1163 
3.4. Geology / Pedology Application 
Qualitative interpretation of the Landsat TM data for the Diamou test site was performed using channels 7,4 and 
2. TM channel 7 (mid-IR) is important for detecting soil boundaries, lithological units, tectonic structures, soil 
and vegetation moisture content. Channels 4 and 2 are useful for land cover, land use and vegetation biomass 
aspects Geological units that could be distinguished include areas of quarzite sandstone, silitic sandstone and 
fine sandstone, the boundary positions showing up mostly through shadow effects at escarpments. 
Comparing the ERS-1 data from the test site with the topographic map, geomorphological 
features such as escarpments and slopes have a major influence on the observed backscatter. In flat regions, 
larger areas of dense vegetation and gallery forests have a tendency to show patterns of relatively bright intensity 
and a characteristic texture, whilst agricultural regions exhibit a smooth texture. Comparison with the 
geological ground-truth data enables the identification in the ERS-1 data of geomorphological features such as 
sandstone tables, whilst other geological boundaries are detectable through bright, linear features that indicate 
slopes, separating different geological units at different heights. 
As an investigation into the synergistic content of the ERS-1 and TM data, various 
combinations of the ERS-1 data and TM-derived vegetation indices were superimposed for different time 
intervals between image acquisition. The combination gives a good view as to areas where vegetation cover is 
an important factor for microwave backscatter. Rocky surfaces and slopes are characterised by areas of high 
backscatter and low TM vegetation index. As expected, increasing the time interval between the acquisition of 
SAR and optical data over the rainy season reduces the overall correlation between the images, due to the 
different vegetation cover. 
4 - MISSION ANALYSIS 
In the Mission Analysis task, which was performed by GEC-Marconi Research Centre, the principal aim is to 
interpret the synergistic temporal sampling requirements derived for each application in terms of various one- 
and two-platform mission analysis scenarios in order to assess whether single-platform satellites combining 
SAR and optical sensors are feasible for future missions, or whether separate spacebome platforms are necessary. 
Two basic types of platform have been considered. For the single-platform scenario, an orbit configuration 
similar to ERS-1/2 and ENVISAT was chosen; for the two-platform scenario, this was combined with an orbit 
configuration similar to LANDSAT 4/5. In the two-platform scenario, the SAR instrument is considered to be 
mounted onboard the ERS / ENVISAT configuration platform and the optical instrument onboard the 
LANDSAT configuration platform. 
For both types of platform, a polar sun-synchronous orbit was selected (altitude approximately 
100 kms lower, and slightly reduced inclination, in the case of the LANDSAT orbit configuration) with repeat 
periods of 3, 14 and 35 days. For the SAR instrument, swath widths of 100 kms (worst case, as for ERS-1) and 
400 kms (best case, as for ENVISAT in wide-swath mode) were considered, with boresight look angles of 20.4° 
and 29.0° respectively. The analysis performed did not take account of operational restrictions on the use of 
SAR such as typically arise from power limitations and the requirement for real-time data transmission to an 
accessible ground station. The optical instrument was selected to have a swath width of either 30 kms (worst 
case) or 60 kms (best case, as for SPOT), in both cases nadir-pointing. The optical instrument also has the 
additional feature of being able to scan either side of nadir by ± 30°, thus increasing the effective swath width to 
920 kms for the ERS / ENVISAT configuration platform and (due to the reduced altitude) 780 kms for the 
LANDSAT configuration platform. For the analysis, a minimum solar elevation angle of 15' was assumed. 
No account was taken of restrictions in data-taking due to cloud cover. 
In the two-platform mission scenario, the two platforms start their repeat periods at the same 
location above the Earth’s surface (i.e. they can be considered to start each repeat period in-phase). As each 
platform has a different number of orbits in the same repeat period, the relative position of the SAR and optical 
instrument swaths will be different for each orbit. Changing the starting point of the two platforms to be out of 
phase would have little impact because the relative positions of the two instrument swaths averaged over the 
repeat period will be similar to that of the in-phase platforms. 
Results of the mission analysis were obtained for various platform, repeat period and 
instrument parameter combinations as a function of latitude (northern hemisphere, mid-Summer) of both return 
time (the time difference between SAR and optical imaging) and longitude coverage. In order to determine 
whether a particular maximum synergistic sampling requirement can be achieved for a given parameter, the