Aquarius SAC D Science Writers Guide

8/6/2019 Aquarius SAC D Science Writers Guide

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SCIENCE WRITERS GUIDE

Aquarius/SAC-D

June 201

National Aeronautics and Space Administration

Studying Earths Salty Seas from Space


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Aquarius/SAC-D SCIENCE WRITERS GUIDE

TABLE OF CONTENTS

Science Overview.............................................................................. 4

Instruments ....................................................................................... 5

FEATURE STORIES

Aquarius to Illuminate Links

Between Salt, Ocean and Climate ................................................ 6

For Aquarius, Sampling Earths Salty Seas rom

Space No Grain o Salt ask ...................................................... 8

Just Add Salt:

Ocean Salinity Measurements rom New NASASatellite Instrument to Advance Climate Forecasts ...................... 10

NASA Goes Below the Surace to Understand Salinity ................ 12

Aquarius Spokespersons................................................................... 14

Aquarius U.S. Science Team Members ............................................ 15

Cover image credit: NASA


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Te international Aquarius/Satlite de Aplicaciones Cientcas(SAC)-D mission will make NASAs rst space-basedmeasurements o salinity the concentration o dissolved salt

at the ocean surace. Ocean surace salinity is one o the missingvariables in satellite studies o Earth.

Tis inormation is critical to improving our understanding otwo major components o Earths climate system: the water cycleand ocean circulation. Aquarius, the primary instrument onthe SAC-D observatory, is expected to provide new insightsinto how the massive natural exchange o reshwater betweenthe ocean, atmosphere and sea ice inuences ocean circulation,

weather and climate.

An experimental NASA Earth System Science PathnderProgram mission, Aquarius will map the entire open ocean oncea week at a resolution o 93 miles (150 kilometers) or at least

three years. Its weekly and monthly average maps o global oceansurace salinity will show how salinity changes rom monthto month, season to season and year to year. Scientists willcombine Aquarius data with in-water measurements o salinityto generate routine maps o ocean salinity distribution. Later inthe mission, Aquarius data will be inter-calibrated and combined

with complementary data rom the European Soil Moisture andOcean Salinity satellite. Aquarius will also serve as a pathnderor possible uture long-term satellite missions to measure oceansurace salinity.

Because ocean surace salinity varies rom place to place andover time, scientists can use it to trace the oceans role in Earths

water cycle. For example, approximately 86 percent o global

evaporation and 78 percent o global precipitation occur overthe ocean. By measuring changes in ocean surace salinity causedby these processes, as well as by ice melting and river runo,

Aquarius will provide important new inormation about howEarths reshwater moves between the ocean and atmosphere andaround the globe.

Knowing more about ocean surace salinity can also helpscientists track ocean currents and better understand oceancirculation. Salinity, together with temperature, determines howdense or buoyant seawater is. Tis, in turn, drives how ocean

waters are layered and mixed. Salinity has a major eect on oceancirculation, including the ow o currents that move heat romthe tropics to the poles.

Aquarius observations will contribute signicantly to improvingcomputer models used to orecast uture climate conditions.

With this new data stream, scientists can begin to understand thecorrelation o changes in salinity with changes in the water cycle,ocean circulation and climate.

Te Aquarius instrument consists o three passive microwaveinstruments (radiometers) to detect the surace emission usedto measure salinity, and an active microwave radar instrument

(scatterometer) to measure the ocean waves that aect theprecision o the salinity measurement. Salinity levels in the openocean generally vary over a narrow range between about 32 and

37 parts per thousand.

Following launch rom Caliornias Vandenberg Air Force Baseaboard a United Launch Alliance Delta II rocket, Aquarius/SAC-D will y in a sun-synchronous orbit 408 miles (657kilometers) above Earths surace.

Aquarius/SAC-D is a collaboration between NASA and Argentinas space agency, Comisin Nacional de ActividadesEspaciales (CONAE), with participation rom Brazil, Canada,France and Italy. Te Aquarius instrument was jointly built byNASAs Jet Propulsion Laboratory, Pasadena, Cali., and NASAsGoddard Space Flight Center, Greenbelt, Md. NASAs LaunchServices Program at the agencys Kennedy Space Center in Florida

provides launch management. JPL will manage Aquarius throughthe missions commissioning phase and will archive missiondata. Goddard will manage the missions operations phase andprocess Aquarius science data. CONAE is providing the SAC-Dobservatory, an optical camera, a thermal camera in collaboration

with Canada, a microwave radiometer, sensors developed byvarious Argentine institutions and the mission operations centerin Argentina. France and Italy are also contributing instruments.

SCIENCE OVERVIEW

This map shows global ocean surace salinity derived rom past in-

water measurements. Salinity is linked to the water cycle -- low-salinity

areas (blue) have more rainall at the surace and higher-salinity areas

(red) have more evaporation rom the surace. Trends over the past

ve decades show that salinity is increasing in the saltier areas and

decreasing in the resher areas, indicating that the water cycle is

accelerating due to climate change, with dry areas around the globe

becoming more arid and rainy areas experiencing even more rainall.

Imagecredit:NOAA/NASA/JPL-Caltech


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INSTRUMENTS

Aquarius, the NASA-built primary instrument on the Aquarius/SAC-D observatory, eatures a design based on more than 30years o remote-sensing salinity research. It will measure ocean

surace salinity by observing thermal emission rom the suraceat 1.413 gigahertz, using three passive microwave instrumentscalled radiometers. Tese radiometers are the most accurate everdeveloped or Earth remote sensing at this requency.

Te strength o the thermal signal emitted in this microwaveband rom the ocean surace depends on both the salinity o theocean water and its temperature. Te thermal emission, measuredas an equivalent brightness temperature in Kelvin, is directlycorrelated to ocean surace salinity. Other things being equal,salty water appears cooler to the radiometers than reshwater.

Over the open ocean, salinity varies globally within a relativelynarrow range between about 32 to 37 parts per thousand. o meet

Aquarius science goals, Aquarius must detect changes in salinity

as small as about two parts in 10,000. Tats equivalent to about apinch (one-eighth o a teaspoon) o salt in a gallon o water. Tiscorresponds to a change in brightness temperature o about 0.1Kelvin, making detecting changes in salinity a very challengingmeasurement or an Earth remote sensing instrument.

Aquarius must correct or intererence with the salinity signalrom other sources, such as ocean surace roughness caused byocean waves. Tis roughness can modiy the emissions and distortthe salinity signal measured rom space. o measure and corrector these eects, Aquarius includes an additional instrumentcalled a radar scatterometer.

Te three Aquarius radiometers are aligned with an 8.2-oot-(2.5-meter) diameter antenna reector to generate three xedbeams at dierent angles relative to the ocean surace. Te beamsorm three ootprints on the ocean surace aligned across a 242-mile (390-kilometer)-wide swath. Tis provides or completeglobal coverage every seven days and produces enough samples ina month to achieve the missions salinity accuracy requirements.

In addition to Aquarius, the SAC-D observatory also includesseven other science instruments and technology packages built byCONAE, the French Space Agency (Centre National dEtudes

Spatiales, or CNES), Italian Space Agency (Agenzia SpazialeItaliana, or ASI) and Canadian Space Agency, or CSA. Tese are:

A Microwave Radiometer (MWR), built by CONAE,that will make complementary measurements o rain,

wind, sea ice and water vapor.

A New InraRed Scanner echnology (NIRS) camera,built by CONAE in collaboration with the CanadianSpace Agency, that will detect orest res on land andmap sea surace temperature.

A High Sensitivity Camera (HSC), built by CONAE,

that will acquire nighttime images o urban lighting andres and aurora events.

A Data Collection System (DCS), built by CONAE,that will be used to relay environmental data romground stations.

Te Radio Occultation Sounder or Atmosphere (ROSA),built by Agenzia Spaziale Italiana, that will measureatmospheric temperature and humidity using a techniqueknown as GPS occultation.

Te CARacterisation et Modelisation de lENvironnement(CARMEN) 1, built by CNES, consists o the ICARE

instrument and three SODAD detectors. ICARE willmeasure the eects o cosmic radiation on electronics,while SODAD will measure the distribution omicroparticles and debris in space.

A echnology Demonstration Package (DP) rounds outthe SAC-D observatorys payloads.

The Aquarius instrument beore being installed on the SAC-D

observatory. The 8.2-by-9.8-oot (2.5-by-3-meter) antenna refector

is stowed the way it will be during launch. Ground commanders will

rotate it to its deployed position about 25 days ater launch. The three

round covers protect the 1.6-oot-diameter (0.5-meter) openings, or

eed horns, to the three radiometers. The covers are removed beore

launch. Signals rom the Aquarius radar scatterometer are also

transmitted and received through these eeds. The instrument has a

total mass o 705 pounds (320 kilograms) and uses 314 watts o power.

Photo

credit:NASA/JPL-Caltech


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Schematic visualization o ocean circulation in the North Atlantic

basin. White arrows depict wind-driven surace currents. Blue arrows

depict density-driven deep currents. This circulation moderates our

climate and is infuenced by changes o ocean surace salinity in the

higher latitudes.

AQUARIUS TO ILLUMINATE LINKS

BETWEEN SALT, OCEAN AND CLIMATE

When NASAs salt-seeking Aquarius instrument ascends to theheavens this June, the moon above its launch site at CaliorniasVandenberg Air Force Base wont be in the seventh house, and

Jupiters latest alignment with Mars will be weeks inthe past, in contrast to the lyrics o the songrom the popular Broadway musical Hair.

Yet or the science team eagerly awaitingAquarius ocean surace salinity data,the dawning o NASAs Age o

Aquarius promises revelations onhow salinity is linked to Earths

water cycle, ocean circulationand climate.

Salinitythe concentrationo salton the ocean suraceis a key missing puzzlepiece in satellite studies oEarth that will improve ourunderstanding o how theocean and atmosphere arecoupled and work in tandemto afect our climate. Whilesatellites already measure sea suracetemperature and winds, rainall,

water vapor, sea level, and ocean color,measurements o ocean surace salinityhave, until quite recently, been limited to sparsedata collected rom ships, buoys and a small number oairborne science campaigns.

From those limited data, we know ocean surace salinity varies byonly about ve parts per thousand globally. Yet a change o justa raction o one part per thousand can inuence the circulationo the ocean. Knowing the salinity o the ocean surace can alsohelp scientists trace Earths water cyclethe process that circulatesreshwater rom the ocean to the atmosphere to the land and backagain to the ocean through rainall, evaporation, ice melt andriver runof. Aquarius, the primary science instrument on the

Aquarius/Satlite de Aplicaciones Cientcas (SAC)-D spacecratbuilt by Argentinas national space agency, Comisin Nacional de

Actividades Espaciales, will help scientists study these complex,interrelated processes and their link to climate.

Recent studies have shown Earths water cycle is speeding up inresponse to climate change, which afects global precipitationpatterns. Currently, scientists study the water cycle by makinginerences rom measurements o how much water is dischargedrom rivers and by measuring precipitation and evaporation ratesusing satellites like NASAs ropical Rainall Measuring Mission.

About 80 percent o Earths water cycle takes place over the ocean,said Aquarius Principal Investigator Gary Lagerloe o Earth &Space Research, Seattle. By measuring ocean surace salinity,

FEATURE STORIES

Aquarius will be able to track how the water cycle is changing inresponse to climate change.

SALINITYAND THE DEEP BLUE SEA

While surace winds drive currents in the upper ocean,deep below the surace, its a diferent story.

Tere, ocean circulation is dominated bychanges in the density o seawater. Tese

changes are determined by salinity andtemperature. Te saltier and colder

the water, the more dense it is. Inparts o the world, cool, high-salinity surace waters becomeso dense that they sink to greatdepths, where they become part

o deep ocean currents. Foundin all ocean basins, these deepcurrents are interconnected andplay an important role inregulating Earths climate bytransporting heat globally.

By revealing changes in patterns oglobal precipitation and evaporation

and showing how these changes mayafect ocean circulation, Aquarius will

help improve predictions o uture climatetrends and short-term climate events, such as

El Nio and La Nia.

Image credit: NASA/Scientic Visualization Studio

A SPOON OF SALT IN A LAKE

Gautama Siddhartha, the ounder o Buddhism, once said, Aspoon o salt in a glass o water makes the water undrinkable. Aspoon o salt in a lake is almost unnoticed.

Such is the challenge aced by the scientists who designed Aquarius

(or more on the technical challenge o the Aquarius mission, seeFor Aquarius, Sampling Earths Salty Seas rom Space No Grain oSalt ask, page 8). Since ocean surace salinity generally averages

just 32 to 37 parts per thousand around the globe, its very hard or asatellite to detect its signal. Te salinity diferences between El Nioand La Nia are very small only about one part per thousand.

Aquarius employs new technologies to be able to detect changesin ocean surace salinity as small as about two parts in 10,000,equivalent to about one-eighth o a teaspoon o salt in a gallon o

water. Its unique, advanced design combines three radiometers,


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Imagecredit:NASA/JPL-Caltech

which measure the salinity signal, with a scatterometer thatcompensates or the efects o ocean surace roughness (waves).Te result is expected to be the most accurate salinity data evermeasured rom space.

Scientists will combine Aquarius maps o global ocean suracesalinity with in-ocean salinity measurements to generate routinemaps o ocean salinity distribution. Later in the mission, Aquariusdata will be inter-calibrated and combined with complementarydata rom the European Soil Moisture and Ocean Salinity satellite.

PEERING INTO A CRYSTAL BALL (OF SALT)

Scientists believe Aquarius will lead to exciting and unexpected newdiscoveriesa minds true liberation o sorts. Tey will be ableto accurately calculate the rate at which surace ocean circulationtransports reshwater. Teyll see how salinity is afected by meltingice, reshwater owing into the ocean, and uxes o reshwater to androm the atmosphere rom rainall and evaporation. Teyll be ableto better study how ocean waters mix vertically. And theyll greatlyreduce uncertainties in calculating the oceans reshwater budget(the net diference between reshwater lost in the ocean throughevaporation and reshwater added to the ocean by precipitationand runof).

Perhaps nowhere is the potential or discovery rom Aquarius higherthan in the Southern Ocean. odays salinity maps dont show manyeatures in the Southern Ocean, said Yi Chao, Aquarius projectscientist at NASAs Jet Propulsion Laboratory, Pasadena, Cali.,

which jointly built Aquarius with NASAs Goddard Space FlightCenter, Greenbelt, Md. Tis is because data there are so sparse.

Yet the Southern Ocean is one o the key deepwater ormation areasin the world and is one o the key drivers o deep ocean circulationand heat transport.

Other areas o particular interest to Aquarius researchers include:

Te Central North Atlantic, where salinity hasbeen observed to be increasing, and the region hasbeen getting more arid

Te Nordic and Labrador Seas, where dense waterorms at the surace and sinks to deep layers in theocean. Aquarius should be able to observe theyear-to-year eects o ice melting on the circulationbetween Greenland and Iceland.

Te Indian Ocean and Bay o Bengal, which have avery large salinity signal but have been less requentlymeasured than the Atlantic and Pacic oceans

And then theres the Arctic Ocean, which has seen signicantchanges in sea ice cover in recent years. Aquarius will provide somesalinity measurements over the Arctic during its ice-ree seasons,though the Aquarius signal is less sensitive over cold water.

Aquarius prime mission will last at least three years, long enoughto map year-to-year variations in salinity that will allow researchersto develop the methodology or and demonstrate the useulness osalinity as a climate data record.

Aquarius data will eventually be used to improve the accuracyo climate orecast models (see Just Add Salt: Ocean SalinityMeasurements rom New NASA Satellite Instrument to

Advance Climate Forecasts, page 10). Ocean surace salinityis not currently well represented in models used by the UnitedNations Intergovernmental Panel on Climate Change in itsassessment reports.

Lagerloe likened Aquarius to an explorer o an unexplored rontier.Well see the ocean in a whole diferent light. When the rst Earthscience satellites launched in the 1970s, we saw ocean eddies or the

rst time and got our rst glimpse o the tremendous turbulence othe ocean. With Aquarius, were going to see things we dont currentlysee. Its as though the blinders will be removed rom our eyes.

ByAlan BuisNASA Jet Propulsion Laboratory

For more inormation on Aquarius, contact:

Gary Lagerloe, Aquarius Principal InvestigatorEarth & Space Research, [email protected]

Yi Chao, Aquarius Project ScientistNASA Jet Propulsion Laboratory, Pasadena, Cali.818-354-8168

[email protected]

Related Links:

Te Aquarius Missionhttp://www.nasa.gov/aquariushttp://aquarius.nasa.gov/http://www.conae.gov.ar

Much o the southern hemisphere ocean has extremely ew or no

in-water salinity measurements. Aquarius will provide measurements

to ll these gaps and provide much more detail about the connection

between surace salinity, ocean currents, rainall changes and

climate. The color scale on the right indicates the number o in-water

surace salinity samples per one-degree latitude-longitude area in theentire historical data base.


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FOR AQUARIUS, SAMPLING EARTHS SALTYSEAS FROM SPACE NO GRAIN OF SALT TASK

Te breakthrough moment or oceanographer Gary Lagerloe,the principal investigator or NASAs new Aquarius mission,came in 1991. Tats when he knew it would be possible to makeprecise measurements o ocean salinity rom space. It has takennearly two decades to turn that possibility into a reality.

Lagerloe was looking at data collected by a NASA aircrat yingover the ocean o the coast o Maryland. It was testing a newradiometer, an instrument that can sense thermal signals emittedby land, clouds and the ocean surace. Te instrument not onlycaptured the unique signature o dissolved salt in the surace

water below, it showed how the waters salt content varied romone side o the Gul Stream to the other.

Tat ight was a turning point, said Lagerloe, a senior scientist

at Earth & Space Research, Seattle. We could clearly see therange that we needed to study salinity rom its lowest levels in theNorth Pacic to the highest salinity levels in the North Atlantic.

FEATURE STORIES

Aquarius is dedicated to making precise measurements oocean salinity over months and years, providing importantnew inormation or climate studies. It will produce monthlymaps o the surace salinity o the global ocean with a 93-mile(150-kilometer) resolution and an accuracy o 0.2 practicalsalinity units, which is equal to about one-eighth teaspoon o saltin a gallon o water. (Practical salinity is a scale used to describe theconcentration o dissolved salts in seawater, nearly equivalent toparts per thousand.) Te mission is to make these measurementscontinuously or at least three years.

Tis is a level o accuracy and stability that has never beenachieved in space beore, said Aquarius Instrument ScientistSimon Yueh, o NASAs Jet Propulsion Laboratory, Pasadena,Cali., which is managing the mission or NASA through itscommissioning phase.

Te rst challenge is that the signal we are measuring is very

small, said Aquarius Deputy Principal Investigator David LeVine, o NASAs Goddard Space Flight Center, Greenbelt, Md.It is a very tiny signal in a noisy environment. In addition,the dynamic rangethe dierence in the signal that comesrom water with low salinity and water with high salinityisalso small.

Te Aquarius instrument has three separate radiometers aimedat the ocean below. Te radiometers are designed to detect andmeasure a particular wavelength o microwave energy beingemitted by the ocean.

Photocredit:NASA/JPL-Caltech

An airborne prototype o the Aquarius instrument was used to test the

measurement capabilities o its design.

Salinity, or saltiness, plays a critical role in ocean circulationand is a key tracer or understanding the oceans role in Earthsglobal water cycle. While satellites routinely provide inormationon sea surace temperature, sea level, ocean color and ocean

winds, historically, no global view o ocean surace salinity hadbeen available. Until very recently, salinity measurements werelimited to those by ships, buoys and oatsand are still ew andar between.

Measuring salinity rom space is extremely challenging and hasbeen one o the last rontiers or ocean remote sensing. TeEuropean Space Agency launched a mission to measure soilmoisture and ocean salinity in 2009. And now the Aquarius/SAC-D mission developed by NASA and Argentinas spaceagency, the Comisin Nacional de Actividades Espaciales,is being readied or launch in June-2011. Te two missionsare complementary, but dier in ocus and technology.One important dierence is that Aquarius uses both aradiometer to detect ocean salinity and a scatterometerradar to correct the radiometers salinity measurements or

wind roughness (waves) at the sea surace. Tis is the rstcombination o this kind used in space or Earth observations,

whereas the European Space Agency mission uses only apassive radiometer.

The Aquarius instrument prototype

was used to test the missions

measurement principle by observing

how 1.413 gigahertz microwave

emissions responded to changes in

salinity in a salt-water test pond.

Ph

otocredit:NASA/JPL

Everything radiates energy,explained Le Vine. Whenyou see the glow o an electric

stove, youre seeing thermalradiation. It is in a range thatour eyes can see. Night-visiongoggles let you see radiationin the inrared part o thespectrum. For Aquarius,

were measuring radiation atmicrowave requencies.

Te radiometers on Aquariusmeasure the microwaveemissions rom the seasurace at 1.413 gigahertz inthe L-band portion o the

electromagnetic spectrum.Tis energy, which ismeasured as an equivalenttemperature called thebrightness temperaturein Kelvin, has a directcorrelation to surace salinity.

Lots o things interere with the salinity signal Aquarius ismeasuring, such as land and atmospheric eects, said Le Vine.Ocean waves are a particularly signicant source o noise that can


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Many natural sources, besides salinity, contribute to the microwave

radiation at L-band (approximately 1.413 gigahertz) measured by

satellites. Correcting the infuence o these natural sources is key to

obtaining Aquarius accurate salinity measurements.

Imagecredit:NA

SA

While Aquarius benets rom advanced technologies such asinternal calibration and sophisticated radiometers, its abilityto measure global ocean surace salinity with unprecedentedaccuracy is the result o years o research and planning.

Te key to making this challenging measurement, say Aquariusscience team members, is in the details. And rom the tiny,detailed measurements o salinity that Aquarius makes, a newbig picture o Earths ocean will emerge.

ByRosemary SullivantNASA Jet Propulsion Laboratory

For more inormation on this topic, contact:

Gary Lagerloe, Aquarius Principal InvestigatorEarth & Space Research, [email protected]

Simon Yueh, Aquarius Instrument ScientistNASA Jet Propulsion Laboratory, Pasadena, [email protected]

David Le Vine, Aquarius Deputy Principal InvestigatorNASA Goddard Space Flight Center, Greenbelt, [email protected]

Frank Wentz, DirectorRemote Sensing Systems, Santa Rosa, Cali.707-545-2904, ext. 16

[email protected]

Related Links:


Ocean Surace Salinityhttp://science.nasa.gov/earth-science/oceanography/physical-ocean/salinity/

conuse the signal rom salinity. Tats why we have an additionalinstrument, a scatterometer, on board to help correct or this.Te scatterometer sends a radar pulse to the ocean surace that isreected back to the spacecrat, providing inormation about theocean surace.

Because o its importance, the 1.413 gigahertz band is protectedor scientic use. Nevertheless, says Aquarius Science eamMember Frank Wentz, director o Remote Sensing Systems,Santa Rosa, Cali., stray signals rom radar, telephone andradio occasionally cause problems. Aquarius radiometers aredesigned to detect much o this intererence and eliminatecontaminated measurements.

Wentz is part o the team creating the complicated mathematicalormulacalled a retrieval algorithmthat Aquarius will use totranslate brightness temperature into measurements o salinity.Its basically a big subtraction process, he said. We gure outall the things that interere with the signal we want and eliminatetheir eect on our measurement. Tis would be challengingenough to do even i the ocean were perectly at like a mirror.

Instead, because o waves, its more like a unhouse mirror thatdistorts everything.

Aquarius primary ocus is to see how salinity varies rom placeto place and changes with time. Tis task would be easier i there

were a greater dierence in the signal between the regions withlow salinity and those with high salinity.

Over the open ocean, salinity is relatively constant. It ranges romabout 32 to 37 parts per thousand. Te corresponding changein brightness temperaturewhat Aquarius measuresis verysmall. Aquarius has been designed to detect changes in salinity assmall as about two parts per 10,000, which corresponds to about0.1 Kelvin. Tis will be about 10 times more accurate than

previous spaceborne radiometer observations o other sea suracecharacteristics, said Yueh.

Aquarius has to be extremely stable as well as sensitive. I wewant to see small things over long periods o time, we have tomake sure that the instrument itsel doesnt change. We need toknow that any variations we observe are real and not caused by theinstrument itsel, said Yueh. Making this happen required specialengineering attention to temperature control and calibration.

Controlling the temperature, critical or maintaining precisionand stability, within a large instrument is difcult. JPL engineershad to design special computer models to understand the systemsthermal behavior and its electronics. Tis had never been donebeore or an instrument o this size operating over months and

years, said Yueh.

All microwave radiometers, including Aquarius, requirea calibration reerence point. Most operational spacecratradiometers continuously turn to look at cold space in orderto calibrate their instruments. Aquarius, however, uses internalcalibration to help retain its stability. We have a big antennaand a large instrument, said Yueh. No one wants to spin thisinstrument around requently to look at an external reerence.


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JUST ADD SALT:OCEAN SALINITY MEASUREMENTS FROM NEWNASA SATELLITE INSTRUMENT TO ADVANCE

CLIMATE FORECASTS

Salt is essential to human lie. Most people dont know, however,that saltin a orm nearly the same as the simple table varietyis just as essential to Earths ocean, serving as a critical driver okey ocean processes. While ancient Greek soothsayers believedthey could oretell the uture by reading the patterns in sprinkledsalt, todays scientists have learned that they can indeed harnessthis invaluable mineral to oresee the utureo Earths climate.

Te oracles o modern climate science are the computer modelsused to orecast climate change. Tese models, which rely on amyriad o data rom many sources, are eective in predictingmany climate variables, such as global temperatures. Yet data or

FEATURE STORIES

Nacional de Actividades Espaciales (CONAE). Aquarius high-tech, salt-seeking sensors will make comprehensive space-basedmeasurements o ocean surace salinity with the precision neededto help researchers better determine how Earths ocean interacts

with the atmosphere to inuence climate. Its a mission thatpromises to be, to quote the old saying, worth its salt.

IMPROVING CLIMATE FORECASTS

We ultimately want to predict climate change and have greatercondence in our predictions. Climate models are the onlyeective means we have to do so, said Aquarius PrincipalInvestigator Gary Lagerloe, a scientist at the Seattle-basedindependent laboratory Earth & Space Research. But, a climatemodels orecast skill is only as good as its ability to accuratelyrepresent modern-day observations.

Density-driven ocean circulation, according to Lagerloe, is

controlled as much by salinity as by ocean temperature. Sea saltmakes up only 3.5 percent o the worlds ocean, but its relativelysmall presence reaps huge consequences.

Salinity inuences the very motion o the ocean and thetemperature o sea water, because the concentration o sea salt inthe oceans surace mixed layerthe portion o the ocean that isactively exchanging water and heat with Earths atmosphereisa critical driver o these ocean processes. Its the missing variablein understanding the link between the water cycle and oceancirculation. Specically, its an essential metric to modelingprecipitation and evaporation.

Accurate ocean surace salinity data are a necessary component to

understanding what will happen in the uture, but can also opena window to Earths climate past. When researchers want to createa climate record that spans previous decadeswhich helps themidentiy trendsits necessary to collect and integrate data romthe last two to three decades to develop a consistent analysis.

Aquarius, and successor missions based on it, will give us, overtime, critical data that will be used by models that study howEarths ocean and atmosphere interact, to see trends in climate,said Lagerloe. Te advances this mission will enable make thisan exciting time in climate research.

TAKING PAST MEASUREMENTS

WITH A GRAIN OF SALT

Anyone whos splashed at the beach knows that ocean water issalty. Yet measuring this simple compound in seawater has been ascientic challenge or well over a century.

Until now, researchers had taken ocean salinity measurementsrom aboard ships, buoys and aircrat but theyd done so usinga wide range o methods across assorted sampling areas and overinconsistent times rom one season to another. Because o thesparse and intermittent nature o these salinity observations,researchers have not been able to ne-tune models to obtain a

Imagecredit:CommitteeonEarthObservationSatellites

Global dierences, on average, between evaporation and precipitation,

the main elements o the global water cycle. Eighty-six percent o

global evaporation is rom the ocean surace, and 78 percent o global

precipitation alls back over the ocean. Changes in these patterns aect

the salinity o the ocean surace. Scientists plan to use Aquarius salinity

data to incorporate these processes into computer models used to

improve predictions o uture climate.

some pieces o the climate puzzle have been scarce, including theconcentration o dissolved sea salt at the surace o the worldsocean, commonly called ocean surace salinity, subjecting themodels to varying margins o error. Tis salinity is a key indicatoro how Earths reshwater moves between the ocean, landand atmosphere.

Enter Aquarius, a new NASA salinity-measurement instrumentslated or launch in June 2011 aboard the Satlite de AplicacionesCientcas (SAC)-D spacecrat built by Argentinas Comisin


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true global picture o how ocean surace salinity is inuencingthe ocean. Aquarius promises to resolve these deciencies, seeingchanges in ocean surace salinity consistently across space andtime and mapping the entire ice-ree ocean every seven days orat least three years.

THE AGE OF AQUARIUS

Research modelers like William Large, an oceanographer at theNational Center or Atmospheric Research in Boulder, Colo., willuse Aquarius ocean surace salinity data, along with precipitationand temperature observations, to round out the data neededto rene the numerical climate models he and his colleagueshave developed.

Tis mission is sure to mark a new era or end users like us,explained Large. Aquarius puts us on the road to implementinga long-term, three-step plan that could improve our climatemodels. Te rst step will be to use Aquarius data to identiy ithere is a problem with our modelswhat deciencies exist, orexample, in parts o the world where observations are sparse.

Second, the data will help us determine the source o theseproblems, he continued. Salinity helps us understand densityand density, ater all, makes ocean waters sink and oat, andcirculate around Earth.

Tird, Aquarius will help us solve the puzzle o whats going onin the ocean itselthe ocean processes, he added. Well pair anocean observation experiment with the satellite mission to explorethe mixing and convectionhow things like salinity are stirred inthe oceanto better determine what processes might be actuallychanging climate. Measuring salinity at the ocean surace willdeliver a pioneering baseline o observations or changes seen bythe next generation o missions in the coming decades.

Weve done all o the advance work leading up to the launch oAquarius, so the proo will be in the actual data, said Lagerloe.Our intent is to put the data out immediately as soon as thesatellite begins transmitting. Beore the end o the rst year, wellbe interpreting exactly what the data are telling us and how they

will benet climate modeling.

By Gretchen Cook-Anderson


Gary Lagerloe, Aquarius Principal InvestigatorEarth & Space Research, Seattle206-726-0501

[email protected]


[email protected]

William Large, Division Director, Climate & Global DynamicsNational Center or Atmospheric Research, Boulder, Colo.303-497-1364

[email protected]

Related Links:



A comparison o the level o detail available rom averaged historical

in-water ocean surace salinity data (top) with the detail that will

be available rom Aquarius ocean surace salinity measurements

(bottom). This new inormation will be used to improve the accuracy

o oceanic computer model simulations that contribute to uture

climate projections.

Imagecredit:NOAA

ImageCredit:GaryLagerloe


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Scientists will set their sights on taking an unprecedented variety o

measurements around one o the saltiest spots in the Atlantic Ocean

as part o the Salinity Processes in the Upper Ocean Regional Study

(SPURS) experiment, in concert with NASAs Aquarius mission.

SPURS will use existing Argo foats and instruments on commercial

cargo ships in addition to surace driters, moored buoys, torpedo-

like gliders, an autonomous submersible, and instruments based on a

research ship to build a detailed, three-dimensional view o the oceanprocesses aecting salinity. In combination with satellite readings

rom Aquarius, SPURS should expand our understanding o whats

driving changes in ocean salinity.

Imagecredit:NASA,

SPUR

S.

NASA GOES BELOW THE SURFACE TOUNDERSTAND SALINITY

When NASAs Aquarius instrument launches this June, itsradiometer instruments will take a skin reading o the oceanssalt content at the surace. From these data o salinity in the top0.4 inch (1 centimeter) o the ocean surace, Aquarius will create

weekly and monthly maps o ocean surace salinity all over theglobe or at least three years. But to better understand whatsdriving changes and uctuations in salinityand how thosechanges relate to an acceleration o the global water cycle andclimate changescientists need to go deeper.

Tats why scientists working on the newest NASA Earth SystemScience Pathnder mission aboard the Argentine-built Aquarius/Satelite de Aplicaciones Cienticas (SAC)-D observatory havedevised a plan. Tey will deploy instruments on oats, researchships, commercial cargo ships, ree-driting platorms, buoys,underwater gliders and an autonomous underwater vehicle to build a3-D view o whats happening beneath the ocean surace that afectssalinity distribution.

Along with temperature, ocean salinity is a key driver o oceancurrents, a critical actor in climate processes, and an indicator oEarths changing water cycle. Measuring salinity rom space has beenone o the great technological challenges o satellite ocean studies.But once Aquarius starts delivering its salinity data, with accuracyequal to a pinch o salt in a gallon o water, a new challenge begins.

Te next question is: How do you understand what the satellitesees? said Yi Chao o NASAs Jet Propulsion Laboratory inPasadena, Cali., and the Aquarius project scientist. Without

deploying instruments under the oceans surace, we do not knowhow to ully interpret the satellite observations o surace salinity.

o help address that question, NASA has a new eld experiment:SPURSSalinity Processes in the Upper Ocean Regional Study.Te experiment, which will sample salinity and other key actors,such as ocean temperature and velocity, will take place rom spring2012 to summer 2013 and will include ve month-long research shipcruises to the center o the saltiest region in the Atlantic Ocean. Inoceanography lingo, its known as the Atlantic salinity maximum,and its located about halway between the southeast U.S. coast andthe western coast o North Arica, at about 25 degrees north and38 degrees west. Many o the methods used or years to take in-ocean measurements o salinity will be put to use, but in a ar more

concentrated and intensive manner, and, or the rst time, theyll beused in combination with Aquarius satellite salinity readings.

SPURS scientists hope to replicate the study in a contrasting,relatively low salinity region elsewhere in the ocean in the uture.

Te scope o the measurements taken during SPURS will givescientists deeper insights into the salinity observations rom

Aquarius and the physical processestemperature changes,currents, turbulence, evaporation, precipitationthat afect salinity.Tese are all aspects o the global water cycle, the continuousmovement o water through the Earth system by evaporation,condensation, precipitation and runof. Water cycles rom the ocean

FEATURE STORIES

to the atmosphere and then back to the ocean, either directly orvia melting ice caps, rivers or underground aquiers. Scientists seeevidence o an accelerating water cycle, driven by climate change.Salinity measurements can indicate how the patterns o reshwatermixing with saltwater are changing due to changes in precipitation,evaporation, and reshwater runof rom rivers and melting ice.

One o the big questions is how much will the water cycle acceleratebecause o warming? said Raymond Schmitt, project scientistor SPURS and an oceanographer at Woods Hole OceanographicInstitution in Woods Hole, Mass. In short, as Earths lowermostatmospheric layer, the troposphere, warms, its ability to hold

water in the orm o water vapor increases. Tis, in turn, increasesevaporation over land and the ocean, and quickens the cycle as a

whole. As precipitation and evaporation patterns changethuschanging how reshwater mixes with salty waterso do salinities.

Were seeing big changes in ocean salinities that can only beexplained by an increase in the water cycle, Schmitt said. Wesee this changing salinity, and we want to relate it to the changing

water cyclebut we have to understand what the ocean is doing.

DESIGNING A MULTI-PLATFORM

EXPERIMENT AT SEA

Te ocean makes up 71 percent o Earths surace area and represents97 percent o the worlds volume o water. Measuring whatshappening with salinity everywhere in the ocean at every depth is


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Imagecredit:N

OAA

SPURS will include

ve month-long

research cruises to

a region known as

the Atlantic Oceans

salinity maximum,

centered around 25

degrees north and38 degrees west. The

cruises will begin in

the spring o 2012

and continue through

the summer o 2013.

The Atlantic salinity

maximum provides

not only a scientically signicant study target, but one that is

logistically easible: The experiment includes U.S. and European

participation. Three cruises will depart rom the United States, one

rom Spain and one rom France. In the uture, scientists hope to

replicate something similar to the SPURS experiment in a less salty

region o the Pacic Ocean.

an impossible task. So the SPURS scientists decided to ocus onone representative region and measure that as a proxy. A network odiferent instruments creates a bounded volume o water to studyin the SPURS experiment.

SPURS precisely identies a specic 3-D portion o the AtlanticOcean, and sets out to measure key ocean processes there asthoroughly as possible. Starting at the surace, commercial cargoships carrying basic salinity gauges and deploying disposablethermometers will criss-cross the target region on their regular traderoutes. Ocean scientists have partnered with commercial ships to dothis or years. SPURS will also take advantage o the existing Argonetwork o proling oats that measure temperature and salinityat the surace and below. Te oats dive as deep as 1.2 miles (2kilometers) while returning to the surace every 10 days to transmittheir measurements via satellite. Te international scienticcollaboration began in the late 1990s and now maintains more than3,000 oats worldwide.

It is the multiple additions beyond these existing measurementsthat will make SPURS more complex than a typical study o

ocean processes. Multiple buoys will take basic meteorologicalmeasurements at the surace. But cables running to anchors on theocean bottom will stretch down as deep as 2.5 miles (4 kilometers)below the surace, while instruments deployed on the cables atdiferent depths will take salinity, temperature and velocity readings,Chao said. SPURS will also draw on data rom NOAAs existingPIRAA (Prediction and Research Array Moored in the Atlantic)network, which uses similar buoys moored to the ocean oor.

In addition, about 75 ree-oating surace driters, outtted withGPS, temperature and salinity instruments, will be deployed in aradius o several hundred kilometers, Chao said. Beneath the surace,NASA will deploy teams o two kinds o gliderstorpedo-likeautonomous devices that use slight changes in buoyancy and wings

to dive up and down and propel themselves orward, collecting datawith instruments onboard.

One class o smaller gliders, called Slocum gliders, which operatein shallower water, will be deployed or 20 to 30 days during eachresearch cruise. Multiple Seagliders will also be deployed or six tonine months at a time. Tese gliders travel in a wider circumerenceand dive to greater depths.

Finally, rom onboard during each o the ve one-month ship cruisesto the site, scientists will operate a CD proler (CD stands orConductivity, emperature and Depth) and a battery-powered,propeller-driven autonomous underwater vehicle that theyll be ableto control remotely.

Salinity has never been measured to the level o detail that SPURSis planning, Chao said.

Te questions Chao, Schmitt and others hope to begin to answerwith SPURS range rom the smallest to the largest scale. For one, what are the physical processes that determine the location andmagnitude o the high-salinity region in the Atlantic being studied?

What is the salinity balance on monthly and seasonal time scales,plus regional and larger spatial scales?

Larger questions include how the ocean will respond to temperatureand reshwater changes likely to come with a warming climate.How will the meridional overturning circulationthe global oceanconveyor belt, which has such a dominant efect on the planetsclimatechange?

We can see in the patterns o salinity change that something bigis going on with the water cycle, Schmitt said. Eighty percent othe water cycle happens over the ocean. We need to document andunderstand how the ocean is responding.

By Patrick LynchNASAs Earth Science News Team



[email protected]

Raymond Schmitt, SPURS Project ScientistWoods Hole Oceanographic Institution, Woods Hole, [email protected]

Related Links:



SPURShttp://spurs.jpl.nasa.gov/


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Less than two months beore launch, team members conduct their

nal checks o the Aquarius instrument at the Spaceport Systems

International Integrated Processing Facility at Vandenberg Air Force

Base, Cali.

Photocredit:NASA/JPL-C

altech

AQUARIUS SPOKESPERSONS

Yi Chao is project scientist or the Aquarius mission at NASAs JetPropulsion Laboratory in Pasadena, Cali., where he provides theinterace between JPLs Aquarius team and non-JPL members o

the Aquarius science team. An oceanographer, his specialties aresatellite oceanography, ocean satellite data analysis, and ocean andclimate modeling.

Arnold Gordon is a member o the Aquarius science team andassociate director o ocean and climate physics at the Lamont-Doherty Earth Observatory at Columbia University in New

York. He will be investigating how the resolution and accuracyo Aquarius data will portray the detailed ocean surace salinitypatterns as observed rom ships and driting sensors within theocean. Gordon has expertise in ocean stratication, circulationand mixing, and its role in Earths climate system.

Eric Ianson is Aquarius program executive at NASA Headquartersin Washington, where he serves as NASAs primary program pointo contact or the mission, ensuring consistent program direction

and execution. His area o specialty is mission development andprogrammatic implementation.

Gary Lagerloe is principal investigator o the Aquariusmission and ounder o Seattle-based Earth & Space Research,a non-prot laboratory. He is responsible or the scientic andtechnical success o the project and compliance with the missionsnancial and regulatory requirements. He is an oceanographer

who specializes in salinity remote sensing, ocean circulationand climate.

William Large is a research modeler and oceanographer at theNational Center or Atmospheric Research in Boulder, Colo.He will use Aquarius ocean surace salinity data, along withprecipitation and temperature observations, to round out the dataneeded to rene the numerical climate models he and his colleagueshave developed.

David Le Vine is deputy principal investigator or the Aquariusmission at NASAs Goddard Space Flight Center in Greenbelt,Md. Le Vine is a specialist in microwave remote sensing, and isresponsible or the Aquarius missions science algorithmtheretrieval o salinity rom the instrument measurements.

Eric Lindstrom is an oceanographer and Aquarius programscientist at NASA Headquarters in Washington where, amongother responsibilities, he assures that mission science is eectivelyintegrated with that o related research programs and that resultso the mission are well known throughout NASA and amongmembers o the public. His specialty is physical oceanographyand climate.

Amit Sen serves as project manager or the Aquarius mission romNASAs Jet Propulsion Laboratory in Pasadena, Cali., where

he is responsible or coordinating and managing all Aquariusactivities on a day-to-day basis within the United States and withinternational partners. He has extensive experience managinginstruments and teams or large and complex internationalsatellite projects like Aquarius.


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An artists rendering o the Aquarius/SAC-D observatory in orbit around Earth as NASAs

Aquarius instrument collects data used to derive ocean surace salinity measurements

over the Pacic Ocean. This visualization was created prior to launch and uses simulated

ocean surace salinity measurements. The satellite orbit and data ootprint are based on

predicted data.

Imagecredit:NASA/S

cientifcVisualizationStudio

Asher, BillApplied Physics Laboratory,University o Washington, Seattle

Bingham, FrederickDepartment o Physics and PhysicalOceanography, University oNorth Carolina Wilmington

Brown, ShannonNASA Jet PropulsionLaboratory, Pasadena, Cali.

Busalacchi, AntonioEarth System ScienceInterdisciplinary Center, University

o Maryland, College Park

Chao, YiNASA Jet PropulsionLaboratory, Pasadena, Cali.

Fukumori, IchiroNASA Jet PropulsionLaboratory, Pasadena, Cali.

Gordon, ArnoldEarth and Environmental Sciences,

Lamont-Doherty Earth Observatory,Te Earth Institute at ColumbiaUniversity, Palisades, N.Y.

Jackson, TomasUnited States Department o

Agriculture Agricultural ResearchService Hydrology and RemoteSensing Laboratory, Beltsville, Md.

Jones, W. LinwoodSchool o Electrical Engineeringand Computer Science, University

o Central Florida, Orlando

Lagerloe, GaryEarth & Space Research, Seattle

Lang, RogerGeorge Washington University,

Washington, D.C.

Large, WilliamClimate & Global Dynamics Division,Earth & Sun Systems Laboratory,

National Center or AtmosphericResearch, Boulder, Colo.

Le Vine, DavidNASA Goddard Space FlightCenter, Greenbelt, Md.

Lindstrom, EricNASA Headquarters,

Washington, D.C.

Maximenko, NikolaiInternational Pacic Research Center,

University o Hawaii, Honolulu

Ponte, RuiAtmospheric and EnvironmentalResearch, Inc., Cambridge, Mass.

Riser, StephenUniversity o Washington,Seattle

Ru, ChristopherUniversity o Michigan,

Ann Arbor

Vandemark, DouglasInstitute or the Study o Earth,Oceans, and Space, Universityo New Hampshire, Durham

Wentz, FrankRemote Sensing Systems,Santa Rosa, Cali.

Yueh, SimonNASA Jet PropulsionLaboratory, Pasadena, Cali.

AQUARIUS U.S. SCIENCE TEAM MEMBERS


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www.nasa.gov

NP-2010-12-183-GSFC

Aquarius SAC D Science Writers Guide

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