Venus Mapping White Paper

Open-File Report 95-519


Figure 1. Radar incidence angle versus latitude for four viewing geometry profiles used during the Magellan mission (table 1). Left-looking (L), right-looking (R), Maxwell left-looking stereo (M), and Cycle 3 left-looking stereo (S) profiles labeled. Actual surface coverage for each profile varies widely.

Figure 2. HH (horizontal transmit, horizontal receive) and HV (horizontal transmit, vertical receive) backscatter coefficients versus root mean square (rms) height for four lava flows in Hawaii. Radar data are average 24-cm wavelength echoes at incidence angles of 30-45o. The rms heights were calculated from 5- to 8-m profiles with 5-cm sample spacing, filtered using a highpass cutoff of 1 m to suppress large-scale topography. Solid lines are best fits to data points. If we assume the mean dielectric constant of these lavas is 5, then we can calculate the shift in echo power due to changes in the dielectric constant. Dotted lines show the modified best-fit line for dielectric values of 10 and 3. Data from other sources show 24-cm HH and HV echoes for these flows remain nearly constant for rms heights greater than 10 cm.

Figure 3. L-band (24 cm) HH-polarization (A) and HV-polarization (B) radar images of Kilauea and the Kau desert collected at three viewing geometries, rectified to a uniform 10 m pixel size. Incidence angles are marked along left side of each image. Of particular interest is Mauna Iki volcanic shield in the upper left of each frame, opposite incidence angle label (marked by a white box in the lower image of A). At high angles (>30o), flows from Mauna Iki are distinct from one another in HH images, whereas at lower angles there is little separation between pahoehoe and a'a surface textures. Compare this with the high degree of unit discrimination possible at all angles with the HV images.

Figure 4. Example radar correlation chart. Connected plot symbols are for five lava flows on Kilauea, with roughnesses that extend from very smooth pahoehoe to jagged, spiny a'a [Campbell and Campbell, 1992]. Solid line is average scattering law for Venus defined by Muhleman [1964]. Three points shown with error bars are selected Venus sample areas listed in table 2.

Figure 5. Real dielectric constant (e) versus bulk density for terrestrial volcanic rocks (basalt, rhyolite, dacite, andesite, and diabase). Data from Ulaby et al. [1988].