A geophysical investigation of a sugar cane plantation, St. Croix, U.S. Virgin Islands: Using multiple techniques to assess a complex industrial site.

An archaeological geophysical investigation was conducted at Estate Whim Plantation Museum (Whim) February 25 to March 5, 1999. Whim is the only preserved and publicly open site on St. Croix that offers a guided interpretation of lifeways and processes associated with the island’s historical role in the sugar trade from the 1 sth to the early 20th centuries. During its operation Whim was not only a plantation, but also housed a factory for on-site cane processing. The plantation and factory were worked by slaves until 1848. While many features remain standing, the original slave village and factory have been buried up to a depth of three meters. Three geophysical techniques were used to assess potential excavation sites. These were: Magnetics (Total field), DC resistivity (square array); and ground penetrating radar (GPR). Ambient noise levels were high due to soil inhomogeneity. The industrial site also contained a complex firebrick foundation with an extremely strong magnetic and resistivity signature which masked more subtle structural features. Low amplitude boundary features were revealed by converting measured resistances to transverse anisotropy plots. The magnetics data required more intensive processing. Removal of an upward continued dataset served as a high pass filter. This was reduced to the pole and converted to pseudogravity sections to perform a horizontal derivative. The GPR survey was performed using 200 MHz antennas; lower than those typically used at archaeological sites. Removal of the average trace from a line and band-pass filtering, indicated numerous shallow diffraction events and discontinuous surfaces not apparent in the raw data. The data from all three techniques were combined to produce maps to assess the site. Processing did not appear to introduce significant artifacts. Interpretation of anomalies (e.g. foundations, firebrick, etc.) proceeded with much greater confidence due to multiple technique results. Several sites within the factory were chosen for excavation in August of 1999, based in-part on the geophysical results. Compared to excavation results, transverse anisotropy and magnetics had been reliable indicators of potential excavation sites. GPR’s service as an interpretive tool was heightened after excavation.