VERY LOW AND ULTRA HIGH FREQUENCY EM SURVEYS OF CEMETERY BURIALS: CAN WE FIND LOST BURIALS?

The Porter/High Street Cemetery, in the town of Danvers, Massachusetts and created in the mid 18th century, is the burial ground for veterans from the French and Indian War through the Spanish-American War. Many of the head and footstones have been moved, broken, or otherwise disturbed, leaving potentially unmarked graves. Ground penetrating radar with a 400mHz antenna and electromagnetic induction at frequencies of 13kHz, 11kHz, and 6kHz was used to try and locate any unmarked graves. Radar and induction profiles were completed across known burials and the signatures compared with anomalies which may represent unmarked burial sites. The 2D radar data was minimally processed but processing did include Hilbert transforms. The data typically placed the anomalies or suspected burial sites in the western portion of the cemetery around 1.5m-2m deep, while in the southeast-northeast region the graves were found to be at a more shallow depth. The average width of the anomalies was found to be approximately 1.6m, with a few wider anomalies present that possibly represent multiple interments. A possible relation between signal amplitude and burial age was also detected, perhaps due to the further resettling of the ground in the graveshaft. The electromagnetic data confirmed the radar results, and a definite pattern emerged indicating the presence of burial sites especially when using the 11kHz quadrature EM data. As a result of this research as many as 15 unmarked and unknown veterans' graves have been identified.