Back-Calibration Of Regional Airborne Gamma-Ray Data Sets From Namibia - Results And Experiences

During 1992/93 and 1995/96 select portions of existing airborne gamma-ray data<br>comprising 210 000 line 1cm flown in west central and southern Namibia were<br>reprocessed. Available data represented 21 different surveys collected over a<br>period of about twenty years with a variety of gamma-ray spectrometers, spectral<br>windows and survey parameters. The compilation involved the interactive digital<br>recovery of 42 000 km of original analogue chart traces. Preliminary digital grids<br>of each radioelement were compiled, verified and used to select representative<br>sites for ground measurements within each survey block. Results obtained from<br>the ground program were used to back-calibrate the airborne data and convert<br>airborne measurements into equivalent ground concentrations of potassium,<br>thorium and uranium. The survey blocks were merged providing a digital master<br>grid. The merged data are available as either contour maps or as digital grids<br>conform in scale and coordinate system with the regional airborne magnetic series<br>of Namibia.