This method of flying is known in the industry as “contour” flying. As a result, contour flying can introduce large differences in sensor height between adjacent lines, which can potentially change the amplitude of geophysical anomalies and impede the ability to grid and interpret data.
To reduce these effects and collect a superior dataset, we will often generate a vertical guidance grid, or “drape” especially for fixed wing surveys, although possible for helicopter surveys it is less common to fly a drape survey as the helicopter pilot has much more control and ability to maneuver in the challenging terrain. Using Geotech’s vast flying experience, we work with our pilots to generate a model of aircraft performance specific to the survey area to be flown. We then apply these limits to a high-resolution satellite elevation model to create the drape grid at various target altitudes and analyze them so we can choose the grid that will produce the best data, and will be the safest to fly. Our clients receive the planned altitude grid in advance of the survey, which can then be adjusted to better achieve their exploration goals.
When flying a Geoscience BC’s TREK fixed-wing magnetic project in 2013, we employed a drape grid for the 100,000+ line-km project in central British Columbia. Here, the drape not only helped us fly in steep terrain, but also mitigated the effects of different pilots’ flying styles as they rotated through the months-long project. Most of the survey block was flown +/-5m of the planned altitude, resulting in an excellent dataset that reduced processing and delivery time, thus aiding in the ability to accurately interpret magnetic anomalies.