Theodore H. Asch

ALLTEM UXO detection and discrimination

ALLTEM is a multi-axis electromagnetic induction system designed for unexploded ordnance (UXO) applications. It uses a continuous triangle-wave excitation and provides good late-time signal-to-noise ratio (SNR) especially for ferrous targets. Multi-axis transmitter (Tx) and receiver (Rx) systems such as ALLTEM provide a richer data set from which to invert for the target parameters required to distinguish between clutter and UXO. Inversions of field data over the Army’s UXO Calibration Grid and Blind Test Grid at the Yuma Proving Ground (YPG), Arizona in 2006 produced polarizability moment values for many buried UXO items that were reasonable and generally repeatable for targets of the same type buried at different orientations and depths. In 2007 a test stand was constructed that allows for collection of data with varying spatial data density and accurate automated position control. The behavior of inverted ALLTEM test stand data as a function of spatial data density, sensor SNR, and position error has been investigated. The results indicate that the ALLTEM inversion algorithm is more tolerant of sensor noise and position error than has been reported for single-axis systems. A high confidence level in inversion-derived target parameters is required when a target is declared to be harmless scrap metal that may safely be left in the ground. Unless high confidence can be demonstrated, state regulators will likely require that targets be dug regardless of any “no-dig” classifications produced from inversions, in which case remediation costs would not be decreased.

Classification of MEC with the ALLTEM at Camp Stanley, Texas

The ALLTEM is a multi-axis electromagnetic induction system designed for unexploded ordnance (UXO) applications. It uses a continuous triangle-wave excitation and provides good late-time signal-to-noise ratio (SNR) especially for ferrous targets. Multi-axis transmitter (Tx) and receiver (Rx) systems such as ALLTEM provide a richer data set from which to invert for the target parameters required to distinguish between clutter and UXO. Inversions of field data acquired between 2006 and 2010 over the Army’s UXO Standardized Test sites at the Yuma Proving Ground (YPG) in Arizona and at the Aberdeen Proving Ground (APG) in Maryland have produced reasonable and generally repeatable results for many UXO items buried at different orientations and depths. In February-March 2011 ALLTEM data was acquired at two locations on the Camp Stanley Storage Activity (CSSA) just north of San Antonio, Texas. Camp Stanley is used to store munitions as well as test, fire, and overhaul munitions components. Site B-20 is an open burn/open detonation (OBOD) area and Site B-27 consists of narrow trenches blasted into limestone containing buried range and munitions debris and possibly MEC. The processing, analysis, and classification techniques developed at the controlled environments of YPG and APG have been applied to these two “live” sites at Camp Stanley. ALLTEM data analysis includes both classical numerical inversion of data from each anomaly and clustering of the raw data by means of a self-organizing map (SOM) via generalized neural network algorithms. Final classification consists of an integration of both the numerical and SOM results.

Curie depth and inversion of aero-magnetic data with implications for Hazards on Pagan Island, Commonwealth of the Northern Mariana Islands

Airborne magnetic data have been used to aid in the hazard assessment on Pagan Island. Pagan Island is small active stratovolcano in the Commonwealth of Northern Mariana Islands approximately 320 km north of Saipan. The magnetic survey was part of a geophysical study that was carried out to evaluate the hazards of the Island in 2013. Pagan Island was evacuated during a major eruption in 1981. Recently the island has been assessed for a military training base, an area for mining pozzolan, and for rehabitation from the displaced population resulting from the 1981 eruption. With the remote location and rugged inaccessible nature of Pagan Island the airborne approach was the only logistically feasible way to provide a comprehensive assessment of the location of the heat sources within the volcano. Both spectral analysis and 3D inversion were used in order to provide two alternative means to determine depth to bottom of magnetic source. Locations of the heat sources within the volcano is one of critical pieces of information required for the government of the Commonwealth of the NorthernMariana Island to asses the safety an ultimately the use of the Pagan Island. Results were consistent between the two approaches and zones of shallow and deep Curie point isotherm were independently identified. The government has utilized these data after comparing with other passive seismic data to assist in the hazard assessment of Pagan Island.