r bulletin 105 — february 2001

Highlights of the ERS-Envisat Symposium2000– The Achievements of ESA’s Earth ObservationProgramme

Y-L. Desnos, S. Rémondière*, C. Zehner, J. Benveniste & M. Doherty Exploitation Development and Project Division, ESA Directorate of ApplicationProgrammes, ESRIN, Frascati, Italy

E. Attema, G.Levrini* & M.Borgeaud **Earth Sciences Division, Envisat System and Payload Division* andElectromagnetics Division**, ESA Directorate of Application Programmes, ESTEC, Noordwijk, The Netherlands

IntroductionThe Gothenburg Symposium provided an idealopportunity to review the European RemoteSensing Satellite (ERS) Programme’s achieve-ments in terms of both science andapplications after close to ten years of satellitedata exploitation. In addition, it provided atimely opportunity to review the imminent

Envisat mission, its data products, and theapproaches being applied to calibration andvalidation. The Symposium’s ScientificCommittee, composed of eminent scientistsand ESA experts, had evaluated 460 submittedAbstracts in establishing the final programme.Following the themes of the EnvisatAnnouncement of Opportunity, they groupedthe accepted contributions into 42 Sessions(Figs. 1 and 2). Each session was chaired by aleading scientist in that particular field ofapplication, and co-chaired by an ESA Earth-observation expert.

This article presents a summary of thehighlights of the Symposium, grouped underthe themes of Atmosphere, Land, Ocean and

The ERS-Envisat Symposium ‘Looking Down to Earth in the NewMillennium’ – organised by ESA and hosted by Chalmers University ofTechnology – took place in Gothenburg, Sweden, from 16 to 20October 2000. This was the fourth ERS Symposium (after Cannes in1992, Hamburg in 1993 and Florence in 1997) and the first EnvisatSymposium, and it was open to all interested parties, from scientiststo operational commercial users and service providers. It provided the540 participants with an opportunity to familiarise themselves with thecurrent status of ERS applications and the capabilities of the follow-on Envisat mission now being readied for launch in mid-2001, and toprovide feedback from their own particular domains.

* SERCO SpA support toESRIN, Frascati, Italy

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Methods

Geodesy

Envisat

Coastal zones

Performances

Land Surface

Temperature Ice

Hydrology Renewable Resources

Sea Surface Temperature

Geology and

Hazards

Oceanography

Topography Atmosphere

Services and Market

Figure 1. Overview of the Symposium content

Figure 2. Overview of the Symposium participation

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Figure 3. GOME ozoneprofiles retrieved within 3 hfrom one ERS orbit on 5 October 2000 (courtesy of RoyalNetherlands MeteorologicalInstitute)

Atmospheric constituentsOwing its nadir-viewing geometry, GOMEprovides the possibility to measure atmosphericconstituents both in the troposphere and in thestratosphere. Formaldehyde (HCHO) in thetroposphere could be retrieved for the first timeon a global scale from space. The detectionand the monitoring of SO2 emissions due tovolcanic events/industrial pollution and NO2

emissions due to biomass burning/industrialpollution extracted from experimental retrievalalgorithms down to the troposphere has beendemonstrated. This newly-gained capability ofobserving tropospheric trace-gas distributionsis a revolutionary step in terms of technicaldevelopment and will lead to a significantenhancement of our ability to investigate the chemistry and physics of the troposphere(Fig. 4).

Minor trace gases, like BrO in the troposphereor OClO activation in the stratosphere,responsible for ozone depletion have beensuccessfully retrieved from GOME measure-ments, providing greater insight into ozonechemistry (Fig. 5).

Global maps of the H2O column above oceansand land have been retrieved. In the future, atropospheric profile with limited spatialresolution will also be available. The feasibility ofgenerating global and regional UV radiationmaps was demonstrated. In combination withassimilation models, this will facilitate future UVforecasting services.

Algorithms for the retrieval of various types ofcloud and aerosol information are increasinglybased on instrument synergy. New cloudalgorithms were presented for extracting cloud

Envisat. The detailed summaries andrecommendations prepared by the chairs andco-chairs of each Session are being publishedin the Symposium Proceedings (ESA SP-461,available from ESA Publications Division).

Highlights of the Atmosphere Session

“A Growing Community using GOME Data”

A total of 58 presentations (34 papers and 24posters) were dedicated to the demonstrationof scientific and application achievements byusing the data from the ERS-2 Global OzoneMonitoring Experiment (GOME) instrument.GOME, a forerunner of future Europeanatmospheric satellite instruments, is still theonly spaceborne spectrometer capable ofobserving the entire spectral range from 240 to 790 nm with high spectral resolution. Thepresentations covered the retrieval of ozone,UV radiation, trace gases other than ozone, the characterisation of cloud and aerosolinformation, calibration and data assimilationtechniques.

OzoneGOME total ozone measurements were usedto detect a mini ozone hole over northwesternEurope on 30 November 1999, and to observethe deepest ozone hole ever over Antarctica inthe third quarter of 2000. Besides the totalozone, ozone profiles are derived from theGOME spectra to provide height-dependentozone information down to the Earth’s surface.Improved processing schemes have demon-strated the possibility to provide this informationto users in near-real-time, so that it can be usedto support measurement campaigns and forassimilating ozone data into numericalforecasting models (Fig. 3).

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Figure 4. Regionalyearly maps of nitrogen

dioxide from GOME,showing air pollutionfrom emissions over

industrial areas(courtesy of Univ. of

Bremen)

Figure 5. Monthly GOMEbromine monoxide mapover the North Pole for

March 2000, showingtropospheric BrO plumes

(courtesy of Belgian Institutefor Space Aeronomy)

fraction and cloud-top height from GOME,Sciamachy and ATSR. Meteorological instituteshave evaluated sample products. Furtherinvestigations will require the refinement of thedefinition of cloud parameters, and consolidationof libraries of aerosol classes, in order to simplifycomparisons between different instrumentsand techniques

ServicesAn important issue has been the setting up ofnew data-delivery services in addition to theexisting offline operational processing at the

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D-PAF, developed by DLR (http://auc.dfd.dlr.de/GOME/index.html). This currently producescalibrated spectra, total column amounts of O3

and NO2, as well as cloud information availableto users on CDs or via an ftp server. The fast-delivery service at KNMI provides global totalozone column, ozone profiles, and cloudinformation to users within three hours afterobservation (http://www.knmi.nl/gome_fd/). Aservice has been set up by the University ofBremen (supported by ESA and DLR) toprovide preliminary GOME data (e.g. ozoneprofiles, OClO, BrO, etc.) in near-real time. Thisservice supports international measurementcampaigns for investigating stratospheric

ozone at mid- and high latitudes in theNorthern Hemisphere in springtime (http://

www. iup.physik.uni-bremen.de/gomenrt2000/).

New radiative transfer models,generating simulated backscatterintensities and weighting functions,have been developed and applied toimprove GOME retrieval algorithms(e.g. Air Mass Factor calculation).

GOME data assimilationOwing to the high variability of the

atmosphere, the generation of global mapsof trace gases is not a trivial task. Assimilation

models (e.g. 4-D VAR) are taking into accountthe movement of the measured trace gas dueto wind fields related to different heights, and itsdependence on the actual chemical state of theatmosphere. It was demonstrated that by usingGOME ozone measurements such a tool isable to propagate information into regionswhere there are no measurements, thusproducing a consistent picture of the entireglobe. Furthermore, reliable ozone forecastingover a time period of about 5 days has beendemonstrated.

All of the experience that has been gained inthe exploitation of GOME data can be directlyapplied to the use of the future Europeanatmospheric instruments on Envisat: GOMOS,MIPAS and Sciamachy.

BrO VC[x1013 molec/cm2]

>8

7

6

5

4

3

2

<1

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Figure 6. Three-track mosaiccovering the 170 km-longsection of the fault thatruptured during the Manyiearthquake (Tibet) on 8November 1997 (courtesy ofJet Propulsion Laboratory)

show the considerable potential of remotesensing.

Some limitations of the SAR interferometrictechnique may be overcome by the emergingPermanent Scatterers technique pioneered byPolitecnico di Milano, which is ready to be usedin pre-operational applications where a longtime-series of SAR images is available for thearea of interest (Fig. 7).

Forest mappingERS InSAR (tandem coherence 1-day)products were shown to be an excellent Earth-observation product for forest/non-forestdelineation. It was also shown that for somespecial meteorological conditions, ERScoherence is also correlated with the borealforest stem volume. An extensive example waspresented from the SIBERIA project (SARImaging for Boreal Ecology and RadarInterferometry Applications), which aimed tomap the central-Siberian forest using threeEarth-observation radar satellites. This was a

joint effort by the German Aerospace Centre(DLR), ESA, and the Japanese Space Agency(NASDA) to collect ERS-1 and -2 and JERS-1data via a mobile receiving station located inMongolia. More than 550 ERS scenes and 890JERS-1 scenes were used to demonstrate thesemi-operational use of radar remote sensingfor very-large-area forest mapping. The finalresults, derived from ERS-1/ERS-2 tandemcoherence and JERS intensity, include geo-referenced maps with six land classes, three ofwhich indicate different levels of timber volume(Fig. 8).

Damage assessmentERS coherence derived using the tandem datawas revealed to be an excellent tool for

Highlights of the Land Session

“A Wide Range of Land Applications”

The widespread use of space-based Earthobservation over land – in particular the use ofERS SAR/InSAR data, – was demonstrated bythe large number of presentations in thisSession (131 papers). The tandem exploitationof the ERS-1 and ERS-2 satellites (1 day repeatcycle) has provided a unique data set for thedevelopment of the repeat-pass interferometry(InSAR) technique.

Seismic studiesSAR interferometry (InSAR) has allowedscientists to obtain surface-displacement mapsand to construct complex fault models thatcould not be generated from seismologicaldata and conventional geodetic techniquesalone. SAR data have been a primary source ofinformation after earthquakes in remote areaswhere little or no in-situ information wasavailable, such as Western China, Iran andTibet. Research is in progress to overcome theloss of coherence in the vicinity of the surfacerupture. A major development has been thesuccessful use of InSAR data to studyinterseismic deformation, the averaging ofseveral interferograms allowing a detectionlevel of better than 1 mm/year in line-of-sightchange (Fig. 6).

Volcano monitoringA number of attempts based on the processingof InSAR archived data have been made tomonitor volcanic deformation. One of theexamples, the computation of a series ofdifferential interferograms has shown thedeformation on the surfaces of four volcanoesin Alaska over several multi-year intervals in the1990s.

LandslidesThe Symposium also illustrated the state of artof SAR applications for landslide mapping andmonitoring, focussing particularly on surfacecharacterisation and the measurement of slowslope movements by means of SARinterferometry. ERS-1/ERS-2 tandem datasets, as well as 35-day repeat interferometricdata sets, have helped to map landslides.

Land subsidenceThe technique of SAR differential interferometryhas been used for the monitoring ofsubsidence created by water/oil pumping,mining and excavation. Subsidence ratesranging from millimetres to more than 1 m peryear have been observed. GPS measurementsand mathematical models were used tovalidate the measurements. The results clearly

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Figure 7. Subsidence mapof the Los Angeles areaobtained by applying thePermanent Scattererstechnique to 56 ERSimages. It shows theaverage subsidence rate,due mainly to oil/gasextraction, water pumpingand seismicity, over theperiod 1992 to 1999. Thecolour scale indicatesmotion of up to 5mm/yr withan accuracy of better than1mm/year (courtesy ofPolitecnico di Milano, TRE)

Figure 8. Mosaic imageshowing forest stem volumeand land use in the Siberian

forest, derived from ERS-1/ERS-2 tandem coherence

and JERS intensity(courtesy of EU CEO

Project, SIBERIA)

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Figure 9. Storm-damagemap of Switzerland, fromwinter 1999/2000, derivedfrom ERS SAR tandemcoherence combined with a Landsat TM image asbackground. Forested areasare in green and damagedforest areas are in red(courtesy of GammaRemote Sensing, SpotImage, Swiss FederalInstitute of TechnologyZurich, and SERTIT)

Figure 10. Flood-extensionmap of a portion of theRiver Meuse (F), which wassubject to flooding in1993/94 (blue) and 1995(cyan). The map wasgenerated from a multi-temporal combination ofERS SAR images (courtesyof SERTIT)

had already been demonstrated in the past. Amajor step towards operational monitoring hasbeen the development of user tools and thetransfer of knowledge to users. Algorithms andprocessing chains have been set up for ricemapping and yield prediction. It is now possibleto achieve mapping within a few days aftersatellite data acquisition. Future developmentswill focus on methodological refinements forlarge-scale mapping and data assimilation intocrop-growth models.

Snow mapping and snow-melt runoffTime sequences of ERS SAR data have beenincorporated into an automatic classificationalgorithm to generate precise snow maps.These maps have then been appliedsuccessfully for accurate real-time forecastingof snow-melt run-off in mountainous areas,confirming the high operational potential of thistechnique (Fig. 11).

mapping burnt areas (Canada andMadagascar) and for assessing forestdamage due to storms (Switzerland).The examples presented illustrated thatthis approach has potential for servicedevelopment (Fig. 9).

Flood mapping and soil-parameterretrievalThe flood-application presentationsdemonstrated the contribution that ERSSAR data can make to the developmentof an operational flood-managementinformation system. It has been shownthat it is possible to produce SAR-based flood-extent maps. The synergyof using SAR-based flood-extent mapswith Very High Resolution (VHR) opticaldata for the production of precise Land-Use Maps brings a significantimprovement in terms of damageassessment and provides valuableinformation for the visualisation of the flooddamage (Fig. 10). In addition, historical series ofERS SAR data are proving to be an essentialinformation source for flood prevention and areserving as reference data for the elaboration offlood-prevention plans.

The use of multi-polarisation SAR data for soil-roughness assessment was presented, alongwith a promising technique for retrievingroughness from ASAR data. The use of spatialmodels of soil-vegetation-atmosphere (SVAT)processes, based on realistic-vegetationgrowth models, has been successfully appliedfor retrieving the soil moisture beneathvegetation.

Rice mapping and monitoringRice-crop mapping and monitoring appears tobe one of the main agricultural applications forERS SAR data. Its potential for this application

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Figure 11. Snow mapgenerated from ERS SAR

ascending and descendingimages. The snow extent on

1 May 2000 is in blue andgreen, that on 6 June 2000

is in green, and areas whereno information could be

retrieved are in yellow(courtesy of Univ. of

Innsbruck and SCEOS)

Figure 12. Temporalsequence of geocoded

displacement maps of aglacier in Svalbard (24 km x45 km). The magnitude d (in

m/day) of the three-dimensional displacement

rate is shown with thefollowing colour scale:

d < 0.1 cyan, 0.1 < d < 0.4yellow, 0.4 < d < 0.7 green,0.7 < d < 1 red, 1< d < 1.3

violet, d > 1.3 blue (courtesyUniv. of Wales, Gamma

Remote Sensing, Univ. ofLeeds)

Ice mappingThanks to the combination of data from ERS’sInSAR and Radar Altimeter, changes are beingdetected after several years of observation inthe glaciers in West Antarctica. The benefit ofreliable time series of data for monitoring thesubtle changes occurring in the polar ice sheetshas been amply demonstrated. An example waspresented for Svalbard in Norway, where asequence of interferograms over a glaciercovering a period from 1992 to 1998 showedthe complete cycle of a glacier surge, frominitiation through fast flow to quiescence (Fig. 12).

TopographyThe generation of accurate height measure-ments from both the Radar Altimeter and SAR

for topography mapping continues to bedemonstrated for large areas. ERS RadarAltimeter ice-mode data were shown to provideaccurate terrain-height information (70% ofcross-over measurements agree to < 5 m). ADigital Elevation Model has been generated forthe whole of the British Isles, using ERStandem interferometry. The DEM generationprocess itself is fully automatic and the modelhas been validated as having a typical accuracyof 8–14 m rms. The resulting DEM is beingused successfully in both hydrological andgeological applications.

ERS tandem data have also been usedsuccessfully to produce a wide-area DEM forthe telecommunications sector in Switzerland.The customer has validated the product.

Highlights of the Ocean Session

“Development of New Services”

ESA Earth-observation data are being usedoperationally, and have been demonstrated tobe a valuable source of information, for coastal-zone mapping and monitoring.

Service developmentERS SAR data have been used to updatecoastal maps for areas where SHOM (FrenchMarine Mapping Agency) has mappingresponsibility. As an example, a 1:50 000 mapof the coastal region around Cayenne, in

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September 1991 October 1991 November 1991 February 1992 March1992

October 1997May 1996January 1996June 1995January 1994

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Figure 13. This sequence ofERS SAR images acquiredbetween 1992 and 1999shows the evolution of thecoastline in French Guiana,with displacements rangingfrom hundreds of metres toseveral kilometres (courtesy of University of Marne LaVallée)

temperature, and ocean colour. A newautomated method has been used to identifyRossby waves, a special class of planetarywaves, and calculate their phase speed.

Significant progress has been made in theclassification of different types of sea featurescommonly observed in SAR images (Fig. 15).The Norwegian Defence Research Establishmenthas been acquiring images along the coast ofNorthern Norway since the early days of theERS-1 mission. The continuous and long-termnature of their SAR image analysis for thecontinental shelf gives the possibility to assessthe signatures and observabilities of variousfeatures during the various seasons of the year.Quantitative information extraction is oftendependent on multi-sensor approaches usingSeaWiFS, AVHRR and/or combinations of SARdata with ocean models. Frequent coverage ofselected sites should be pursued to learn moreabout the variability of the features and theirsignatures in SAR images.

Wind and wavesScientific progress was demonstrated for wind-and wave-field retrieval from the three mainsensors – altimeter, scatterometer and SAR – inboth image and wave mode (Fig. 16).Altimeters have provided estimates of the windspeed and the significant wave height forpotential operational services. The Ocean andSea Ice Satellite Application Facility (OSI SAF

French Guiana, has already been issued bySHOM. Further work is in progress, includingan analysis of the legal implications inherent inthe use of Earth-observation data for chart andmap updating (Fig. 13).

The Dutch company ARGOSS has applied thebathymetry assessment system based on theuse of ERS SAR data in Indonesia. The averagemeasurement error was found to be around10 –11 cm. Discussions with business partnersare underway and it is expected to start fulloperations in 2001.

The Tromsø Satellite Station (TSS) in Norwayprovides an operational oil-spill detectionservice for customers from both governmentand offshore oil companies. This wasdeveloped using ERS and is based on joint useof Radarsat and ERS SAR imagery. Theavailability of Envisat is expected to make asignificant contribution to the service’scapability in terms of both update times andservice area covered. A change in legislation,which requires oil companies to undertakeenvironmental-monitoring activities, is expectedto add to demand for this service.

NOAA is presently demonstrating near-real-time services to a range of government users inAlaska, including the Department of Fisheriesand the National Weather Service. The presentservices cover coastal wind-field data andfishing-vessel surveillance based on Radarsat.It is planned to use ASAR data once Envisat islaunched and to expand the service providedto include sea/river ice monitoring and oil-spillsurveillance. About one year will be required toinvestigate the capabilities of ASAR before jointexploitation of ASAR and Radarsat is possible.

Ocean dynamicsThe Ocean Dynamics session demonstrated thatprojects are moving from instrument-capabilityto application demonstration. Results werepresented from a variety of missions (ERS,Topex Poseidon, GFO) as well as from differentinstruments on board ERS-2 (RA, ATSR, SAR),dealing with oceanographic phenomena atdifferent spatial and temporal scales.

The continuing improvement in the ERSAltimeter data, both in terms of operationaltimeliness and ability to identify processes thatwould not have been possible even in therecent past, was highlighted by the ocean-dynamics community. A noteworthy illustrationis the real-time monitoring of the tropicalPacific. Meanwhile, the 1997 El Niño data is stillbeing used for research in this field (Fig. 14).There was also a presentation of a novelsynergistic use of altimetry, sea-surface

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Figure 15. A NOAA-15 AVHRR thermal image and an ERS-2 SAR image acquired inFebruary 2000. Both images show the features of mesoscale surface circulation inthe northern portion of a subarctic front south of Vladivostok. Colour scale: violet:00C, blue: 1°C, green: 2°C , yellow: 3°C, red: 4°C (courtesy of Pacific OceanologicalInstitute, Russian Academy of Sciences)

supported by Eumetsat and hosted byMeteoFrance) is preparing a pre-operationalwind product based on ERS-2 scatterometerdata. Preparatory work is in progress for thewind product from the ASCAT scatterometer tobe flown on Metop. The potential of ERS SCATfast-delivery products for detecting andmonitoring cyclones has been demonstrated.74% were retrieved with an average of twoalarms per day.

Different methodologies have been applied inextracting wind and wave fields from image-and wave-mode data. Possibilities for thesuccess-ful extraction of wind fields wereshown for a grid of about 1 km x 1 km for winddirection and 0.1 km for wind speed. TheTromsø Satellite Station (TSS) provides anoperational service for high-resolution wind-fieldobservations based on cross-spectral analysis.Current numerical models provide windinformation at a resolution of 25 km, while thenew SAR wind service can provide informationwith 12 km resolution.

Operational use of ScanSAR Radarsat windmaps is in place at the Danish MeteorologicalInstitute. A similar Envisat ASAR 500 km x 500km wind product is required.

Sea iceThe Canadian Sea-Ice Service hasdemonstrated using ERS and Radarsat theimportance of a fully operational end-to-endsea-ice information system. ASAR data fromEnvisat will provide a complementary source ofdata and bridge the gap to Radarsat-2.Scientific research for sea-ice thicknessestimation is in progress using ERS Radar

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Figure 14. Sea-level elevationanomalies measured with the

ERS-2 Radar Altimeter overthe tropical Pacific during

the last El Niño event. Sea-level anomalies are averaged

over 7 days with 1 degreeresolution. There is an

abnormally high sea levelnear the West Coast of

South America along theEquator (red, +35cm), which

leads to the disappearanceof fish and a radical switch inthe regional climate in termsof rainfall. At the same time,

the sea level drops in theWestern Equatorial Pacific(deep blue, -20cm), where

extreme droughts devastatecrop yields and increase firehazards (courtesy of DEOS,

Delft University, andESA/ESRIN)

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Figure 16. High-resolutionSAR wind map of the Gulf of Alaska near Cook Inlet.This map was derived froma Radarsat wide-scan SAR scene collected on 24 December 1999 inpreparation for thevalidation of Envisat ASARwind fields. The arrowsshow the wind fieldpredicted from the GlobalAtmospheric PredictionModel (NOGAPS) (courtesyof John Hopkins Univ.Applied Physics Laboratory)

In preparation for this new and challengingmission, a number of different actions weretaken, ranging from public-relations activities(movie, pins, posters, stands, 1:10 scale-modeldisplay, etc.) to the distribution of technicaldocumentation (leaflets, brochures, sciencereports for each Envisat instrument) and theopening of a web site for monitoring andreporting on the 674 projects selected in theframework of the Envisat Announcement ofOpportunity.

A set of 10 CDs containing Envisat simulatedproducts and a tool (called ‘EnviView’)designed to open, display and navigate theproducts, were distributed to each participantto help users familiarise themselves with thecontent and format of future Envisat dataproducts. For ESA, this early distribution ofEnviView was intended to promote feedbackand recommendations on how to improve thetool’s capabilities before the launch. EnviViewwill be maintained throughout the mission andwill be offered free to all Envisat users (Fig. 17).

The special Envisat session was mainlydevoted to the calibration and validation of themission instruments and products. The numberof instruments to be calibrated and the widerange of geophysical products to be validatedmake this task an unprecedented challenge.ESA is committed to delivering products to

Altimeter measurements as well as ERS SARimagery. Use of ERS SAR and ATSR incombination has been shown to be successfulin detecting sea-ice freezing, melting, evolution,and kinematics.

Sea-Surface Temperature (SST)Responding to the primary objective of theATSR mission, ATSR/SST is being usedsuccessfully to evaluate the long-term (1991–2000) change in Sea-Surface Temperature on aglobal scale. A clear warming is observed in theWestern Pacific, whereas a cooling down isobserved in the Eastern Pacific. The Atlantic isalso warming up, but to a lesser degree.According to the results so far, the global SSTis increasing by about 0.1 deg per year and thesea level is rising by about 0.1 cm per year.

Wind scatterometerGlobal products are generated at CERSATderived from the ERS AMI-Wind instrument,complemented by data from similar sensors onnon-ESA platforms. In particular, a global-windatlas and a sea-ice atlas have been producedand distributed worldwide as a majorcontribution to climate studies. In particular, thewind atlas, distributed to 1500 users, has beenincluded in the WOCE dataset as a referencefor wind measurement.

GeodesyERS Altimeter data, especially those from thegeodetic mission, are being used to computevery detailed gravity-anomaly maps. Recentdevelopments have shown improvements incoastal regions and extension towards thepole. A near-global gravity-anomaly field map isnow available at 2˙x2˙ resolution. Cross-validation against in-situ data indicate that theaccuracy of the field is around 6 mgal even inshallow oceans and around topographicfeatures. Work is in progress to improveresolution and accuracy, especially in areaswith strong meandering currents. At the sametime, mean sea-surface models are beingproduced and compared.

Highlights of the Envisat Session

“Getting Ready for Launch”

Gothenburg was the first combinedERS/Envisat Symposium. The EnvisatProgramme was therefore presented in thePlenary Session, and there was a specialsession devoted to the overall Envisatcalibration/validation approach (15 papers). Afull day was devoted to sessions on theopportunities for science and applicationdevelopment offered by the Envisat sensors (37papers).

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Figure 17. A set of theEnvisat Simulated Product

CDs

the users starting 6 months after launch, whichis currently scheduled for mid-2001. Within the first 6 months in orbit (so-called‘Commissioning Phase’) and after a first fewweeks dedicated to switch-on and dataacquisition (so-called ‘SODAP Phase’), anumber of teams of experts will carry out thecore calibration and validation programme,under ESA’s responsibility and overall co-ordination. The aim is to achieve the release ofgood-quality products starting at the end of theCommissioning Phase. The detailed plan ofaction and the techniques and strategies thatwill be used were presented in detail by variousspeakers representing the calibration andvalidation teams.

ASARThe ASAR calibration approach is based on thesuccessful ERS approach. The challenge lies inthe increased number of instrument modes and products that the ASAR on Envisat willdeliver.

Already initiated calibration studies werereported, as well as results concerning the useof polarimetry for land-use classification. Theuse of airborne C-band and dual-polarisationdata, experimented with in Denmark with theairborne EMISAR data, significantly improvescrop-type classification, paving the way for apotentially successful Envisat application.

Important experiments will also be performedwithin the ASAR calibration/validation scheme,with the possibility of performing SAR inter-ferometry using wide-swath-mode data and ofperforming interferometry between Envisat andERS-2.

RA-2RA-2 will be inter-calibrated with respect toseveral other altimeter systems, in particularERS-2 and Jason-1. In addition, absoluterange calibration will be carried out to the levelof 1 cm residual inaccuracies, using thenorthwest Mediterranean Basin as a referencesurface. For the first time, the sigma-zeroabsolute calibration will be attempted. Asynthesis of methods and tools to cross-calibrate all geophysical parameters retrievedfrom altimeter data has already been initiated,as well as results from cross-calibrating ERS-2and Topex-Poseidon. Another group involved inthe absolute calibration campaign presentedan indirect approach using tide gauges,together with a direct approach using GPSbuoys. GPS buoys are also used for altimeterdrift monitoring. Taking advantage of the twofrequencies on RA-2, a new parameter is being estimated: the Ku-band backscatterattenuation; its definition and validation werealso presented.

ESA presented the significant improvements inRA-2’s capabilities over previous altimetricmissions and the major conceptual evolution ofthe ground processing strategy. This evolutionleads to highly enhanced data products,particularly in terms of the quality of the near-real-time data for supporting internationalclimate-study programmes such as GODAEand GOOS.

AATSRThe calibration studies for the Envisat AATSRhave demonstrated that the instrument satisfiesthe strict performance criteria required to meetits scientific goals: the global measurement of

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Figure 18. The ESA EarthObservation ExploitationProjects Web Site

sets such as the Radar Altimeter data fromERS-1. The ERS SAR tandem data archiveremains a unique source of data for numerousapplications presented at the Symposium, anduse and exploitation of this archive is expectedto continue to grow. The Envisat data willensure ERS data continuity for a number of keyapplications, and for global-change monitoringin particular. The user needs for new productsand services have been gathered, with manyusers stressing the development of new usertools and encouraging further development ofon-line services. The need for continuous andtimely access to data is a key factor fordeveloping applications: Envisat will respond tothis need thanks to the availability of onboardsolid-state recorders and data relay throughArtemis, and the near-real-time processingcapability.

Every Symposium participant received aquestionnaire aimed at soliciting theircomments on ESA Earth-observation dataexploitation and their expectations in terms offuture ESA technical support. Some 180responses were collected and the detailedresults will be published in February 2001. Thequestionnaire also informed participants aboutthe new Category-1 (CAT-1) Web site (Fig. 18),which under the new ERS-Envisat data policy

sea-surface temperatures to an accuracy of 0.3 K, the monitoring of global vegetationcoverage, and the retrieval of cloud properties.The need for high-accuracy shipboard devicesfor a proper validation of AATSR sea-surfacetemperatures was highlighted. The developmentof an algorithm and the validation of thegenerated product for providing global LSTswere presented.

Sciamachy, GOMOS and MIPASAs for Sciamachy, the GOMOS and MIPASvalidations are carried out through acombination of balloon campaigns, high-altitude aircraft campaigns, model assimilation(both Numerical Weather Prediction Model andChemical Transport Models), satellite inter-comparison, and ground-based measurements.The validation of the GOMOS, MIPAS andSciamachy products is being co-ordinated by asingle group, the Atmospheric ChemistryValidation Team.

MERISThe Medium Resolution Imaging Spectrometer(MERIS) is the first space-borne Europeanoptical sensor dedicated to the observation ofocean colour. It features 15 spectral bands,programmable in width and position, coupledwith a resolution of 300 m that will provide dataof outstanding radiometric precision andscientific interest. The in-flight instrumentcalibration of MERIS will use on-board sunlitcalibration diffuser plates, which have beencharacterised to an absolute accuracy of 1%.The validation of Top Of the Atmosphere (TOA)radiance measured by MERIS will be achievedby comparison with TOA radiances derivedfrom vicarious calibration methods. The oceanchlorophyll concentration will be validated usingopen-ocean dedicated ship campaigns inseveral coastal waters (mainly European) andlong-term measurements from fixed buoys. Thenew water-vapour and cloud products will bevalidated through model assimilation and adedicated helicopter campaign. The widecommunity of 322 Principal Investigators,selected via the Envisat Announcement ofOpportunity, using MERIS data will contributeto the development of a variety of scientific andoperational applications.

User recommendations and feedbackThe Gothenburg Symposium provided theopportunity to capture the recommendationsexpressed by ERS/Envisat data users, both inthe specialised sessions and during the finalclosing session.

Having noted that the algorithms have evolvedand products have improved, users expressedthe need for reprocessing of some ERS data

ers-envisat symposium 2000

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Figure 19. Evaluation byPrincipal Investigators of the

status of their projects,classified by application

theme. Blue and green referto projects at the research

stage, while yellow andorange indicate matured

projects. Red indicates thatPrincipal Investigators feel

that their product, algorithmor service is ready for

operational use

allows users to submit scientific projectproposals at any time to ESA for use inresearch and application development insupport of the mission objectives. Theproposals are peer-reviewed by the Category-1Advisory Group formed by external scientists(35 members) using web-based tools. Theselected Principal Investigators (PIs) can getaccess, after signing ESA standard terms andconditions, at reproduction cost or even free ofcharge subject to the approval of the EarthObservation Programme Board.

The PIs were asked to evaluate the status oftheir projects with the following question: “On ascale of 1 (pure research), 5 (pilot project) to 10(ready for market), how to operational do youthink your project is?” Their responses aresummarised, by application domain, in Figure19. The graph shows that the ERS and EnvisatAOs cover a wide spectrum, from pureresearch to applications development. The PIsexpressed a need for continuous research.There is a clear indication that, in domains suchas forest mapping, hazards, atmosphere,coastal zones, methods, floods and storms, anumber of PIs felt their project had attained itsresearch objectives. In the future, specificthematic workshops will be organised by ESAto support and foster science and applicationdevelopment where appropriate.

ConclusionThe ERS-Envisat Symposium provided aunique opportunity to demonstrate thecontribution of the ERS-1 and ERS-2 missionsto the monitoring of our environment and to thecontinual development of Earth-observation

applications since 1991. The presentationsmade during the Symposium ranged from pureresearch, to the demonstration of applicationsand development of services and markets. Thefeedback collected from the Symposiumattendees will be used to improve ESA’sproducts and services.

The Envisat mission is now being readied forlaunch. It will ensure ERS data continuity andwill enhance the European capability to monitorour environment. The new and improvedEnvisat sensors, algorithm and products willfurther develop the use and exploitation ofEarth-observation data and will allow users toderive high-level information and products. ESAis preparing itself to work closely with the 674Envisat Principal Investigators, with the supportof its Earth-observation application engineers.The Envisat PI’s reporting web site has alreadybeen opened for this purpose.

AcknowledgementsWe would like to acknowledge the hospitality ofthe Chalmers University of Technology inhosting the Symposium, and the ScientificCommittee, Chairs/Co-chairs for their work insupporting the programme preparation.Special thanks go to the Organising Committeefor setting up a unique infrastructure, whichgreatly facilitated information exchange. Wealso acknowledge all attendees of and exhibitorsat the Symposium for their presentations andfeedback. We would also like to thank the ESAstaff involved in the Symposium’s organisationand in the preparation of the Proceedings.

s

r bulletin 105 — february 2001

34

Earth Motion, Landslides, Earthquakes,Volcanoes (14 responses)

Atmosphere (18 responses)

Sea Ice (9 responses)

Geodesy, Performance, Methods(22 responses)Forestry, Agriculture and Vegetation (13 responses)

Floods and Storms, Hydrology (15 responses)

Land Cover / Use, LST (14 responses)

Envisat (14 responses)

Ocean Dynamics, Sea Features, SST,Wind / Waves (26 responses)

Coastal Zones (11 responses)

Ice (8 responses)

1 to 2 (Research)

0% 20% 40% 60% 80% 100%

3 to 4 5 to 6 7 to 8 9 to 10 (Operational)

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