Surface Water Interferometric Altimeter Concept

• Ka-band SAR interferometric system with 2 swaths, 50 km each

• WSOA and SRTM heritage• Produces heights and co-registered all-weather imagery• 200 MHz bandwidth (0.75 cm range resolution)• Use near-nadir returns for SAR altimeter/angle of arrival

mode (e.g. Cryosat SIRAL mode) to fill swath• No data compression onboard: data downlinked to NOAA

Ka-band ground stations

1. The ProblemThe Problem 2. Science Questions & Societal Applications2. Science Questions & Societal Applications

3. MeasurementsMeasurements RequiredRequired Images of h, which yield images of dh/dt and dh/dx

dh/dx

h

from SRTM

4. The SolutionThe Solution KaRIN: Ka-band Radar Interferometer. SRTM, WSOA heritage.

Images of h globally every 8 days.

100% Inundated!

In-situ cannot measure thisIn-situ cannot measure this

Participants

Rodrigo Abarca del Rio, Jose Achache, Graeme Aggett, Doug Alsdorf, Kwabena Asante, Sima Bagheri, Georges Balmino, Richard Bamler, Luis Bastidas, Subhashranjan Basu, Okke Batelaan, Paul Bates, Marc De Batist, Matt Becker, Ed Beighley, Philippa Berry, Keith Beven, Mike Bevis, Charon Birkett, Mark Bishop, Leonid Bobylev, Mikhail Bolgov, Bodo Bookhagen, Jeff Booth, Elizabeth Boyer, Rafael Bras, Alex Braun, Andrew Brooks, Richard Bru, Stephen Burges, Stéphane Calmant, Anny Cazenave, Michael Coe, Jean-François Crétaux, Bruno Cugny, Bob Curry, Sunil Kumar De, Stephen Dery, Reinhard Dietrich, Remco Dost, Claude Duguay, Victor Dukhovnyi, Bernard Dupre, Micheal Eineder, Theodore Endreny, Vivien Enjolras, Jay Famiglietti, Balazs Fekete, Naziano Filizola, Andrew Folkard, Bruce Forsberg, Rick Forster, Peter Gege, Nick van de Giesen, Santiago Giralt, Scott Goetz, Kalifa Goita, Richard Gross, Jean-Loup Guyot, Stephen Hamilton, Peter Hildebrand, Simon Hook, Matt Horritt, Martin Horwath, Paul Houser, Jinming Hu, Walter Illman, Hiroshi Ishidaira, Shafiqual Islam, Stephane Jacquemoud, Mike Jasinski, Ola Johannessen, Natalie Johnson, Hahn Chul Jung, Jobaid Kabir, Josef Kellndorfer, Brian Kiel, Yunjin Kim, Jean Klerkx, Toshio Koike, Alexei Kosarev, Andrey Kostianoy, Pascal Kosuth, Chuck Kroll, Venkat Lakshmi, Bruno Lazard, Sergey Lebedev, Brigitte Leblon, John Lenters, Dennis Lettenmaier, Xu Liang, Peter Luk, Yaoming Ma, Ian Maddock, Jun Magome, Dushen Mamatkanov, Ramiz Mamedov, Marco Mancini, Bryan Mark, Thomas Maurer, Kyle McDonald, Daene McKinney, John Melack, Yves Ménard, Carolyn Merry, Philip Micklin, George Miliaresis, Nelly Mognard, Delwyn Moller, Alberto Montanari, Andreas Neumann, Stefan Niemayer, Eni G Njoku, Daniel O'Connell, Tamlin Pavelsky, Christa Peters-Lidard, Al Pietroniro, Lasse Pettersson, Bill Plant, Shavkat Rakhimov, Jacques Richard, Ernesto Rodriguez, Ake Rosenquist, Carlos Saavdera, Stein Sandven, Frank Schwartz, Frédérique Seyler, Yongwei Sheng, C.K. Shum, Murugesu Sivapalan, Leonard Sklar, James Smith, Larry Smith, Detlef Stammer, Bob Su, Kuniyoshi Takeuchi, Ryan Teuling, Julian Thompson, Eric Thouvenot, Wim Timmermans, Laurent Tocqueville, Kevin Toomey, Peter Troch, Susan Ustin, Zoltan Vekerdy, Charles Vörösmarty, Wolfgang Wagner, Claudia Walter, Matt Wilson, Eric Wood, Naama Raz Yaseef, Ouan-Zan Zanife, Jianyun Zhang, Yunxuan Zhou

Measurements required to answer questions such as these require multi-

dimensional sampling protocols distributed globally – essentially a space based

solution. Water surfaces are strongly reflective in the electromagnetic spectrum, thus nadir viewing radar altimeters have been highly successful in measuring the

elevation of the world’s oceans. Expansion of this technology to inland

waters, which have much smaller spatial dimensions than the oceans, has met with some success despite the construction of

existing radar altimeters for ocean applications which are designed to

average over relatively large areas, and hence are problematic for surface water applications where the lateral extent is

comparatively limited.

the WatER SatelliteWater Elevation Recovery Mission

A Joint ESA•NASA Proposal EffortNelly Mognard, E.U. WatER PI, nelly.mognard@cnes.fr, www.legos.obs-mip.fr/recherches/missions/water/

Doug Alsdorf, U.S. WatER PI, alsdorf.1@osu.edu, www.geology.ohio-state.edu/water

“Where is water stored on Earth’s land surfaces, and how does this storage vary in space and time?”

Although in situ gauge measurements are the backbone of much of our understanding of surface water dynamics globally, these gauge networks provide essentially no information about floodplain flows and the dynamics of

wetlands. In situ networks are generally best in the industrialized world and are worse in sparsely settled areas

(e.g., high latitudes and tropics). For instance, the network of stream gauges in the Potomac River (expressed in number of

gages per unit drainage area) is about two orders of magnitude greater than in the Amazon River basin.

In-situ methods provide a one-dimensional, point-based view of water surfaces in situations where a well defined channel boundary confines

the flow. In practice, though, water flow and storage changes in many riverine environments are not simple, and involve the spatially complex

movement of water over wetlands and floodplains and include both diffusive flows and narrow confined (channel) hydraulics. Wetlands and floodplains are governed by the dynamics of

water movement, and as described next, are vital to ecology and to climate and weather.

Global models of weather and climate could be constrained spatially and temporally by stream discharge and surface storage measurements. Yet this constraint is rarely applied, despite modeling results showing that

precipitation predicted by weather forecast models is often inconsistent with observed discharge. For example, Roads et al. (2003) found that the predictions of runoff by numerical weather prediction and climate models

were often in error by 50%, and even 100% mismatches with observations were not uncommon. Coe (2000) found similar results for climate model predictions of the discharge of many of the world’s large rivers. The

inter-seasonal and inter-annual variations in surface water storage volumes as well as their impact on balancing regional differences between precipitation, evaporation, infiltration and runoff are not well known.

Lacking spatial measurements of wetland locations and sizes, hydrologic models often do not properly represent the effects of

surface storage on river discharge. Errors can exceed

100% because wetlands moderate runoff through

temporary storage and change the surface area available for

direct interception of precipitation and free

evaporation. While earth system models continue to

improve through incorporation of better soils, topography, and

land-use land-cover information, their representations of the

surface water balance are still greatly in error, in part due to the

absence of an adequate observational basis for

quantifying river discharge and surface water storage.

Recent efforts have demonstrated that direct water surface-to-atmosphere carbon

evasion are an important component of the carbon cycle. Calculation of organic carbon fluxes requires knowledge of

the spatial distributions of aquatic ecosystem habitats,

such as herbaceous macrophytes and flooded forests, and estimates of carbon evasion require

measurements of the spatial and temporal variations in the

extents of inundation.

WatER will be an interferometric altimeter which has a rich heritage based on (1) the many highly successful ocean

observing radar altimeters, (2) the Shuttle Radar Topography Mission (SRTM), and (3) a development effort for a Wide Swath Ocean Altimeter. WatER would provide surface elevation data in a 120 km wide swath using two Ka-band synthetic aperture

radar (SAR) antennae at opposite ends of a 10 m boom. Interferometric SAR processing of the returned pulses will yield a 5m azimuth and 10m to 70m range resolution, with elevation accuracy of ± 50 cm. Polynomial based averaging increases

the height accuracy to about ± 3 cm. The orbital repeat cycle is designed to permit a global sampling of all surface water bodies

every 8 days using a collection of ascending and descending tracks in a 16 day repeat period.

Designed by Natalie Johnson, the Ohio State University

Predicted dh/dt

Actual dh/dt

cm

cm

Coverage from a pulse limited altimeter severely under samples rivers and especially lakes16-day repeat (i.e.,

Terra) coverage misses ~30% of rivers and ~70% of lakes in the data bases (CIA-2; UNH; UH)

120 km swath instrument misses very few lakes or rivers~1% for 16-day repeat

and ~7% for 10-day repeat

0 5 10 15

0 5 10 15

Funding provided by CNES, JPL, the Ohio State University, and the Terrestrial Hydrology

Program at NASA

SRTM DEM

1993 Beruri

0

100

200

300

400

500

600

700

800

900

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

11 Apr: 618 cm

26 Feb: 375 cm

dh = 243 cm

Predicted dh/dt

cm

1993 Itapeua

0

100

200

300

400

500

600

700

800

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

11 Apr: 561 cm

26 Feb: 372 cm

dh = 189 cm

1993 Manacapuru

0

100

200

300

400

500

600

700

800

900

1000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

11 Apr: 772 cm

26 Feb: 532 cm

dh = 240 cm