The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
Figure 1. Quadrangle Jel3 from global mosaic of Europa at 1 
km resolution. Map is in Lambert equal area projection. 
Figure 2. Controlled mosaic of an arcuate scarp in the 
concentric multiring Valhalla impact basin, Callisto. High- 
resolution mosaic (at 55 m/pixel, and including downlink gaps) 
has been overlain on low-resolution global mosaic for context. 
2.2 Topography 
Topographic data of the Galilean satellites is sparse but critical 
for understanding their geologic evolution. Topographic 
mapping is now essentially complete for all possible stereo and 
PC sites. Almost all topographic mapping sites are restricted 
to 1 to-4 image mosaics of small discontinuous areas of the 
surfaces, providing 10 and 70% global topographic coverage 
(with best at Io and poorest for Callisto and Ganymede). Stereo 
mapping parameters are completely nonsystematic from site to 
site. Many stereo sites were acquired at relatively high solar 
illumination, precluding use of coincident photoclinometry. 
Europa (Figure 3) is the happy exception to this rule. 
2.3 Geology and Geophysics 
On Ganymede, viscous relaxation of impact craters and furrows 
dominates ancient cratered terrains. Mapping of these craters 
indicates that relaxation and the higher heat flow responsible 
for it ceased (or declined) at or shortly after the time of bright 
terrain formation. Ancient impact features larger than 100 km 
are also radically different from similar sized recently formed 
impact basins, showing a clear evolution with age (Schenk 1993; 
Schenk, 2002; Schenk et al., 2004b). This variability reveals 
the effects of decreasing heat flow with time. Topography has 
also shown that smooth lanes of bright terrain are 
topographically depressed, consistent with emplacement by 
lower-viscosity water lavas (Schenk e al., 2001a). On Callisto, 
landform degradation dominates (Figure 2), creating “smooth” 
areas of dark material. The uniform albedo of these deposits 
allows us to use PC techniques. These units are not entirely 
“smooth,” but are heavily cratered and in some areas feature 
undulating topography and linear ridges that could be 
compressional in origin. 
Figure 3. Controlled DEM of fault-bounded plateau on Europa. 
High-resolution mosaic (44 m/pixel) has been colour-coded to 
show topography (reds high, blues low). Relief across fault 
scarp (arrow) is -400 m (Nimmo and Schenk, 2006). 
Topographic range shown is ~750 m. Data from stereo- 
photoclinometry combined. 
Discoveries on Io include a 40-m deep lavas channel (Schenk 
and Williams, 2004), one of the largest landslides in the Solar 
System (Schenk and Bulmer, 1998) as well as measurements of 
smaller scale mass wasting deposits (Moore et al., 2001), and 
global topographic surveys of shield volcanoes (Schenk et al., 
2004a) and mountain distributions and elevations (Schenk et al., 
2001b; Williams et al., 2004). 
On Europa, additional DEM work has discovered the wavy 
topography of chaos (as evidence supporting the diapiric model: 
Schenk and Pappalardo, 2004), a 250-m-deep dark depression 
of unusual composition (Prockter and Schenk, 2005), and the 
thickness of the ice shell based on changes in impact crater 
morphology (Schenk, 2002). Topographic mapping has also 
been important in characterising surface slopes on Europa as 
constraints on landing craft and radar instrument designs 
(Schenk, 2005). 
Among the highlights on Europa is the unexpectedly high range 
of relief. Often quoted as having relief of only a few hundred 
meters, several sites have been found where relief exceeds 800 
meters (e.g., Prockter and Schenk, 2005; Schenk et al., 2008), 
both above and below the local mean. In addition, regional 
scale variations are pronounced. Some regions of Europa are 
divided into topographic provinces, dominated by either flat or 
undulating ridged plains, plains pocked by numerous 
depressions, or by rugged disrupted terrains. Normal faults 
350-400 meters high have been identified (Figure 3: Nimmo 
and Schenk, 2006). The persistence of these high amplitude