Ground Penetrating Radar Measurements in Shallow Water Environments—A Case Study

Abstract

In this study, we investigate GPR measurements in freshwater of less than 5 m at four different locations to derive rules of thumb in terms of depth penetration, resolution, and material contrasts of the method for 200 and 400 MHz antennas under field conditions. The objective is to improve the attractiveness of the method for archaeological issues in water, as there are hardly any studies on this subject so far. The depth penetration of 2–4 m is negligibly influenced by the choice of the 200 or 400 MHz antenna. Organic material in the water column also does not affect the water depth but offers new fields of applications for mapping and volume estimation of biomass in lakes with GPR. The horizontal resolution in the cm range in the direction of the profile and in the dm range across the profile could not be improved by the narrow antenna radiation pattern of 0.1 for materials of 45% porosity to water-saturated sand. Large reflection coefficients also show, for example, granite to sand and gyttja to wood. The water column has a considerable effect on the data quality of the 400 MHz antenna from a depth of 2 m due to the antenna ringing. Furthermore, multiples must be expected in a water column <0.5 m. The method can especially complement the common geophysical methods of seismics and geoelectrics to exclude material ambiguities. The major advantage is the simple setting of the land equipment in the water.

Keywords

• GPR
• archaeological prospection
• shallow water zone
• fresh water