[show abstract][hide abstract] ABSTRACT: COSMOS (Campaign for validating the Operation of Soil Moisture and Ocean Salinity), and NAFE (National Airborne Field Experiment) were two airborne campaigns held in the Goulburn River catchment (Australia) at the end of 2005. These airborne measurements are being used as benchmark data sets for validating the SMOS (Soil Moisture and Ocean Salinity) ground segment processor over prairies and crops. This paper presents results of soil moisture inversions and brightness temperature simulations at different resolutions from dual-polarisation and multi-angular L-band (1.4 GHz) measurements obtained from two independent radiometers. The aim of the paper is to provide a method that could overcome the limitations of unknown surface roughness for soil moisture retrievals from L-band data. For that purpose, a two-step approach is proposed for areas with low to moderate vegetation. Firstly, a two-parameter inversion of surface roughness and optical depth is used to obtain a roughness correction dependent on land use only. This step is conducted over small areas with known soil moisture. Such roughness correction is then used in the second step, where soil moisture and optical depth are retrieved over larger areas including mixed pixels. This approach produces soil moisture retrievals with root mean square errors between 0.034 m3 m− 3 and 0.054 m3 m− 3 over crops, prairies, and mixtures of these two land uses at different resolutions.
[show abstract][hide abstract] ABSTRACT: Snow cover appears as a key indicator in climate change, and the ability to remotely measure the physical properties of snow is of vital importance. Current model-based approaches used to interpret satellite and airborne data need much stronger experimental confirmation. PolInSAR is a promising emerging technique for the measurement of snow depth. It exploits the polarisation dependence of scattering mechanisms to estimate scattering phase centre heights, which can be extrapolated to retrieve snow depth. Both modelling work and previous experimental campaigns indicate that the X and Ku-bands are particularly suited for retrieving the physical properties of a snow pack as they are sensitive to both the surface and volume characteristics. However, no comprehensive assessment of the operational potential and limitations of PolInSAR are yet available for snow. This work investigates the conditions under which PolInSAR produces accurate results with respect to snow parameters such as structural features and metamorphic state, as well as technical sensor specifications. A field study of the PolInSAR X- and Ku-band response of alpine snow was carried out with the UKÂ¿s Ground-Based SAR (GBSAR) system in a measurement campaign in the Austrian Alps during early 2007. Complementary detailed snow state and structural parameters were also recorded, as well as environmental meteorological data. A brief outline of the experimental technique is presented, and an example of an interferometric product.
Synthetic Aperture Radar (EUSAR), 2008 7th European Conference on; 07/2008
[show abstract][hide abstract] ABSTRACT: The Soil Moisture and Ocean Salinity (SMOS) mission is a joint ESA-CNES (F)-CDTI (E) mission within the ESA Living Planet Program, and it was the second ESA Earth Explorer Opportunity Mission to be selected. The mission objectives of SMOS are to provide soil moisture and ocean salinity observations for weather forecasting, climate monitoring, and the global freshwater cycle. This paper will describe the scientific campaigns performed to date, as well as the plans for the on-orbit calibration and validation activities.
IEEE Transactions on Geoscience and Remote Sensing 04/2008; · 3.47 Impact Factor
[show abstract][hide abstract] ABSTRACT: The retrieval of snow parameters, and snow water equivalent in particular, are key parameters in hydrology and climate research. Theory, ground-based signature research and analysis of spaceborne scatterometry suggests that the high- frequency combination of Ku- and X-band active microwave sensors is an excellent tool for the retrieval of snow physical properties. In order to validate this, a snow measurement campaign was carried out with the University of Cranfield's portable Ground-Based Synthetic Aperture Radar (GB-SAR) System during the winter of 2006/7 at two test-sites in the Austrian Alps close to Innsbruck. Fully polarimetric X-and Ku-band backscatter signatures were acquired over a range of incidence angles (~20deg-70deg), with the active sensor operating predominately in SAR mode, but occasionally also in InSAR mode. Microwave signatures and snow properties were measured on seven different dates. Detailed complementary meteorological and snow metamorphic conditions were also recorded.
[show abstract][hide abstract] ABSTRACT: The CoSMOS (Campaign for validating the Operation of the Soil Moisture and Ocean Salinity mission) campaign was conducted during November of 2005 in the Goulburn River Catchment, in SE Australia. The main objective of CoSMOS was to obtain a series of L-band measurements from the air in order to validate the L-band emission model that will be used by the SMOS (Soil Moisture and Ocean Salinity) ground segment processor. In addition, the campaign was designed to investigate open questions including the Sun-glint effect over land, the application of polarimetric measurements over land, and to clarify the importance of dew and interception for soil moisture retrievals. This paper summarises the campaign activities, and presents progress on the analysis of the CoSMOS data set.
[show abstract][hide abstract] ABSTRACT: Three atmospheric-chemistry sensors form part of the ENVISAT payload that has been placed into orbit in March 2002. This paper will discuss the validation aspects of these instruments. Although the main validation phase for the atmospheric instruments of ENVISAT will be completed soon, ongoing validation products will continue throughout the lifetime of the ENVISAT mission. The long-term validation phase will: -Provide assurance of data quality and accuracy for applications such as climate change research -Investigate the fully representative range of geophysical conditions -Investigate the fully representative range of seasonal cycles -Perform long term monitoring for instrumental drifts and other artefacts -Validate new products.
[show abstract][hide abstract] ABSTRACT: Soil Moisture and Ocean Salinity (SMOS) is an Earth Explorer Opportunity Mission from the European Space Agency with a launch date in 2007. Its goal is to produce global maps of soil moisture and ocean salinity variables for climatic studies using a new dual-polarization L-band (1400-1427 MHz) radiometer Microwave Imaging Radiometer by Aperture Synthesis (MIRAS). SMOS will have multiangular observation capability and can be optionally operated in full-polarimetric mode. At this frequency the sensitivity of the brightness temperature (T<sub>B</sub>) to the sea surface salinity (SSS) is low: 0.5 K/psu for a sea surface temperature (SST) of 20°C, decreasing to 0.25 K/psu for a SST of 0°C. Since other variables than SSS influence the T<sub>B</sub> signal (sea surface temperature, surface roughness and foam), the accuracy of the SSS measurement will degrade unless these effects are properly accounted for. The main objective of the ESA-sponsored Wind and Salinity Experiment (WISE) field experiments has been the improvement of our understanding of the sea state effects on T<sub>B</sub> at different incidence angles and polarizations. This understanding will help to develop and improve sea surface emissivity models to be used in the SMOS SSS retrieval algorithms. This paper summarizes the main results of the WISE field experiments on sea surface emissivity at L-band and its application to a performance study of multiangular sea surface salinity retrieval algorithms. The processing of the data reveals a sensitivity of T<sub>B</sub> to wind speed extrapolated at nadir of ∼0.23-0.25 K/(m/s), increasing at horizontal (H) polarization up to ∼0.5 K/(m/s), and decreasing at vertical (V) polarization down to ∼-0.2 K/(m/s) at 65° incidence angle. The sensitivity of T<sub>B</sub> to significant wave height extrapolated to nadir is ∼1 K/m, increasing at H-polarization up to ∼1.5 K/m, and decreasing at V-polarization down to -0.5 K/m at 65°. A modulation of the instantaneous brightness temperature T<sub>B</sub>(t) is found to be correlated with the measured sea surface slope spectra. Peaks in T<sub>B</sub>(t) are due to foam, which has allowed estimates of the foam brightness temperature and, taking into account the fractional foam coverage, - the foam impact on the sea surface brightness temperature. It is suspected that a small azimuthal modulation ∼0.2-0.3 K exists for low to moderate wind speeds. However, much larger values (4-5 K peak-to-peak) were registered during a strong storm, which could be due to increased foam. These sensitivities are satisfactorily compared to numerical models, and multiangular T<sub>B</sub> data have been successfully used to retrieve sea surface salinity.
IEEE Transactions on Geoscience and Remote Sensing 05/2004; · 3.47 Impact Factor
[show abstract][hide abstract] ABSTRACT: A number of experiments using ground-based and airborne sensors have shown the high potential of L-band passive microwave radiometry for estimating and monitoring surface soil moisture. This has led to the Soil Moisture and Ocean Salinity (SMOS) mission, a European Space Agency (ESA) Earth Explorer Opportunity mission. SMOS has the objective to observe soil moisture over land and sea surface salinity over sea, both key parameters for atmospheric, oceanographic and hydrological predictive models. In preparation of SMOS, the EuroSTARRS airborne campaign was carried out in November 2001. Multi-angular measurements of the surface brightness temperature at L-band (1.4 GHz) at vertical polarization were acquired by the ‘Salinity Temperature and Roughness Remote Scanner’ (STARRS) radiometer from the Naval Research Laboratory (NRL, USA) over several sites in Southern France, the Pyrenees and Eastern Spain. The chosen sites represent specific land conditions and vegetation canopies where microwave surface emission models need further investigation, and include: dense forests, shrubs and scrubland, mixed areas of different vegetation covers and areas with variable topography. This paper gives an overview of the experiment, including a discussion of the objectives, description of the sites, details of the microwave measurements and some first results of the campaign. First, a principal component analysis of the forest brightness temperature measured at different configurations illustrates the sensitivity of brightness temperature to biomass conditions for coniferous trees. Then, the microwave signature of the vegetation covers considered in this study—coniferous forest at Les Landes (France), mixed deciduous/coniferous stands at the Agre forest (France), shrubland, vineyards and orchards at the Valencia site (Spain)—is illustrated, in particular as regards to the dependence of the L-band emissivity to biomass conditions.
International Journal of Remote Sensing 01/2004; 25(1):177-194. · 1.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: horizonal (H) polarization up to 0.5 K/(m/s), and decreasing at vertical (V) polarization down to 0.2 K/(m/s) at 65 incidence angle. The sensitivity of to significant wave height extrapolated to nadir is 1 K/m, increasing at H-polarization up to 1.5 K/m, and decreasing at V-polarization down to 0.5 K/m at 65 .A modulation of the instantaneous brightness temperature is found to be correlated with the measured sea surface slope spectra. Peaks in are due to foam, which has allowed estimates of the foam brightness temperature and, taking into account the frac- tional foam coverage, the foam impact on the sea surface brightness temperature. It is suspected that a small azimuthal modulation 0.2-0.3 K exists for low to moderate wind speeds. However, much larger values (4-5 K peak-to-peak) were registered during a strong storm, which could be due to increased foam. These sensitivities are satisfactorily compared to numerical models, and multiangular data have been successfully used to retrieve sea surface salinity.
IEEE T. Geoscience and Remote Sensing. 01/2004; 42:804-823.
[show abstract][hide abstract] ABSTRACT: 1] Soil moisture and ocean salinity at surface level can be measured by passive microwave remote sensing at L-band. To provide global coverage data of soil moisture and ocean salinity with three-day revisit time, the Earth Explorer Opportunity Mission SMOS (Soil Moisture and Ocean Salinity) was selected by ESA (European Space Agency) in May 1999. SMOS single payload is a Y-shaped 2-D aperture synthesis interferometric radiometer called MIRAS (Microwave Imaging Radiometer by Aperture Synthesis). SMOS presents some particular imaging peculiarities: variation of incidence and azimuth angles, different radiometric sensitivity and accuracy at each direction (pixels), and geometric polarization mixing. Therefore, the accuracy of the geophysical parameter retrieval depends on the knowledge of the angular dependence of the emissivity over a wide range of incidence and azimuth angles. The accuracy of the sea surface salinity retrievals depends on our capability to correct the wind-induced variation of the brightness temperatures. To better understand wind effects, ESA sponsored the WInd and Salinity Experiment 2000 (WISE-2000) from November 15, 2000, to January 16, 2001, in the Casablanca oil rig, at 40 km off the coast of Tarragona (Spain). This paper is divided into two parts. First, it presents the derived sensitivities of the brightness temperatures at vertical and horizontal polarizations with wind speed, and compares to Hollingers measurements and numerical simulations. Second, these results are applied to the SMOS sea surface salinity (SSS) retrieval problem for different tracks within the swath. It is shown that, except for low SSS and sea surface temperature (SST), the retrieved SSS has a RMS error of approximately 1 psu in one satellite pass. Citation: Camps, A., et al., L-band sea surface emissivity: Preliminary results of the WISE-2000 campaign and its application to salinity retrieval in the SMOS mission, Radio Sci., 38(4), 8071, doi:10.1029/2002RS002629, 2003.
[show abstract][hide abstract] ABSTRACT: Envisat is ESA's advanced Earth observing satellite launched in March 2002 and is designed to provide measurements of the atmosphere, ocean, land and ice over a five-year period. After the launch and the switch-on period, a six-month commis-sioning phase has taken place for instrument calibration and geophysical validation, concluded with the Envisat Calibration Review held in September 2002. In addition to ESA and its industrial partners in the Envisat consortium, many other companies and research institutes have contributed to the calibration and validation programme under ESA contract as expert support laboratories (ESLs). A major contribution has also been made by the Principal Investigators of approved proposals submitted to ESA in response to a worldwide "Announcement of Opportunity for the Exploitation of the Envisat Data Products" in 1998. Working teams have been formed in which the different participants worked side by side to achieve the objectives of the calibration and validation programme. Validation is a comparison of Envisat level-2 data products and estimates of the differ-ent geophysical variables obtained by independent means, the validation instruments. Validation is closely linked to calibration because inconsistencies discovered in the comparison of Envisat Level 2 data products to well-known external instruments can have many different sources, including inaccuracies of the Envisat instrument calibration and the data calibration algorithms. Therefore, initial validation of the geophysical variables has provided feedback to calibration, de-bugging and algorithm
[show abstract][hide abstract] ABSTRACT: Sea surface salinity can be measured by passive microwave remote sensing at L-band. In May 1999, the European Space Agency (ESA) selected the Soil Moisture and Ocean Salinity (SMOS) Earth Explorer Opportunity Mission to provide global coverage of soil moisture and ocean salinity. To determine the effect of wind on the sea surface emissivity, ESA sponsored the Wind and Salinity Experiment (WISE 2000). This paper describes the field campaign, the measurements acquired with emphasis in the radiometric measurements at L-band, their comparison with numerical models, and the implications for the remote sensing of sea salinity.
IEEE Transactions on Geoscience and Remote Sensing 11/2002; · 3.47 Impact Factor
[show abstract][hide abstract] ABSTRACT: The US Salinity Temperature and Roughness Remote Scanner (STARRS) was exploited during an European campaign in 2001 (EuroSTARRS) supporting the scientific preparation of the Soil Moisture and Ocean Salinity (SMOS) mission. This paper is intended to introduce the EuroSTARRS experiment set-up and to provide an overview of all activities performed during this campaign.
[show abstract][hide abstract] ABSTRACT: Part of ESA's Earth Observation Envelope Programme (EOEP) is intended to advance our understanding of the various processes occurring in the Earth's biosphere/geosphere, and their interactions with the atmosphere. Thus, the Programme's `Theme 3: Geosphere/Biosphere' focusses on the modelling and monitoring of land-surface processes, the study of interactions, and the analysis of climate impacts on the biosphere, with the objective of enhancing our skills in predicting the evolution of the Earth system. Real-life applications such as weather forecasting, crop-yield estimation, precision farming, the management of renewable and non-renewable resources, as well as environmental-hazard monitoring/forecasting, would all benefit from improved process model descriptions. A spaceborne scientific mission addressing the provision of information on geospheric/biospheric processes and their interactions with the atmosphere is currently being formulated. This mission implies the need for an instrument with high spectral and angular resolution and a very high radiometric performance, operating in the reflective and thermal parts of the spectrum, not only to identify but also to quantify the key variables driving the processes.
[show abstract][hide abstract] ABSTRACT: In the framework of the preparation of a future spaceborne Land Surface
Processes mission, the European Space Agency (ESA) has carried out the
airborne campaigns DAISEX (Digital Airborne Imaging Spectrometer
Experiment), to demonstrate the retrieval of key biophysical variables
from hyperspectral/multiangular observations covering the spectral range
from the visible to the thermal infrared. To provide the required
spectral information, several available instruments were used: DAIS,
HYMAP, ROSIS and POLDER. Since no sensor exists providing the required
spectral information with multiangular capabilities, a combination of
strategies was used to get adequate multiangular information. Several
angular views are available for each ground point using POLDER and
wide-angle field-of-view hyperspectral sensors such as HyMAP, and flying
several lines for different solar elevations along and across the solar
principal plane. Flight lines and flight times were carefully selected
to acquire data in hot-spot and darkspot viewing configurations in order
to maximise angular information and to cover the maximum range of
illumination/viewing angular conditions. Corresponding in-situ data were
acquired simultaneously to each flight. Information extraction
techniques from the hyperspectral/multiangular datasets are described,
and the different role of the spectral and angular information is
discussed in the context of the retrieval of biophysical variables,
where both spectral and angular information play a complementary role in
[show abstract][hide abstract] ABSTRACT: The WISE 2000 and WISE 2001 field campaigns were sponsored by ESA to gather experimental data to improve the knowledge of the L-band brightness temperature dependence with wind speed at different incidence angles and azimuth angles. The goal is to help the development of sea surface salinity retrieval algorithms for SMOS Earth Explorer Mission of the European Space Agency. The L-band AUtomatic RAdiometer (LAURA) plus other sensors to characterize the sea surface state were installed at the Casablanca oil rig, 40 km south east off the coast of Tarragona in Spain. During WISE 2000 wind conditions were low-to-moderate, but during WISE 2001 two strong storms beat the Catalonian coast with sustained winds higher than 100 km/h at the platform meteorological station (69 m height). The first results of the radiometric measurements (azimuth and elevation scans) acquired with LAURA during the WInd and Salinity Experiment (WISE-2001) are presented.