Air-FTG® vs. Airborne Gravity
Bell Geospace acquired an Air-FTG® survey that is partially coincident with the 2003 Airborne Gravity (GT-1A) test survey flown in West Arnhem Land, Northern Territory, Australia. Both surveys were flown at 655m above mean sea level, with 2 km line spacing oriented E-W and 20 km tie line spacings oriented N-S.
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Figure 1. Location of test survey
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Figure 2.Air-FTG® survey lines over free air gravity from 2003 airborne gravity survey. The area within the yellow rectangle has been used for the comparison.
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Comparison of Regional Airborne Gravity and Air-FTG® data from Northern Territory, Australia
Figure 3 shows a comparison of both data sets. Note the differences between the Air-FTG® and conventional airborne gravity data. For both systems the largest measured density contrast comes from the terrain (a). Although both the airborne gravity (b) and the Air-FTG® (c) free air data approximate the terrain, as expected, the airborne gravity lacks high frequencies necessary to resolve the finer details recorded by Air-FTG®. Even considering the wide line spacing of 2km, Air-FTG® data offers more discernable and detailed information than the conventional airborne gravity.
Comparison of Regional Airborne Gravity and Air-FTG® data from Northern Territory, Australia
Part II: Low Frequencies
Figure 3. Air-FTG® and airborne gravity data that has undergone 5 km (A, D), 10 km (B, E), and 20 km (C, F) low pass filters. Note that even at the lowest practical frequencies for this survey, the Air-FTG® data compares well to the first vertical derivative of the airborne gravity data.
Figure 4. Power spectra of the airborne gravity and Air-FTG® data show that Air-FTG® contains greater energy at low frequencies. It appears that the airborne gravity data amplitude has been reduced by a 4 km low-pass filter. The Air-FTG® data contains greater energy at high frequencies than the airborne gravity data.
