COMPENSATION OF VEGETATION EFFECT ON THE RETRIEVAL OF
SNOW PARAMETERS FROM BACKSCATTERING MEASUREMENTS: A
CONTRIBUTION TO CoReH2O MISSION
Giovanni Macelloni, Marco Brogioni, Francesco Montomoli, Giacomo Fontanelli
IFAC-CNR – Italy
Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy
The COld REgions Hydrology High-resolution Observatory (CoReH2O) is one of the three satellite missions
selected for scientific and technical feasibility studies (Phase-A) within the Earth Explorer Programme of the
European Space Agency (ESA). The principal objective of the CoReH2O mission is the spatially detailed
frequently measurement of snow and ice in order to advance the knowledge and prediction of the water cycle
in cold regions and to improve the representation of the cryosphere in climate models. The proposed sensor
is a dual frequency SAR, operating at Ku-band (17.2 GHz) and X-band (9.6 GHz), VV and VH
polarizations, with a swath width of about 100 km. The principal products obtained from the mission will be
the evaluationof the extent, the water equivalent (SWE) and melting state of the seasonal snow cover and the
snow accumulation on glaciers. In order to estimate SWE from the backscattering measurements, it is
necessary to separate the signal of the snow volume from the contribution of the background target (e.g. soil
features like roughness and steepness, vegetation cover, etc.) and also to account for effects of grain size on
scattering. The presence of vegetation has a significant impact on the propagation of the radar signal at Xand Ku-band, depending on its structure, biomass, water content and cover fraction. While for herbaceous
vegetation or sparse forest, the influence on the backscattering seems not to be significant and the contribute
of snow dominates the radar signal, for dense forest (even in case of a moderate biomass), the vegetation
signal strongly covers the signal from snow and, consequently, compromises the sensitivity to snow
parameters. A model analysis, was conducted by using a radiative transfer model for snow-covered vegetated
terrain developed and tested at CoReH2O configuration, showed that for biomass higher than 150 m3/ha,
and CF higher than 0.3-0.4 the sensitivity to SWE disappeared at all frequencies and polarizations.
Moreover when the cover fraction is in the 0-0.3 range or biomass varies between 0-150 m3/ha, an operative
procedure could be applied to take into account the effect of vegetation in the retrieval algorithm. The
adopted procedure is based on the above mentioned analytical model and the information has been derived
from high resolution SAR images. Assuming that in a sparse boreal forest is possible to identify at least
some not vegetated pixels, the scattering characteristics of vegetation could be derived by using an iterative
approach. This information, derived at the beginning of snow season, is during the snow accumulation period
and exploited in the SWE retrieval. An example of this approach, using real SAR data acquired by
TerraSARX over Sodankylae Area (Finland), is finally presented in the paper.