AGU: Fall meeting, 1996, V 77, N 46, p F175.

Comparison of Snow Liquid Water Measurements with a Denoth Meter and Finnish Snow-Fork, Niwot Ridge, Colorado


Our objectives in comparing snow surface wetness measurements using two dielectric sensors was twofold: (i) to determine the spatial variability of surface wetness within a pixel for remote sensing platforms such as AVIRIS, and (ii) to evaluate performance advantages and disadvantages with the two instruments. The Denoth meter is a capacitance probe which measures an area of 13 x 9 cm2, operates at 27 MHz and requires a separate density measurement to solve for the imaginary part of the permittivity. The Finnish snow-fork samples an area of 6 x 2 cm2, operates at 1 GHz and simultaneously measures both parts of the permittivity. Data were collected in a cold-lab as well as on Niwot Ridge, a continental alpine site located in the Colorado Front Range at an elevation of 3500 m. The non-destructive nature of half-space, or surface, samples by both instruments allowed for comparison of measurements over the same surface. Snow-fork measurements of percent wetness by volume were consistently greater than the Denoth meter. Mean values (n = 122) were 1.5 times that of the Denoth sensor, with an 18% narrower range than the Denoth meter. In particular, the Denoth meter was much more sensitive to low values of liquid water, with a minima of 0.84% compared to 4.0% by the snow-fork. Linear regression showed a low (r2 = 0.147) but significant relationship (P < .00001). Ideas on physical reasons for differences, as well as practical application of measurements, are discussed.