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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Atmospheric variability experiment /AVE II/ pilot experiment

The Atmospheric Variability Experiment (AVE II) was conducted in May 1974. Rawinsonde releases were made at 54 upper-air stations in two thirds of the eastern U.S. at 3-hr intervals for a 24-hr period. Radar data were obtained from 11 stations located near the center of the observational area, and as many data as possible were collected from the Nimbus 5, NOAA 2, ATS-3, and DMSP satellites. The present paper provides an overview of the experiment and describes how the user community can obtain copies of the data.

Turner, R. E.↗
NASA NTRS1975

An optical/digital processor - Hardware and applications

A real-time two-dimensional hybrid processor consisting of a coherent optical system, an optical/digital interface, and a PDP-11/15 control minicomputer is described. The input electrical-to-optical transducer is an electron-beam addressed potassium dideuterium phosphate (KD2PO4) light valve. The requirements and hardware for the output optical-to-digital interface, which is constructed from modular computer building blocks, are presented. Initial experimental results demonstrating the operation of this hybrid processor in phased-array radar data processing, synthetic-aperture image correlation, and text correlation are included. The applications chosen emphasize the role of the interface in the analysis of data from an optical processor and possible extensions to the digital feedback control of an optical processor.

Casasent, D.↗
NASA NTRS1975

Side looking radar calibration study

Calibration of an airborne sidelooking radar is accomplished by the use of a model that relates the radar parameters to the physical mapping situation. Topics discussed include: characteristics of the transmitters; the antennas; target absorption and reradiation; the receiver and map making or radar data processing; and the calibration process.

Edwards, W. D.↗
NASA NTRS1976

Research on regional numerical weather prediction

Extension of the predictive power of dynamic weather forecasting to scales below the conventional synoptic or cyclonic scales in the near future is assessed. Lower costs per computation, more powerful computers, and a 100 km mesh over the North American area (with coarser mesh extending beyond it) are noted at present. Doubling the resolution even locally (to 50 km mesh) would entail a 16-fold increase in costs (including vertical resolution and halving the time interval), and constraints on domain size and length of forecast. Boundary conditions would be provided by the surrounding 100 km mesh, and time-varying lateral boundary conditions can be considered to handle moving phenomena. More physical processes to treat, more efficient numerical techniques, and faster computers (improved software and hardware) backing up satellite and radar data could produce further improvements in forecasting in the 1980s. Boundary layer modeling, initialization techniques, and quantitative precipitation forecasting are singled out among key tasks.

Kreitzberg, C. W.↗
NASA NTRS1976

Surface roughness estimation at three points on the lunar surface using 23-CM monostatic radar

Differences in quasi-specular scattering by the lunar surface have been observed at 23-cm wavelength by using earth-based radar. By taking advantage of libration, three subradar points were isolated, and distinct scattering laws were identified for terrain near Hipparchus, Sinus Medii, and the crater Schroeter F. Interpretations of lunar radar data should henceforth incorporate a recognition that these variations take place. Unidirectional rms surface slope estimates of 6-8 deg in the Central Highlands and 4-5 deg in old mare are appropriate to horizontal scales of 100 m.

Simpson, R. A.↗
NASA NTRS1977

Verification by Viking landers of earlier radio occultation measurements of surface atmospheric pressure on Mars

The landing of Viking 1 in Chryse Planitia on July 20, 1976 provided the first opportunity to obtain measurements of atmospheric pressure directly from the surface of Mars. A computation was conducted to predict the atmospheric pressure at the landing site before the landing itself. The relative altitude between occultation points and the Viking 1 site was obtained with the aid of earth-based planetary radar data taken in 1967. The data cover Martian latitudes from 19 deg N to 24 deg N. The investigation indicates that the radio occultation results from Mariner 9 closely correspond to the actual surface pressure on Mars.

Kliore, A. J.↗
NASA NTRS1977

Digital exploitation of synthetic aperture radar

A digital processing and analysis scheme for use with digitized synthetic aperture radar data was developed. Using data from a four channel system, the imagery is preprocessed using specially designed software and then analyzed using preexisting facilities originally intended for use with MSS type data. Geometric and radiometric correction may be performed if desired, as well as classification analysis, Fast Fourier transform, filtering and level slice and display functions. The system provides low cost output in real time, permitting interactive imagery analysis. System information flow diagrams as well as sample output products are shown.

Wagner, H. L.↗
NASA NTRS1977

Radar image processing module development program, phase 3

The feasibility of using charge coupled devices in an IPM for processing synthetic aperture radar signals onboard the NASA Convair 990 (CV990) aircraft was demonstrated. Radar data onboard the aircraft was recorded and processed using a CCD sampler and digital tape recorder. A description of equipment and testing was provided. The derivation of the digital presum filter was documented. Photographs of the sampler/tape recorder, real time display and circuit boards in the IPM were also included.

Source record↗
NASA NTRS1978

Development and flight tests of a Kalman filter for navigation during terminal area and landing operations

A Kalman filter for aircraft terminal area and landing navigation was implemented and flight tested in the NASA Ames STOLAND avionics computer onboard a Twin Otter aircraft. This system combines navaid measurements from TACAN, MODILS, air data, radar altimeter sensors along with measurements from strap-down accelerometer and attitude angle sensors. The flight test results demonstrate that the Kalman filter provides improved estimates of the aircraft position and velocity as compared with estimates from the more standard complementary filter. The onboard computer implementation requirements to achieve this improved performance are discussed.

Schmidt, S. F.↗
NASA NTRS1977

Preliminary geologic evaluation of L-band radar imagery: Arkansas test site

The relatively small angles of incidence (steep depression angles) of the L-band system provide minimal shadowing on terrain back-slopes and considerable foreshortening on terrain fore-slopes which sacrifice much of the topographic enhancement afforded by a more oblique angle of illumination. In addition, the dynamic range of the return from vegetated surfaces is substantially less for the L-band system, and many surface features defined primarily by subtle changes in vegetation are lost. In areas having terrain conditions similar to those of northern Arkansas, and where LANDSAT and shorter wavelength aircraft radar data are available, the value of the JPL L-band imagery as either a complimentary or supplementary geologic data source is not obvious.

Macdonald, H.↗
NASA NTRS1977

Viking Radio Occultation Measurements of the Martian Atmosphere and Topography: Primary Mission Coverage

Radio occultation measurements were made at approximately 50 locations on Mars with the Viking Orbiter 1 S (2.3 GHz) and X (8.4 GHz) band tracking links during October 1976. The measurements have been used to study the topography and atmosphere of Mars at latitudes ranging from about 75 deg S to 70 deg N. By using the ingress and egress times obtained from the observed limb diffraction effects together with the best ephemerides available for the orbiter and the planet we have determined the surface elevations at the occultation points relative to the reference areoid. The observations agree with Mariner 9 and radar data to within 2 km. The mean atmospheric pressure at the areoid level was found to be 5.9 mbar during the northern midsummer season, a value which agrees quite well with data obtained at the landing sites. By comparing the new electron density measurements with earlier Mariner data we have determined that the temperature and the plasma scale height of the upper atmosphere appear to be functions of solar activity.

Fjeldbo, G.↗
NASA NTRS1977

Severe thunderstorm internal structure from dual-Doppler radar measurements

Dual-Doppler radar data were analyzed for three different times during the life cycle of a severe thunderstorm. The thunderstorm developed a double vortex inside as a tornado was generated beneath the cloud. The organized kinematic and precipitation internal structure of the thunderstorm support a theoretical double-vortex thunderstorm model that was developed earlier. The horizontal perturbation and relative winds, vertical winds, horizontal divergence and vorticity are compared for the three different times of measurement. The measurements and theoretical model provide new explanations of the severe thunderstorm and the relationship of associated tornadoes.

Eagleman, J. R.↗
NASA NTRS1978

Chatanika radar observations of ionospheric and field-aligned currents

A method for estimating field-aligned current densities from ground-based measurements of the horizontal ionospheric currents at two or more latitudes using the Chatanika incoherent scatter radar is presented. It is assumed that the one-dimensional divergence of the horizontal currents approximates the current density of a field-aligned current sheet. The field-aligned current densities found via radar data agree with those given by simultaneous magnetic observations by the Triad satellite. It is noted that downward or upward field-aligned currents having densities of 10 to the -6th to 10 to the -5th A/sq m are achieved in the evening or morning sector. The densities are further increased during periods of increased geomagnetic activity and when current directions are reversed. This reversal generally occurs during auroral oval expansion.

Kamide, Y.↗
NASA NTRS1978

Effect of weighting on time sidelobe suppression

Weighting simulations in the time domain were considered to shape the time-compressed pulse waveform. The digital input radar data were 32 bit I,Q, and simulated data from a point target, imaged by a Seasat-A type system. Weighting functions tested include stepped-amplitude distributions, (with 1 through 5 steps), and the cosine-squared plus pedestal distribution. Effects treated include mainlobe ratio, signal to noise ratio, and nearest sidelobe suppression.

Dicenzo, A.↗
NASA NTRS1978

SAR/LANDSAT image registration study

The author has identified the following significant results. Temporal registration of synthetic aperture radar data with LANDSAT-MSS data is both feasible (from a technical standpoint) and useful (from an information-content viewpoint). The greatest difficulty in registering aircraft SAR data to corrected LANDSAT-MSS data is control-point location. The differences in SAR and MSS data impact the selection of features that will serve as a good control points. The SAR and MSS data are unsuitable for automatic computer correlation of digital control-point data. The gray-level data can not be compared by the computer because of the different response characteristics of the MSS and SAR images.

Murphrey, S. W.↗
NASA NTRS1978

Electronic SAR processors for space missions

This paper reports some interim results relating to an on-going effort to develop an electronic processor for real-time processing of synthetic aperture radar data. An experimental laboratory processor is being developed as a testbed for design of onboard processors for future space missions. This paper describes the configuration of the experimental processor and discusses technical factors pertaining to the design.

Wu, C.↗
NASA NTRS1979

Comments on the Venus rotation pole

Possible orientations of the Venus rotation pole as a function of planetary oblateness are calculated, taking into account the variation of the orbital inclination and motion of the nodal line produced by long-term planetary perturbations and assuming the obliquity to be fully damped. If the obliquity is stabilized against solar tides by core-mantle viscous coupling, a fully damped obliquity is the expected state. An analysis of earth-based radar data from 1964 to 1977 yields a pole position which lies near damped pole positions of small oblateness, no more than about 10 to the 6th. Possible implications of this result are considered.

Ward, W. R.↗
NASA NTRS1979

Height dependence of spread F bubble drift velocities

Vertical bubble velocities in equatorial spread F have been investigated analytically by Ott (1978), Osakow and Chaturvedi (1978), all of whom found a proportionality of the vertical velocity to bubble depletion density. The paper presents radar data from two equatorial sites which support theoretical predictions that vertical drift velocities of spread F bubbles increase with height on the bottomside of the F layer. This increase is shown to result from the proportionality of bubble drift velocity to density depletion amplitude, which itself increases with height. The measured rate of increase is found to be dU/dh equals about 2 m/s km. It is concluded that this is consistent with numerical simulation results within a factor of 2.

Hudson, M. K.↗