Sarah G. R. Devriese

Enhancement of Magnetic Data by Stable Downward Continuation for UXO Application

The magnetic method has been proven to be a successful geophysical tool for the detection of unexploded ordnance (UXO). Aeromagnetic surveys are advantageous since they can acquire data over large areas. The downside is that magnetic anomalies due to multiple metallic targets can overlap significantly due to flight height restrictions. Such overlap combined with the acquisition noise may significantly decrease the signal-to-noise ratio of data. These adverse effects can mask the true level of contamination at a site during the initial assessment based on the magnetic method as well as decrease the overall effectiveness of discrimination during the active clearance stage. We propose a method to ameliorate these difficulties using stable downward continuation, which reconstructs the field at a lower observation height from the observed data. The stable algorithm formulates the downward continuation as an inverse problem and incorporates the expected power spectrum of UXO anomalies. The power spectrum preserves the spectral properties and subdues the amplification of high-frequency noise. Synthetic and field examples show that the algorithm can reliably reconstruct the magnetic anomaly at the ground surface within the limitation imposed by the noise. The reconstructed field exhibits significant enhancement compared to the original data.

Archaeological investigations using geophysics at Chimney Rock Great House, Colorado

In this talk, we present results from a geophysical investigation at the Chimney Rock Great House using magnetics, electromagnetics, and DC resistivity. Our data is focused on a grid southwest of the Great House, where we use geophysics to detect potential buried walls. These walls may be covered by 1 to 3 m of fill as a result of nearby excavations in the 1920s, and should be approximately 0.5 m thick. Using geophysics, we were able to identify several potential targets in the multiple datasets, which are consistent with sketches from earlier archaeological digs. Through our investigations, we have likewise gained a better understanding of the geophysical responses of buried walls at Chimney Rock.