644 



Figure 9. Geosat AfsASURED Sea Scrface Gravity Anomaues and Predicted Seafloor Topography in 



THE SOVTHERN INDIAN OCEAN 



IHH 



Large scale features of Earth 's sub-surface structure are revealed through the use ofaltimetry measurements from space. 



The left figure illustrates Ceosat geodetic repeat mission data south ofiO°S that has previously been declassified. At right is a depiction of seafloor 

 topography derived from these Geosat alUmetry data Comparison with shipboard bathymetry data would show a high degree of correlation between the 

 directly measured (ship) and inferred (satellite) bathymetry. 



c. Scieniific Utility 



Geodynamic applications of the satellite altiir.etry data include: 



• Location of uncharted features for planning detailed shipboard 

 surveys and improving bathymetric charts; 



A review of the available unclassified and declassified data 

 suggests that additional altimetry from either Geosat or European 

 Space Agency ERS- 1 coverage will lead to a major improvement 

 in the resolution of the marine gravity field, especially in the 

 low latitude regions. 



Investigation of seafloor morphology and isostasy; 



Identification of fracture zone trends lor improving plate 

 reconstruction models; 



Determination of the global distribution and loading histories 

 of undersea volcanoes; 



Location of manne sedinientary basins for hydrocarbon 

 exploration; 



Constraining shallow mantle convection processes including 

 those beneath mid-ocean ridges. 



In July 1 99 1 , the European Space Agency launched the ERS- 1 

 spacecraft into a high inclination (98.5^) low altitude (780 km) 

 orbit similar to the Geosat orbit. While its primary mission is 

 to collect synthetic aperture radar ( SAR) images, it also carries 

 a pulse-limited radar altimeter that is similar in design to the 

 altimeters aboard Seasat and Geosat. In April 1994, ERS-1 

 began a geodetic mapping phase along a dense 168-day repeat 

 ground track. Two 168-day missions have been completed by 

 ERS- 1 and it is now possible to "see" any features that are 

 "seen" in the Geosat GM data, as the measurement precision 

 and spatial resolutions of the two data sets are similar. 



16 



