A Critique of the Triangle Method and a Version Suitable for Estimating Soil Moisture from Satellite Imagery

A simple version of the triangle model is proposed, that of a right triangle, which allows one to estimate from remote thermal/optical measurements the evapotranspiration fraction and surface soil moisture availability without reference to external variables even in the absence of a full range of vegetation cover and soil dryness. To date however, the triangle method has yet to be applied widely in the field, partly because of the triangle’s limitations and partly due to its complexity whereby prospective users would be unequipped or unwilling to handle its technical aspects, including its mathematical requirements. After a brief description of the triangle geometry, the paper deals with current misconceptions in the use of the triangle/trapezoid method, including the way in which plants deal with water stress. The last part poses a scenario showing how the right triangle model could be applied easily and routinely at field level by the non-specialist.