bensi 8/1/07 5:03 pm page 30 · 2007. 8. 2. · programmes, estec, noordwijk, the netherlands...

Earth Explorers

ESA’s family of Earth Explorer satellites is

ldesigned in response to specific criticalissues raised by Earth-scientists, while

demonstrating new observation technologies.The first six Explorer missions are beingprepared for launch and, in March 2005, theAgency released a new Call-for-Ideas focusedon processes that are fundamental forunderstanding the changing ‘Earth System’. Sixcandidates were selected in May 2006 forassessment. The final selection is expected in2010, for launch in 2014/2015.

IntroductionThe Earth Explorer missions, as part ofESA’s Living Planet Programme, seek toadvance our understanding of the diff-erent ‘Earth System’ processes and todemonstrate new observing techniques.There are six missions already underdevelopment:

GOCE (Gravity Field and Steady-StateOcean Circulation Explorer), due forlaunch in early 2008, will providehigh-resolution gravity data to improvethe global and regional models ofEarth’s gravity and ‘geoid’ (the shape

Paolo Bensi, Michael Berger,Malcolm Davidson, Paul Ingmann,Joerg Langen, Helge Rebhan& Pierluigi SilvestrinScience, Application & Future TechnologiesDepartment, Directorate of Earth ObservationProgrammes, ESTEC, Noordwijk,The Netherlands

Jean-Loup Bézy, Yannig Durand, Chung-Chi Lin& Florence HélièreProjects Department, Directorate of EarthObservation Programmes, ESTEC, Noordwijk,The Netherlands

esa bulletin 131 - august 2007 31

Bensi 8/1/07 5:03 PM Page 30

of a global ocean at rest used as areference).

SMOS (Soil Moisture and OceanSalinity), due for launch in 2008, willglobally map soil moisture and oceansalinity to improve the representationof land in global atmosphericcirculation models and to characterisethe role of the ocean in the climatesystem.

ADM-Aeolus (Atmospheric DynamicsMission), due for launch in 2009, willmake novel advances in global wind-profile observations and provideglobal wind information that is crucialto climate research and numericalweather prediction.

CryoSat-2, due for launch in 2009, willdetermine the rate of change ofvariations in the thickness and mass ofpolar marine ice and continental ice-sheets in response to climate changes.CryoSat-2 replaces CryoSat, the firstExplorer mission, which was lost atlaunch in 2005.

Swarm, due for launch in 2010, is aconstellation of three satellites tosurvey the geomagnetic field and itsevolution. It will provide new insightsinto the Earth System by improvingour understanding of the Sun’sinfluence and Earth’s interior.

EarthCARE (Earth Clouds and Radia-tion Explorer), due for launch in 2012,is a joint European-Japanese missionto measure cloud and aerosol proper-ties to help understand their inter-actions with Earth’s radiative processesand climate-change predictions.

In March 2005, ESA released a newCall-for-Ideas to scientists from ESAMember States and Canada to solicitproposals for the next Earth Explorer.The scientific priorities focused on theglobal carbon and water cycles,atmospheric chemistry, climate and thehuman element as a cross-cutting issue.Twenty-four proposals were receivedand evaluated as ‘Core’ missions (theseaddress specific areas of great scientificinterest; ‘Opportunity’ missions arefaster, cheaper and not necessarily led byESA). Six candidates were short-listed

Analysing the reflected radar beamwould provide information on the forestvertical structure and height, with thepotential to extend the observationrange and/or to increase the estimationaccuracy of biomass products.

The secondary objectives arise fromthe opportunity to explore Earth’ssurface with a longwave SAR for thefirst time. New information on icestructure, ice thickness and subsurfacegeomorphology in arid areas would beexpected.

The satellite would carry the side-looking radar in a Sun-synchronousorbit optimised to reduce ionosphericeffects on signal propagation. The orbitwould cover all forested areas every25 days globally to satisfy the majormission objectives.

BIOMASS would be the first missiondedicated to estimating biomassglobally using low-frequency SARobservations.

TRAQChanges in the composition of Earth’stroposphere (altitude 0–7/17 km) are aserious and growing problem in manyregions of the world. The compositionaffects air quality regionally andglobally as well as the climate viaradiatively active trace gases andaerosols. TRAQ would assess the airquality changes at global and regionalscales, determine the strength and

in May 2006 for dedicated assessments,with industrial activities beginning inMay/June 2007:

– BIOMASS (to monitor Earth’s biomassfor carbon assessment);

– TRAQ (TRopospheric compositionand Air Quality);

– PREMIER (PRocess Explorationthrough Measurement of Infraredand millimeter-wave Emitted Radia-tion);

– FLEX (FLuorescence Explorer);– A-SCOPE (Advanced Space Carbon

and Climate Observation of PlanetEarth);

– CoReH2O (Cold Regions HydrologyHigh-resolution Observatory).

BIOMASSThe greatest uncertainties in the globalcarbon cycle involve estimating howcarbon dioxide is taken up by land. Themission aims to improve the presentassessment and future projection of theterrestrial carbon cycle by providingconsistent global maps of forest biomassand forest area, forest disturbances andrecovery with time, and the extent andevolution of forest flooding. Forestbiomass is a key factor in the carboncycle but it falls in a critical gap inexisting measurement techniques. Whencoupled with biophysical models, above-ground biomass provides information oncarbon dioxide stocks and fluxes and is a

distribution of the sources and sinks oftrace gases and aerosols influencing airquality, and help in the understandingof the role of tropospheric compositionin the global change.

A new synergistic sensor concept isproposed: a high spectral resolutionpushbroom shortwave spectrometer(SWS) in the range from ultraviolet tonear-infrared; a high spectral resolutionacross-track scanning longwave spectro-meter (LWS) in the thermal-infraredwith an embedded cloud imager and a multi-view polarisation-resolvingpushbroom radiometer. A shortwave-infrared band is also required; it would be included either in the LWS orSWS.

The cloud imager is a dual-bandinfrared instrument that would optimisein real time the pointing direction of thethermal-infrared spectrometer towardsareas clear of clouds. The mission willoffer a pixel size of 15–40 km,depending on the spectral bands.

TRAQ’s orbit is selected to offer near-global coverage and unique diurnal timesampling with up to five daytimeobservations over Europe and othermid-latitude regions. This can beachieved by using a non-Sun-synchronous low drifting orbit with aninclination around 57º.

TRAQ would provide the followingparameters: ozone, nitrogen dioxide,sulphur dioxide, HCHO (formalde-hyde), water vapour and HCOOCH(1,2-ethanedione) tropospheric columnsfrom the ultraviolet/visible/near-infraredspectral region; carbon monoxide andmethane tropospheric columns from theshortwave infrared spectral region;height-resolved tropospheric profiles ofozone and carbon monoxide from thethermal-infrared channels; detailedtropospheric aerosol characterisationfrom the multi-view polarisation-resolving radiometer and in combina-tion with the ultraviolet/visible/near-infrared spectrometer.

TRAQ would be the first mission fullydedicated to air quality and the scienceissues around tropospheric compositionand global change.

PREMIERThe primary aim of PREMIER is toexplore the processes that control thecomposition of the mid/upper tropo-sphere and lower stratosphere (altitude3/10–51/58 km). It would be the firstmission to explore from space the linksbetween atmospheric composition andclimate globally in unprecedented detailand, for the first time, with sufficientresolution.

PREMIER would observe the distri-butions of trace gases, particulates andtemperature in this region down to finerscales than any previous satellite mission.It would also facilitate integration withmeasurements made at higher resolutionat particular locations and times byground and airborne instruments.

The secondary aim is to the exploreprocesses that control the compositionof the lower troposphere/boundarylayer and the links to higher layers.

Through synergy with Europe’s

sensitive indicator of changes in land useand natural biophysical processes.

The BIOMASS primary objectiveswould be achieved through a P-band(435 MHz) synthetic aperture radar(SAR). Finding the above-groundbiomass from calibrated SAR imageswill take advantage of the high sensitiv-ity of P-band reflection to biomass.

Complementary classification techni-ques would exploit the polarisation ofthe radar signatures from different typesof forest to label surface features bycomparison with known reference cases.

Earth Observation

esa bulletin 131 - august 2007esa bulletin 131 - august 2007 www.esa.intwww.esa.int 3332

Earth Explorers

TRAQ Characteristics

Mission duration: 3–5 yearsOrbit: drifting low orbit, inclination ~57º Coverage: latitudes 40ºS–60ºNRevisit time: 3 monthsTemporal sampling: up to 5 times/day over

continental areas within 40–55ºNInstruments: UV/visible/near-infrared

spectrometer (SWS); thermal-infraredspectrometer (LWS); shortwave infrared(either SWS or LWS); infrared CloudImager; multi-view polarisation resolvingradiometer

Resolution: 15–40 km (UV/shortwaveinfrared), 15 km (thermal-infrared); 1 km(Cloud Imager); 1–4 km (multi-viewpolarisation resolving radiometer)

BIOMASS Characteristics

Mission duration: 5 yearsOrbit: Sun-synchronous, local time ~06:00 Coverage: global, vegetated areasRevisit time: 25 daysInstrument: P-band (435 MHz) synthetic

aperture radarPolarisation: full polarimetry and/or

circular/dual polarisationData acquisition: single-pass/repeat-pass

polarimetric interferometryResolution: ≤50 x 50 m (≥4 looks)Swath width: ≥100 km

BIOMASS: global measurements of forest biomassTRAQ: air quality and long-range transportof air pollution

Bensi 8/1/07 5:04 PM 2

of a global ocean at rest used as areference).

SMOS (Soil Moisture and OceanSalinity), due for launch in 2008, willglobally map soil moisture and oceansalinity to improve the representationof land in global atmosphericcirculation models and to characterisethe role of the ocean in the climatesystem.

ADM-Aeolus (Atmospheric DynamicsMission), due for launch in 2009, willmake novel advances in global wind-profile observations and provideglobal wind information that is crucialto climate research and numericalweather prediction.

CryoSat-2, due for launch in 2009, willdetermine the rate of change ofvariations in the thickness and mass ofpolar marine ice and continental ice-sheets in response to climate changes.CryoSat-2 replaces CryoSat, the firstExplorer mission, which was lost atlaunch in 2005.

Swarm, due for launch in 2010, is aconstellation of three satellites tosurvey the geomagnetic field and itsevolution. It will provide new insightsinto the Earth System by improvingour understanding of the Sun’sinfluence and Earth’s interior.

EarthCARE (Earth Clouds and Radia-tion Explorer), due for launch in 2012,is a joint European-Japanese missionto measure cloud and aerosol proper-ties to help understand their inter-actions with Earth’s radiative processesand climate-change predictions.

In March 2005, ESA released a newCall-for-Ideas to scientists from ESAMember States and Canada to solicitproposals for the next Earth Explorer.The scientific priorities focused on theglobal carbon and water cycles,atmospheric chemistry, climate and thehuman element as a cross-cutting issue.Twenty-four proposals were receivedand evaluated as ‘Core’ missions (theseaddress specific areas of great scientificinterest; ‘Opportunity’ missions arefaster, cheaper and not necessarily led byESA). Six candidates were short-listed

Analysing the reflected radar beamwould provide information on the forestvertical structure and height, with thepotential to extend the observationrange and/or to increase the estimationaccuracy of biomass products.

The secondary objectives arise fromthe opportunity to explore Earth’ssurface with a longwave SAR for thefirst time. New information on icestructure, ice thickness and subsurfacegeomorphology in arid areas would beexpected.

The satellite would carry the side-looking radar in a Sun-synchronousorbit optimised to reduce ionosphericeffects on signal propagation. The orbitwould cover all forested areas every25 days globally to satisfy the majormission objectives.

BIOMASS would be the first missiondedicated to estimating biomassglobally using low-frequency SARobservations.

TRAQChanges in the composition of Earth’stroposphere (altitude 0–7/17 km) are aserious and growing problem in manyregions of the world. The compositionaffects air quality regionally andglobally as well as the climate viaradiatively active trace gases andaerosols. TRAQ would assess the airquality changes at global and regionalscales, determine the strength and

in May 2006 for dedicated assessments,with industrial activities beginning inMay/June 2007:

– BIOMASS (to monitor Earth’s biomassfor carbon assessment);

– TRAQ (TRopospheric compositionand Air Quality);

– PREMIER (PRocess Explorationthrough Measurement of Infraredand millimeter-wave Emitted Radia-tion);

– FLEX (FLuorescence Explorer);– A-SCOPE (Advanced Space Carbon

and Climate Observation of PlanetEarth);

– CoReH2O (Cold Regions HydrologyHigh-resolution Observatory).

BIOMASSThe greatest uncertainties in the globalcarbon cycle involve estimating howcarbon dioxide is taken up by land. Themission aims to improve the presentassessment and future projection of theterrestrial carbon cycle by providingconsistent global maps of forest biomassand forest area, forest disturbances andrecovery with time, and the extent andevolution of forest flooding. Forestbiomass is a key factor in the carboncycle but it falls in a critical gap inexisting measurement techniques. Whencoupled with biophysical models, above-ground biomass provides information oncarbon dioxide stocks and fluxes and is a

distribution of the sources and sinks oftrace gases and aerosols influencing airquality, and help in the understandingof the role of tropospheric compositionin the global change.

A new synergistic sensor concept isproposed: a high spectral resolutionpushbroom shortwave spectrometer(SWS) in the range from ultraviolet tonear-infrared; a high spectral resolutionacross-track scanning longwave spectro-meter (LWS) in the thermal-infraredwith an embedded cloud imager and a multi-view polarisation-resolvingpushbroom radiometer. A shortwave-infrared band is also required; it would be included either in the LWS orSWS.

The cloud imager is a dual-bandinfrared instrument that would optimisein real time the pointing direction of thethermal-infrared spectrometer towardsareas clear of clouds. The mission willoffer a pixel size of 15–40 km,depending on the spectral bands.

TRAQ’s orbit is selected to offer near-global coverage and unique diurnal timesampling with up to five daytimeobservations over Europe and othermid-latitude regions. This can beachieved by using a non-Sun-synchronous low drifting orbit with aninclination around 57º.

TRAQ would provide the followingparameters: ozone, nitrogen dioxide,sulphur dioxide, HCHO (formalde-hyde), water vapour and HCOOCH(1,2-ethanedione) tropospheric columnsfrom the ultraviolet/visible/near-infraredspectral region; carbon monoxide andmethane tropospheric columns from theshortwave infrared spectral region;height-resolved tropospheric profiles ofozone and carbon monoxide from thethermal-infrared channels; detailedtropospheric aerosol characterisationfrom the multi-view polarisation-resolving radiometer and in combina-tion with the ultraviolet/visible/near-infrared spectrometer.

TRAQ would be the first mission fullydedicated to air quality and the scienceissues around tropospheric compositionand global change.

PREMIERThe primary aim of PREMIER is toexplore the processes that control thecomposition of the mid/upper tropo-sphere and lower stratosphere (altitude3/10–51/58 km). It would be the firstmission to explore from space the linksbetween atmospheric composition andclimate globally in unprecedented detailand, for the first time, with sufficientresolution.

PREMIER would observe the distri-butions of trace gases, particulates andtemperature in this region down to finerscales than any previous satellite mission.It would also facilitate integration withmeasurements made at higher resolutionat particular locations and times byground and airborne instruments.

The secondary aim is to the exploreprocesses that control the compositionof the lower troposphere/boundarylayer and the links to higher layers.

Through synergy with Europe’s

sensitive indicator of changes in land useand natural biophysical processes.

The BIOMASS primary objectiveswould be achieved through a P-band(435 MHz) synthetic aperture radar(SAR). Finding the above-groundbiomass from calibrated SAR imageswill take advantage of the high sensitiv-ity of P-band reflection to biomass.

Complementary classification techni-ques would exploit the polarisation ofthe radar signatures from different typesof forest to label surface features bycomparison with known reference cases.

Earth Observation


Earth Explorers

TRAQ Characteristics

Mission duration: 3–5 yearsOrbit: drifting low orbit, inclination ~57º Coverage: latitudes 40ºS–60ºNRevisit time: 3 monthsTemporal sampling: up to 5 times/day over

continental areas within 40–55ºNInstruments: UV/visible/near-infrared

spectrometer (SWS); thermal-infraredspectrometer (LWS); shortwave infrared(either SWS or LWS); infrared CloudImager; multi-view polarisation resolvingradiometer

Resolution: 15–40 km (UV/shortwaveinfrared), 15 km (thermal-infrared); 1 km(Cloud Imager); 1–4 km (multi-viewpolarisation resolving radiometer)

BIOMASS Characteristics

Mission duration: 5 yearsOrbit: Sun-synchronous, local time ~06:00 Coverage: global, vegetated areasRevisit time: 25 daysInstrument: P-band (435 MHz) synthetic

aperture radarPolarisation: full polarimetry and/or

circular/dual polarisationData acquisition: single-pass/repeat-pass

polarimetric interferometryResolution: ≤50 x 50 m (≥4 looks)Swath width: ≥100 km

BIOMASS: global measurements of forest biomassTRAQ: air quality and long-range transportof air pollution

Bensi 8/1/07 5:04 PM Page 32

MetOp satellite, flying in tandem, thecomposition of the lower tropospherewill be clearly discriminated from that ofhigher layers. The mission objectives callfor 3-D sounding of the mid/uppertroposphere and stratosphere by two

instruments are: a coarse resolutionvisible/near-infrared spectrometer and a6-channel shortwave infrared imager forbasic vegetation parameters, a thermal-infrared radiometer with four channelsfor estimating the temperature of thevegetation canopy. An optional off-nadir two–three band visible/ short-wave-infrared imager would help tocorrect for atmospheric effects.

A single satellite in a Sun-synchronousorbit is the baseline for the mission. Alocal time of 10:00 would provideadequate balance between maximumfluorescence emission and maximumsolar illumination. A spatial resolutionof the order 100–300 m is required.

A-SCOPEA-SCOPE, like other missions toobserve carbon dioxide from space,would be an innovative source of datafor understanding the carbon cycle andvalidating inventories of greenhouse gasemissions. It would provide near-globalcoverage with good time resolution,mapping the sources and sinks ofcarbon dioxide on a scale of 500 km orbetter. This is a major improvement overtoday’s observation network and forth-coming in situ and space systems.

A-SCOPE would be the first missiondedicated to measuring carbon dioxidewith an active ‘Differential AbsorptionLidar’ (DIAL) sensor. It would providebetter accuracy and spatial andtemporal coverage than the plannedsatellites carrying passive sensors: OCO(Orbiting Carbon Observatory; NASA)

complementary limb-sounders at infra-red and mm/sub-mm wavelengths. Thelimb would be imaged at high resolutionto account for the effects of clouds andto derive cloud/aerosol properties.

The infrared sounder is an imagingFourier transform spectrometer either ina high spectral resolution mode, opti-mised for observation of minor tracegases or in a high spatial resolutionmode, optimised to resolve atmosphericstructure.

The mm/sub-mm sounder is a limb-sounding heterodyne receiver with achannel in the 320–360 GHz range formeasurements of the main target speciesof water, ozone and carbon monoxide(or with a slight spectral shift to observehydrogen cyanide, HDO water isotope,nitrous oxide, chlorine monoxide, nitricacid) in the upper troposphere/lowerstratosphere altitude range, and achannel in the 488–504 GHz range withimproved sensitivity to stratospherictarget species (such as chlorine mon-oxide, nitrous oxide, water and itsisotopes). The instrument would bedeveloped as a Swedish national contri-bution to the mission.

FLEXThe mission would improve our know-ledge of the carbon cycle by globallymeasuring the efficiency of photo-synthesis of ecosystems. Photosynthesisby land vegetation is an important

and GOSAT (Greenhouse gases Observ-ing Satellite; JAXA). Only active sensingwould provide high-accuracy measure-ments and truly global, day/nightcoverage under both clear and broken-cloud conditions.

DIAL would measure the reflectionsfrom Earth’s surface and clouds tops oflaser pulses at slightly different wave-lengths. Carbon dioxide in the atmos-phere would absorb some of the laserlight, varying with wavelength. Thedifferences between the two wavelengthsyields the concentration of carbon

dioxide, with a target minimum accuracyof 1.5 parts per million by volume and agoal of 0.5 ppmv. Suitable absorptioncan be found in the near-infrared around1.6 μm and 2.1 μm.

In both spectral regions, temperaturesensitivity and interference from watervapour and other trace gases can beminimised by careful selection of thelaser’s exact wavelengths.

A camera operating in the visible,near-infrared and thermal-infrared witha narrow swath width of 50 km wouldput the measurements in context with abroader view of the clouds and Earth’ssurface texture.

CoReH2OThe mission aims at all four sciencepriorities identified in the Call for Ideas,with emphasis on the global water cycleand significant contributions inunderstanding the global carbon cycle,atmospheric chemistry and climate, aswell as assessing the human impact onthese aspects.

The mission would focus on detailedobservations of important snow, ice andwater-cycle parameters. It would improveour understanding and modelling ofsurface processes and surface/atmos-phere exchange mechanisms in regionswhere snow and ice play a major role inthe water and energy cycles, as well as inbiospheric processes.

The key parameters to be founddescribe a snow layer: extent, thicknessand water-equivalent (the amount ofwater from the instantaneous melting of

component of the global carbon cycle,closely linked to the hydrological cyclethrough transpiration. This type ofinformation has never been availablebefore from space observations.

Fluorescence under sunlight is asensitive and direct probe of photo-synthesis in both healthy and perturbedvegetation. It gives an early indication ofplant stress before it can be observed bymore conventional means. For FLEX,direct fluorescence measurements ofvegetation chlorophyll are proposed,complemented by hyperspectral reflect-ance and canopy temperature to helpinterpret the fluorescence.

The core instrument is a spectrometerto measure the fluorescence in the blue,red and far-red using the ‘FraunhoferLine Discriminator’ method.

The fluorescence of chlorophyll in thered and far-red is the key for monitoringphotosynthesis. Blue-green fluorescenceadds information about the vegetation’sstatus and health. The complementary

Earth Observation


Earth Explorers

FLEX Characteristics

Mission duration: 3–5 seasonal cycles innorthern and southern hemispheres

Orbit: Sun-synchronous, local timedescending node around 10:00

Coverage: global coverage of land surfaces(56ºS–75ºN)

Revisit time: 1 weekInstruments: Fluorescence Spectrometer;

Visible/Near-Infrared ImagingSpectrometer (0.45–1 μm); ShortwaveInfrared Imager (1.4–2.2 μm); ThermalInfrared Imaging Radiometer (8.8–12 μm);optional multi-view Visible/ShortwaveInfrared Imager

Resolution: 100–300 m

A-SCOPE Characteristics

Mission duration: 3–5 yearsOrbit: Sun-synchronous Coverage: near-globalInstruments: nadir-viewing pulsed-laser DIAL

at 2.1 μm or 1.6 μm; visible/near-infrared/thermal-infrared Imaging Camera

Vertical resolution: total columnHorizontal resolution: DIAL 50 km along-

track; Imaging Camera 100 m

PREMIER Characteristics

Mission duration: 4 yearsOrbit: Sun-synchronous in tandem with

MetOp (835 km)Coverage: near-global, latitudes 80ºS–80ºNInstruments: Infrared Limb Sounder (IRLS);

Infrared Cloud Imager (IRCI); MicrowaveLimb Sounder (MWLS)

Vertical coverage: IRLS 48 km (3/10–51/58km arctic/tropics); IRCI 25 km(3/10–28/35 km arctic/tropics); MWLS23 km (5–28 km upper troposphere/lowerstratosphere, 12–35 km stratosphericmode)

Vertical sampling: IRLS 0.5–2 km (dependingon mode and range); IRCI 0.5 km; MWLS1.5 km

Horizontal sampling: IRLS 25–80 km across-track, 50–100 km along-track; IRCI 4 kmacross-track, 8–50 km along-track; MWLS≤ 50 km (≤ 300 km in stratospheric mode)along-track

PREMIER: atmospheric processes linking trace gases,radiation, chemistry and climate

FLEX: global photosynthesis A-SCOPE: global carboncycle and regional carbondioxide fluxes

Bensi 8/1/07 5:04 PM Page 34

a snow pack). These observations willhelp data-assimilation systems, numericalweather prediction and climate models,and the understanding and modelling ofland-cryosphere-atmosphere exchangeprocesses.

The secondary objectives aim at ice-surface parameters that would help theanalyses of sea-ice dynamics in local andglobal climate models.

Producing this geophysical informa-tion depends on backscatter measure-ments from a synthetic aperture radar atX- and Ku-band at relatively highresolution. Ku-band is more sensitive toshallow dry snow, while X-band providesgreater penetration of deeper snowlayers. The combination of observationsat two frequencies would improve theaccuracy of the snow information andprovide a high level of information onsea ice, ice sheets and glaciers.

Measurements of the polarisation ofthe reflected radar pulses are importantfor separating surface and volumescattering and for estimating the snowwater equivalent.

The mission is based on a singlesatellite in a Sun-synchronous orbit witha local time early in the morning ataround 06:00 to avoid the effects ofdaily warming and melting. The missionwould be divided into two phases: thefirst phase (2 years) with revisits every3 days, in order to observe the morerapid processes in selected test areas.These frequent visits are at the expenseof limited coverage. The second phase(2–3 years) would revisit every 15 days,with near-global coverage of snow andice areas.

The Selection ProcessThe current cycle will lead to theselection in 2010 of the seventh EarthExplorer, due for launch in 2014/2015.As in the previous cycles, the process hasfour steps. The first step (Phase-0:mission assessment) began in 2006 withthe nomination of the Mission Assess-ment Groups that provide independentadvice to the Agency for the definitionof the detailed scientific objectives ofthe missions, the consolidation of themission requirements, the definition ofrequired scientific support and theproduction of the Reports for Assess-ment. The other major element of thisstep is the Phase-0 industrial studies,beginning in May/June 2007 to identifyend-to-end implementation concepts foreach mission as well as their preliminaryfeasibility in terms of required technol-ogy and compliance with programmeconstraints. The assessment step willconclude with a User ConsultationProcess that reviews the assessments andproposes a short-list of candidates toenter the next step in 2009 (Phase-A:mission feasibility).

At the end of Phase-A in 2010, asecond User Consultation Process willrecommend the final candidate to enterthe development phases (B/C/D) andfinally join the Earth Explorer family asthe seventh mission of the series.

AcknowledgmentsThe authors thank the members of theMission Advisory Groups supportingESA in the mission definition. e

Earth Observation

esa bulletin 131 - august 2007 www.esa.int36

CoReH2O Characteristics

Mission duration: 5 years Orbit: Sun-synchronous, local time 06:00 Coverage: test sites (phase-1); global

coverage of snow and ice areas (phase-2)Revisit time: 3 days (phase-1); ≤15 days

(phase-2)Instrument: dual-frequency (9.6/17.2 GHz)

synthetic aperture radarPolarisation: dual (vertical-vertical; vertical-

horizontal)Resolution: ≤50 x 50 m (≥5 looks)Swath width: ≥100 km

CoReH2O: detailed observations of key snow,ice and water cycle characteristics

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bensi 8/1/07 5:03 pm page 30 · 2007. 8. 2. · programmes, estec, noordwijk, the netherlands...

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