Surface Water Interferometric Altimeter Concept

1
1. The Problem
2. Science Questions Societal Applications
100 Inundated!
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.

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 worlds 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.
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.
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.
In-situ cannot measure this
the WatER Satellite Water Elevation Recovery
Mission A Joint ESANASA Proposal Effort Nelly
Mognard, E.U. WatER PI, nelly.mognard_at_cnes.fr,
www.legos.obs-mip.fr/recherches/missions/water/ Do
ug Alsdorf, U.S. WatER PI, alsdorf.1_at_osu.edu,
www.geology.ohio-state.edu/water Where is water
stored on Earths land surfaces, and how does
this storage vary in space and time?
3. Measurements Required Images of h, which
yield images of dh/dt and dh/dx
4. The Solution KaRIN Ka-band Radar
Interferometer. SRTM, WSOA heritage.
Images of h globally every 8 days.
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 worlds 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.
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

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.

• Coverage from a pulse limited altimeter severely
  under samples rivers and especially lakes
• 16-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

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
Funding provided by CNES, JPL, the Ohio State
University, and the Terrestrial Hydrology
Program at NASA
Designed by Natalie Johnson, the Ohio State
University