The WBSCAT Polarimetric Synthetic Aperture Scatterometer for Retrieval
of In-Situ Time-Series of Snow Structure
Abstract
WBSCAT is a new terrestrial microwave scatterometer supporting
polarimetric observations over 1 to 40 GHz. This instrument is being
developed for the European Space Agency (ESA) to conduct microwave
studies of a wide range of ground covers including snow and ice. This
instrument is built upon the heritage of SnowScat , operating over the
range of 9.2 to 17.8 GHz, that has been used for generating tomographic
time-series of snow pack and is part of the ongoing ESA SnowLab project
[2]. WBSCAT, like its predecessor, acquires coherent data and can
measure polarimetric scattering matrices, interferometric phase, and
coherence. Both instruments will be operated in Winter 2018/2019 in
Davos Laret, Switzerland mounted on a 10- meter tower and performing
multiple daily observations of the snow pack. Either instrument can be
attached to a 2.2-meter linear scanner inclined at 45-degrees permitting
tomographic snow profiling [1]. The WBSCAT instrument uses
radial-scan aperture synthesis to acquire independent observations of
the scattering volume and also to restrict the field of view to the
undisturbed test site, despite wide antenna beamwidths at low
frequencies. The 6 horn antennas, with overlapping frequency ranges of 1
to 6, 2 to 18, and 10 to 40 GHz, are mounted approximately 60 cm
radially from the rotation axis of the pan/tilt scanner. The antennas
can be scanned between +35 and -45 degrees in elevation and +/- 90
degrees in azimuth, creating a synthetic aperture. The aperture
dimensions are mostly determined by the antenna pattern, but at low
frequencies, the antenna beamwidth exceeds 90 degrees. Aperture
synthesis substantially increases the number of looks for improved
radiometric resolution and is a novel approach for ground-based
microwave scatterometry. Combining ranging information along with WBSCAT
aperture synthesis perpendicular to the line of sight, has the potential
for direct 3D imaging of the snow pack.