[Zurück]

L. Brocca, F. Melone, T. Moramarco, W. Wagner, S. Hasenauer:
"ASCAT soil wetness index validation through in situ and modeled soil moisture data in central Italy";
Remote Sensing of Environment, 114 (2010), 11; S. 2745 - 2755.

Reliable measurements of soil moisture at global scale might greatly improve many practical issues in
hydrology, meteorology, climatology or agriculture such as water management, quantitative precipitation
forecasting, irrigation scheduling, etc. Remote sensing offers the unique capability to monitor soil moisture
over large areas but, nowadays, the spatio-temporal resolution and accuracy required for some hydrological
applications (e.g., flood forecasting in medium to large basins) have still to be met. The Advanced
SCATterometer (ASCAT) onboard the Metop satellite (VV polarization, C-band at 5.255 GHz), based on a
large extent on the heritage of the ERS scatterometer, provides a soil moisture product available at a coarse
spatial resolution (25 km and 50 km) and at a nearly daily time step. This study evaluates the accuracy of
the new25 km ASCAT derived saturation degree product by using in situ observations and the outcomes of a
soil water balancemodel for three sites located in an inland region of central Italy. The comparison is carried
out for a 2-year period (2007-2008) and three products derived from ASCAT: the surface saturation degree,
ms, the exponentially filtered soil wetness index, SWI, and its linear transformation, SWI*, matching the
range of variability of ground data. Overall, the performance of the three products is found to be quite good
with correlation coefficients higher than 0.92 and 0.80when the SWI is comparedwith in situ and simulated
saturation degree, respectively. Considering SWI*, the root mean square error is less than 0.035 m3/m3 and
0.042 m3/m3 for in situ and simulated saturation degree, respectively.More notably,when thems product is
compared with modeled data at 3 cm depth, this index is found able to accurately reproduce the temporal
pattern of the simulated saturation degree in terms of both timing and entity of its variations also at fine
temporal scale. The daily temporal resolution and the reliability obtained with the ASCAT derived
saturation degree products represent the preliminary step for its effective use in operational rainfall-runoff
modeling.