The Proposed WatER Mission and Oceanographic Applications

1
The Proposed WatER Mission and Oceanographic
Applications
The following slides provide a very brief
overview of the WatER technology, called KaRIN
(Ka-band Radar Interferometer) and potential
oceanographic applications. Please read the
first three slides if you have only a little
time, whereas the remainder provide some more
detail. The Hydrospheric Mapper uses the same
KaRIN instrument, but the satellite and
operations are designed for oceanographic uses.
We welcome everyone to join and participate in
WatER!
Doug Alsdorf, U.S. WatER PI, alsdorf.1_at_osu.edu
Nelly Mognard, EU WatER PI, nelly.mognard_at_cnes.fr
Ernesto Rodriguez, JPL Engineer of
KaRIN Lee-Lueng Fu, JPL, Topex/Poseidon Project
Scientist and over 150 participants from more
than 20 countries, world wide
Seed funding from Ohio State University, CNES,
JPL, and the Terrestrial Hydrology Program at
NASA
www.geology.ohio-state.edu/water
www.legos.obs-mip.fr/recherches/missions/water
2
Altimeter System Characteristics
3
Oceanic Processes Resolved by Different Missions

• TOPEX/Poseidon, Jason, and OSTM are primarily
  targeting basin scales (broken lines).
• WSOA extends the window to cover large eddies
  and fronts
• HM extends the window to cover coastal upwelling
  and other small-scale processes important to
  bio-physical interactions.
• Without HM, the details of ocean surface
  geostrophic currents cannot be fully resolved.

HM
Jason OSTM
4
Key Trade Issues Between WatER and the
Hydrosphere Mapper (HM)

• Both WatER and HM share an identical radar
  hardware. HM complements WatER with a water
  vapour radiometer for making wet tropospheric
  delay corrections. This is a relatively minor
  addition since the OSTM radiometer can be used
  directly.
• In order to reduce cost and increase system
  stability, a sun-synchronous orbit was chosen for
  WatER. This orbit selection is not optimal for
  the observation of tides, since the solar tides
  are aliased.
• The oceanographic community is divided about the
  importance of this many believe open ocean tides
  are known with an appropriate accuracy, while
  others worry about coastal tides, non-linear
  tides, and long period tidal aliasing in the
  global sea level rise signal. This is the primary
  disagreement between the WatER and HM user
  communities.
• A solution exists which will meet both the WatER
  and ocean requirements (including tides) at
  greater cost than the WatER concept.
• Many of the HM science goals, which concentrate
  on ocean mesoscale signals and bathymetry, will
  be met with the WatER instrument a radiometer.

5
Different Altimeter Coverage Capabilities
OSTM Sampling (10 day cycle)
WSOA Sampling (10 day cycle)
Hydrosphere Mapper (16 day cycle)
6
Ocean Eddies Transport Heat Affecting Global
Climate Change

• OSTM does not resolve eddies.
• WSOA would resolve open ocean eddies at low and
  mid latitudes, but
• only HM could resolve small eddies in coastal
  and high-latitude oceans.

WSOA resolution
observations
with eddies
without eddies
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Small-Scale Variability of the Ocean Unresolved
by Nadir Altimetry
ground tracks of Jason (thick) and T/P (thin)
Tandem Mission
10 km scale eddies Resolvable by HM
100 km
100 km scale eddies resolvable by WSOA
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Meeting Bathymetry Requirements

• The bathymetry requirements are (Sandwell et
  al)
• 1 mrad slope accuracy
• 4 km spatial resolution
• Using conventional altimetry (e.g., the proposed
  Abyss mission) these requirements could be met
  with a 6-year mission
• Coverage limited does not include higher
  latitudes
• Ocean mesoscale variability may limit slope
  accuracy
• The Hydrosphere Mapper will achieve the goals of
  the Abyss mission in less than 1-year data
  collection. Additional time can be used to reduce
  mesoscale ocean errors.

Current state of knowledge of Geoid Slope
From Sandwell et al.
Hydropshere Mapper slope accuracy after 14 days
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Surface Water Measurement Requirements

• Height accuracy 5 cm - 10 cm
• Current nadir-altimeter capability 20 cm - 30
  cm
• Hydrosphere Mapper 1 cm precision, 5 cm - 7cm
  systematic errors
• Slope accuracy 10 mrad (1 cm/ 1km)
• Current nadir capability cannot be done due to
  lack of swath imaging
• Hydrosphere Mapper better than 3 mrad in a
  single measurement for most rivers
• Spatial resolution 100 m imaging
• Nadir altimetry 2 km
• Hydrosphere Mapper better than 100 m
• Spatial coverage global
• Nadir altimetry misses most wetlands and 1/3 of
  rivers
• Hydrosphere Mapper complete coverage
• Temporal coverage 2 weeks in tropics, better
  at higher latitudes
• Nadir altimetry 10 day repeats
• Hydropshere Mapper meets requirements
• Requirements derived from Alsdorf and Lettenmaier
  (Science, 2003) and the NASA Surface Water
  Working Group

10
Nadir Altimeters are Incapable of Mapping
Wetlands and Non-Channelized Flow

• Wetlands are globally distributed. Nadir
  altimetry will miss 73 of all wetlands
• Nadir altimetry will miss 33 of all rivers,
  including multiple rivers in the top 100 by
  discharge.
• Wetlands and floodplains have non-channelized
  flow, are geomorphically diverse point
  measurements(I.e., nadir altimetry) will not
  provide necessary Q and DS.
• Need a global dataset of Q and DS concomitant
  with other hydrologic missions (e.g., soil
  moisture, precipitation). Q DS verify global
  hydrologic models.

Non-Channelized Flow
Wetland distribution
Matthews, E. and I. Fung, GBC, 1, 61-86, 1987.
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Example of Wetland Flow ComplexitiesNeed for an
imaging instrument
Interferometric SAR measurements of ?h/?t show
temporal and spatial dynamics in wetland flows
(arrows) that can only be measured with image
based technologies, not nadir altimetry. These
dynamic hydraulics govern sediment and
biogeochemical fluxes (e.g., carbon cycle).
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.