Processing and inversion of SkyTEM data for high resolution hydrogeophysical surveys

Abstract

The SkyTEM system is specially designed for hydrogeophysical surveys with gate times from about 10 microseconds to 5 - 10 milliseconds. SkyTEM data does not need any sort of bias correction. To obtain data with a repeatability better than 5%, the data processing and inversion need to take into account a number of parameters. The SkyTEM system monitors at all times the movement of the transmitter frame in the airspace by measuring GPS position, the altitude and the tilt. In the subsequent data processing the altitude is filtered using recursive filters to remove reflections from tree tops. The tilt is entered to calculate the altitude perpendicular to the ground at the centre of the frame. Also the exact altitude of the receiver coil is calculated along with an area reduction factor compensating for the reduced horizontal area of the coils when they are tilted. Data are averaged using trapezoid formed filters allowing for a small average of the early time gates and a larger average of the late time gates obtaining as small a lateral average as possible Data are inverted using the Laterally Constrained Inversion (LCI) algorithm with a parameterized and/or a smooth model. The forward response include modelling of the full transmitter waveform, low-pass filters in the instrument and a front gate preventing the primary field from the current turn-off to saturate the amplifiers when the current is turned off. Furthermore, the altitude is entered in the inversion as a constrained inversion parameter.