Limitations in Validating Derived Soil Water Content from Thermal/Optical Measurements Using the Simplified Triangle Method
Department of Geography and Regional Planning, Federal University Dutsin-Ma, Dutsin-Ma PMB 5001, Katsina State, Nigeria
Department of Meteorology, Penn State University, State College, PA 16801, USA
School of Continuing Education, Bayero University, Kano PMB 3011, Kano State, Nigeria
Author to whom correspondence should be addressed.
Remote Sens. 2020, 12(7), 1155; https://doi.org/10.3390/rs12071155
Received: 23 February 2020 / Revised: 26 March 2020 / Accepted: 31 March 2020 / Published: 4 April 2020
(This article belongs to the Special Issue Monitoring Soil Degradation by Remote Sensing)
We assess the validity of the surface moisture availability parameter (Mo) derived from satellite-based optical/thermal measurements using the simplified triangle method. First, we show that Mo values obtained from the simplified triangle method agree closely with those generated from a soil/vegetation/atmosphere/transfer (SVAT) model for scenes over a field site at the Allahabad district, India. Next, we compared Mo values from the simplified triangle method for these same overpass scenes with surface soil water content measured at depths of 5 and 15 cm at this field site. Although a very weak correlation exists between remotely sensed values of Mo for the full scenes and measured soil water content measured at both depths, correlations increasingly improve for the 5 cm samples (but not for the 15 cm samples) as pixels were limited to increasingly smaller vegetation fractions. We conclude that the simplified triangle method would yield reasonable values of Mo and demonstrate good agreement with ground measurements, provided that validation is limited to pixels with little or no vegetation and to soil depths of 5 cm or less.