f Terrain corrections and the compilation of gravity data sets from various sources

Calculation of terrain corrections from digital terrain models is a frequent problem when reprocessing old gravity data and especially when several surveys, often of different ages and with different processing histories have to be made compatible prior to producing a new map. The continental scale gravity data compilation projects undertaken by the GETECH group at the University of Leeds - the African Gravity Project (1986 - 1988), the South American Gravity Project (1988 - 1991), the South East Asia Gravity Project (1991 - 1994) and the West - East Europe Gravity Project (1991 - 1994) - involve tollating and re-processing of hundreds of surveys collected over the last 50 years. The actual gravity measurements from these vintage surveys are generally good, but the processing does not always match modern standards - in particular full terrain corrections are frequently not measured or recorded and thus terrain corrections have to be calculated from whatever digital terrain model can be compiled.