The estimation of the surface moisture of a vegetated soil using aerial infrared photography

The bidirectional reflectance of near infrared wavelengths of electromagnetic radiation from a vegetation canopy is primarily determined by the relative area and reflectance of the canopy and canopy dependent components: leaves, non-green vegetation, soil and shadow. It has been shown that when the percentage cover of leaves and non-green vegetation are both known and constant and the effect of shadow is minimal, then the near infrared bidirectional reflectance from the-canopy is negatively related to surface soil moisture.

This study was based on the above observation to estimate surface soil moisture of a vegetated soil from remotely sensed measurements of near infrared bidirectional reflectance.

The near infrared bidirectional reflectance, surface soil moisture and vegetation cover were measured at 10 heathland sites on 18 dates. The surface soil moisture was significantly related (at better than the 1 per cent level) to the Y axis intercept, when near infrared bidirectional reflectance (Y) was regressed against the percentage cover of green vegetation (X). This relationship between soil moisture and canopy reflectance was then used to enable the surface soil moisture of vegetated heathland soil to be estimated by means of five flights of black and white infrared aerial photography. It proved possible to estimate the surface soil moisture of the vegetated soil with an accuracy of ±18·4 percent at the 95 percent confidence limits. Possible improvements to the technique are discussed.