The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2 QOS 
978 
of the map. Our earlier use of a simple parallax-height ratio had 
overestimated the relief in this area by a factor of 1.5. One 
exception to the current good agreement is that the SAR 
topography elevations along the southern boundary of Mayda 
Insula lie several hundred meters below the stereo elevations 
and, in fact, well below the elevation of the surrounding 
coastline. We believe the SAR topography, which compares 
intensities in the overlapping RADAR beams, is affected by the 
strong bright-dark transition at the coast when it falls within the 
overlap area. Radarclinometry profiles show excellent 
agreement with the stereo DTM in some areas, but elsewhere 
are clearly distorted by variations in the intrinsic radar- 
brightness of the surface. 
Another test of the reliability of the results is that the putative 
shorelines are expected to have a constant elevation, at least 
within a particular lake or sea. Measurement of the shoreline 
elevations is difficult in many places because steep coastal 
slopes are present but are barely resolved in the images. The 
DTM itself appears to resolve features ~5 km in horizontal 
extent but not smaller. Shoreline elevations extracted from the 
DTM vary by no more than 100-200 m in areas without steep 
slopes, and we expect that careful interactive measurements 
will refine this limit. A surprising result of our initial mapping 
is that the automated matching algorithm returned results in all 
but the darkest portions of the seas. Some of the moderately 
dark areas clearly show features that may be the solid bottom 
seen through a liquid layer of varying thickness, or possibly 
variations in the texture and liquid content of an exposed but 
wet surface. Other areas show little to the eye that can be 
distinguished from random speckle noise. We are therefore in 
the process of constructing a reliable map of the dark areas, 
based on interactive measurements of only those features that 
can be measured with confidence. Such mapping may shed 
light on the depth of the lakes and thus Titan’s inventory of 
liquid hydrocarbons (Lorenz et al., 2008a). Alternatively, if it 
shows that the dark areas vary in elevation by more than the 
maximum thickness of methane-ethane liquid through which 
the bottom would be visible, this would decrease the likelihood 
that the dark areas are liquid-filled lakes. 
As in other areas of Titan studied, relief is gentle, with a total 
range of elevations slightly more than 1000 m. For example, 
the interior of Mayda Insula is 1100-1200 m higher than the 
“coast” 40 km away, for an average slope of 1.5°. Local slopes 
are higher, but seldom exceed 5°. In the western half of the 
DTM, numerous flat-floored, steep-walled depressions are 
present, but, again, the local relief is only ~500 m and the 
“steep” bounding slopes are less than 5°. Similar depressions 
are seen elsewhere in the polar region, sometimes with small 
lakes in their interiors. Measurement of the absolute elevations 
of these small lakes is expected to shed light on the rates of 
evaporation, replenishment, and infill or drainage by 
subsurface flow (Hayes et al., 2008). We will be undertaking 
more extensive mapping in the polar regions and elsewhere as 
reprocessed BIDRs become available, and hope to show some 
of the results at the ISPRS Congress. 
4. MOON 
4.1 Mini-RF 
The decade 2001-2010 is a “second golden age” of lunar 
exploration, with one mission to Earth’s natural satellite 
already completed, four more under way or about to launch in 
2008, and several others in various stages of planning (Kirk et 
al., 2008c, this conference). A major focus of investigation for 
many of these missions is the possible presence of water ice at 
the lunar poles, which was suggested by the anomalously 
strong returns detected in a bistatic radar observation with the 
Clementine mission (Nozette et al., 1996) and bolstered by the 
detection of hydrogen at the poles by the Lunar Prospector 
mission (Feldman et al., 2001). Water ice deposits “cold 
trapped” in the permanently shadowed craters near the poles 
would be of great scientific interest and would be a valuable 
resource to future lunar exploration and development if the 
concentration of ice were sufficiently high. The Clementine 
result has met with skepticism, however (Simpson and Tyler, 
1999), and the matter is not yet settled. The Mini-RF radar 
instrument (Bussey et al., 2008), which will be flown in 
varying forms on both the ISRO Chandrayaan-1 mission and 
the NASA Lunar Reconnaissance Orbiter (LRO), is primarily 
intended to address the existence and distribution of lunar polar 
ice deposits. The former mission is currently scheduled to 
launch in 2008 June or July, the latter in October, though either 
may be delayed. Both versions of the instrument will be 
capable of SAR imaging in the S band (13 cm A.) with —150 m 
resolution and 75 m pixel scale, and will record the full 
polarization state of the returned signal in order to better 
distinguish ice from diffuse scattering from rough or blocky 
surfaces. The Chandrayaan-1 radar, also known as Forerunner, 
will be able to observe both poles for a period of 32 days, as 
often as four times a year, building up a complete mosaic of 
image strips covering latitudes 80° to near the pole on each 
occasion. The area nearest the pole that is not covered in these 
normal sequences may be observed at lower resolution in a 
scatterometric mode in some of the observation periods, or may 
be imaged by decreasing the incidence angle. The latter option 
would also provide strong stereo coverage of some near-polar 
areas in addition to the fair stereo coverage provided by 
adjacent image strips fanning out from the poles. The LRO 
Mini-RF lacks the scatterometer mode but operates at X band 
(3 cm X) in addition to S band, has a zoom mode with 7.5 m 
pixel scale, and can also be used for interferometric 
observations to derive topography. As an engineering demon 
stration, the LRO Mini-RF will only be operated for a few 
minutes per month during the one-year nominal mission, but 
expanded observation opportunities may be hoped for in the 
planned extended (science) mission. 
4.2 Radargrammetry Plans 
Initial processing of the Mini-RF data will be performed by the 
VEXCEL Corporation, which will produce both Level 1 
(unprojected) and Level 2 (map projected) geometric versions 
of the SAR images. The Level 2 products are directly 
analogous to Cassini BIDRs in that they are in Oblique 
Cylindrical projection aligned with the ground track. Level 1 
products, however, are not map projected, but are gridded in a 
coordinate system consisting of the time at which zero Doppler 
shift was observed and the range (transformed to approximate 
ground range). Products of both levels will contain multiple 
bands containing the full set of polarization parameters 
recorded by the instrument. 
The USGS ISIS 3 system (Anderson et al., 2004) will be used 
for higher level processing, both by us for systematic carto 
graphic production and by other Mini-RF team members for 
scientific analyses. Basic functions include algebraic mani 
pulation of the polarization data to calculate maps of derived 
quantities such as circular polarization ratio, and production of