Ponencia presentada en: III Congreso de la Asociación Española de Climatología “El agua y el clima”, celebrado en Palma de Mallorca del 16 al 19 de junio de 2002.This work was carried out in the
framework of the ESA-ESTEC contract no: 15949/02/NL/SF, and the Spanish National Space
Research Programme Project no: PNE-009/2001-C-03

Antolín Tomás, Carmen

Berger, Michael

Boutin, Jacqueline

Calvet, Jean-Christophe

Etcheto, Jacqueline

Ferrer, Ferran

Font, Jordi

Kerr, Yann

López Baeza, Ernesto

Main, Bruce E.

Miller, Jerry

Pellarin, Thierry

Saleh Contell, Kauzar

Simmonds, Lester

Wesson, Joel

Wigneron, Jean-Pierre

Wursteisen, Patrick

English

Ferrer i Marco, Ferran

Agencia Estatal de Meteorología

449THE EuroSTARRS-2001 AIRCRAFT CAMPAIGN OF THEEUROPEAN SPACE AGENCY IN SUPPORT OFTHE SMOS MISSIONErnesto LO´PEZ-BAEZA1 2, Michael BERGER3, Patrick WURSTEISEN3,Jean-Christophe CALVET4, Jacqueline ETCHETO5, Jordi FONT6, Yann KERR7,Jerry MILLER8, Jean-Pierre WIGNERON9, Lester SIMMONDS10,Carmen ANTOLI´N TOMA´S2, J. Ferran FERRER2, Kauzar SALEH CONTELL1,Jacqueline BOUTIN5, Thierry PELLARIN4, Joel WESSON8, and Bruce E. MAIN10(1) Universitat de Valencia, Facultat de Fı´sica. Departament de Termodina´mica Unidad deInvestigacio´n de Teledeteccio´n. Grupo de Climatologı´a desde Sate´lites C/ Dr Moliner, 50.Burjassot. 46100 Valencia. Tel.: +34.96.3983118, Fax: +34.06.3983385, Ernesto.Lopez@uv.es(2)Centro de Investigaciones sobre Desertificacio´n (CIDE), Valencia, Spain(3) ESTEC/ESA - Land Surfaces Unit, P.O. Box 299, 2200 AG Noordwijk, The Netherlands(4) Me´te´o France CNRM, 42 av G. Coriolis, 31057 Toulouse Cedex 1, France(5) LODYC, UPMC, 4 Place Jussieu. 75252 Paris Cedex 05, France(6) CMIMA-CSIC, Passeig Maritim, 37-39, 08003 Barcelona, Spain(7) CESBIO, 18 Avenue Edouard Belin. 31401 TOULOUSE CEDEX 4, France(8) NRL, Stennis Space Center, MS 39529. USA(9) INRA Bioclimatologie, B.P. 81, 33883 Villenave d’Ornon CEDEX , France(10) University of Reading. Department of Soil Science, United Kingdom1. INTRODUCTIONThe EuroSTARRS campaign of the European Space Agency (ESA) is an aircraft campaign de-signed to help scientists to prepare the SMOS (Soil Moisture and Ocean Salinity) Mission, whichwill be launched early in 2006 (Figure 1), to acquire global measurements of soil moisture andocean salinity which are two parameters that play a key role in the determination of climate. Be-sides getting data of these two quantities, scientists will be able to incorporate these measurementsin Numerical Prediction Models and Climate Models in order to significantly improve their anal-yses and predictions.The EuroSTARRS-2001 campaign took place from 17 to 23 November 2001 implying a totalnumber of six sites in Europe, between land surfaces of different nature and ocean surfaces. Theobjective of the campaign, as regards soil moisture estimation, was to investigate the effect of dif-ferent vegetated covers on the L-band passive microwave signal received at the STARRS (SalinityTemperature and Roughness Remote Scanner) sensor (Figure 2) under different observation an-gles. As far as ocean measurements are concerned, the objective was to measure the influenceof different meteorological parameters, among other wind speed, on the measurement of oceansalinity. The results of the campaign are of fundamental importance to finish the preparation ofthe algorithms that will permit the estimation of soil moisture content and ocean salinity from themicrowave measurements acquired from space, before the satellite is actually launched.450 E. LO´PEZ-BAEZA, M. BERGER, P. WURSTEISEN, J.C. CALVET, J. ETCHETO, J.FONT, Y.KERR, J. MILLER, J.P. WIGNERON, L. SIMMONDS, C. ANTOLI´N TOMA´S, J.F. FERRER, K.SALEH CONTELL, J. BOUTIN, T. PELLARIN, J. WESSON AND B.E. MAINFigure 1: Artist vision of the SMOS Mission.Figure 2: The STARRS sensor and a sketch of the measurement acquisition from the aircraft.Different land surface sites were selected in Europe from Nezer Forest in Les Landes (France), tostudy coniferous forests, Agre Forest near Toulouse (France), to study deciduous forests, the cityof Toulouse, to study urban environments, and an area of matorral and Mediterranean forests inthe Requena area (Valencia, Spain) (Figure 3).In the transit flight from France to Spain, the Dornier 228 aircraft from the German AerospaceCentre (DLR, Germany) (Figure 4) over flew an area of the Pyrenees to get some acquisitions topreliminary study the influence of topography on the brightness temperature.THE EUROSTARRS-2001 AIRCRAFT CAMPAIGN OF THE EUROPEAN SPACE AGENCY INSUPPORT OF THE SMOS MISSION451Figure 3: Land surface study areas, (in red), and ocean sites (in green).Figure 4: Dornier 228 aircraft from DLR holding the STARRS sensor (left), and detail of thetransit flight across the Pyrenees (right).The salinity sites were chosen, on the one hand, in the Bay of Biscay, around the French Gascognebuoy, to study the effect of strong changes in salinity from the coast to the inner part of theAtlantic Ocean, and on the other hand, around the Casablanca oil rig, near the end of the Ebroriver (Tarragona), to mainly study the effect of wind speed on the salinity measurements andinvestigate azimuth dependence effects (Figure 3).452 E. LO´PEZ-BAEZA, M. BERGER, P. WURSTEISEN, J.C. CALVET, J. ETCHETO, J.FONT, Y.KERR, J. MILLER, J.P. WIGNERON, L. SIMMONDS, C. ANTOLI´N TOMA´S, J.F. FERRER, K.SALEH CONTELL, J. BOUTIN, T. PELLARIN, J. WESSON AND B.E. MAIN2. THE STARRS INSTRUMENTThe STARRS instrument was provided by the Naval Research Laboratory (NRL, USA) and in-stalled onboard the Dornier aircraft. The radiometer measures the passive microwave radiationemitted by the land surface or the sea surface at a wavelength (L-band, 1,40-1,426 GHz) thatenables scientists to estimate the respective soil moisture content or sea surface salinity. In itsnormal operation mode, the radiometer measures six crosstrack beams simultaneously (Figure 2)and builds a 2-D image as the aircraft moves along track In addition to the L-band radiometer, anadir viewing C band radiometer (5-7 GHz) and a thermal infrared (TIR) 2-band radiometer canalso acquire data at the same time. The antenna was mounted at right angles to the direction offlight and tilted by 12o to acquire a wider range of incidence angles (Figure 5). This could sim-ulate SMOS angular observations which will have a maximum incidence angle of 55o. STARRSusually acquires six tracks of data along each flight track.Figure 5: Situation of the STARRS radiometer under the Dornier 228 fuselage.3. SCIENCE OBJECTIVESThe derivation of soil moisture (SM) and sea surface salinity (SSS) products from multi- angularSTARRS data will support the development of retrieval algorithms for SMOS. In addition theEuroSTARRS-2001 Campaign will provide other main benefits, as follows:The campaign will be a valuable opportunity to obtain datasets from multiple sites withdifferent surface characteristics. Subsequent analysis will help characterise the effects oflook angle on brightness temperature.The data collected for SSS analysis will provide information relating to the effect of per-turbing factors such as sea state and temperature.THE EUROSTARRS-2001 AIRCRAFT CAMPAIGN OF THE EUROPEAN SPACE AGENCY INSUPPORT OF THE SMOS MISSION453More specific scientific objectives are summarised in Table 1.Table 1: EuroSTARRS-2001 Scientific Objectives.VegetationCharacterise the τ (vegetation optical depth) / look angle relationshipsfor a range of vegetation typesValidate the proposed SMOS SM retrieval algorithms, especially in con-text with a wider range of vegetation typesEstimate specific multi-angular microwave signatures from low altitudeflights over different land cover types with varying wetness conditionsStudy the effect of topography on radiometric signal from homogeneousvegetation in areas of different topographyValidate the retrieval of mixed pixels through comparison of data ac-quired at low altitude with data acquired at high altitudeProvide data for a variety of forest types and variations within standsExplore the implications of mixed pixels for retrieving SM withinforested areasInvestigate the sensitivity of the retrieval algorithms to pixel size varia-tion resulting from multi-angle observationAcquire data from urban areas to investigate the emissions from differentland use classes and determine the impact of RFIOceansProduce SSS gradients by operating STARRS from the coast out to seaInvestigate azimuth dependence effects4. EUROSTARRS OPERATIONS4.1. CalibrationThe STARRS instrument is generally stable and relatively minor calibration activities are requiredto check the IR, L- and C-band sensors. A split window technique is employed to account foratmospheric variations.Calibration is best carried out at the start and at the end of the campaign. Considering the requiredinstrument integration time, the operating speed of the Dornier 228 and other factors, it was esti-mated that the size of calibration water bodies to be used need to be in the order of 2 km by 1 km.454 E. LO´PEZ-BAEZA, M. BERGER, P. WURSTEISEN, J.C. CALVET, J. ETCHETO, J.FONT, Y.KERR, J. MILLER, J.P. WIGNERON, L. SIMMONDS, C. ANTOLI´N TOMA´S, J.F. FERRER, K.SALEH CONTELL, J. BOUTIN, T. PELLARIN, J. WESSON AND B.E. MAINCalibration flights were made primarily down the long dimension of a water body (small lake),with some flights at right angles to this axis. This latter case is to ensure that all tilted antennacomponents receive emissions from the water at the same time. In situ measurements of laketemperature and an estimate of wind strength was made at the same time of the overflight. It isimportant that temperature measurements are representative of the lake and this is why they weretaken at a depth of 10cms. In order to avoid sun glint calibration flights were conducted duringhours of darkness, however, early morning and late afternoon were also accepted. Three lakeswere identified as being suitable for the calibration activities, namely:Sanguinet-Cazaux lake (near Nezer, Les Landes, site), N44 30.00 W1 10.00Lac de Rieume (near Toulouse), N43 25.02 E001 09.25Contreras Reservoir (near Valencia site), N39 33.560 W1 30.237During the first test flight in Germany, calibration activities were also conducted over the lake’Ammersee’. During the campaign, there was a calibration flight over the Lac de Rieume on 19November and over the Contreras Reservoir on 21 November (Figure 6).Figure 6: Sketch of the Dornier 228 flight lines over the Contreras Reservoir (Valencia Site) anddetail of the calibration measurement over the lake surface.4.2. Land Soil Moisture DataWhilst the STARRS antenna was fixed so as to image in the along track direction, STARRS ac-quires six parallel beams of data quasi-simultaneously. Table 2 shows the potential for data acqui-sition over land from a single flight line with the configuration selected for this campaign (antennawith 12o installation tilt relative to the horizontal).THE EUROSTARRS-2001 AIRCRAFT CAMPAIGN OF THE EUROPEAN SPACE AGENCY INSUPPORT OF THE SMOS MISSION455Table 2: Viewing angles available due to 12o tilt of STARRS antenna.STARRS Beam Identifier Incidence angle (with 12o shift)3L -26.5o2L -9.0o1L +5.5o1R +13.0o2R +34.0o3R +50.5oIn order to construct multi-angle data sets of individual pixels, multiple passes of the test site wererequired.Table 3 provides an example, based on the Valencia Site requirements, of the potential for acquir-ing multiple angle data from the STARRS instrument installed onboard the Dornier 228 (antennawith a 12 tilt). Note that pixels 6/7/8 are viewed in all possible angles at both altitudes.Table 3: Availability of different viewing angles for land sites.Pixel 1 2 3 4 5 6 7 8 9 10 11 12 13LineLow altitude (300m pixel):1 26.5 9 5.5 19.5 34 50.52 26.5 9 5.5 19.5 34 50.53 26.5 9 5.5 19.5 34 50.54 26.5 9 5.5 19.5 34 50.55 26.5 9 5.5 19.5 34 50.56 26.5 9 5.5 19.5 34 50.57 26.5 9 5.5 19.5 34 50.58 26.5 9 5.5 19.5 34 50.5High altitude (900m pixel):1 ...19.5 34 50.52 ...5.5 19.5 34 50.53 ....9 5.5 19.5 34 50.54 26.5 9 5.5 19.5 345 26.5 9 5.5 19.5...6 26.5 9 5.5...Figure 7 shows the realization of Table 3 over the Valencia Site both for the low- and the high-altitude flights.The specific objectives for the Valencia Site were:To acquire multi-angular observations over uniform vegetation covers within the observedpixel. The homogeneous vegetation types studied were matorral, vineyards (bare soil at thetime of the campaign), pine trees, almond trees and olive trees.456 E. LO´PEZ-BAEZA, M. BERGER, P. WURSTEISEN, J.C. CALVET, J. ETCHETO, J.FONT, Y.KERR, J. MILLER, J.P. WIGNERON, L. SIMMONDS, C. ANTOLI´N TOMA´S, J.F. FERRER, K.SALEH CONTELL, J. BOUTIN, T. PELLARIN, J. WESSON AND B.E. MAINTo acquire multi-angular observations over non-homogeneous pixels in order to be ableto validate scaling algorithms (disaggregation). The area was very much appropriate tocarry out multi-angular air observations from two different altitudes over non-homogeneouspixels (higher altitude pixels) resulting from the mixture of homogeneous vegetated surfacescorresponding to the lower altitude flights.Figure 7: Low altitude flight lines (left) and high altitude flight lines (right) drawn over a land usemap of the area at the scale 1:100,000.Due to the mountains close to the study area (Sierra de Juan Navarro) and because of safetyreasons, the low altitude flights (13 in total with a separation between them of 200m) could onlybe performed at an average altitude of about 600m, whereas the high altitude flights (4 in totalwith a separation between them of 500m) were performed at about 1800m (see Figure 7). Themeasurements were done near midday in order that the surface could change soil moisture contentvery little during the measuring time thus avoiding dew effect,The main interest of the Valencia Site measurements was, on the one hand, the acquisitions forthe first time over matorral and other Mediterranean ecosystem species, and to get to know thebehaviour of the emitted microwave signal as a function of the observation geometry, assumingdifferent soil moisture content degrees in the different surfaces observed. On the other hand, thedifferent homogeneous land uses were chosen in such a way that a number of them could begrouped in a mixed larger pixel for the high altitude observations, so that, to be able to analyseand study the effects of scaling changes, specifically the disaggregation of the complex signalacquired over the mixed pixel into the simple acquisitions of the low altitude homogeneous pixels(Figure 8).THE EUROSTARRS-2001 AIRCRAFT CAMPAIGN OF THE EUROPEAN SPACE AGENCY INSUPPORT OF THE SMOS MISSION457Figure 8: Left: Homogeneous pixels (in red, 300 x 300 m size) defined under the low altitudeflight lines, and mixed pixel (in blue, 900 x 900 m size) defined under the high altitude flight lines.Right: Detail of the mixed pixel containing some of the homogeneous pixels. M1, M2, and M3 arethe matorral pixels and P1 and P2 the pine tree pixels. The green dots indicate the exact positionof the sampling points located by GPS.Besides the aircraft acquisitions, the other important component of the campaign was the groundmeasurements performed over the different surface types, as reference for the STARRS measure-ments. Thus, in the land experiments, a complex deployment was displayed for the ground mea-surements of soil moisture content, vegetation parameters, radiative temperature (thermal) of thedifferent surfaces, surface roughness, stone percent cover, soil texture, etc. (Figure 9).4.3. Sea Surface Salinity DataGiven that the SMOS mission will be able to provide data with an up to 55o incidence angle,it was desirable to simulate this performance using STARRS. For the collection of SSS data theaircraft flew 10 circles of 1600 m radius, at an aircraft banking angle of 22o. This resulted in theacquisition of data with incidence angles from 0o up to 80o. These circular flights were performednear the buoys and the platform in order to maximize the benefit of the correlative measurements.To avoid problems associated with sun glint, flights collecting data over the sea took place aftersunset. Sunset was defined as being 30 minutes after the Sun had gone beneath the horizon.Over the Casablanca petrol platform and over the sea buoys placed near by, researchers from theBarcelona Institute of Oceanography measured wind velocity and sea surface temperature andsalinity at the same time that the Dornier 228 was getting the STARRS acquisitions over the area(Figure 10).458 E. LO´PEZ-BAEZA, M. BERGER, P. WURSTEISEN, J.C. CALVET, J. ETCHETO, J.FONT, Y.KERR, J. MILLER, J.P. WIGNERON, L. SIMMONDS, C. ANTOLI´N TOMA´S, J.F. FERRER, K.SALEH CONTELL, J. BOUTIN, T. PELLARIN, J. WESSON AND B.E. MAINFigure 9: Soil moisture content, alometric vegetation parameters, roughness and percent cover ofstones ground measurements (respectively, left to right and up to bottom).5. CONCLUSIONSThis paper is intended to give a general overview of the EuroSTARRS-2001 campaign, its motiva-tion, rationale and technical design. A description of the processing of the STARRS data acquiredduring this campaign, its analysis and preliminary results are given also in this book (SALEH etal., 2002).EuroSTARRS is one of the most complex campaigns ESA has ever organised. It was necessary tomake sure that various European ground teams coordinate. The effort dedicated to the campaignclearly reflects the importance of the two quantities under consideration, that is, soil moistureand ocean salinity, which should be better known in order to be able to improve forecasts andpredictions of the numerical meteorological and climate models.On the one hand, soil moisture levels determine health and vigour status of vegetation and play animportant role in the correct determination of evapotranspiration and run-off, thus influencing theTHE EUROSTARRS-2001 AIRCRAFT CAMPAIGN OF THE EUROPEAN SPACE AGENCY INSUPPORT OF THE SMOS MISSION459amount of solar radiation that is absorbed in the land surface. On the other hand, ocean salinity isdefinitely responsible for the ocean currents, main drivers of the global climate.The main scientific part of the work is presently being carried out, starting by the data processingand aiming at a deep analysis and interpretation of the results. The STARRS acquisitions are firstquality data and their geo-referencing is highly accurate: viewing angles were obtained within 1to 2 degrees, and the flight lines match almost perfectly to an accuracy of 5m. This should lead toa valuable data-base including several observation angles over the same pixels on the ground. Itis envisaged to study the effect of the under story, litter and the influence of the percentage stonecover within the observed area.The University of Valencia is collaborating with the Institut National de Recherche Agronomique(INRA) at Bordeaux and theCentre National de la RechercheMeteorologique (CNRM) at Toulousefor the analysis of the data set.Figure 10: Casablanca data acquisition by EuroSTARRS aircraft (A = Actinia Platform, C =Casablanca Platform). Right Transect followed by the Garcı´a del Cid research ship from theSpanish Research Council (CSIC) around the Casablanca and Actinia petrol platforms.6. ACKNOWLEDGMENTSThe added complexity of the Valencia Site measurements required the material and human helpfrom institutions that willingly and readily provided. The Climatology from Satellites Group andthe CIDE from the University of Valencia sincerely acknowledge the collaboration provided bythe Regional Ministry for Environment and VAERSA (Valenciana de Aprovechamiento Energe´ticode Residuos S. A.), by the Environment Section of the Town Hall of Valencia and its MunicipalFoundations of Parks and Gardens and of the School of Gardening and Landscape, the Jucar460 E. LO´PEZ-BAEZA, M. BERGER, P. WURSTEISEN, J.C. CALVET, J. ETCHETO, J.FONT, Y.KERR, J. MILLER, J.P. WIGNERON, L. SIMMONDS, C. ANTOLI´N TOMA´S, J.F. FERRER, K.SALEH CONTELL, J. BOUTIN, T. PELLARIN, J. WESSON AND B.E. MAINHydrological Council and the owners of the farms where most of the measurements took place(Coto Mangla.no). As far as the Valencia Site is concerned, this work was carried out in theframework of the ESA-ESTEC contract no: 15949/02/NL/SF, and the Spanish National SpaceResearch Programme Project no: PNE-009/2001-C-03.7. REFERENCESSALEH, K., CALVET, J.-C., WIGNERON, J.-P., PRIOR, J., and LO´PEZ-BAEZA, E. (2002):Microwave Radiometry For Soil Moisture Monitoring: Preliminary Results From The Eurostarrs-2001 Campaign (this book).

The EuroSTARRS-2001 aircraft campaign of the European Space Agency in support of the SMOS Mission

Lopez-Baeza, Ernesto

Kerr, Yann H.

Antolin Tomas, Carmen

Ferrer, J. Ferran

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The EuroSTARRS-2001 aircraft campaign of the European Space Agency in support of the SMOS mission

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The EuroSTARRS-2001 aircraft campaign of the European Space Agency in support of the SMOS Mission

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