University of Twente Student Theses


Detectability of forest rainfall interception through GNSS signal measurement with low-cost receiver

Sarungallo, C. (2022) Detectability of forest rainfall interception through GNSS signal measurement with low-cost receiver.

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Abstract:Forest rainfall Interception is the portion of the gross rainfall that does not reach the soil due to the leaves and branches of the tree. It is one of the important aspects related to hydrology. It influences the climate system through its role in the hydrological cycle. Forest rainfall interception influences the amount of infiltration on the forest floor, sub-surface run-off, soil moisture as well as flood generation. This study attempts to detect forest rainfall interception using GNSS measurement with a low-cost antenna. The global National Satellite System (GNSS) is a constellation of satellites for timing and positioning. The signals from GNSS are influenced (degraded) by the nearby surface of an object and can be recorded as Signal to Noise ratio (SNR) using a low-cost GNSS antenna. SNR from GNSS is such undervalued information as the signals that travel through the atmosphere and forest will degrade the GNSS signal which is commonly discarded for positioning purposes. However, the SNR information has been successfully used to derive geophysical information such as snow depth, soil moisture, wind speed, etc. The attenuation of the GNSS signals due to forest has been analysed by Liu et al. (2017) to predict attributes such as biomass, and diameter at the breast height (DBH) of the forest. This opens up an idea to analyse the effect of GNSS signal attenuation due to rainfall interception. Forest rainfall interception in this study was estimated using a physical-based model by Gash, Lloyd, and Lachaud (1995). The low-cost GNSS antenna receiver was installed under the canopy that continuously received the signals transmitted by GNSS satellites. The signals recorded in SNR were correlated to the forest rainfall interception that has been estimated using Gash et al. (1995) model in an attempt to test the ability to detect interception with a low-cost antenna. The SNR data was represented in two metrics from each pass of a single satellite which are the mean value and intercept value of the quadratic polynomial of SNR data. This was performed in two different scenarios based on the azimuth angle of 0-120°and elevation angle of 20-70°for scenario I and it was a 60-90°azimuth angle and 40-60°elevation angle for scenario II. It was hypothesized that SNR data will have a negative/reverse correlation with forest rainfall interception as the presence of water will attenuate/degrade the signals. However, the metrics extracted from these two scenarios established in this study did not give a significant correlation when they were plotted against forest rainfall interception. Some of the challenges and limitations highlighted might influence this current study. these issues are the lack of in-situ measurements for meteorological data and the latest data for forest parameters, and the impact of atmospheric attenuation remains unknown. Hence, for future study, these issues should be solved or minimized.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Subject:38 earth sciences
Programme:Geoinformation Science and Earth Observation MSc (75014)
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