Engineering topics

Harmon, J. K.

Publications and source records attributed to Harmon, J. K..

28 records · Page 2

NASA NTRS1989

Radar observations of Comet Halley

Five nights of Arecibo radar observations of Comet Halley are reported which reveal a feature in the overall average spectrum which, though weak, seems consistent with being an echo from the comet. The large radar cross section and large bandwidth of the feature suggest that the echo is predominantly from large grains which have been ejected from the nucleus. Extrapolation of the dust particle size distribution to large grain sizes gives a sufficient number of grains to account for the echo. The lack of a detectable echo from the nucleus, combined with estimates of its size and rotation rate from spacecraft encounters and other data, indicate that the nucleus has a surface of relatively high porosity.

Campbell, D. B.↗

NASA NTRS1986

Radar altimetry of Mercury - A preliminary analysis

Altitude measurements derived from 2380 MHz radar observations of the equatorial zone of Mercury collected between 1978-1984 at Arecibo Observatory are analyzed. The altitude profiles, which span from 20-90 deg longitude at a resolution of 0.15 deg (longitude) by 2.5 deg (latitude), are compared with geologic maps of Mercury. The depths and shapes of the craters and basins are examined; it is observed that Mercurian craters are shallower than lunar craters. The plains of Tir Planitia, Caloris Basin, and circum-Caloris are studied and it is hypothesized that the plains are of a volanic origin. The ridges, scarps, and fault zones detected in the altimetry data are described.

Harmon, J. K.↗

NASA NTRS1985

Volcanism and Rift Formation in Beta Regio, Venus: New Radar Results

A high resolution (approximately 2 km) image of Beta Regio, Venus, obtained with the Arecibo radar system, reveals additional details of structure which seem to confirm past suggestions that this region consists of a rift system and associated volcanism. Numerous long linear features approximately parallel to the north-south trending trough discovered by the Pioneer-Venus Orbiter are interpreted as being indicative of extensive faulting and the detail for the radar reflectivity anomaly coincident with Theia Mons suggests that it is a major volcano situated on what would be the western bounding fault of the rift system.

Campbell, D. B.↗

NASA NTRS1985

Mercury radar altimetry: A preliminary analysis

Range-Doppler radar observations were made of the planet Mercury over the six year period 1978-1983. Approximately 30 continuous altitude profiles were obtained, each spanning between 20 and 90 degrees of longitude. The profiles are located in the equatorial zone of Mercury between 5 deg S and 12 deg N latitude. Approximately 40% of the total coverage is in the unimaged hemisphere.

Harmon, J. K.↗

NASA NTRS1985

Mars - Dual-polarization radar observations with extended coverage

Arecibo Observatory radar observations of Mars at 13 cm wavelength have yielded accurate measurements of the full backscatter spectrum in two orthogonal polarizations, and constitute the first global view of the small scale surface roughness distribution on Mars. Areas of maximum depolarization correlate well with the volcanic regions Tharsis and Elysium. Comparisons between the moon and Mars using radar data, ground truth, and simple scattering models, suggest that Mars possesses a relatively high average coverage by decimeter-scale rocks. Attention is also given to quasi-specular scattering results, of which the most unusual were obtained over the Olympus Mons aureole region.

Harmon, J. K.↗

NASA NTRS1984

Venus - Volcanism and rift formation in Beta Regio

A new high-resolution radar image of Beta Regio, a Venus highland area, confirms the presence of a major tectonic rift system and associated volcanic activity. The lack of identifiable impact craters, together with the apparent superposition of the Theia Mons volcanic structure on the rift system, suggest that at least some of the volcanic activity occurred in relatively recent geologic time. The presence of topographically similar highland areas elsewhere on Venus (Aphrodite Terra, Dali Chasma, and Diana Chasma) suggests that rifting and volcanism are significant processes on Venus.

Campbell, D. B.↗

NASA NTRS1984

Volcanism and rift formation in Beta Regio, Venus: New radar results

A high-resolution (approximately 2 km) image of Beta Regio, Venus, obtained with the Arecibo radar system, reveals additional details of its structure which seem to confirm past suggestions that this region consists of a rift system and associated volcanism. Numerous long linear features approximately parallel to the north-south trending trough discovered by the Pioneer-Venus Orbiter are interpreted as being indicative of extensive faulting and the detail for the radar reflectivity anomaly coincident with Theia Mons suggests that it is a major volcano situated on what would be the western bounding fault of the rift system.

Campbell, D. B.↗

NASA NTRS1983

Venus - Identification of banded terrain in the mountains of Ishtar Terra

High resolution images obtained with the Arecibo radar system at a wavelength of 12.6 centimeters reveal numerous parallel 10- to 20-kilometer-wide bands of high radar backscatter situated on and oriented parallel to the major mountain ranges of the Ishtar Terra region of Venus. Geometric and morphological characteristics suggest that the bands represent earth-like tectonic deformational features, such as folds and faults.

Campbell, D. B.↗

NASA NTRS1982

Radar measurement of small-scale surface texture - Syrtis Major

Available data on Syrtis Major is examined and compared in light of lunar experience in order to infer the small-scale structure and study the problem of origin and present state. The radar data are reviewed, introducing three previously unpublished sets of observations obtained during the 1978 Mars opposition. Syrtis Major is shown to be smooth and relatively homogeneous when sensed at centimeter wavelengths, root mean square surface slopes ranging from more than 1.5-2.0 deg in the east to less than 0.5 deg along the western margin at wavelength 12.6 cm. Radar reflectivity increases from about 5% to about 12% across Syrtis Major, being greatest near the western margin. A self-consistent model for the surface of Syrtis Major is arrived at which includes structure on all scales. It is shown that the moon is not a good radar analog for Syrtis Major.

Simpson, R. A.↗

NASA NTRS1978

Comparison of 74-MHz interplanetary scintillation and IMP 7 observations of the solar wind during 1973

Solar wind velocities measured by earth-orbiting spacecraft are compared with velocities determined from interplanetary scintillation (IPS) observations for 1973, a period when high-velocity streams were prevalent. The spacecraft and IPS velocities agree well in the mean and are highly correlated. No simple model for the distribution of enhanced turbulence within streams is sufficient to explain the velocity comparison results for the entire year. Although a simple proportionality between density fluctuation level and bulk density is consistent with IPS velocities for some periods, some streams appear to have enhanced turbulence in the high-velocity region, where the density is low.

Coles, W. A.↗