Neutron moisture probes: the minimum error attainable.

Abstract

The effect of the soil parameters dry density mass absorption and mass scattering coefficients on the neutron flux at the detector of a neutron moisture probe has been described previously by a set of polynomial equations. The partial derivatives of these equations have been used to determine the deviation introduced into water density calculation by a one per cent inaccuracy in each of the parameters. Accuracy of measurement of the soil parameters is discussed and applied to a typical soil at various water densities. The accuracy to which soil parameters can be measured is examined and found to be approximately +- 2% for the dry soil density +- 1% for the mass absorption coefficient and +- 2% for the mass scattering coefficient. Using these data together with a statistical accuracy of +- 1% in the probe count rate the minimum error achievable for the water density varies between +- 3.5% at a water density of 0.06 g cm - 3 and +- 1.55% at a water density of 0.41 g cm - 3.