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All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Real-Time Feature Tracking Using Homography

This software finds feature point correspondences in sequences of images. It is designed for feature matching in aerial imagery. Feature matching is a fundamental step in a number of important image processing operations: calibrating the cameras in a camera array, stabilizing images in aerial movies, geo-registration of images, and generating high-fidelity surface maps from aerial movies. The method uses a Shi-Tomasi corner detector and normalized cross-correlation. This process is likely to result in the production of some mismatches. The feature set is cleaned up using the assumption that there is a large planar patch visible in both images. At high altitude, this assumption is often reasonable. A mathematical transformation, called an homography, is developed that allows us to predict the position in image 2 of any point on the plane in image 1. Any feature pair that is inconsistent with the homography is thrown out. The output of the process is a set of feature pairs, and the homography. The algorithms in this innovation are well known, but the new implementation improves the process in several ways. It runs in real-time at 2 Hz on 64-megapixel imagery. The new Shi-Tomasi corner detector tries to produce the requested number of features by automatically adjusting the minimum distance between found features. The homography-finding code now uses an implementation of the RANSAC algorithm that adjusts the number of iterations automatically to achieve a pre-set probability of missing a set of inliers. The new interface allows the caller to pass in a set of predetermined points in one of the images. This allows the ability to track the same set of points through multiple frames.

Clouse, Daniel S.↗
NASA NTRS1979

The hard X-ray burst spectrometer on the solar maximum mission

The primary scientific objective of the spectrometer is to provide a greater understanding of the role of energetic electrons in solar flares. This will be achieved by observations of high energy X-rays in the energy range from 20 to 200 keV with time resolution of 0.128s on a continuous basis and as short as 1 ms for limited intervals. The X-ray detector is an actively shielded CsI(Na) crystal with a thickness of 0.635 cm and a sensitive area of 71 sq cm. In the first year after launch, it is expected that approximately 1000 flares above the sensitivity threshold of 0.2 photons/(sq cm s) lasting for one second, will be detected.

Orwig, L. E.↗
NASA NTRS1979

Integrated infrared detector arrays for low-background astronomy

Existing integrated infrared detector array technology is being evaluated under low-background conditions to determine its applicability in orbiting astronomical applications where extended integration times and photometric accuracy are of interest. Preliminary performance results of a 1 x 20 elements InSb CCD array under simulated astronomical conditions are presented. Using the findings of these tests, improved linear- and area-array technology will be developed for use in NASA programs such as the Shuttle Infrared Telescope Facility. For wavelengths less than 30 microns, extrinsic silicon and intrinsic arrays with CCD readout will be evaluated and improved as required, while multiplexed arrays of Ge:Ga for wavelengths in the range 30 to 120 microns will be developed as fundamental understanding of this material improves. Future efforts will include development of improved drive and readout circuitry, and consideration of alternate multiplexing schemes.

Mccreight, C. R.↗
NASA NTRS1981

A statistical analysis of the low-energy geosynchronous plasma environment. I - Electrons. II - Ions

Data on the geosynchronous plasma environment between approximately 30 eV and 80 keV are analyzed statistically. Nearly 50 days of 10 minute averages of the first four moments of the distribution function from low-energy plasma detectors on the ATS-5 and ATS-6 geosynchronous satellites were used. The data were studied in terms of occurrence frequency, local time variations, and response to geomagnetic activity. These techniques revealed marked differences in the ATS-5 and ATS-6 data bases. When translated into a 2-Maxwellian representation, it was found that (1) the ATS-6 data covered an energy range not covered by ATS-5 (between 1 and 50 eV) and (2) there was a definite change in the ion plasma between the ATS-5 and ATS-6 measurements. Simple expressions are derived to simulate the relationship between the four moments, and a model is presented, which takes into account the ATS-5 and ATS-6 plasma variations. Despite the differences in the ion data, the accuracy of the four-moment representation was found valid for characterizing the geosynchronous electron population.

Garrett, H. B.↗
NASA NTRS1983

Design and performance of the Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument

Design and performance data are analyzed for the Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument, which has been developed for the NASA Earth Radiation Budget Satellite (ERBS). SAGE II is designed to monitor globally, from 70 degrees S to 70 degrees N latitude, the vertical distribution of stratospheric aerosols, ozone, water vapor, and nitrogen dioxide by measuring the extinction of solar radiation through the earth's atmosphere during the ERBS observatory solar occultations. A flat scanning mirror reflects solar radiation into a Cassegrain type telescope, which forms a solar image on the entrance slit of a grating spectrometer. The instantaneous-field-of-view of the SAGE II is scanned along the vertical solar diameter by the elevation scan mirror. The optical system is contained within an azimuth gimbal which tracks the solar radiometric centroid during the data event, while the spectrometer isolates seven spectral wavelengths from 0.385-1.02 micrometers. The seven channels of the spectrometer use silicon photodiode dedectors operated in the photovoltaic mode. The detector outputs are multiplexed into a serial data stream for readout by the ERBS telemetry system, with each output being sampled 64 times per second and digitized to 12 bit resolution.

Zaun, N. H.↗
NASA NTRS1985

Feasibility of self-structured current accessed bubble devices in spacecraft recording systems

The self-structured, current aperture approach to magnetic bubble memory is described. Key results include: (1) demonstration that self-structured bubbles (a lattice of strongly interacting bubbles) will slip by one another in a storage loop at spacings of 2.5 bubble diameters, (2) the ability of self-structured bubbles to move past international fabrication defects (missing apertures) in the propagation conductors (defeat tolerance), and (3) moving bubbles at mobility limited speeds. Milled barriers in the epitaxial garnet are discussed for containment of the bubble lattice. Experimental work on input/output tracks, storage loops, gates, generators, and magneto-resistive detectors for a prototype device are discussed. Potential final device architectures are described with modeling of power consumption, data rates, and access times. Appendices compare the self-structured bubble memory from the device and system perspectives with other non-volatile memory technologies.

Nelson, G. L.↗
NASA NTRS1985

Electron capture decay of cosmic rays: A model of the inhomogeneous interstellar medium

Traditional analyses of cosmic ray composition seek to identify the sources through a determination of a the isotopic abundances of these nuclei prior to acceleration. At the same time, it is both necessary and interesting to understand the nature of the medium through which cosmic rays pass before arriving at detectors. In fact, only within a model of the interstellar medium (ISM) sampled by cosmic rays can a refined estimate of source composition be made. An elaboration of the traditional model of the ISM used in studying cosmic ray propagation is explored. Inhomogeneity of the ISM is accomodated in this model. Within this model it is found that the abundances of some electron apture isotopes, are very sensitive to density inhomogeneities which might be expected in the ISM. These nuclei therefore measure the penetration of heavy cosmic rays into interstellar clouds.

Letaw, J. R.↗
NASA NTRS1984

Absolute spectral irradiance measurements of lightning from 375 to 880 nm

The time-integrated emissions from cloud-to-ground lightning have been recorded in the 375-880 nm region, using a spectrometer-detector and multichannel analyzer system capable of absolute spectral irradiance measurements. A schematic drawing of the detector-analyzer system is presented, and the experimental setup is described. A total of ten flashes containing 46 individual strikes were recorded and compared to recordings of 500 flashes from 1981. The average spectral irradiance from 375 to 695 nm for flashes at about 15 km was 3.5 x 10 to the -5th J/sq m per stroke with a standard deviation of 2.0 x 10 to the -5th and a range from 0.7 x 10 to the 0.7-6.8 x 10 to the -5th J/sq m per stroke. The average stroke spectra irradiance from 650 to 880 nm for the same strokes was 1.2 x 10 to the -5th, with a standard deviation of 0.7 x 10 to the -5th and a range from 0.5 to 3.2 x 10 to the -5th J/sq m per stroke. A summary table of spectral irradiance values in 50 nm increment is presented. Analysis of the spectral emission data show that unresolved neutral hydrogen lines (NI) at 744.2 nm were more intense than H-alpha emission at 656.3 nm. The strong emission of a flash with a continuing current was identified as cyanogen (CN) emission.

Orville, R. E.↗
NASA NTRS1985

Fluctuations of precipitated electron intensity in flickering auroral arcs

Electron spectra associated with two aurorae observed by ground-based television are reported. One auroral arc was observed to flicker, large variations in the precipitated electron energy occurring on a time scale of 114 ms. The major variations occur at the higher energies of the 0.5-20 keV range covered by the detectors. Changes in the particle flux occur primarily in the pitch angle range 0 to 60 deg. Analysis of the video data shows a larger variation in intensity along the lower border of the arc in keeping with the results of the electron spectra. The second arc was not observed to flicker, and the associated electron spectra and video data show no large variations in precipitated electron energy or video intensity modulation. While pitch-angle distributions tend to be field-aligned in the first arc, the distributions in the second arc are nearly isotropic or peaked from 60 to 90 deg in the downward hemisphere.

Spiger, R. J.↗
NASA NTRS1987

Gas chromatographic instrumentation for the analysis of aerosols and gases in Titan's atmosphere

Instrumentation presently being developed by NASA for the collection and analysis of organic gases and aerosols in Titan's atmosphere is described together with the results of the preliminary experiments. For the aerosols, stepwise pyrolysis was shown to be a suitable method for preparing complex organic material for gas chromatography (GC), and a pyrolysis-gas chromatograph was developed and successfully used to analyze a simulated Titan aerosol. Atmospheric gases will be collected by a low-pressure gas sampling system using large-volume sample loops and analyzed by GC. The results of preliminary studies using a 20 cu cm sampling system and a very sensitive metastable ionization detector showed that hydrocarbon components at the 10 ppb level can be detected. Studies are in progress on shortening the overall analysis time by improving the pyrolysis system, the gas sampling system, and the associated gas chromatograph. Further development of the gas sampling system is planned to ensure rapid collection of samples adequate for analysis by GC over the entire range of pressures to be encountered during the probe's descent.

Scattergood, T. W.↗
NASA NTRS1987

Differential CCD photometry of faint asteroids in crowded star fields and nonphotometric sky conditions

It is demonstrated that the use of an imaging CCD detector array allows photometric observations of comparatively faint asteroids moving rapidly through a complex background of star images. The shortage of observing time is alleviated by taking advantage of the presence of comparison stars that are observed simultaneously on the CCD imaging area and at small angular separations from the asteroid. These reference stars allow the effects of thin cirrus clouds or haze to be compensated to a degree adequate for the acquisition of scientifically original data.

Wisniewski, W. Z.↗
NASA NTRS1988

DS/LPI autocorrelation detection in noise plus random-tone interference

The authors present and analyze a frequency-noncoherent two-lag autocorrelation statistic for the wideband detection of random BPSK signals in noise-plus-random-multitone interference. It is shown that this detector is quite robust to the presence or absence of interference and its specific parameter values, contrary to the case of an energy detector. The rule assumes knowledge of the data rate and the active scenario under H0. It is concluded that the real-time autocorrelation domain and its samples (lags) are a viable approach for detecting random signals in dense environments.

Hinedi, S.↗
NASA NTRS1992

Open-Loop Acquisition Of Frequency In BPSK

Proposed open-loop analog/digital signal-processing system would be Costas-loop error detector functioning in closed-loop manner overall. Detector estimates difference between frequency of input signal and internal reference oscillator. Estimate used to close frequency-control loop. Precise symbol timing not necessary. Performance better than systems that effect open-loop acquisition using integrators instead of low-pass filters in arms of Costas loops and in which performance varies with symbol timing.

Shah, Biren N.↗
NASA NTRS1991

Design and performance of an Automatic Gain Control system for the High Energy X-Ray Timing Experiment

The High Energy X-Ray Timing Experiment (HEXTE), currently under development for the X-Ray Timing Explorer (XTE) mission, employs a closed loop gain control system to attain 0.5 percent stabilization of each of eight-phoswich detector gains. This Automatic Gain Control (AGC) system utilizes a split window discriminator scheme to control the response of each detector pulse height analyzer to gated Am-241 X-ray events at 60 keV. A prototype AGC system has been implemented and tested within the gain perturbation environment expected to be experienced by the HEXTE instrument in flight. The AGC system and test configuration are described. Response, stability and noise characteristics are measured and compared with theoretical predictions. The system is found to be generally suitable for the HEXTE application.

Pelling, Michael R.↗
NASA NTRS1993

Preliminary GPS orbit determination results for the Extreme Ultraviolet Explorer

A single-frequency Motorola Global Positioning System (GPS) receiver was launched with the Extreme Ultraviolet Explorer mission in June 1992. The receiver utilizes dual GPS antennas placed on opposite sides of the satellite to obtain full GPS coverage as it rotates during its primary scanning mission. A data set from this GPS experiment has been processed at the Jet Propulsion Laboratory with the GIPSY-OASIS 2 software package. The single-frequency, dual antenna approach and the low altitude (approximately 500 km) orbit of the satellite create special problems for the GPS orbit determination analysis. The low orbit implies that the dynamics of the spacecraft will be difficult to model, and that atmospheric drag will be an important error source. A reduced-dynamic solution technique was investigated in which ad hoc accelerations were estimated at each time step to absorb dynamic model error. In addition, a single-frequency ionospheric correction was investigated, and a cycle-slip detector was written. Orbit accuracy is currently better than 5 m. Further optimization should improve this to about 1 m.

Gold, Kenn↗
NASA NTRS1998

Spectral Characterizations of the Clouds and the Earth's Radiant Energy System (CERES) Thermistor Bolometers using Fourier Transform Spectrometer (FTS) Techniques

Fourier Transform Spectrometer (FTS) techniques are being used to characterize the relative spectral response, or sensitivity, of scanning thermistor bolometers in the infrared (IR) region (2 - >= 100-micrometers). The bolometers are being used in the Clouds and the Earth's Radiant Energy System (CERES) program. The CERES measurements are designed to provide precise, long term monitoring of the Earth's atmospheric radiation energy budget. The CERES instrument houses three bolometric radiometers, a total wavelength (0.3- >= 150-micrometers) sensor, a shortwave (0.3-5-micrometers) sensor, and an atmospheric window (8-12-micrometers) sensor. Accurate spectral characterization is necessary for determining filtered radiances for longwave radiometric calibrations. The CERES bolometers spectral response's are measured in the TRW FTS Vacuum Chamber Facility (FTS - VCF), which uses a FTS as the source and a cavity pyroelectric trap detector as the reference. The CERES bolometers and the cavity detector are contained in a vacuum chamber, while the FTS source is housed in a GN2 purged chamber. Due to the thermal time constant of the CERES bolometers, the FTS must be operated in a step mode. Data are acquired in 6 IR spectral bands covering the entire longwave IR region. In this paper, the TRW spectral calibration facility design and data measurement techniques are described. Two approaches are presented which convert the total channel FTS data into the final CERES spectral characterizations, producing the same calibration coefficients (within 0.1 percent). The resulting spectral response curves are shown, along with error sources in the two procedures. Finally, the impact of each spectral response curve on CERES data validation will be examined through analysis of filtered radiance values from various typical scene types.

Thornhill, K. Lee↗
NASA NTRS2001

Preliminary Results From The First Flight of ATIC

The Advanced Thin Ionization Calorimeter (ATIC) instrument is designed to measure the composition and energy spectra of Z = 1 to 28 cosmic rays over the energy range approximately 10 GeV - 100 TeV. The instrument was calibrated in September 1999 at CERN using accelerated electron, proton and pion beams. ATIC was launched as a long duration balloon test flight on 12/28/00 local time from McMurdo, Antarctica. After flying successfully for about 16 days the payload was recovered in excellent condition. Absolute calibration of the detector response was made using cosmic-ray muons. The data analysis algorithm which was developed with Monte Carlo simulations and validated with the CERN beam test will be used for the flight data analysis. Preliminary results of the proton and helium spectra will be reported in this paper.

Seo, E. S.↗
NASA NTRS2001

Preliminary Results From the First Flight of ATIC

The Advanced Thin Ionization Calorimeter (ATIC) instrument is designed to measure the composition C and energy spectra of Z = 1 to 28 cosmic rays over the energy range approximately 10 GeV - 100 TeV. The instrument was calibrated in September 1999 at CERN using accelerated electron, proton and pion beams. ATIC was launched as a long duration balloon test flight on 12/28/00 local time from McMurdo, Antarctica. After flying successfully for about 16 days the payload was recovered in excellent condition. Absolute calibration of the detector response was made using cosmic-ray muons. The data analysis algorithm which was developed with Monte Carlo simulations and validated with the CERN beam test will be used for the flight data analysis. Preliminary results of the protons and C helium spectra will be reported in this paper.

Seo, E. S.↗