Potential of High-resolution Detection and Retrieval of Precipitation Fields from X-band Spaceborne Synthetic Aperture Radar over land

X-band Synthetic Aperture Radars (X-SARs),
able to image the Earth’s surface at metric resolution, may
provide a unique opportunity to measure rainfall over land
with spatial resolution of about few hundred meters, due to
the atmospheric moving-target degradation effects. This capability
has become very appealing due to the recent launch
of several X-SAR satellites, even though several remote sensing
issues are still open. This work is devoted to: (i) explore
the potential of X-band high-resolution detection and
retrieval of rainfall fields from space using X-SAR signal
backscattering amplitude and interferometric phase; (ii) evaluate
the effects of spatial resolution degradation by precipitation
and inhomogeneous beam filling when comparing to
other satellite-based sensors. Our X-SAR analysis of precipitation
effects has been carried out using both a TerraSAR-X
(TSX) case study of Hurricane “Gustav” in 2008 over Mississippi
(USA) and a COSMO-SkyMed (CSK) X-SAR case
study of orographic rainfall over Central Italy in 2009. For
the TSX case study the near-surface rain rate has been retrieved
from the normalized radar cross section by means of
a modified regression empirical algorithm (MREA). A relatively
simple method to account for the geometric effect
of X-SAR observation on estimated rainfall rate and firstorder
volumetric effects has been developed and applied. The
TSX-retrieved rain fields have been compared to those estimated
from the Next Generation Weather Radar (NEXRAD)
in Mobile (AL, USA). The rainfall detection capability of
X-SAR has been tested on the CSK case study using the
Correspondence to: F. S. Marzano
(marzano@die.uniroma1.it)
repeat-pass coherence response and qualitatively comparing
its signature with ground-based Mt. Midia C-band radar in
central Italy. A numerical simulator to represent the effect of
the spatial resolution and the antenna pattern of TRMMsatellite
Precipitation Radar (PR) and Microwave Imager (TMI),
using high-resolution TSX-retrieved rain images, has been
also set up in order to evaluate the rainfall beam filling phenomenon.
As expected, the spatial average can modify the
statistics of the high-resolution precipitation fields, strongly
reducing its dynamics in a way non-linearly dependent on the
rain rate local average value.