Classifying Terrestrial Based Forest Photography with Geographic Information Systems to Model Signal Loss

GPS L-band signals are attenuated by vegetation, which makes it problematic to predict the quality of signal reception in forested areas. To predict GPS signal attenuation, a quantitative measure of the local forest structure and density is necessary. Terrestrial based hemispherical sky-oriented photographs (HSOPs) can be used to rapidly and remotely sample the structure and density of forest canopy. We report here the results of a study performed to determine the attenuation of GPS signals in forests, by correlating changes in the signal-to-noise ratio (SNR) of the received GPS signals under different canopies, using the observed canopy closure at the directed location of individual GPS satellite vehicles (SVs) derived from terrestrial photography. The results of this study verify that the loss of signal is strongly correlated with the local structure and density of the forest, and we demonstrate how the calculated canopy closure can be used to better predict the attenuation of the GPS signals. The results of this research also pertain to satellite communications, cellular signals, and perhaps the estimation of biomass from L-band radar.