This dissertation presents a method for determining the relative permittivity of surface and sub-surface layers, such as a layer of snow on the ground and the hidden ground layers. In summer, the traditional two-ray model is expanded to three rays, where the new ray penetrates the top layer of ground until it is reflected by a change in the earth medium. In the winter, a five-ray model is used where snow covers the same ground. Measurements were taken in a field area measuring approximately 6800 m2 with the transmitter and receiver in close proximity to the area of interrogation, and where the ground exhibited lateral homogeneity. A genetic algorithm is used to determine the electrical characteristics of the ground and snow layers based on results from measurements taken from four positions and nine heights at each position, in summer and winter. At a frequency of 2.35 GHz, the snow covering the ground during the winter campaign was found to have a relative permittivity of 11.3.
https://www.ece.unb.ca/petersen/pubs/theses/students/Br25/