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.
