Engineering topics

Shapiro, Irwin I.

Publications and source records attributed to Shapiro, Irwin I..

26 records · Page 2

NASA NTRS1991

Io's radar properties

Arecibo 13 cm wavelength radar observations during 1987-90 have yielded echoes from Io on each of 11 dates. Whereas Voyager imaged parts of the satellite at resolutions of several km and various visible/infrared measurements have probed the surfaces's microscale properties, the radar data yield new information about the nature of the surface at cm to km scales. Our observations provide fairly thorough coverage and reveal significant heterogeneity in Io's radar properties. A figure is given showing sums of echo spectra from 11 dates.

Ostro, Steven J.↗

NASA NTRS1991

Radar studies in the solar system

We are actively engaged in observations of asteroids and comets, both as planned targets and as targets of opportunity. The most recent example of the latter is asteroid 1991 AQ, which was discovered optically on January 14, 1991 and found to be rapidly nearing Earth. Due in part to our previous success in obtaining useful radar data on short notice, we were able to schedule time on the Arecibo radar on January 28-31, when the asteroid was within the Arecibo declination window. Each day during the period, a fresh ephemeris was made including all available data, both optical and radar. With further processing, the results of the observations are expected to include detailed two-dimensional images of the asteroid and information on its surface properties, size, shape and spin. The observing program also included two other asteroids, two of the four Galilean satellites of Jupiter, the satellites of Mars, and the planet Mercury. Analysis of newly available radar observations of Venus has led to a refinement of the spin vector of that planet and has thereby provided a coordinate basis for the Magellan spacecraft mapping mission.

Shapiro, Irwin I.↗

NASA NTRS1991

Forced nutations of the earth: Influence of inner core dynamics. I - Theory. II - Numerical results and comparisons. III - Very long interferometry data analysis

A treatment is presented of the nutation problem for an oceanless, elastic, spheroidally stratified earth, with the dynamical role of the inner core explicitly included in the formulation. Solving the enlarged system of equations shows that a new almost diurnal eigenfrequency emerges. A rough estimate places it not far from the prograde annual tidal excitation frequency, so that possible resonance effects on nutation amplitudes need careful consideration. Tables are provided that exhibit the sensitivities of various relevant quantities, the eigenfrequencies and the coefficients which appear in the resonance expansion, as well as the nutation amplitudes at important tidal frequencies, to possible errors in the earth parameters which enter the theory set forth. Finally, the analysis of 798 VLBI experiments performed between July 1980 and February 1989 and the determination from this analysis of corrections to selected coefficients in the International Astronomical Union 1980 theory of the nutations of the earth are discussed.

Mathews, P. M.↗

NASA NTRS1990

Geodesy by radio interferometry - The application of Kalman filtering to the analysis of very long baseline interferometry data

The application of Kalman filtering techniques to the analysis of VLBI data is discussed. The VLBI observables are geometrically related to the geodetic and astrometric parameters which can be determined from them. However, contributions to the observables from the clocks at, and the atmospheres above, the VLBI sites must be accounted for if reliable estimates of geodetic and astrometric parameters are to be obtained. Here, an implementation of a Kalman filter to account for stochastic behavior on those parameters which vary during the course of a VLBI experiment is discussed. Both the nature of the stochastic processes which should be used in the model for the VLBI data and the implementation of the Kalman filter estimator are considered. It is concluded that the Kalman filter is appropriate for analyzing VLBI data.

Herring, Thomas A.↗

NASA NTRS1990

Radar images of asteroid 1989 PB

Radar observations of the near-earth asteroid 1989 PB, made shortly after its optical discovery, yield a sequence of delay-Doppler images that reveal it to consist of two distinct lobes that appear to be in contact. It seems likely that the two lobes once were separate and that they collided to produce the current 'contact-binary' configuration.

Ostro, Steven J.↗

NASA NTRS1989

Studies of regional and global tectonics and the rotation of the earth using very-long baseline interferometry

Progress in the areas of data analysis, atmospheric delay calibration and software conversion is reported. Over 800 very long baseline interferometry (VLBI) experiments were analyzed in the last 6 months. Reprocessing of the Mark III VLBI data set is almost completed. Results of analysis of the water-vapor radiometer (WVR) data were submitted and a preprint of a related paper is attached. Work on conversion of the VLBI analysis software from HP1000 to Unix based workstations is continuing.

Shapiro, Irwin I.↗

NASA NTRS1988

Radar studies in the solar system

The ephemerides needed to acquire radar data at Arecibo from observations of various solar-system objects was developed. The resultant data to test fundamental laws of gravitation and to determine the size, shape, topography, and spin vectors of the targets were analyzed. The surface properties of these objects through their radar scattering and polarization characteristics were studied. The observing program also included Arecibo observations of Mercury, Venus, and the Galilean satellites of Jupiter. The Mercury observations at Arecibo were all within a week of the epoch of a closure point (same surface position as a previous observation), and one was matched by a near-simultaneous observation at Goldstone.

Shapiro, Irwin I.↗

NASA NTRS1987

VLBI observations of 23 hot spots in the starburst galaxy M82

The simultaneous 2.3 and 8.4 GHz VLBI observations of 23 hot spots in the nuclear region of M82 presented indicate the presence of six hot spots at 2.3 GHz, but only one at 8.4 GHz. Attention is given to a mapping of the brightest hot spot, 41.9+58, at 2.3 GHz, which exhibits a complex brightness distribution whose angular width in the NE-SW direction is 45 mas at the 10-percent contour. These data are consistent with the hot spots in M82 being powerful SNRs, with ages between about 10 and 300 yr.

Bartel, Norbert↗