Modeling GPS Signal Loss in Forests Using Terrestrial Photogrammetric Methods

William C. Wright and Benjamin E. Wilkinson

Peer Reviewed

Abstract:	This study proposes a novel method to predict Global Positioning System (GPS) signal loss in forested areas. We explore the relationships between forest parameters mensurated using traditional techniques, terrestrial-based hemispherical sky-oriented photos (HSOPs), GPS signalto-noise ratios (SNRs), and individual GPS signal dropouts. Microwave signals suffer from reflection, absorption, and scattering while propagating through vegetative media, which cause signal attenuation and therefore deteriorate signal reception. HSOPs can be used to rapidly sample the leaf area index (LAI) and gap fractions at particular angles from zenith in forested areas. Changes in the observed SNR of received GPS L-band signals under forest canopies are correlated with forest parameter estimates calculated using HSOPs and traditional forest measurements to establish approximate descriptions of signal attenuation. Using ordinary least squares regression a predictive model is presented. We outline the key forest parameters used with resulting R 2 values ranging from 0.613 to 0.830 and RMSEs ranging from 1.94 to 4.11 decibels. In this study, simple models are presented that effectively predict signal attenuation while using only the minimum number of statistically significant parameters making the results easy to replicate.
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	3094 - 3099
Cite this article:	Wright, William C., Wilkinson, Benjamin E., "Modeling GPS Signal Loss in Forests Using Terrestrial Photogrammetric Methods," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 3094-3099.
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