Satellite Altimetry Status

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Satellite Altimetry Status ProductsPart 2Do
GODAE models need upcoming altimetry missions ?
G.Dibarboure G.Larnicol J.Lambin
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Introduction

• Starting points ( ) recent history shows
  that we should not take altimetry for granted
• Operations of old missions difficult to carry on
  (GFO, Jason-1, ENVISAT)
• Decision process for new missions long and
  complex (Jason-3 not fully approved)
• Specific OSE/OSSE/impact studies were performed
  by CLS ( ) upon requests from CNES ESA
  to provide material in a time span compatible
  with the decision process
• What is at stake for the long term ( ) ?
• Old missions decommissioned, future ones not
  approved (risk no data whatsoever)
• Integration of subpar missions in DUACS not
  certain (risk no SLA product whatsoever)
• The role of GODAE as a prescriber for the
  altimetry constellation
• Questions for GODAE members ( )
  considering operational metrics
• What should be the status of routine GODAE
  indicators when a satellite is added/lost ?
• Can we use OSE/OSSE outputs to refresh evidence
  that GODAE models need altimetry ?
• Can routine metrics show evidence that GODAE
  specifically needs mission X or Y ?
• Does this still holds if they are subpar
  (degraded performance, aging, drifting orbit) ?
• Should OSSEs performed on the observing system
  itself remain a quick and cheap complement to
  model-based recommendations ?

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Recent altimetric events (1/2)

• Jason tandem now fully operational
• Excellent results and consistency between Jasons
  (July 08)
• Used by DUACS in August 2008 (anomaly on Jason-1)
• But the Jason tandem started only in early March
  09 (no green light from project, conservative
  Cal/Val approach)
• With more operational evidence, could we have
  gained up to 6 months of tandem
• General statements (3 - 4 sats) and tandem
  results were considered well-published ? Mostly
  ignored in 2008
• WARNING Nasa funding for Jason-1 after 2010
• Recently jeopardized (do you need a tandem
  anyway?)
• Can we use GODAE outputs to illustrate the need
  for more tandem data and the specific need for
  extended Jason-1 operations ? (deadline July)

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Map of Absolute Dynamic Topography Animation
Jason-2 vs Tandem
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Recent altimetric events (2/2)

• GFO stopped after 11 years of service after a
  critical onbard failure
• Twice, Navy ( NOAA) asked for evidence that
  operations were still worth funding despite her
  aging problems and limited coverage
• Inputs based on operational DUACS metrics
  provided with highlights of GFO contribution ?
  Operations successfully defended twice
• Can routine metrics from models providemore
  evidence if a similar case arise ?
• Can we deploy them fast enough to be compatible
  with the decision process ?
• Should minimalistic outputs from DUACS remain an
  official complement to model studies as a
  contribution to a dedicated GODAE task force ?

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Formal mapping error of the multi-satellite
objective analysis in of the signal variance
(black line), and missing GFO data on ocean (grey
histogram) and quality levels (colors)
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• Blue level 3 missions nominal
• Green level  2 missions 100, GFO 50
• Orange level 1 mission unavailable
• Crimson level 1 mission unavailable anomaly
  on a second mission

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What about altimeter oldies ?
of additional variance when geodetic data from
ERS-1 are added to T/P

• Jason-1 status (8yo gt extended lifespan)
• Intruments are performing well (tandem gt JA1/TP)
• Most redundant equipment safeties burnt already
• The next major failure might be the last one
• ENVISAT status (7yo gt extended lifespan)
• Degraded quality (S-Band lost)
• Option considered by ESA drifting phase by
  mid-2010 ? Any use for altimetry users ?
• Geodetic phase of ERS-1 in DUACS since 2008
• Extended phase of ENVISAT can be used by DUACS
  after 2010 (but with additional errors)
• Multi-satellite mapping OSE a driftingdegraded
  ENVISAT is still a noteworthy sampling addition
• Are drifting data relevant for GODAE models ?
  Despite the additional errors ?

Map of SLA (1994/07/20) for TP (left) and
TPERS1geodetic (right)
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Upcoming additions to DUACS

• AltiKa likely available in DUACS in 2011
  probably in line with ENVISAT quality with minor
  concerns about influence of rain
• CryoSat
• Launched in December 09, data possibly available
  during the commissionning phase (if requirement
  is adamant)
• Ocean L2 product still being discussed but not
  secured(CryoSat-specific requirements from GODAE
  might help)
• Limitation no dual frequency, no radiometer,
  drifting orbit
• OSSE DUACS ? Same results as for drifting ENVISAT
  (sampling wins over error budget)
• Would GODAE models also benefit from improved
  processing and minimized errors? (ongoing project
  SLOOP)
• More generally, would drifting altimetry
  (geodeticocean) be acceptable for models
  despite the additional errors ?

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Mapping-based impact study for CryoSat and AltiKa
mapping reconstruction error normalized by the
mapping error of Jason-2 alone
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Other opportunities

• Sentinel 3 tandem ?
• Sampling from one S3 is good (mapping OSSE)
• S3-B fully redundant sampling (for altimetry,
  OC-oriented)
• Alternative orbit options can better exploit the
  S3A/S3B tandem
• We will need more evidence to back-up the need
  for a S3 altimetry tandem
• HY-2 ? (Chinese mission with CNES contribution)
• Availability in Near Real Time not confirmed
• Actual quality level still unknown
• New ground track geodetic phase after 2 years
• Should we run a dedicated OSSE to back-up the
  the need for HY-2 data ?
• A second Geosat follow-on ?
• Jason-class quality ? Open data policy ?
• Ground track and orbit-related sampling values
  well-known

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Mapping-based OSSE for Sentinel-3A mapping
reconstruction error in the Gulf Stream
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Three altimeters in operations ?

• OSE/OSSE figures of merit can be used in a
  combinatorial probabilistic model
• To quantify the ability of a given satellite to
  strengthen the constellation
• To see if mission X or Y would be a better option
• To identify false improvements (redundant
  sampling) or critical periods
• Probability model to get
• 3 fully operational missions (100 of the time)
• On different ground tracks (Jason-1 / Jason-2,
  AltiKa / ENVISAT)
• CalVal phase redundant sampling (failure prob
  cancelled by Ja-2)
• Interleaved phase probabilities stack
• At nominal quality level (e.g mapping OSSE says
  CryoSat 50)
• Typical figures
• Nominal satellite lifespan 75 chance to have
  the ground track covered
• Probabilistic death at 2.2 nominal lifespan
• Risk of failure at launch (or early life
  anomalies) not taken into account

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Do GODAE models need a reference mission ?
Regional MSL trend differences between Jason and
GFO (-10/10 mm/year)

• Jason-3 is not fully approved (do we need it
  anyway ?)
• Primary use high-precision and reference ground
  track (ongoing OSE-like work on MSL
  applications)
• Can be used to minimize geographically correlated
  errors on other missions (TP era ?)
• In 2013, other missions might achieve a good
  POD level (acceptable large scale errors ? TBC)
• DUACS maps do need a large scale reference
• What about GODAE models ?
• Would mesoscale-oriented missions be enough or
  do models need good accuracy on large scale as
  well ?
• What new GODAE metrics (OSSE/routine indicators)
  could help illustrate long-term need for a
  reference mission ?

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Global MSL trend for Jason and ENVISAT after
2004, Jason was used to detect and minimize
errors on ENVISAT
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Conclusion (1/2)

• Altimetry constellation status
• New Jason tandem operational and ENVISAT still
  active ? OK status today
• Constellation remains extremely fragile (no
  spare, Jason-1 operations stopped in 2011?)
• Funding new missions and operations on old
  satellites is difficult
• General considerations (3 4 satellites) are not
  enough (we need to ask for mission X or Y)
• Even what might seem obvious requirements (Jason
  S3 tandems, Jason-3) need new or  refreshed 
  scientific evidence ? Altimetry should not be
  taken for granted
• CLS performed many OSE or OSSE-like studies
• Generally short and mission/application oriented
  ? useful when we either lack time or money
• The outputs are now used to build DUACS
  operational Key Performance Indicators
• Advantages of the DUACS approach analyses
  limited to the observing system
• Useful as a cheap complement to detailed
  model-based outputs
• Easy to set up and customize (comparing 20
  variants is possible ? helpful for early designs)
• More sensitive to subtle differences (changes in
  orbit, payload, processing)

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Conclusion (2/2)

• This work does not replace in-depth impact
  studies based on models
• GODAE model requirements would be an order of
  magnitude stronger if provided with solid
  evidence based on recent OSE/OSSE, metrics, and
  indicators (agency/mission specific)
• If routine model metrics can supplement OSSE
  studies, it is important to exploit them to
  illustrate major events on the altimetric
  constellation
• DUACS impact studies can incorporate new metrics
  derived from model-based outputs
• Integrating subpar missions and Real Time high
  or low priority for DUACS (sampling vs error) ?
• To be a strong altimetry prescriber, GODAE needs
  a specific task force
• Able to run quick impact studies to assess the
  gain/loss associated to a major change in the
  constellation ? In a time span compatible with
  the agencies calendar needs
• Able to make mid-term requirements about upcoming
  opportunities with new and solid evidence
• To have more weight, impact studies performed
  without models need to remain in line with model
  requirements, and they need to be one component
  of this GODAE task force

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