Calibrated and Repeatable Data

The SkyTEM system is the only one-time calibrated, allowing for direct comparison with previous SkyTEM and ground based or borehole EM datasets together.

The nature of both SkyTEM’s frame and the hardware means that the raw data is well-calibrated (i.e. system bias is below background noise level and there is negligible drift). The receiver coils are placed so as to be null-coupled to the primary field of the transmitter, in order to minimise the self-response of the system. The bias signal from the transmitter is very low, meaning that regular excursions to high altitude to monitor the bias response are not necessary during each flight. In terms of applications and benefits to customers, this means that:

• Data can be processed and inverted in the field, allowing rapid assessment of survey results and planning of infill lines whilst a survey is in progress.
• This preliminary EM data, delivered within 48 hours of acquisition, is very similar to final office-processed data;
• No levelling of the electromagnetic data is required between flights or infill campaigns Surveys done at different times and with different SkyTEM instruments can be seamlessly stitched together (see Figure 1). This gives the option of flying multiple systems concurrently on large surveys for faster completion of acquisition;
• Results can be used for quantitative analysis of data (e.g. groundwater quality vs. geophysical response) and 4D monitoring (i.e. time-lapse) datasets can be acquired for groundwater monitoring applications.

In-Loop Geometry

In-loop geometry means fewer corrections need to be applied to correct for lag offsets, thus preserving the integrity of the originally measured data, together with higher accuracy as to where the anomaly originated. Additionally, the rigid slung load platform’s position and orientation is continuously monitored and together with its separation from the aircraft means that Caesium-vapour magnetic data is not being corrected with lower frequency response fluxgate data in the compensation calculations. Corrections regarding frame geometry are actual and not approximated.

Confidence in the DATA

Unlike many other systems, SkyTEM’s low drift means that frequent flights to high altitude to determine drift corrections are not required (some systems require this test several times per flight). On longer surveys, repeat flights to high altitude are conducted approximately weekly in order to verify that the null-coupling, bias and standard deviations have not changed. High altitude checks are also performed following any potential damage to the frame (e.g., hard landing) or replacement of major electronic components.

• Primary Field Compensation (PFC) allows earlier time channel data to be used in the aLCI inversion, thus resolving shallow layers even more effectively than before.

A spectral analysis will be performed daily on raw, unstacked data to monitor for VLF and sferic activity. In any case our primary sensor (due to the in-loop design of the system) is the Z and is significantly less affected than other systems.
Data will be re-flown at the Contractor’s expense when the standard deviation of the normally processed late (e.g. 8904 μs for the 304) time gate EM channel continuously exceeds 2 nV/m2 for Z-component data and 6nV/m for X-component data over a horizontal distance of 2 km under normal (conditions free of man-made interference e.g powerline interference, radio transmitter, etc) survey conditions.