| dc.description.abstract | Satellite remote sensing is a useful source of observations of land surface
hydrologic variables and processes and could be a practical substitution
of conventional in-situ monitoring. Most of hydrological dynamic
processes change not only throughout the years but also within weeks or
months and their monitoring requires frequent observations. The most
prominent advantage of the remote sensing technologies is that they
offer a synoptic view of the dynamics and spatial distribution of
phenomena and parameters, often difficult to monitor with traditional
ground survey, with a frequent temporal coverage. Many of the variables
in the land surface water balance can now be observed with satellite
techniques thanks to an extensive development over the last decades.
Often the problem connected to the use of remotely sensed data is their
accuracy that, according to the sensor used and to the application
considered, can ranges from moderate to excellent.
The objective of this thesis has been to evaluate the use of satellite
remote sensing techniques for the monitoring of two variables useful for
hydrology applications: water body extension and soil moisture
monitoring.
The capability to map water surface is important in many hydrological
applications, in particular accurate information on the extent of water
boundary is essential for flood monitoring and water reservoir
management. Often, this information is difficult to retrieve using
traditional survey techniques because water boundaries can be fast
moving as in floods or may be inaccessible. In this PhD thesis, an
artificial basin for which in-situ information about the water extension
are available is used as case study. The area extension recorded daily by
the dam owner is compared to the one retrieved by using satellite images
acquired from SAR and TM/ETM+ sensors. The outcomes of the
analysis show that satellite images are able to map water body surfaces
with a good accuracy. The analysis also highlighted the factor to be taken
into account while using types of sensors.
Soil moisture is recognized as a key variable in different hydrological and
ecological processes as it controls the exchange of water and heat energy
between land surface and the atmosphere. Despite the high spatial
variability of this parameter it has been demonstrated that many satellite
sensors are able to retrieve soil moisture information of the surface layer
at catchment scale. Among other sensors, the Scatterometer is very
useful for climatic studies and modelling analysis thanks, respectively, to
the temporal frequency, global coverage and to the long time series
availability. Even though the ERS Scatterometer has been designed to
measure the wind over the ocean surface, in recent years it has been
pointed out that backscattering measurements have high potentiality for
soil moisture retrieval.
The second task of this PhD thesis, concerning the use of satellite data
for soil moisture monitoring, has been developed at Serco S.p.A. in the
framework of the Advanced Scatterometer Processing System (ASPS)
project developed by ESA (European Space Agency) to reprocess the
entire ERS Scatterometer mission. Since the beginning of the ERS-1
Scatterometer mission in 1991 a long dataset of C-band backscattering
signal from the Earth surface is available for studies and researches. This
is a very consistent dataset, but in particular for climatology studies it is
important to have high quality and homogeneous long term observation
as also stated in the key guidelines included in the Global Climate
Observing System (GCOS) from the World Meteorological Organization
(WMO).
The main goal of this task has been the generation of the new
Scatterometer ASPS products with improved data quality and spatial
resolution. This achievement required a long preparation activity but
represents an important contribution to the C-band Scatterometer
dataset available to the scientific community. In order to evaluate the
usage of the re-processed Scatterometer data for soil moisture
estimation, the backscattering measurements derived in the new ASPS
products have been then compared to in-situ volumetric soil moisture
data and the relationship between radar backscattering and soil moisture
measurements has been investigated under different conditions: angle of
incidence, angle of azimuth, data measurements resolution, season of the
year.
Analysis results show that a relationship between the C-band
backscattering coefficient and the in-situ volumetric soil moisture exists
and takes into account the incidence and azimuth angles and the
vegetation cover. [edited by author] | en_US |
