Why a Hydrology Mission Needs TwoDimensional Acquisitions of Water Surface Elevations

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Why a Hydrology Mission Needs Two-Dimensional
Acquisitions of Water Surface Elevations
Doug Alsdorf Ohio State Univ. Paul Bates
Univ. of Bristol Dennis Lettenmaier Univ. of
Washington Delwyn Moller JPL Ernesto
Rodriguez JPL Matt Wilson Univ. of Exeter
We welcome everyone to join and participate in
WatER!
Seed funding from Ohio State University, CNES,
JPL, and the Terrestrial Hydrology Program at
NASA
www.geology.ohio-state.edu/water
alsdorf.1_at_osu.eduwww.legos.obs-m
ip.fr/recherches/missions/water
nelly.mognard_at_cnes.fr
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Three Key Points for this Talk

• One
• We do not want to do gauging from space!
• Two
• Profiling altimetry does not sample all of the
  worlds freshwater bodies and provides almost no
  knowledge of wetland flow.
• Three
• Wetlands and floodplains have complex flow that
  require 2D sampling.

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Science and Application Objectives for WatER

• Primary Objective of WatER
• To determine where water is stored on Earths
  land surfaces, and how this storage varies in
  space and time.
• Additional Hydrology Goals
• Improve our understanding of flood hazards by
  measuring flood waves and water elevations, which
  are critical for hydrodynamic models.
• Freely provide water volume information to
  countries who critically rely on rivers that
  cross political borders.
• Map the variations in water bodies that
  contribute to disease vectors (e.g., malaria).

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Measurements Required to Address Science
Applications Themes h, ?h/?x, ?h/?t, and area,
globally, on a weekly basis
?S in floodplains, wetlands, lakes S ?h/?t of
inundated area
Muskingum R., Ohio
Siberian Arctic
Q in rivers fn(h, ?h/?x, ?h/?t, and area)
Alsdorf, D. and D. Lettenmaier, Science,
1485-1488, 2003.
Photos B. Kiel, K. Frey
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Stream Gauges
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Gauging from Space
OSTP 2004 Does the United States have enough
water? We do not know. What should we do? Use
modern science and technology to determine how
much water is currently available
Amazon 6 M km2, 175,000 m3/s U.S. 7.9 M km2,
Mississippi 17,500 m3/s
Birkett, C.M., L.A.K. Mertes, T. Dunne, M.H.
Costa, and M.J. Jasinski,Journal of Geophysical
Research, 107, 2003. Hirsch, R.M., and J.E.
Costa, EOS Transactions AGU, 85, 197-203, 2004.
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Problems With Profiling Altimeters Global
Coverage

• Global lake and river coverage study using
  Terras 16-day repeat cycle (98º inclination,
  sun-synchronous).
• Profiling Altimeter
• 32 of the rivers and 72 of the worlds lakes
  are not sampled
• 14 and 9 of the worlds top 150 rivers and lakes,
  respectively, are not sampled (largest missed
  discharge is nearly 10000 m3/s, largest missed
  area is 6000 km2)
• About half of worlds rivers sampled only once or
  not at all, no ?h/?x thus no Q. Remaining half
  will have a ?t in the ?h/?x.
• Temporal sampling is not weekly
• Swath Interferometer
• 1 of rivers and lakes are missed by an imager
• Swath provides h, ?h/?x, ?h/?t, and area in one
  overpass
• Temporal sampling is weekly, or better

Alsdorf, D., E. Rodriguez, and D. Lettenmaier,
Measuring surface water from space, Reviews of
Geophysics, in review.
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5. Thawing permafrost and associated thermokarst
development is causing lakes and wetlands to
expand in northern Siberia...
Photo courtesy of Karen Frey
L. Smith AGU 2005 Frontier Lecture
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...but disappear further south
Smith et al., Science, 2005
L. Smith AGU 2005 Frontier Lecture
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Spaceborne Measurements Are NOT a Gauge
Replacement Strategy, but are complementary
Gauges have a high temporal sampling which can be
complemented by the vast spatial sampling
available from spaceborne technologies.
Lake Water Surface Area North of 45.5N is 589,000
km2 Wetland area North of 45.5N is 4.5M km2
Amazonian wetlands are 750,000 km2
Gauges are not installed in these complex
hydro-geomorphologies, and it is very unlikely
that a network of in-situ measurements will ever
be placed in such environments, thus there are no
gauges to replace. 1D in-situ methods are
incapable of measuring these 2D hydraulics.
Photos L. Hess, K. Frey
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Problems With Profiling Altimeters Local Coverage
cm
SRTM DEM
m
Actual dh/dt
cm
dt 44 days
dt 44 days
dt 44 days
cm
Predicted dh/dt
Predicted dh/dt
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1D Sampling Estimate 2D Sampling Observed
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Floodplain Hydraulics from Repeat Pass
Interferometric SAR
Perspective views of dh/dt. Surface water
mission should be capable of measuring these
hydraulics.
12 Jul 96 15 Apr 96
29 Jun 97 2 Apr 97
Views are 70x70km
Flow hydraulics vary across these images.
Floodplains are not bathtubs. Arrows indicate
that dh/dt changes across floodplain channels.
11 Apr 93 26 Feb 93
DEM
Alsdorf et al., Nature, 404, 174-177, 2000
Alsdorf et al., Geophysical Research Ltrs., 28,
2671-2674, 2001 Alsdorf et al., IEEE TGRS, 39,
423-431, 2001.
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Floodplain Flow Directions from Interferometric
SAR
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Channel Slope and Amazon Q from SRTM
Q m3/s Observed SRTM Error Tupe 63100 62900 -0.3
Itapeua 74200 79800 7.6 Manacapuru 90500 84900 -6
.2
10 km
Mannings n method
LeFavour and Alsdorf, GRL, 2005 Kiel et al.,
PERS, 2006
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Conclusions
WatER is not a gauge replacement strategy. It is
an altogether new way of understanding water
storage and flow. Water fluxes and volume
changes are more than a 1D process. Profiling
altimeters repeat 1D, in-situ gauge approaches
whereas WatERs KaRIN will provide
two-dimensional h, dh/dt, and dh/dx about once a
week, thus yield ?S and Q globally
We welcome everyone to join and participate in
WatER!
www.geology.ohio-state.edu/water
www.legos.obs-mip.fr/recherches/missions/water