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At least 631 records · Page 35

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NASA NTRS1989

Passive millimeter-wave imaging - A tool for remote sensing

This paper describes a program of airborne radiometric imaging at 90 GHz and 140 GHz. Using high sensitivity (below 1 K) and high angular resolution (0.5-1.0 degree), high quality images have been made. The following measurements are discussed: cloud and fog penetration at 90 GHz, discrimination between agricultural and urban areas, discrimination between different vegetation types, detection of vehicles on roads, detection and classification of airports and airplanes, ship detection and quantitative oil spill sensing. The application of information enhancement techniques with automatic and real time application aspects is also described, and results of applied techniques for contrast and contour enhancement are shown.

Suess, Helmut↗

NASA NTRS1990

Faults in the Mojave Desert, California, as revealed on enhanced Landsat images

Landsat TM images, subjected to four-component processing through which lithologies can be discriminated by their contrasting absorption and reflection at IR wavelengths, have revealed previously unsuspected strike-slip and normal faults in the central and eastern Mojave Desert. These discriminations, which extend to ferric and ferrous iron and to hydroxyl content without compromise of landform depiction, represent a novel type of geophysical display for geologic mapping in regions of well-exposed bedrock; the faults thus discovered form part of an extensive regional network of right shear which connects Death Valley region faults with those in the San Andreas system.

Ford, J. P.↗

NASA NTRS1990

An infrastructure assessment of alternative Mars Transfer Vehicles

Development and evolutionary paths for many space transportation elements must be considered as the United States space program embarks on the Space Exploration Initiative (SEI). A central element of the space transportation infrastructure necessary to support the SEI is Mars Transportation System (MTS). This system consists of the Mars Transfer Vehicle (MTV) and Mars Excursion Vehicle. This paper describes the process and results in evaluating the alternate MTV propulsion concepts. Primary discriminators in evaluating different options for the MTV alternatives are: requirements for earth-to-orbit delivery, on-orbit facility and assembly requirements, and mission performance. Propulsion candidates assessed in this paper include nuclear thermal propulsion, nuclear electric propulsion, solar electric propulsion, and cryogenic chemical propulsion (LO2/LH2). The primary discriminators as well as additional selection criteria will be discussed for each MTS alternative.

Holdridge, Jeffrey D.↗

NASA NTRS1990

Mesoscale monitoring of the soil freeze/thaw boundary from orbital microwave radiometry

A technique was developed for mapping the spatial extent of frozen soils from the spectral characteristics of the 10.7 to 37 GHz radiobrightness. Through computational models for the spectral radiobrightness of diurnally heated freesing soils, a distinctive radiobrightness signature was identified for frozen soils, and the signature was cast as a discriminant for unsupervised classification. In addition to large area images, local area spatial averages of radiobrightness were calculated for each radiobrightness channel at 7 meteorologic sites within the test region. Local area averages at the meteorologic sites were used to define the preliminary boundaries in the Freeze Indicator discriminate. Freeze Indicator images based upon Nimbus 7, Scanning Multichannel Microwave Radiometer (SMMR) data effectively map temporal variations in the freeze/thaw pattern for the northern Great Plains at the time scale of days. Diurnal thermal gradients have a small but measurable effect upon the SMMR spectral gradient. Scale-space filtering can be used to improve the spatial resolution of a freeze/thaw classified image.

Dobson, Craig↗

NASA NTRS1991

Ordinary chondrites - Multivariate statistical analysis of trace element contents

The contents of mobile trace elements (Co, Au, Sb, Ga, Se, Rb, Cs, Te, Bi, Ag, In, Tl, Zn, and Cd) in Antarctic and non-Antarctic populations of H4-6 and L4-6 chondrites, were compared using standard multivariate discriminant functions borrowed from linear discriminant analysis and logistic regression. A nonstandard randomization-simulation method was developed, making it possible to carry out probability assignments on a distribution-free basis. Compositional differences were found both between the Antarctic and non-Antarctic H4-6 chondrite populations and between two L4-6 chondrite populations. It is shown that, for various types of meteorites (in particular, for the H4-6 chondrites), the Antarctic/non-Antarctic compositional difference is due to preterrestrial differences in the genesis of their parent materials.

Lipschutz, Michael E.↗

NASA NTRS1990

An optimal sensing strategy of a proximity sensor system for recognition and localization of polyhedral objects

An algorithm is presented for the recognition and localization of thre-dimensional polyhedral objects based on an optical proximity sensor system capable of measuring the depth and orientation of a local area of an object surface. Emphasis is given to the determination of an optimal sensor trajectory or an optimal probing, for efficient discrimination among all the possible interpretations. The determination of an optimal sensor trajectory for the next probing consists of the selection of optimal beam orientations based on the surface normal vector distribution of the multiple interpretation image (MII) and the selection of an optimal probing plane by projecting the MII onto the projection plane perpendicular to a selected beam orientation and deriving the optimal path on the projection plane. The selection of optimal beam orientation and probing plane is based on the measure of discrimination power of a cluster of surfaces of an MII. Simulation results are shown.

Lee, Sukhan↗

NASA NTRS1990

New drift chamber technology for high energy gamma-ray telescopes

Work to develop a low-power amplifier and discriminator for use on space qualifiable drift chambers is discussed. Consideration is given to the goals of the next generation of high-energy gamma-ray telescope design and to how the goals can be achieved using xenon gas drift chambers. The design and construction of a low power drift chamber amplifier and discriminator are described, and the design of a quad-time-to-amplitude converter is outlined.

Hunter, Stanley D.↗

NASA NTRS1991

Overview of the NASA-sponsored HSCT propulsion system studies

A brief overview of the NASA-sponsored HSCT propulsion system studies is presented that includes objectives, approach, schedules, and a summary of interim results highlighting the NASA in-house studies. Seven propulsion system concepts have been considered to date and comparatively evaluated on a first-order basis using takeoff gross weight (TOGW) as the main discriminator. Only two concepts have been screened out thus far and it is apparent that TOGW is not a strong discriminator. However, the first-order screening process did not account for differences in propulsion installation effects or climb-noise suppression penalties-both of which may strongly influence the screening process.

Strack, William C.↗

NASA NTRS1990

Television image compression and small animal remote monitoring

It was shown that a subject can reliably discriminate a difference in video image quality (using a specific commercial product) for image compression levels ranging from 384 kbits per second to 1536 kbits per second. However, their discriminations are significantly influenced by whether or not the TV camera is stable or moving and whether or not the animals are quiescent or active, which is correlated with illumination level (daylight versus night illumination, respectively). The highest video rate used here was 1.54 megabits per second, which is about 18 percent of the so-called normal TV resolution of 8.4MHz. Since this video rate was judged to be acceptable by 27 of the 34 subjects (79 percent), for monitoring the general health and status of small animals within their illuminated (lights on) cages (regardless of whether the camera was stable or moved), it suggests that an immediate Space Station Freedom to ground bandwidth reduction of about 80 percent can be tolerated without a significant loss in general monitoring capability. Another general conclusion is that the present methodology appears to be effective in quantifying visual judgments of video image quality.

Haines, Richard F.↗

NASA NTRS1991

The biogeochemistry of microbial mats, stromatolites and the ancient biosphere

Stromatolites offer an unparalleled geologic record of early life, because they constitute the oldest and most abundant recognizable remains of microbial ecosystems. Microbial mats are living homologs of stromatolites; thus, the physiology of the microbiota as well as the processes which create those features of mats (e.g., biomarker organic compounds, elemental and stable isotopic compositions) which are preserved in the ancient record. Observations of the carbon isotopic composition (delta C-13) of stromatolites and microbial mats were made and are consistent with the hypothesis that atmospheric CO2 concentrations have declined by at least one to two orders of magnitude during the past 2.5 Ga. Whereas delta C-13 values of carbonate carbon average about 0 permil during both the early and mid-Proterozoic, the delta C-13 values of stromatolitic organic matter increase from an average of -35 between 2.0 and 2.6 Ga ago to an average of about -28 about 1.0 Ga ago. Modern microbial mats in hypersaline environments have delta C-13 values typically in the range of -5 to -9, relative to an inorganic bicarbonate source at 0 permil. Both microbial mats and pur cultures of cyanobacteria grown in waters in near equilibrium with current atmospheric CO2 levels exhibit minimal discrimination against C-13. In contrast, hot spring cyanobacterial mats or cyanobacterial cultures grown under higher CO2 levels exhibit substantially greater discrimination. If care is taken to compare modern mats with stromatolites from comparable environments, it might be possible to estimate ancient levels of atmospheric CO2. In modern microbial mats, a tight coupling exists between photosynthetic organic carbon production and subsequent carbon oxidation, mostly by sulfate reduction. The rate of one process fuels a high rate of the other, with much of the sulfate reduction occurring within the same depth interval as oxygenic photosynthesis. Other aspects of this study are presented.

Desmarais, D. J.↗

NASA NTRS1992

Coded 16-CPFSK for downlink applications

A bandwidth-efficient constant-envelope Proof-of-Concept (POC) modem is described. The modem was developed on an Advanced Modulation Techniques Development contract for the NASA/Lewis Research Center. The POC modem employs 16-ary Continuous Phase Frequency Shift Keying (16-CPFSK) modulation. The 16 frequencies are spaced every 1/16th baud rate which produces a compact spectrum allowing 2 bits/sec/Hz operation. The modem is designed for 200 mb/s Time Division Multiple Access (TDMA) application with 100 MHz adjacent channel spacing. Overall rate 3.4 convolutional coding is incorporated. The demodulator differs significantly from typical quadrature phase detector approaches in that phase is coherently measured by processing the baseband output of a frequency discriminator. Baud rate phase samples for the baseband processor are subsequently decoded to yield the original data stream. The method of encoding onto the 16-ary symbol-ending phase nodes, together with convolutional coding gain, results in near Quadrature Phase Shift Keying (QPSK) theoretical performance. The modulated signal is of constant envelope; thus the power amplifier can be saturated for peak performance. The spectrum is inherently bandlimited and requires no RF filter for sidelobe containment. Two novel theoretical techniques are used in this 16-CPFSK modem: (1) coherent phase measurements are obtained by processing an FM discriminator baseband output; and (2) modulation is accomplished via a closed-loop-linearized voltage controlled oscillator (VCO).

Davis, Robert↗

NASA NTRS1992

Space sickness predictors suggest fluid shift involvement and possible countermeasures

Preflight data from 64 first time Shuttle crew members were examined retrospectively to predict space sickness severity (NONE, MILD, MODERATE, or SEVERE) by discriminant analysis. From 9 input variables relating to fluid, electrolyte, and cardiovascular status, 8 variables were chosen by discriminant analysis that correctly predicted space sickness severity with 59 pct. success by one method of cross validation on the original sample and 67 pct. by another method. The 8 variables in order of their importance for predicting space sickness severity are sitting systolic blood pressure, serum uric acid, calculated blood volume, serum phosphate, urine osmolality, environmental temperature at the launch site, red cell count, and serum chloride. These results suggest the presence of predisposing physiologic factors to space sickness that implicate a fluid shift etiology. Addition of a 10th input variable, hours spent in the Weightless Environment Training Facility (WETF), improved the prediction of space sickness severity to 66 pct. success by the first method of cross validation on the original sample and to 71 pct. by the second method. The data suggest that WETF training may reduce space sickness severity.

Simanonok, K. E.↗

NASA NTRS1992

Binary optical filters for scale invariant pattern recognition

Binary synthetic discriminant function (BSDF) optical filters which are invariant to scale changes in the target object of more than 50 percent are demonstrated in simulation and experiment. Efficient databases of scale invariant BSDF filters can be designed which discriminate between two very similar objects at any view scaled over a factor of 2 or more. The BSDF technique has considerable advantages over other methods for achieving scale invariant object recognition, as it also allows determination of the object's scale. In addition to scale, the technique can be used to design recognition systems invariant to other geometric distortions.

Reid, Max B.↗

NASA NTRS1991

An optimal sensing strategy for recognition and localization of 3-D natural quadric objects

An optimal sensing strategy for an optical proximity sensor system engaged in the recognition and localization of 3-D natural quadric objects is presented. The optimal sensing strategy consists of the selection of an optimal beam orientation and the determination of an optimal probing plane that compose an optimal data collection operation known as an optimal probing. The decision of an optimal probing is based on the measure of discrimination power of a cluster of surfaces on a multiple interpretation image (MII), where the measure of discrimination power is defined in terms of a utility function computing the expected number of interpretations that can be pruned out by a probing. An object representation suitable for active sensing based on a surface description vector (SDV) distribution graph and hierarchical tables is presented. Experimental results are shown.

Lee, Sukhan↗

NASA NTRS1992

Sensor placement for diagnosability in space-borne systems - A model-based reasoning approach

This paper presents an approach to evaluating sensor placements on the basis of how well they are able to discriminate between a given fault and normal operating modes and/or other fault modes. In this approach, a model of the system in both normal operations and fault modes is used to evaluate possible sensor placements upon the basis of three criteria. Discriminability measures how much of a divergence in expected sensor readings the two system modes can be expected to produce. Accuracy measures confidence in the particular model predictions. Timeliness measures how long after the fault occurrence the expected divergence will take place. These three metrics then can be used to form a recommendation for a sensor placement. This paper describes how these measures can be computed and illustrated these methods with a brief example.

Chien, Steve↗

NASA NTRS1991

Inferring vegetation characteristics using a knowledge-based system

A knowledge-based system for inferring physical and biological surface properties of vegetation using nadir and/or directional reflectance data as input is developed. A portion of this system has been developed to discriminate between user-defined vegetation classes using spectral and directional reflectance relationships. This discrimination program was used to classify targets into user-defined ground cover and plant height classes. The program learns class descriptors from samples (both positive and negative) of spectral, directional reflectance data of natural surfaces (bare soils, natural vegetation, and agricultural vegetation). The system is designed to handle any combination of directional view angles. The explicit relationships used in the class descriptions include greater-than relationships between combinations of two view angles and maximum and minimum value relationships. The class descriptions are used to classify an unknown target using the same directional views. The program was tested by learning class descriptions of various categories of percent ground cover and vegetation height.

Kimes, D. S.↗

NASA NTRS1992

Guidance and dispersion studies of National Launch System ascent trajectories

The National Launch System (NLS) is a joint concept, between DoD and NASA, for building a family of new launch vehicles. Two of the many choices to be made are the trajectory shaping methods and the onboard guidance scheme. This paper presents results from some ongoing studies to address these issues. First, potential gains from new guidance concepts are listed. Next the paper gives a list of possible discriminators between different guidance schemes, lists a number of potential guidance schemes, and explains two in some detail. A reference scheme is tested to determine its performance versus the discriminators. Finally, results from some special studies using the reference guidance scheme are given, including the effects of closed-loop guidance initiation time, time of enforcement of sideslip, vehicle roll for engine out, time and location of an engine out, use of load relief control, and use of day of launch wind biasing.

Hanson, John M.↗

NASA NTRS1991

Perceiving the coherent movements of spatially-separated features

When a partially-occluded object is represented in an image, it is defined by a set of spatially-separated features that may be registered at different spatial scales. To understand the image, human vision must organize these fragmented optical features into common and distinct object surfaces. Although the common fate of moving features often is considered a primary source of reliable information for image segmentation, little is known of the visual system's capacity to discriminate the coherent relative movements of spatially-separated features. In a series of experiments, observers viewed elements whose movements were correlated (direction and magnitude) or were uncorrelated. Our results indicate that observers can discriminate the two types of movement about as well as they can detect any movement at all. Moreover, the ability to perceive coherent movements is maintained under a variety of conditions including differences in the elements' spatial frequency content, spatial position and contrast, and temporal phase shifts between the spatially-correlated displacements. These results suggest that coherent relative motion may be a fundamental source of information exploited by vision, despite considerable variability in the spatial and temporal characteristics of the individual features.

Mowafy, Lyn↗