic acid.

Infrared Absorptions near Three Microns Recorded over the Polar Cap of Mars

During the Mariner 7 flyby of Mars, the infrared spectrometer recorded distinct, sharp absorption. near 3020 and 3300 reciprocal centimeters between 61�S and 80�S. at the edge of the southern polar cap, with maximum optical density near 68�S and 341�E. These hands, which match in frequency the v3 bands of methane and ammonia, can be associated with previously unreported spectral features of solid carbon dioxide exceeding 1 millimeter in thickness. Possible reasons for the geographic localization are discussed.

Evidence for Solid Carbon Dioxide in the Upper Atmosphere of Mars

The infrared spectra recorded by Mariner 6 and 7 show reflections at 4.3 microns. which suggest the presence of solid carbon dioxide in the upper atmosphere of Mars.

Passive Fourier-transform infrared spectroscopy of chemical plumes: an algorithm for quantitative interpretation and real-time background removal

We present a ratioing algorithm for quantitative analysis of the passive Fourier-transform infrared spectrum of a chemical plume. We show that the transmission of a near-field plume is given by τ(plume) = (L(obsd) - L(bb-plume))/(L(bkgd) - L(bb-plume)), where τ(plume) is the frequency-dependent transmission of the plume, L(obsd) is the spectral radiance of the scene that contains the plume, L(bkgd) is the spectral radiance of the same scene without the plume, and L(bb-plume) is the spectral radiance of a blackbody at the plume temperature. The algorithm simultaneously achieves background removal, elimination of the spectrometer internal signature, and quantification of the plume spectral transmission. It has applications to both real-time processing for plume visualization and quantitative measurements of plume column densities. The plume temperature (L(bb-plume)), which is not always precisely known, can have a profound effect on the quantitative interpretation of the algorithm and is discussed in detail. Finally, we provide an illustrative example of the use of the algorithm on a trichloroethylene and acetone plume.

Martian topography from the Mariner 6 and 7 infrared spectra

Mars topography from Mariner 6 and 7 IR spectra, discussing geographical resolution, surface carbon dioxide pressure, depressions, ridges and valleys

The composition of the Martian atmosphere: Minor constituents

Abstract The Mariner 6 and 7 infrared spectrometers provided data which, in principle, determine upper limits on the possible atmospheric abundance of every gaseous substance that was undetected but which has recognized absorptions in the accessible spectral region, 1.9 to 14.4 μ. Through supporting laboratory determinations of curves of growth under pressure broadening conditions appropriate to Mars, upper limits can be specified (expressed first in cm-atm, STP, for a vertical column and then in parts per million) for the following gases: NO 2 ( 3 ( 3 O 2 ( 2 (⩽0.0037, 0.52); OCS ( 3 ( 4 ( 2 O ( 2 S ( 6 , NF 3 , Cl 2 CO, CF 4 , CHF 3 , Br 2 CO, SiF 4 ; less than 6.0ppm (or, 2 F 6 , CO 3 , F 2 CO, C 2 H 4 , BF 3 , CS 2 , CHCl 3 , C 2 H 6 , H 2 CO, CH 3 F, C 6 H 6 , CH 2 I 2 ; less than 50ppm (or, 2 H 2 , HCN, CH 2 Br 2 , CH 2 Cl 2 , CH 3 Br, PH 3 , CH 3 I, and CH 3 Cl. These upper limits are compared to earlier limits based upon terrestrial measurements. The present limits placed upon the possible atmospheric content of the molecules C 3 O 2 and CO 3 are of particular interest because of their relevance to the photochemistry of the Martian atmosphere.

Thermal infrared spectral band detection limits for unidentified surface materials.

Infrared emission spectra recorded by airborne or satellite spectrometers can be searched for spectral features to determine the composition of rocks on planetary surfaces. Surface materials are identified by detections of characteristic spectral bands. We show how to define whether to accept an observed spectral feature as a detection when the target material is unknown. We also use remotely sensed spectra measured by the Thermal Emission Spectrometer (TES) and the Spatially Enhanced Broadband Array Spectrograph System to illustrate the importance of instrument parameters and surface properties on band detection limits and how the variation in signal-to-noise ratio with wavelength affects the bands that are most detectable for a given instrument. The spectrometers sampling interval, spectral resolution, signal-to-noise ratio as a function of wavelength, and the samples surface properties influence whether the instrument can detect a spectral feature exhibited by a material. As an example, in the 6-13-mum wavelength region, massive carbonates exhibit two bands: a very strong, broad feature at ~6.5 mum and a less intense, sharper band at ~11.25 mum. Although the 6.5-mum band is stronger and broader in laboratory-measured spectra, the 11.25-mum band will cause a more detectable feature in TES spectra.

Mariner Mars 1969 infrared spectrometer.

The infrared spectrometer that recorded spectra of the atmosphere and surface of Mars during the Mariner 6 and 7 flyby missions is described. The instrument continuously scanned the 1.9-micro to 14.4-micro spectral region at 10 see per scan. Approximately 1% spectral resolution was furnished by two rotating, circular, variable interference filters. The spectral region 1.9-6.0 micro was recorded with a PbSe detector cooled to 175 K by radiation to deep space. The spectral region 3.9-14.4 micro was modulated by a cold (175 K) tuning fork chopper and recorded with a mercury-doped germanium detector cooled to 22 K by a Joule-Thomson two-stage (N(2) and H(2)) cryostat. The total weight of the instrument was 17.4 kg (monochromator plus electronics, 11.5 kg; gas delivery system, 5.9 kg), and it consumed 11 W of power.

Spectral anomalies in the 11 and 12 μm region from the Mariner Mars 7 Infrared Spectrometer

Two hundred-forty infrared spectra acquired by the 1969 Mariner Mars 7 Infrared Spectrometer (IRS), spanning the wavelength region 1.8-14.4 micron (5550-690/cm), have recently been recovered and calibrated in both wavelength and intensity. An examination of these IRS spectra has revealed absorptions at 11.25 and 12.5 micron that have not previously been reported for Mars. A search of the literature and spectral data bases shows that materials that exhibit a doublet at 11.25 and 12.5 micron are rare. In this paper we examine potential causes for these features and include a detailed discussion of carbonates, goethite, CO2 ice, and water ice. CO2 ice and water ice measured in transmission do not exhibit bands that match those recorded at 11.25 and 12.5 micron for Mars, which indicates that CO2 or water ice clouds are not the source of these features. Since these bands show no clear correlation with atmospheric path length, they are most likely caused by a surface material. In the IRS database they appear to be exceptionally intense in the western part of the Hellas basin. Goethite exhibits bands that are a good spectral match, but confirming whether goethite causes the features will require additional studies of the 20-50 micron region. These studies will require laboratory measurements of weathering coatings and an examination of spectra recorded of Mars by the 1971 Mariner Mars Infrared Interferometer Spectrometer (IRIS; 5-50 micron 2000200/cm) and the 1996 Thermal Emission Spectrometer (TES; 6-50 micron 1667-200/cm).