2. Calculate terrain corrections. The majority of gravity stations received have no terrain
correction recorded and those which do need terrain corrections extending to a
common radius of 166.7km.
Once the gravity data are processed, terrain data can also be used for production of
isostatic anomalies and for geoid computations.
5' x 5' grids have been produced for Africa and South East Asia, a 3' x 3' grid for South
America, a 4km x 4km grid for Europe and an 8km x 8km grid for FSU.
The four main sources of terrain data used are:
1. Heights of gravity stations on land and bathymetry associated with marine surveys.
These are generally relatively accurate and well located.
2. Preexisting topographic grids. These are mostly national grids, but the worldwide
ETOP05, despite its serious problems, was also used where nothing else is available.
3. Topographic maps. Digitised contours and spot heights give variable quality terrain
data, depending on the scale and contour interval of the map and also the local
topography.
4. Coastline data. Coastlines were used as zero values to help constrain what is often the
least well defined part of the grid.
These continental grids have been linked together with ETOP05 and other grids for
USA and Antarctica to produce a worldwide DTM at 5' x 5' resolution. This "Global
DTM5" (figure 3) is a unique product due to the huge contribution from gravity station
heights. It should have many uses beyond its original purpose.
Availability of Data: The digital terrain models for the Earth at 5' x 5', Europe at 2.5' x
2.5' and South America at 3' x 3' are available from GETECH.
Acknowledgments. These projects represent the efforts of H. AI-Biatty, S. Aspland,
S. Campbell, P. Chevalier, R Daniels, G. Gifford, A. Hollins, N. Hunt, M. Lawrence,
D. Manton, K. McKenna, S. Neil, L. Rapson, S. Spink, S. Williams, I Windle and the
authors at GETECH. We acknowledge the help of our various collaborators, with special
thanks to the International Gravity Bureau (BGI) , the International Scientific
Environmental Centre (ISEC) in Moscow and the University of Sao Paulo (EPUSP). The
sponsors of the various projects who enabled the whole thing to go ahead are Agip,
Amoco, Arco, BHP, BP, British Gas, Chevron, Conoco, Elf Aquitane, Exxon, Hunt,
JNOC, Marathon, Mobil, PDVSA, Petrobras, Phillips, Placid, ShelllPecten, Sun, Texaco,
Total and Unocal. The co-operation of national groups is gratefully acknowledged; these
include Albania, Angola, Argentina, Australia, Austria, Bangladesh, Belgium, Bolivia,
Botswana, Brazil, Bulgaria, Cameroun, Chile, China, Colombia, Costa Rica, Croatia,
Czechoslovakia, Denmark, Ecuador, EI Salvador, Finland, FSU, France, Germany,
231
correction recorded and those which do need terrain corrections extending to a
common radius of 166.7km.
Once the gravity data are processed, terrain data can also be used for production of
isostatic anomalies and for geoid computations.
5' x 5' grids have been produced for Africa and South East Asia, a 3' x 3' grid for South
America, a 4km x 4km grid for Europe and an 8km x 8km grid for FSU.
The four main sources of terrain data used are:
1. Heights of gravity stations on land and bathymetry associated with marine surveys.
These are generally relatively accurate and well located.
2. Preexisting topographic grids. These are mostly national grids, but the worldwide
ETOP05, despite its serious problems, was also used where nothing else is available.
3. Topographic maps. Digitised contours and spot heights give variable quality terrain
data, depending on the scale and contour interval of the map and also the local
topography.
4. Coastline data. Coastlines were used as zero values to help constrain what is often the
least well defined part of the grid.
These continental grids have been linked together with ETOP05 and other grids for
USA and Antarctica to produce a worldwide DTM at 5' x 5' resolution. This "Global
DTM5" (figure 3) is a unique product due to the huge contribution from gravity station
heights. It should have many uses beyond its original purpose.
Availability of Data: The digital terrain models for the Earth at 5' x 5', Europe at 2.5' x
2.5' and South America at 3' x 3' are available from GETECH.
Acknowledgments. These projects represent the efforts of H. AI-Biatty, S. Aspland,
S. Campbell, P. Chevalier, R Daniels, G. Gifford, A. Hollins, N. Hunt, M. Lawrence,
D. Manton, K. McKenna, S. Neil, L. Rapson, S. Spink, S. Williams, I Windle and the
authors at GETECH. We acknowledge the help of our various collaborators, with special
thanks to the International Gravity Bureau (BGI) , the International Scientific
Environmental Centre (ISEC) in Moscow and the University of Sao Paulo (EPUSP). The
sponsors of the various projects who enabled the whole thing to go ahead are Agip,
Amoco, Arco, BHP, BP, British Gas, Chevron, Conoco, Elf Aquitane, Exxon, Hunt,
JNOC, Marathon, Mobil, PDVSA, Petrobras, Phillips, Placid, ShelllPecten, Sun, Texaco,
Total and Unocal. The co-operation of national groups is gratefully acknowledged; these
include Albania, Angola, Argentina, Australia, Austria, Bangladesh, Belgium, Bolivia,
Botswana, Brazil, Bulgaria, Cameroun, Chile, China, Colombia, Costa Rica, Croatia,
Czechoslovakia, Denmark, Ecuador, EI Salvador, Finland, FSU, France, Germany,
231