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