Estimation of Radio Attenuation in Radiata Pine Canopy Using Aerial Lidar and Terrestrial GNSS

Data from terrestrial GNSS receivers have been combined with point clouds from aerial lidar to estimate the average attenuation coefficients of foliage in planted pine forests at GNSS frequencies. The absorption and scattering of radio signals due to the presence of vegetation can degrade signals from communications and satellite-based navigation systems, making accurate estimates of attenuation essential for predicting equipment performance. Given the potentially limited ability of lidar to penetrate dense foliage, a method was developed to estimate the average attenuation of signals based on distance travelled beneath the maximum height envelope of tree canopies. This was accomplished by using aerial lidar data to determine the outer surface of the forest canopy based on the maximum height in each horizontal bin. Each GNSS satellite detection vector was then analysed to determine the total length traversed inside of the canopy envelope. Application to regions of planted radiata pine in a managed forest outside Adelaide, South Australia, yielded average attenuation coefficient estimates for satellites with a 30–60° elevation angle of 0.36 dB ${\mathrm{m}}^{-1}$ for 10-year-old medium-height and 0.35 dB ${\mathrm{m}}^{-1}$ for 19-year-old tall trees. The demonstrated method and results provide site and vegetation-type-specific data to inform predictive models of GNSS receiver performance at specific locations.