Energy compensated terrain corrections for aeroradiometric measurements

Abstract:

Aerial radiological measurements are used the world over as a source of geophysical data, with applications in resource exploration, environmental evaluation and restoration, as well as radiological emergency response. In the absence of human-produced contamination, the radiological signature primarily reflects the distribution of natural radioisotopes of K, U and Th in the environment (NORM), and thus provides information about the geochemical composition of bedrock as well as the operation of the surficial processes that redistribute these radioisotopes. The DOE maintains a capability, called the Aerial Measuring System (AMS), whose primary mission is that of nuclear and radiological emergency response, but also supports both geophysical and environmental measurements. AMS maintains a high spatial resolution aerial radiological capability that is able to map the distribution of radio-elements. AMS systems are calibrated for these measurements with concrete pads that have been doped with known quantities of NORM. This calibration procedure is valid, even at high altitude, if the terrain below the aircraft is flat within the resolution of the detectors. However, in practice, AMS aircraft regularly acquire data over rough terrain and so to accurately report the data an algorithm has been developed to account for the effects of terrain below the aircraft. The algorithm is based on the work of Schwarz et al. (1992), using high-resolution (0.1 – 10m) digital elevation models. A correction factor is calculated using geometry and a physics based estimation of energy attenuation and scattering. This allows for the possibility of full spectral terrain correction, or simply a correction to extracted isotope values from the spectra. While the algorithm is useful for low flying helicopters (~50m), the terrain effect is more pronounced as the sensor approaches the ground. With the advent of drone based sensors, this work becomes more critical for data accuracy.

Schwarz, Georg & Klingele, E.E. & Rybach, Ladislaus. (1992). How to handle rugged topography in airborne gamma-ray spectrometry surveys.

“This work was done by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy and supported by the Site-Directed Research and Development Program. DOE/NV/03624--0835