Engineering topics
Publications and source records attributed to Roth, L. E..
We examine quantitative aspects associated with the hypothesis of nebular lightnings as a source of impulse magnetic fields. Our findings support our previous accretion model in which a presence of impulse magnetic fields was of a key necessity. Additional information is contained in the original extended abstract.
To the effects of impulse magnetic field in protoplanetary nebula (fast melting, cooling and magnetization of chondrules), there is added another possible effect - mechanism associated with the forces of attraction between magnetized planetesimals. Additional information is contained in the original extended abstract.
A total of 108 13-cm wavelength scans conducted for the 23 to -22 deg latitude regions of Mars during the 1971-1982 oppositions are of sufficiently high resolution to allow elevation differences of as much as 3 km over less than 10 deg longitude to be observed; most of this local relief is furnished by structural elements of impact craters. The data set has allowed identification of 152 complex degraded craters, some as small as 25 km diameter. Measured crater depths rarely exceed 2.5 km, and low exterior relief rather than overall low relief seems to be the distinguishing characteristic of large degraded craters. Processes other than fluvial sedimentation appear to have contributed to crater shallowing.
Since reflectivity is a quantity characteristic of a given target at a particular geometry, the same (temporally unchanging) target examined by radar on different occasions should have the same reflectivity. Zisk and Mouginis-Mark noted that the average reflectivities in the Goldstone Mars data increased as the planet's S hemisphere passed from the late spring into early summer. The same data set was re-examined and the presence of the phenomenon of the apparent seasonal variability of radar reflectivity was confirmed. Two objections to these findings are addressed: (1) reflectivity variations may be present in the Goldstone Mars data as a result of an instrument/calibration error; and (2) the variations were introduced into the analysis through comparing reflectivities from two incompatible subsets of the data.
The results of a point-by-point examination of the Goldstone topography data in the Martian highlands suggest that, at the 100 m range resolution, the rims of large craters are barely distinguishable against the surrounding terrain. Craters are described topographically.
Detection of the seasonally variable radar reflectivity in the Goldstone Mars data (the Solis Lacus radar anomaly and the proposed interpretation in terms of the near-surface presence of liquid water created a controversy in the planetary science community. Over the past year, skepticism was voiced about the reality of the phenomenon of a seasonally variable radar reflectivity anywhere on Mars. The necessary background information and the pertinent data are reviewed in a format perhaps more convincing than that employed in the original presentation of the discovery. A summary of the results and recommendations for future work are included.
The 1971/1973 Mars data set acquired by the Goldstone Solar System Radar was analyzed. It was established that the seasonal variations in radar reflectivity thought to occur in only one locality on the planet (the Solis Lacus radar anomaly) occur, in fact, over the entire subequatorial belt observed by the Goldstone radar. Since liquid water appears to be the most likely cause of the reflectivity excursions, a permanent, year-round presence of subsurface water (frozen or thawed) in the Martian tropics can be inferred.
Imaging data acquired with the Shuttle Imaging Radar (SIR-A) over the hyperarid region of Egypt/Sudan clearly show surface penetration through the sand cover. Even though absorption does occur in the sand layer, surface refraction leads to a steeper incidence angle at the sand/bedrock interface resulting in a stronger backscatter. A simple backscatter model shows that for a low-loss thin sand layer the presence of the covering layer enhances the capability to image the subsurface interface, particularly at large incidence angles and HH polarization.
The hypothesis that an extraordinary radar smoothness of a lunar target suggests that ground moisture is rest on the assumption that on the penetration-depth scale, the dielectric constant be an isotropic quantity. In other words, the planet's surface should have no vertical structure. Results of modeling exercises (based on the early lunar two-layer models) conducted to simulate the behavior of radar reflectivity, at S-band, over Solis Lacus, without manipulating the dielectric constant of the base layer (i.e., without adding moisture) are summarized. More sophisticated, explicit, rather than iterative multi-layer models involving dust, duricrust, mollisol, and permafrost are under study. It is anticipated that a paradoxical situation will be reached when each improvement in the model introduces additional ambiguities into the data interpretation.
The paper discusses Martian altitudes measured by radar during the oppositions of 1971 and 1973 using the 64-m antenna at Goldstone, Calif. The resultant topographic profiles substantiate a zonal classification of the volanic flows blanketing the south flanks of Arsia Mons, and they confirm the existence of a secondary, parasitic shield, attached from the SSW to the main Arsia shield. The secondary shield is about 400 km in diameter at its base and at least 4 km high at its center. The distribution and orientation of the lunar mare - like ridges in Sinai Planum appear to be independent of the regional gradients. Segments of the chaotic terrain at the eastern terminus of Valles Marineris are located down to 6 km below the level of the surrounding plains.
A procedure is presented that permits determination of the shape of the gravity field due to an arbitrary mass configuration with circular symmetry. The procedure is used to model the shape of the field associated with the lunar circular basins. The mean slopes of the equipotential surfaces generated by a superisostatic deposit corresponding to a near-surface Crisium-size mascon are calculated to fall within the range from 1:700 to 1:1000; those generated by a mantle rebound of the same excess mass, at 60 km below the lunar surface, cluster around the value of 1:1500.
A parametric analysis of the coherent electromagnetic losses due to scattering from volume weak inhomogeneities is reported. It is shown that even in the case of very weak inhomogeneities, the loss could be appreciable in a resonance region and thus play a more dominant role than conductivity losses.