1-1risk reduction studies for swot february 1, 2008 swot surface water and ocean topography mission...

1-1Risk Reduction Studies for SWOT February 1, 2008

SWOTSWOT

Surface Water and Ocean Topography Mission

Risk Reduction Activities

Surface Water and Ocean Topography Mission

Risk Reduction Activities

Ernesto Rodríguez

Jet Propulsion Laboratory

California Institute of Technology


SWOTSWOT Risk Reduction StudySelection Process

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


SWOTSWOT Water HM: Year 1 ObjectivesWater 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.


SWOTSWOT Task 1: Oceanography science studiesTask 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).


SWOTSWOT Task 2: Hydrology science studiesTask 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).


SWOTSWOT Key Outcome from Science StudiesKey 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?


SWOTSWOTTask 3: Mission Orbital Design

Definition

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 > 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).

Example Water HM sampling (9.95 days)

140 km


SWOTSWOT Key OutcomeKey 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


SWOTSWOT

Task 4: Instrument Error Budget and Calibration

Task 4: Instrument Error Budget and Calibration

time / distance along track

XoverN-2

XoverN-1

XoverN

XoverN+1

XoverN+2

calibration points

s/c roll

deviationfrom fit

92, 130, 166 GHz

Path delay (PD) error from 3-12 km as a function of PD and cloud liquid water (CLW) standard deviation

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.

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).


SWOTSWOT Ocean Cross-Over Calibration ConceptOcean 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 over-

constrained linear system.

• Interpolate along-track baseline

parameters between calibration regions by

using smooth interpolating function (e.g,

cubic spline.)


SWOTSWOTWSOA Distribution of Time Separation

Between Calibration RegionsWSOA Distribution of Time Separation

Between Calibration Regions

The revisit statistics will change for SWOT due to orbit changes


SWOTSWOT WSOA Sea Surface Height PerformanceWSOA Sea Surface Height Performance

Pixel Size: 14 km

Height error includes both random and residual systematic errors

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”.


SWOTSWOT Height Error Performance for 14 km Resolution

Height Error Performance for 14 km Resolution

• Error estimated based on T/P cycles 22-39

• No smoothing to height data has been applied

LANL Model Variability

Simulation RSS Error Simulation Normalized Error


SWOTSWOT WSOA Velocity Estimation ErrorWSOA Velocity Estimation Error

Estimation window:45km

LANL Model Geostrophic Velocity

WSOA Simulated Geostrophic Velocity


SWOTSWOT V Component Velocity ErrorV Component Velocity Error

Error estimated based on T/P cycles 22-39


SWOTSWOT Assessment of Wet-Tropo ErrorsAssessment 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?


SWOTSWOT Hydrology IssuesHydrology 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?


SWOTSWOT Task 5: Mission and Instrument Definition Study

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).


SWOTSWOT Key IssuesKey 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?


SWOTSWOTTask 6: Field Observations of Fresh Water

BodiesTask 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?


SWOTSWOT SWOT Mission Definition Year 2 Objectives

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.


SWOTSWOT Technology Risk ReductionNASA IIP

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-I’s)– Proposals expected to be adjudicated in

Spring (or early summer?)


SWOTSWOT Technology Risk ReductionNASA IIP

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

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