VALIDATION STRATEGY FOR SATELLITE-DERIVED SOIL MOISTURE IN TROPICAL REGION Chan Fong Chi (a) and Mohd Nadzri Md Reba (a*)
a) Faculty of Built Environment and Surveying, Universiti Teknologi Malaysia (UTM), 81310 UTM Johor Bahru, Johor, MALAYSIA-
Abstract
Continuous and distributed in-situ soil moisture (SM) measurements are crucial in the calibration and validation of Soil Moisture Active Passive (SMAP) data. The existing public database of the International Soil Moisture Network (ISMN) in tropical regions compared to other climate zone, thus impeding the validation of the SMAP products in tropical regions. Several data records in tropical regions includes MySMnet in Malaysia and VDS network in Vietnam. Additionally, the tropical climate experiences frequent rainfall and higher humidity in the dense vegetation which poses distinct challenges to the calibration of satellite SM products. Such dynamics contribute to inconsistency in field data and are increase the diurnal and nocturnal variation of surface-to-atmosphere interactions. Therefore, the objectives of this research are twofold: first, to compare the correlation of the SMAP products with- (a) in-situ measurements different upscaling techniques on the, (b) in-situ measurement at different temporal integrations- and second, to validate the collocated SMAP SM with the in-situ SM. To address the scarcity of in-situ SM data in tropical regions, the research has deployed a MIE soil moisture network six stations and a weather station to collect soil moisture, temperature and humidity data hourly from May to November 2024. The in-situ measurement from MySMnet, VDS network and MIE network has been upscaled to the SMAP-scale using Voronoi Diagram, arithmetic average- while analysis for temporal variability by using median temporal integration was performed to compare with SMAP within a 2-hour, 3-hour, 4-hour proximity in both AM and PM variants. Statistical metrics, like unbiased Root Mean Square Error (ubRMSE), are utilised to evaluate the temporal variability and consistency between both data. The results reveal differences in soil moisture levels between. This study is expected to provide insights into the strategy of calibration and validation of SMAP in tropical environments.
