Interpreting Land-Use History by Integrating Aerial Photographs, Near-Surface Geophysics, and Field Observations Into a Digital Database

Abstract

Near-surface, non-invasive field geophysics was used to investigate the land-use history of a 60-aere former industrial site in Lancaster, Pennsylvania. A proton-precession magnetometer and a Geonics EM31 non-contacting electromagnetic conductivity meter were used to measure eleven profiles across the site. Based on all the available data, four major land-use areas are distinguished: building foundation areas, excavated areas (clay mining), landfills and background areas. The geophysical data show distinct signatures for these land-use classifications. The conductivity readings can be characterized by their median values and standard deviations within each of these classifications: a) sports fields (background), 7.5 ±2.8 millisiemens per meter (mS/m); b) excavated areas, 4.6 ±3.4 mS/m; c) building foundations, 7.7 ±4.0 mS/m; and d) landfill areas: 34.0 ±30.8 mS/m. For magnetics, the median (with background subtracted) and standard deviation within each classifications are: 1) sports fields (background), −0.9 ±8.7 nanoteslas (nT); 2) excavated areas, −0.8 ±10.8 nT; 3) building foundations, −96.2 ±291.0 nT; 4) landfill areas, 37.7 ±473.9 nT. Both conductivity and magnetics show similar patterns, although conductivity provides clearer visual discrimination between land-use types. The in-phase conductivity data are consistent with the land-use patterns determined from the aerial photographs and the other geophysical data. Zero (negative) readings occur over areas with high metal content such as the buildings foundations area and the landfill area. Clay pit areas show uniformily low readings consistent with the lack of metallic objects in these areas. All the data, including historical aerial photographs, historical land-cover information, geophysical data, topography, hydrology, and existing buildings and infrastructure were integrated into a digital database. Data such as historical aerial photographs provided temporal (past) information about the land-use history of the site, while the geophysical data provided current information about the type and spatial distribution of land use. The integration of the geophysical data with other data in a digital database is an effective tool for interpreting land-use history and understanding present environmental conditions