Eritrea accuracy study test area

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

MWH Geo-Surveys differential GPS survey crew and equipment. Over 45,000 gravity stations were surveyed from 2004 through 2008 using differential GPS instruments from Magellan. All of the GPS positions were surveyed in Real Time Kinematic (RTK) mode with accuracies of 2 cm or better.  The Magellan RTK base with a ProMarkTM 500 GPS rover are shown in this photo.

MWH Geo-Surveys differential GPS survey crew and equipment. Over 45,000 gravity stations were surveyed from 2004 through 2008 using differential GPS instruments from Magellan. All of the GPS positions were surveyed in Real Time Kinematic (RTK) mode with accuracies of 2 cm or better. The Magellan RTK base with a ProMarkTM 500 GPS rover are shown in this photo.

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.

Location of PhotoSat’s Eritrea stereo satellite surveying accuracy test area, 100km west of the Red Sea.

Location of PhotoSat’s Eritrea stereo satellite surveying accuracy test area, 100km west of the Red Sea.

54,436 ground survey points in the PhotoSat Eritrea stereo satellite surveying accuracy study area.  The black areas are detailed grids of survey points.  These detailed grids have survey points every 20m along lines separated by 100m.

54,436 ground survey points in the PhotoSat Eritrea stereo satellite surveying accuracy study area. The black areas are detailed grids of survey points. These detailed grids have survey points every 20m along lines separated by 100m.

An approximately evenly distributed 300m by 300m grid of survey points.  These 10,024 points were selected to provide an even distribution of accuracy check points.  An even distribution of survey points gives the best measurement of the satellite survey accuracy.

An approximately evenly distributed 300m by 300m grid of survey points. These 10,024 points were selected to provide an even distribution of accuracy check points. An even distribution of survey points gives the best measurement of the satellite survey accuracy.