Linear variable filter design and fabrication for LWIR is now commercially available for use in the
development of airborne reconnaissance or surveillance systems. The linear variable filter is attached
directly to the cold shield of the focal plane array. The resulting compact spectrometer assemblies are
completely contained in the Dewar system. This approach eliminates many of the wavelength calibration
problems associated with current prism and grating systems and also facilitates the cost effective design
and fabrication of aerial sensing systems for specific applications. An optimal 32 band linear-variablefilter-
based system for detecting and discriminating a set of 11 chemicals representing a high probability
of occurrence during a typical emergency response chemical incident was determined in a companion
paper entitled "Linear Variable Filter Optimization for Emergency Response Chemical Detection and
Discrimination". This paper addresses the effects of atmospheric water vapor on the performance of this
optimal 32 band linear-variable-filter-based system. This paper also determines at what increased
concentration levels above the optimal system design goal of 30 ppm-m can detection and discrimination
of these 11 chemicals be achieved in realistic but imperfect atmospheric water vapor removal scenarios.
Airborne passive hyperspectral infrared spectral measurements of chemical vapors in the
atmosphere have been completed over a wide variety of locations throughout the United States.
These measurements are part of the US EPA emergency response chemical disaster mitigation
capability. Analysis and regional comparison of these atmospheric measurements reveals a glycol
constituent, which has been noted during flooding conditions along the Southern Gulf Coast Region
and the Midwestern United States. This discussion will describe several differences in the natural
atmospheric background for vapor species identified in various regions of the country. There are
two possible sources for this constituent in these regions one is a natural source the other is an
anthropogenic source. The paper will highlight the usefulness of passive infrared spectral
measurements to determine key atmospheric indicators correlated with locations of major flooding
along with the identification of naturally occurring species.
Determining the extent to which large power plant emission sources interacting with atmospheric
constituents affect the environment could play a significant role in future U.S. energy production
policy. The effects on the environment caused by the interaction between power plant emissions
and atmospheric constituents has not been investigated in depth due to the lack of calibrated
spectral data on a suitable temporal and spatial scale. The availability of NASA's space-based
Atmospheric Infrared Sounder (AIRS) data makes it possible to explore, and begin the first steps toward establishing, a correlation between known emission sources and environmental indicators. An exploratory study was conducted in which a time series of 26 cloud-free AIRS data containing two coal-fired power plants in northern New Mexico were selected, acquired, and analyzed for SO2 emissions. A generic forward modeling process was also developed to derive an estimate of the expected AIRS pixel radiance containing the SO2 emissions from the two power plants based on published combustion analysis data for coal and available power plant documentation. Analysis of the AIRS NE&Dgr;R calculated in this study and subsequent comparison with the radiance values for SO2 calculated from the forward model provided essential information regarding the suitability and risk in the use of a modified AIRS configuration for monitoring anthropogenic point source emissions. The results of this study along with its conclusions and recommendations in conjunction with additional research collaboration in several specific topics will provide guidance for the development of the next generation infrared spectrometer system that NASA is considering building for environmental monitoring.
Spectroscopic measurements of infrared molecular transitions in gas plumes are evaluated for their potential to yield a reliable remote sensing technique for determination of plume temperature. Under optically thin conditions, the ratio of intensities from two different CO2 transitions has no dependence on molecular concentration, but has sufficient thermal sensitivity to be used as a temperature diagnostic. Fine spectral resolution is not required. Experimental results involving simultaneous thermocouple and spectroscopic measurements support the use of spectroscopic intensity ratios to determine stack plume temperatures. Measurements involve a plume from a vehicle exhaust and a stack plume from a propane-burning portable plume generator. Observed CO2 emission near 4.26 µm is affected by optical thickness and by self-absorption of emitted radiation by the cool outer regions of the plume. Measurements on the wings of molecular bands mitigate these absorption effects. Relationships between absorptive and emissive spectral intensities are developed that allow calibration of the temperature diagnostic using readily available absorption spectra. Based on data spanning a range of plume temperatures from 310 to 606 K, the root-mean-square difference between the spectroscopically derived temperatures and thermocouple data is 22 K.
Results are reported from a continuing program of research into the physics and spectroscopy of heated stack plumes. Simultaneous thermocouple and spectrometer measurements are used to study sideways-directed plumes from an internal combustion engine and a propane-burning plume generator. A previously-reported result, that the ratio of optically thin signals from two CO2 transitions can be used to determine plume temperature, is confirmed by comparison of thermocouple and spectrometer measurements over a wide range of temperatures. The basic physics of molecular emission and absorption of radiation is discussed and is used to calibrate the relationship between the spectroscopic ratio and plume temperature. The result is a spectroscopic plume temperature diagnostic that contains no adjustable parameters, and can be calibrated by use of published absorption spectra. Data relating to the accuracy of the technique are discussed.
This paper is a collaborative effort between the US EPA's Technology Applications and Research & Development groups to generate commercial interest in the development of cost effective sensors appropriate for the requirements of organizations in the CIVIL sector chartered with providing emergency first response support. The US EPA Region-7 Technology Applications Group maintains the Airborne Spectral Photometric Environmental Collection Technology (ASPECT) System. This system provides the US EPA with operational 24 hour/seven days a week emergency response remote chemical detection capability. Data collected by the ASPECT system along with the first responder requirements will be encapsulated in a manner suitable for guiding the efforts of commercial sensor system manufactures (e.g., effluents of interest, bounding concentrations/abundances, bounding environmental background parameters, sensor radiometric performance requirements for high-confidence response/action, operational readiness timelines, etc.). This paper is intended to provide the requirements, initiate and guide the synthesis process for sensor(s) and instrument packages providing sufficient area coverage, spectral resolution, and sensitivity to detect, selectivity to identify, image, and map hazardous chemical plumes. It is believed this effort will facilitate cost effective and timely state of the art sensor/system technology development suitable for CIVIL emergency response needs in compact automated packages.
KEYWORDS: Spectroscopy, Absorption, Carbon dioxide, Black bodies, Temperature metrology, Near field optics, Near field, Bioalcohols, Infrared radiation, Quantum optics
The movements, structure, and dynamics of a heated stack plume are revealed by thermocouple and spectrometer measurements. A three-dimensional thermocouple array provides temperature data at two-second intervals. An animated display allows the temperature and position variations of a plume to be visualized, and demonstrates that the plume parameters have significant temporal variation at positions more than a few feet from the stack. Plots of temperature vs. downstream position show the transition from the "near field" to the "far field" regime. For a sideways-directed momentum plume, the temperature varies as the reciprocal of the downstream position. These results are consistent with published data and with theoretical expectations. Spectrometer data suggest that the shape of the 4.26-micron CO2 transition depends on radial position in the plume. Spectra taken near the plume edge are relatively flat-topped, whereas measurements taken near the centerline show a line reversal due to absorption. These results are consistent with a plume structure involving a hot, optically thick core surrounded by an envelope of cooler gas.
Remote sensing using midwave and longwave spectroscopy has been shown to be capable of detecting gaseous effluents from a stack plume release. In general, measurements have been made through the plume cross-section. This paper discusses experiments and measurements conducted to examine the relative merits of viewing the plume's cross-section or viewing the plume along the axis of the plume flow. While viewing along the plume's flow axis increases the path length, additional factors such as wind variance and the effects of optically thick cells may begin to appear.
Spectral emissivity measurements gathered in the longwave infrared region of the spectrum during a recent airborne hyperspectral data collection experiment indicated that the spectral emissivity of certain organic polymers changed by as much as 10% throughout the day. Inorganic and many other organic materials that were measured at the same time during this experiment showed no change. As this was an unexpected event, a subsequent experiment was designed to make emissivity measurements of several organic and inorganic materials over a 24-hour period/diurnal cycle. The results from this experiment confirmed that certain materials showed a significant spectral emissivity variation over this period. This paper will discuss some possible explanations for this variation and emphasize the significance and implications of this fact on the integrity of spectral emissivity measurements and spectral libraries being constructed in this wavelength region.
Spectroscopic measurements of infrared CO2 transitions in gas plumes are reported, and evaluated for their potential to yield a reliable remote sensing technique for determination of plume temperature. Measurments were made on two types of plumes: a sideways-directed plume from a vehicle exhaust, and a stack plume from a propane-burning portable plume generator. Modeling of CO2 emission near 4.25 μm from the portable plume generator does not yield a temperature diagnostic due to heavy and unpredictable atmospheric absorption. The 4.25 μm band is optically thick in the vehicle exhaust plume measurements. For the vehicle plume, the blackbody Planck equation is used to derive temperatures that agree with results of thermocouple measurements. The ratio of optically thin signals obtained in the vicinity of the 4.25 μm and 14.4 μm transitions is related to temperature in accordance with Boltzmann statistics. For these experimental conditions, the ratio calculated from the Boltzmann distribution has similar temperature dependence to the ratio obtained from the blackbody Planck equation. Because the ratio of signals obtained at two optically thin wavelengths is independent of concentration, this technique has promise for field measurement of plume temperatures.
Using a Fourier transform infrared field spectrometer, spectral infrared radiance measurements were made of several generated gas plumes against both a uniform sky and terrestrial background. Background temperature, spectral complexity, and physical homogeneity each influenced the success of emissive infrared spectral sensing technology in detecting and identifying the presence of a gas plume and its component constituents. As expected, high temperature contrast and uniform backgrounds provided the best conditions for detectibility and diagnostic identification. This report will summarize some of SITAC's findings concerning plume detectability, including the importance of plume cooling, plumes in emission and absorption, the effects of optical thickness, and the effects of condensing plumes on gas detection.
Terrain categorization and target detection algorithms applied to Hyperspectral Imagery (HSI) typically operate on the measured reflectance (of sun and sky illumination) by an object or scene. Since the reflectance is a non-dimensional ratio, the reflectance by an object is nominally not affedted by variations in lighting conditions. Atmospheric Correction (also referred to as Atmospheric Compensation, Characterization, etc.) Algorithms (ACAs) are used in application of remotely sensed HSI datat to correct for the effects of atmospheric propagation on measurements acquired by air and space-borne systems. The Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes (FLAASH) algorithm is an ACA created for HSI applications in the visible through shortwave infrared (Vis-SWIR) spectral regime. FLAASH derives its physics-based mathematics from MODTRAN4.
The Spectral Information Technology Applications Center has developed software capability to perform roll correction and geo-rectification, using pitch, roll and yaw for data collected by the Night Vision Imaging Spectrometer as well as its high-resolution panchromatic camera. This paper describes the roll-correction algorithm and its software interface to the Boeing C-MIGITS II INS/GPS system for correction of pitch, yaw and roll. It also describes the geo-rectification algorithm and its interface to the ENVI geo-rectification software routines.
This paper presents an overview of the latest version of a MODTRAN4-based atmospheric correction (or "compensation") algorithm developed by Spectral Sciences, Inc. and the Air Force Research Laboratory for spectral imaging sensors. New upgrades to the algorithm include automated aerosol retrieval, cloud masking, and speed improvements. In addition, MODTRAN4 has been updated to correct recently discovered errors in the HITRAN-96 water line parameters. Reflectance spectra retrieved from AVIRIS data are compared with "ground truth" measurements, and good agreement is found.
A planetary rover, like a spacecraft, must be fully self-contained. Once launched, a rover can only receive information from its designers, and if solar powered, power from the sun. As the distance from Earth increases, and the demands for power on the rover increase, there is a serious tradeoff between communication and computation. Both of these subsystems are very power hungry, and both can be the major driver of the rover's power subsystem, and therefore, the minimum mass and size of the rover. This paper discusses this situation in more detail, and discusses software techniques that can be used to reduce the requirements on both communication and computation, allowing the overall robot mass to be greatly reduced.
KEYWORDS: Sensors, Infrared sensors, Sensor performance, Control systems design, Magnetic sensors, Prototyping, Mars, Artificial intelligence, Control systems, Infrared radiation
This paper describes the control system for Rocky IV, a prototype microrover designed to demonstrate proof-of-concept for a low-cost scientific mission to Mars. Rocky IV uses a behavior-based control architecture which implements a large variety of functions displaying various degrees of autonomy, from completely autonomous long-duration conditional sequences of actions to very precisely described actions resembling classical AI operators. The control system integrates information from infrared proximity sensors, proprioceptive encoders which report on the state of the articulation of the rover's suspension system and other mechanics, a homing beacon, a magnetic compass, and contact sensors. In addition, significant functionality is implemented as 'virtual sensors', computed values which are presented to the system as if they were sensors values. The robot is able to perform a variety of useful tasks, including soil sample collection, removal of surface weathering layers from rocks, spectral imaging, instrument deployment, and sample return, under realistic mission- like conditions in Mars-like terrain.
KEYWORDS: Sensors, Control systems, Sensor fusion, Actuators, Control systems design, 3D modeling, Mobile robots, Environmental sensing, Computer architecture, Process control
Exploiting prior knowledge about the general characteristics of an environment can reduce the amount of sensing required. For example, in an indoor environment floors tend
to be flat and walls tend to be straight and static. In such an environment, simple range sensors can provide enough information to support robust sensor-driven goal-directed navigation. This paper will describe a navigation experiment using a real robot, and speculate on how the techniques used can be extended to other domains.
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