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Making Sense of Satellite Data
University of Valencia
Space technology facilitates humanity and science with a global revolutionary
view of the Earth through the acquisition of Earth Observation satellite data.
Satellites capture information over different spatial and temporal scales and
assist in understanding natural climate processes and in detecting and explaining
climate change.
Accurate Earth Observation data is needed to describe climate processes by
improving the parameterisations of different climate elements. One area of study
is clouds and aerosols, and their role and effects on radiation. Soil moisture, ocean
salinity and other elements that play key roles in climate are also studied. Earth
Observation data should be able to detect changes of climate elements that may
be indicators of climate change.
Algorithms to produce geophysical parameters from raw satellite observations
should go through selection processes or participate in intercomparison
programmes to ensure performance reliability. Geophysical parameter datasets,
obtained from satellite observations, should pass a quality control before they are
accepted in global databases for impact, diagnostic or sensitivity studies.
Calibration/Validation, “Cal/Val”, is the activity that endeavours to ensure that
remote sensing products are highly consistent and reproducible. This is an evolving
discipline that is becoming increasingly important as more long-term studies on
global change are undertaken, and new satellite missions are launched. Calibration
is the process of quantitatively defining the system responses to known,
controlled signal inputs. Validation is the process of assessing, by independent
means, the quality of the data products derived from the system outputs.
Agencies usually undertake calibration of their respective mission satellite
systems. However, to extend this beyond the commissioning phase is potentially
difficult. Thus, well-instrumented benchmark test sites and data sets for
calibration should be supported, particularly for land applications, to provide
calibration information to supplement/substitute for on-board calibration,
ensuring continuity and reliability to access their data with minimal delay.
| Fig 1) Different approaches to validation of low spatial resolution satellite remote sensing products.
Upper left: top of the atmosphere CERES shortwave (SW, purple dots) and longwave (LW, light blue dots) radiances together with Streamer radiative transfer code simulated radiances obtained from field campaign measurements
(dark blue dots). The agreement is good even considering the forward and backward radiances separately. Bottom left: Observation geometry of a CERES Programmable Azimuth Plane Scanning exclusively defined over the Valencia Anchor Station. The polar diagram shows the viewing zenith (VZA) and relative azimuth (RAA) angles. Right: Preparations for SMOS soil moisture product validation at a control area within the Valencia Anchor Station. The picture shows homogeneous environmental units defined according to the combinations of different land
uses and soil types present in the region. A picture of a soil moisture probe is shown over a matorral area. |
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Activities
The Climatology from Satellites Group is active in three complementary
research lines:
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Calibration of low spatial resolution remote sensing data and products in the
framework of GERB, SMOS, EPS/MetOp satellite missions. This programme
develops field campaign activities at the Valencia and the Alacant Anchor
Stations. We also develop methodologies using meteorological models to
interpolate/extrapolate 3D atmospheric fields of significant parameters. |
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Earth radiative balance studies in the framework of GERB, CERES, SEVIRI,
EarthCARE satellite missions. Development of Angular Dependence Models
(ADMs) for the derivation of integrated fluxes from the original satellite angular
radiance measurements, and taking into account the anisotropic characteristics
of the observed scene. A large database of simulated scenes under different
atmospheric conditions (cloud situations, aerosol types and concentrations,
temperature and humidity profiles,…) and surface types (ocean, land vegetated,
desert, snow,…) is being built using the Monte-Carlo photon transport algorithm
of the EarthCARE Simulator |
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The measurement of soil moisture with passive microwaves in the framework
of the SMOS mission. Microwave L-band characterisation of natural vegetation
(Mediterranean ecosystem species), thus contributing to the SMOS soil
moisture retrieval algorithm in collaboration with Dr. J.-P. Wigneron and Dr.
Kauzar Saleh, EPHYSE, INRA-Bordeaux, France. We have developed a network of
distributed soil moisture probes within the Anchor Stations that communicate
via radio with a PC-based ftp server. The final aim is to map soil moisture
content at SMOS pixel scale (about 30 x 30 km2) from the ground network
point measurements. The network will also be used for soil moisture validation
in hydrological and meteorological models |
The Valencia and the Alacant Anchor Stations
Anchor Stations are carefully selected locations at which instruments measure
quantities that are needed to run, calibrate or validate models and algorithms.
These are needed to quantitatively evaluate satellite data and convert it into
geophysical information. The instruments collect measurements of basic
quantities over a long timescale. Measurements are made of meteorological
and hydrological background data, and of quantities not readily assessed at
operational stations. Anchor Stations also offer infrastructure to undertake
validation experiments. These are more detailed measurements over shorter
intensive observation periods.
The Valencia Anchor Station is situated in a reasonably homogeneous area in the
region of Utiel-Requena Plateau (Valencia, Spain). Most of its surface is dedicated
to vineyards. Topographic slopes are below 15%, with differences below 300 m.
The region’s climate is continental with Mediterranean influence. Annual mean
temperature is about 13ºC and total annual precipitation about 400 mm.
The Alacant Anchor Station is situated in the region of Vinalopó Mitjà (Alacant, Spain), which is the most degraded agricultural part of the Valencia Community
Autonomous Region. Land use is similar to that in the Valencia Anchor Station,
with vineyards, Mediterranean matorral and shrubs and some dry winter
cereals. Topography is also flat with a slightly undulated terrain. The climate is
Mediterranean arid with annual average temperature about 15ºC and total annual
precipitation of about 250 mm.
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Fig. 2) Valencia and Alacant Anchor Stations
The Alacant Anchor Station undergoes a water stress shortage as compared to the Valencia Anchor Station. Monitoring and comparing meteorological parameters
and energy fluxes between both Stations will be significant to understanding interactions between desertification and climate. The high resolution MERIS image (22
March 2002) highlights a most suitable area in Europe for low-resolution satellite remote sensing instrument validation. |
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