Monitoring of seasonal influence on spatial distribution of moisture content at a natural Kanto loam site using ground wave of GPR

Ground penetrating radar (GPR) ground wave was used at a natural Kanto loam (i.e. Andisol) site to examine the influence of seasonal variations on surface soil-moisture content. Kanto loam is a type of volcanic ash soil found widely distributed in Japan. In order to investigate the influence of surface soil conditions on GPR based estimates, the study site was divided in two zones: with and without vegetation. Measurements were conducted at regular intervals during a three month monitoring period. Results indicated that GW was sensitive to the surface soil conditions as well as to seasonal variations. A significant increase in moisture content was observed in the vegetated zone over that of the bare zone during a period of a day after precipitation (i.e. September 1^st). It shows that in the vegetated zone moisture in plants themselves, including roots, stems, and leaves, affects GPR measurements, leading to higher moisture content than in the bare zone. However, the influence of vegetation was not found to have a large impact during periods of good weather. The effectiveness of surface soil conditions with seasonal variations on GPR-based moisture content provided a clear insight to agricultural management prospectivies. This research confirmed that Kanto loam can be a good GPR site for noninvasive mapping of moisture content regardless of the presence of organic matter, silt, and clay content.