Eritrea accuracy study test area:
In 2008 PhotoSat acquired over 50,000 ground survey points on a 50km by 20km area just west of Asmara, the capital of Eritrea. These points were surveyed as part of a mining exploration gravity study. The survey points are expected to be accurate to 2cm in elevation
Elevation surveys for gravity studies are very high quality
The Eritrea gravity study was conducted to locate areas of dense, metal rich, rock. The dense areas of metallic ore exert a slight gravitational pull that can be detected by very precise gravity meters. To detect the difference between gravitational pull from a metallic ore body and a slight change in the elevation of the gravity meter, the elevation of the gravity meter must be known to better than 10cm. The gravitational pull of the earth decreases with increasing elevation. Consequently elevation surveys that are conducted for gravity studies are very high quality and checked carefully.
Survey point distribution:
The complete coverage of over 50,000 survey points is shown in the total figure below. The survey consisted of a regional grid and detailed grids of survey points. The regional grid has survey points on 300m by 300m centers. The detailed survey grids have survey points every 20m along lines separated by 100m.