Determination of volumetric soil water content (VSWC) is essential in many fields such as agriculture, hydrology, and ecology, etc. Currently, there are several methods to determine VSWC for example gravimetric, time-domain reflectrometry (TDR), capacitance probe methods, etc. In this research, ground penetrating radar (GPR) was used to determine VSWC of a loamy soil at experimental field in the center of learning network for the region, Chulalongkorn University, Changwat Saraburi, Thailand. The GPR was set up in the ground wave fixed offset method with 400 and 900 MHz central frequency antennas, which have transmitter and receiver offsets of 1.00 m and 0.405 m, respectively. By estimate the relative dielectric permittivity of soils, these values were converted to VSWC by Topp’s equation. The results of VSWC calculated from soil samples at different depths (10, 20 and 30 cm) were used as the references. Besides, there were three experiments to see how GPR can detect variation of VSWC with times. The results revealed that GPR 400 MHz has high correlation with gravimetric method at dry condition at depth of 10 to 30 cm with VSWC about 10 to 15%. And at wet condition, the result is reasonable at depth 10 to 20 cm with VSWC around 30%. GPR 900 MHz is not related to gravimetric method but the results are looked well in dry condition. In the time monitoring of VSWC, the results of GPR 400 MHz in three experiments changed with time, but not for GPR 900 MHz. So, GPR method is appropriate for estimating VSWC due to the easy of data acquisition and processing. In addition, the soil water content from capacitance probe was not reliable when comparing to the VSWC from gravimetric method due to the limitation of experiment.

Thesis (M.Sc.)--Chulalongkorn University, 2014