guideline and standards for skytem measurements, processing and ...

January 2011
The following tables show recommended processing settings for the different data from the SkyTEM system
The settings must always be adjusted to the actual survey area, target geology, flight speed etc.
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GPS x- and y-positions are fitted stepwise to a polynomial of an order that can be specified in the processing
phase. Furthermore the GPS-position can be shifted in the flight direction (x-direction) to position the
data in the optimum lateral focus point for the actual SkyTEM-configuration. The lateral focus point for the
SkyTEM-configuration is approximate 2/3 the distance from the frame center to Rx-coil position. This gives
at negative shift of the GPS-data if the GPS-receivers are placed at nose of the frame (normal setup). The
GPS-shift is based on calculations of the frame orientation from the GPS-positions. Hovering measurements
result in a poor determination of the frame orientations, due to the uncertainty of the GPS-positions.
Parameters Value Comment
Device All Use one or all devices
Beat Time [s] 0.5 Sample rate for the time array which all navigation data are averaged
into
Filter Length [s] 9 The length of the filter for each polynomial fit.
Polynomial Order 2 The order of the polynomial
Reposition in x-direction [m] -20 / -26 Shift of the GPS-position in flight direction (x-direction).
Working values for normal SkyTEM-setup: Small frame -20 m;
Big frame: -26 m
" !!
Tilt data are filtered using a median filter to eliminate potential outliers. Tilt data are used to correct altitude
and voltage data. Tilt data are measured as the deviation from normal in degrees in the x- and y-direction.
It is presumed that the transmitter frame is rigid.
Parameters Value Comment
Device All Use one or all devices
Median Filter ON Turns the filter on and off
Median Filter Length [s] 3 Length of the filter
Average Filter Length [s] 2 Part of the data from Median Filter Length to use for in each step
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!!
The transmitter altitude is found using a number of lasers placed on the frame. The lasers measure the
distance to the ground, but are also influenced by reflections from tree tops, bushes, etc., which results in a
seemingly lower altitude. The main issue of altitude processing is therefore to remove reflections from the
lasers. An automatic tilt correction is, however, also made. Furthermore, the final output is corrected for the
fact that the lasers are not placed in the middle of the transmitter frame, while the position of the frame is
defined as the center.
Filtering of altitude data is done using a two-step polynomial fit working separately on each device: Step
one involves repeated cycles of fitting a polynomial to the data while continuously discarding outlying data,
predominantly those of relatively low altitude. This results in an increasingly better data fit, where more and
more undesired reflections are removed. The fit is done in steps where a certain amount of data is fitted at
a time. Based on the fit, data are removed from a small portion of this interval after which the program
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