Engineering topics

Peterfreund, A. R.

Publications and source records attributed to Peterfreund, A. R..

12 records

NASA NTRS1985

Surface characteristics of Venus derived from Pioneer Venus altimetry, roughness, and reflectivity measurements

Pioneer Venus data sets for global topography, surface roughness, and reflectivity are analyzed, and the geological significance of some of the distinctive surface types is locally calibrated by examining high-resolution images from the Venera lander spacecraft and the Arecibo Observatory. Regional rock and bedrock surfaces are found to cover the majority of the planet. The relatively smooth rock and bedrock surfaces probably represent lava flows. Porous and unconsolidated fine materials cover less than about 27 percent of the surface. The distribution of soil surfaces indicate that they are the result of local weathering and small amounts of lateral transport. Several hypotheses for the origin of the high-dielectric materials which cover a small portion of the surface are discussed.

Head, J. W., III↗

NASA NTRS1985

Surface Units on Venus Derived from Pioneer-venus Altimetry, Roughness, and Reflectivity Measurements

The nature of the Venusian surface was revealed by Pioneer-Venus (PV) observations to be diverse at scales from tens to hundreds of kilometers. Spatial correlations of elevation, surface roughness, and radar reflectivity were investigated as a means of assessing the degree of homogeneity of surface radar properties within topographic provinces and develop a map of possible geologic boundaries. Correlations were performed in a supervised fashion whereby unit boundaries were selected on the basis of statistical and empirical studies of the individual data sets. Interpretations of these units in terms of geologic characteristics are based on the determination of physical units which are model dependent.

Peterfreund, A. R.↗

NASA NTRS1984

Geological, structural, and geomorphological analyses from SIR-B

A Shuttle Imaging Radar-B (SIR-B) study designed to develop a better understanding of the application of radar in geological studies is described. The specific objectives for deltaic environments include the examination of delta morphology and the intertidal zone, the surface expression of shallow bathymetry, the characterization of vegetation cover, and the water balance of the delta. In impact crater environments, the goals include the establishment of the radar characteristics of exposed craters and the application of this knowledge to test for the detectability of very poorly exposed craters.

Head, J. W., III↗

NASA NTRS1984

Geology of Maxwell Montes, Venus

Maxwell Montes represent the most distinctive topography on the surface of Venus, rising some 11 km above mean planetary radius. The multiple data sets of the Pioneer missing and Earth based radar observations to characterize Maxwell Montes are analyzed. Maxwell Montes is a porkchop shaped feature located at the eastern end of Lakshmi Planum. The main massif trends about North 20 deg West for approximately 1000 km and the narrow handle extends several hundred km West South-West WSW from the north end of the main massif, descending down toward Lakshmi Planum. The main massif is rectilinear and approximately 500 km wide. The southern and northern edges of Maxwell Montes coincide with major topographic boundaries defining the edge of Ishtar Terra.

Head, J. W.↗

NASA NTRS1984

Venus: Global distribution of Pioneer-Venus radar roughness and reflectivity and global correlation of altimetry, roughness and reflectivity observations

An improved version of the Pionner-Venus orbital data was used for a statistical analysis of global radar roughness and (alpha(0)) (rho) reflectivity. Classification maps of the venusian surface are produced in a supervised manner on the basis of statistical and empirical studies of the individual data sets. The primary objective is to assess the degree of homogeneity of surface radar properties within topographic provinces in order to map possible geologic boundaries. Maps were produced by correlating two data sets at a time. Classification of specific regions, such as Ishtar, has demonstrated that distinct geological units can be identified.

Head, J. W.↗

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 NTRS1981

Visual and infrared observations of wind streaks on Mars

Global correlations of the regions in which three Martian wind streak types (bright, dark, splotch-related) vary according to latitude, elevation, albedo, color, and predawn residual temperature provide constraints on models of streak formation and modification. Bright streaks are relatively stable and occur over a wide range of geographical surfaces. They are elevation-independent, suggesting that their formation is due to atmospheric dust fallout. Dark streaks appear variable from 20 to 40 deg S and at elevations between 3 and 7 km. They are associated with dark surfaces, having high thermal inertias. Splotch-related streaks occur at elevations between 0 and 6 km and at areas of either low or high thermal inertias, which is the cause of its modifying surface winds. Data are graphically presented, and the methods of data collection are fully explained. Regional studies of various types of streaks in Syrtis Major, Syria Planum, Oxia Palus, Mesogea and Pettit Craters, and Noachis confirm that the correlations found at the global level also occur at regional scales.

Peterfreund, A. R.↗

NASA NTRS1980

The opacity of some local Martian dust storms observed by the Viking IRTM

In this paper some Viking infrared thermal mapping (IRTM) measurements of local Martian dust storms observed in the southern tropical region of the planet between solar longitudes of 225 and 262 deg are analyzed. The derived opacities of these storms show that in the most opaque regions of the cloud, the optical thickness may be approximately 6. Away from the individual clouds, the opacity is approximately 2, which is still about four times the background level of dustiness in the Martian atmosphere. Considerable structure in the derived opacity is found which will create corresponding variations in the atmospheric heating, which in turn may have an important feedback upon the local winds.

Hunt, G. E.↗

NASA NTRS1979

Mars - The north polar sand sea and related wind patterns

Viking Orbiter 2 images of the north polar region reveal an enormous sand sea (erg) covering an area of greater than 500,000 sq km around the perennial ice cap. All dunes are either transverse or barchan. The various dune morphologies and modifications of primary dune types reflect a wind regime having more than one wind direction. In the summer, two major wind directions prevail: (1) off-pole winds that become easterly due to coriolis forces and (2) on-pole winds that become westerly. During the winter and/or spring, only the on-pole winds exist. Strong winds greater than 75 m/s are required for sand accumulation to form the thick transverse dunes. The strongest winds in the north polar region are thought to exist during summer over the transverse dune field between 110 deg and 220 deg W; this area is a relatively warm belt (temperature greater than 230 K) between two ice zones (temperature less than 220 K). The lack of well-developed longitudinal dunes implies that the dune field is young. The relationship of the present dune field to the perennial ice indicates that the dunes began to form after the formation of the present ice cap.

Tsoar, H.↗

NASA NTRS1979

Thermal infrared properties of the Martian atmosphere. I - Global behavior at 7, 9, 11, and 20 microns

Infrared observations of Mars by the Viking infrared thermal mapper (IRTM) are presented for conditions of both a relatively clear and a dust-laden atmosphere. The 7-, 9-, 11-, and 20-micron bands of the IRTM respond differently to radiation emitted through and by a dusty atmosphere, permitting characterization of the global atmospheric state, monitoring of secular changes, and derivation of optical depth information. Surface temperature behavior is found to be greatly modified by the diminution of insolation and thermal blanketing resulting from global dust storms. Brightness temperature at 7 microns is employed to estimate surface temperatures in the presence of dust absorption. The difference (T7) is indicative of airborne dust when thermal contrast exists between the surface and atmosphere. The diurnal behavior of T7-T9 reveals changes in the contrast; the sign of the differential reverses as the surface, warmer than the atmosphere in daytime, becomes cooler than the atmosphere at night. IRTM observations of local areas at varying emission angle yield optical depths indicative of global trends. Two global dust storms in 1977 produced large optical depth changes: at 9 microns the optical depth became as large as 2.0.

Martin, T. Z.↗

NASA NTRS1979

Thermal infrared properties of the Martian atmosphere. III - Local dust clouds

Prior to and during the Martian global dust storms in 1977, local dust clouds were identified from thermal observations. Local dust clouds appear up to 40 K cooler than the surrounding region in the daytime and appear warm at night. In contrast to their well-developed and consistent thermal signatures, local dust clouds exhibited little albedo contrast. Multiple observations of the same areas show that local dust clouds form and dissipate in a few days or less, and clouds were observed to move with velocities of from 14 to at least 32 m/sec. Local dust clouds are common along the receding edge of the south polar cap (observed primarily for orbiter imaging) and in the restricted area -10 deg to -30 deg, 80 deg to 125 deg W (observed primarily by the infrared thermal mapper); several of the latter occurred over a ridge in Claritas Fossae, indicating strong topographic control. In their active growing stage, local dust clouds are probably about 8 km high and have relatively abrupt tops. The accumulation of dust from local clouds reached similar levels immediately prior to both global storms, supporting the hypothesis that such dust accumulations are responsible for triggering the global dust storms.

Peterfreund, A. R.↗

NASA NTRS1977

Thermal and Albedo Mapping of Mars During the Viking Primary Mission

The behavior of Mars as observed by the Viking infrared thermal mapper (IRTM) is considered. The IRTM is a 28-channel, 4-telescope radiometer that operated in six spectral bands. The studies considered include observations from the interplanetary phase through data collection on November 7, 1976. During this interval, thermal mapping of the whole Martian surface has been possible. Attention is given to polar temperatures, global albedos, predawn temperatures, a thermal inertia contour map, geometry considerations, clouds, aspects of predawn warming, and observations of earth.

Kieffer, H. H.↗