UGV-Based Mapping of Forest Transmissivity Using GPS Measurements

Abstract

This paper presents a practical technique to estimate canopy transmissivity at multiple locations using two sets of Global Positioning System (GPS) measurements. One receiver is mounted on unmanned ground vehicle (UGV) that traverses on forest floor while another identical receiver is located on a tripod that provides a reference data in an open area. One-way transmissivity at various elevation angles and locations are obtained by taking the logarithmic difference between measurements (GPS carrier-to-noise density ratio C/N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> ) under canopy and open area under the assumption of negligible multipath. We carried out several experiments in early 2020 to test the multipath assumption where we ignore the multiple scattering involving ground reflections under forest canopy. The preliminary results indicate indeed this is the case, leading to the fact that the UGV-based GPS receiver collects mainly attenuated and scattered signal withing the vegetation. The approach can be utilized for quantification of vegetation water content that is needed for large scale spaceborne soil moisture calibration validation efforts.