Transcript Document

SWOT
Surface Water and
Ocean Topography Mission
Risk Reduction Activities
Ernesto Rodríguez
Jet Propulsion Laboratory
California Institute of Technology
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Risk Reduction Study
Selection Process
SWOT
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Mission Definition Studies: required prior to mission start!
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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
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Technology Risk Studies: required to retire major mission technology risks
prior to mission start
– On NASA side: Instrument Incubator Program (IIP) proposal
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Programmatic goals:
– Coordinated progress between CNES phase zero studies and NASA studies
– Mission Concept Review in FY 2009
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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 sciencecost 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 sciencecost 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:
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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 sunsynchronous orbit is not feasible. Candidate
orbits with inclination > 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)
140 km
Deliverables:
– Orbit definition document (5/2008).
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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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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:
1. 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.
2. 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.
3. Assess the impact of the nadir altimeter and multi-channel
radiometer.
calib ration points
deviation
from fit
Spacecraft Roll
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Task 4: Instrument Error Budget and
Calibration
s/c roll
Xov er
N -2
Xov er
N -1
Xov er
N
Xov er
N +1
Xov er
N +2
time / distance along track
Path delay (PD) error from 3-12 km as a function of
PD and cloud liquid water (CLW) standard deviation
92, 130, 166 GHz
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).
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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 (<5
days)
• For each cross-over, estimate the
baseline roll and roll rate for each of the
passes using altimeter-interferometer and
interferometer-interferometer cross-over
differences, which define an overconstrained 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”.
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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.
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Observations will be coupled with wind and surface
conditions to better define limiting cases
Predict mission impact or constraints
Deliverables:
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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 Reduction
NASA 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-I’s)
– Proposals expected to be adjudicated in
Spring (or early summer?)
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Technology Risk Reduction
NASA 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
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