Surface%20Water%20and%20Ocean%20Topography%20Mission%20Risk%20Reduction%20Activities

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Surface Water and Ocean Topography MissionRisk
Reduction Activities

• Ernesto Rodríguez
• Jet Propulsion Laboratory
• California Institute of Technology

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Risk Reduction StudySelection Process

• Mission Definition Studies required prior to
  mission start!
• Define mission science requirements
• Assess the feasibility of meeting the measurement
  requirements ( iterate)
• Define mission implementation requirements
  (feasibility cost iterate)
• Retire phenomelogy risks (Wet tropo, river
  backscatter/resolution, EM bias, iterate)
• Mission definition plan iterated during November
  and December with SWG
• Technology Risk Studies required to retire major
  mission technology risks prior to mission start
• On NASA side Instrument Incubator Program (IIP)
  proposal
• Programmatic goals
• Coordinated progress between CNES phase zero
  studies and NASA studies
• Mission Concept Review in FY 2009
• Detailed discussions on the partnering
  responsibilities, schedule and milestones are
  ongoing and will be clarified in this meeting and
  a subsequent meeting (Monday) in Toulouse

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Water HM Year 1 Objectives

• The SWOT design must be tuned to meet the science
  requirements from both communities in the most
  efficient fashion.
• This requires formalizing both the science
  requirements as well as the mission and
  instrument design, so as to deliver accurate
  performance, risk and cost assessments.
• The proposed FY08 overall objectives are
• Finalize science goals and derive level 1
  requirements
• Formalize a mission and system design and assess
  its end-to-end performance.
• Identify all instrument and mission risk areas
  and perform cost assessment.
• These objectives are implemented as six separate
  tasks, described in the following viewgraphs.

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Task 1 Oceanography science studies

• Objective the Science Working Group will
  identify the mission Level 1 ocean science
  requirements and rationale with detailed
  science-cost trade-offs.
• Rationale The science requirements constitutes
  the baseline that enables the mission definition
  team to start developing a mission and instrument
  design.
• Approach
• Definition of the science scope and significance
  for sub-mesoscale processes and translation into
  measurement requirements (April 2008 workshop)
• Review and development of improved coastal and
  internal tide models.
• Review of state-of-the-art mesoscale atmospheric
  water vapor modes and development of improved
  algorithms for conventional radiometer
  water-vapor retrieval in coastal areas.
• Develop science questions in mesoscale air-sea
  interaction processes.
• Deliverables
• SWG report (10/2008).

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Task 2 Hydrology science studies

• Objective the Science Working Group will
  identify the mission Level 1 hydrology science
  requirements and rationale with detailed
  science-cost trade-offs.
• Rationale The science requirements constitutes
  the baseline that enables the mission definition
  team to start developing a mission and instrument
  design.
• Approach
• Definition of the spatial and temporal sampling,
  spatial resolution, and height accuracies
  requirements for understanding water storage
  changes.
• Studies coordinated with Virtual Mission studies
  funded by NASA terrestrial hydrology program
• Studies also coordinated with ongoing studies at
  LEGOS and Bristol
• Deliverables
• SWG report (10/2008).

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Key Outcome from Science Studies

• Science definition document (Level-1
  requirements)
• Instrument team (on both sides) need this by 2007
• Although this goal may be a bit too aggressive
• A preliminary working version would be nice, of
  course
• Some important issues
• Full coverage needed (no gaps, land or ocean)?
• Temporal sampling requirements?
• Required small and long wavelength accuracy?
• Land Coastal mask?
• Data product definition?
• Data product latency?

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Task 3 Mission Orbital Design Definition
Example Water HM sampling (9.95 days)

• Objective To finalize an orbit selection that
  balances and satisfies the hydrology and
  oceanographic requirements and constraints
• Rationale Finalizing the orbit selection is
  imperative as a key driver for many instrument
  and mission design decisions
• Approach Due to tidal aliasing, a
  sun-synchronous orbit is not feasible. Candidate
  orbits with inclination gt 75o and altitudes
  ranging from 800-1000km are proposed that are
  acceptable in terms of sampling and coverage
  goals.
• Down-select orbit based on mission (i.e. launch
  vehicle candidacy/cost), instrument (i.e. power)
  and scattering predictions (i.e. achievable swath
  based on geometry)
• Deliverables
• Orbit definition document (5/2008).

140 km
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Key Outcome

• Define orbit altitude, inclination, and subcycles
• Needed to define calibration accuracy
• Needed for instrument power
• Needed for sizing antenna
• Needed to define launch vehicle
• Needed to define ground stations required

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Task 4 Instrument Error Budget and Calibration

• Objective Develop an integrated measurement
  error budget and calibration simulation tools
  capable of predicting mission performance for
  design trade-studies.
• Rationale To optimize instrument performance by
  characterizing noise errors and developing
  necessary calibration schemes.
• Approach Three primary subtasks will be
  developed
• An integrated measurement error budget for the
  system that accounts for random and systematic
  instrument noise errors, as well as
  (uncompensated) wet-tropospheric delays and the
  impact of vegetation.
• To develop and validate suitable calibration
  schemes (cross-over and DEM-based) using
  realistic errors sources and tailored to a) open
  ocean, b) coastal regions and c) large inland
  water bodies, and rivers, wetland, and small
  lakes.
• Assess the impact of the nadir altimeter and
  multi-channel radiometer.
• Deliverables
• Instrument error budget (7/2008).
• Calibration techniques for error mitigation
  (8/2008)
• Nadir altimeter and radiometer system
  requirements document (8/2008)
• Error budget for floodplain topography (9/2008).

Path delay (PD) error from 3-12 km as a function
of PD and cloud liquid water (CLW) standard
deviation
92, 130, 166 GHz
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Ocean Cross-Over Calibration Concept

• Roll errors are the dominant error source for
  WSOA and must be removed by calibration. Residual
  range and phase errors are also removed.
• Assume the ocean does not change significantly
  between crossover visits (lt5 days)
• For each cross-over, estimate the baseline roll
  and roll rate for each of the passes using
  altimeter-interferometer and interferometer-interf
  erometer cross-over differences, which define an
  over-constrained linear system.
• Interpolate along-track baseline parameters
  between calibration regions by using smooth
  interpolating function (e.g, cubic spline.)

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WSOA Distribution of Time Separation Between
Calibration Regions
The revisit statistics will change for SWOT due
to orbit changes
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WSOA Sea Surface Height Performance
Input roll errors based on Alcatel 99 study 2
dominant components with 50 sec/97cm and 2 sec/2
cm periods/amplitudes - worst case assumption
since both error sources are inside the
1sec-80sec passband.
Pixel Size 14 km
Height error includes both random and residual
systematic errors
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Height Error Performance for 14 km Resolution
LANL Model Variability

• Error estimated based on T/P cycles 22-39
• No smoothing to height data has been applied

Simulation Normalized Error
Simulation RSS Error
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WSOA Velocity Estimation Error
LANL Model Geostrophic Velocity
Estimation window 45km
WSOA Simulated Geostrophic Velocity
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V Component Velocity Error
Error estimated based on T/P cycles 22-39
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Assessment of Wet-Tropo Errors

• Use regional models to generate realistic
  wet-tropo signals (coast, inland rivers, large
  bodies)
• Simulate instrument raw heights
• Assess error magnitude and spatial scale
• Does error need to be corrected?
• Can error be corrected by large scale NWP wet
  tropo?
• What is the impact of a radiometer?
• How well does land calibration work?

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Hydrology Issues

• How well does land calibration work?
• What is to be done with rivers above SRTM
  coverage?
• Can high latitude frequent revisits be used so
  that DEM calibration is not required?
• Can river bed/flood-plain topography be retrieved
  with significant accuracy?
• Is this a mission data product?

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Task 5 Mission and Instrument Definition Study

• Objective To formalize an instrument and mission
  design that meets the science Level 1
  requirements
• Rationale To mature the mission/instrument
  design to support a detailed mass/power/cost
  assessment in Year 2.
• Approach
• Definition of key instrument parameters.
• Define the instrument to block diagram level, to
  identify its mechanical configuration, derive
  data rate budgets, and to identify key critical
  technology drivers.
• Identify key spacecraft requirements and
  implementation solutions that meet power
  generation (for continuous science data
  collection in the selected orbit), data handling
  (examining on-board compression, Solid-State
  Recorders, downlink subsystems, and ground
  stations requirements), and attitude control
  system requirements (accounting for mast, antenna
  and solar panel dynamics error budgets).
• Deliverables
• Mission definition document (8/2008).
• Instrument definition document (10/2008).

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Key Issues

• What are the measurement components?
• Jason type altimeter AMR or AltiKA with
  integrated radiometers
• What are the power requirements on the
  spacecraft?
• What are the attitude roll requirements of the
  spacecraft? Which spacecraft meet these
  requirements?
• What data rate is required?
• How can we download it?
• How can we process it?
• Are there key technologies that need to be
  developed prior to mission start?

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Task 6 Field Observations of Fresh Water Bodies

• Objective Expand Ka-band field observations of
  fresh water bodies to a greater range of
  environmental conditions.
• Rationale Initial observations indicate
  fundamental limits to the spatial resolution, and
  possibly swath loss at higher incidence angles
  (more pronounced at higher orbits). More
  comprehensive observations and analysis will help
  assess the extent of potential data compromise.
• Approach Using the same radar system as the
  previous campaign we will redeploy for a longer
  duration to capture a greater range of
  conditions.
• Observations will be coupled with wind and
  surface conditions to better define limiting
  cases
• Predict mission impact or constraints
• Deliverables
• Scientific journal paper reporting observations
  and analysis (9/2008).
• Question what about the EM bias for the ocean?

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SWOT Mission Definition Year 2 Objectives

• The overall objective for Year 2 is to ensure a
  FY10 start of Phase-A studies.
• To this end, we proposed to perform the following
  tasks (to be refined after year 1 studies)
• Provide a detailed mass and power breakdown with
  costing for the possible mission scenarios.
• Refine bus and launch vehicle accommodation
  requirements.
• Develop the suite of documents required for the
  Mission and System Readiness reviews.
• Design the ground data system and mature key
  algorithms for the data processing system.
• Retiring the critical risk items identified
  during the Year 1 studies.
• Refine the science questions initiated during
  Year 1.
• Define the science data products at levels 2 and
  3.

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Technology Risk ReductionNASA IIP

• The latest AO release of the NASA IIP was
  targeted for technology risk reduction of NRC
  decadal review missions
• JPL submitted a SWOT IIP proposal
• Lee Fu PI (Rodríguez, Alsdorf, Esteban, Brown,
  Hodges others co-Is)
• Proposals expected to be adjudicated in Spring
  (or early summer?)

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Technology Risk ReductionNASA IIP

• Technologies addressed
• On-board processor
• Needs to do onboard range compression, SAR
  processing, interferometry, averaging
  (calibration?)
• PRF is 10 faster than WSOA!
• Ka-band antenna
• Ka-band, long (4m) and skinny (15cm). What is
  the right architecture? Deployment? Multipath?
• High-frequency radiometer
• If one is needed, does it cover the swath? Nadir?
  How to implement it within current architectures?
• Proposal details fall under ITAR restrictions for
  the moment