Aquarius/SAC-D Mission Error Validation and Early Orbit Corrections Gary Lagerloef

Aquarius/SAC-D MissionError Validation and Early Orbit Corrections Gary Lagerloef6th Science Meeting; Seattle, WA, USA19-21 July 2010

219-21 July 2010

Error Validation & Early Orbit Corrections – Lagerloef6rh Science Meeting, Seattle, WA, USA

Three Phases

1. Pre-Launch

2. In Orbit Checkout (Launch + 45 days)

3. IOC + 6 months

319-21 July 2010


Phase 1 – Pre-Launch

• What: Generate a set of special case 7-day cycles– Specific cases: biases, drifts, etc, in following charts

• How: Use the operational mission simulator.– Start with daily files from RSS

– Add spurious signal for specific case study (see below)

– Input these to the mission simulator as test cases.

– Distribute and analyze (science team)

• Timetable:– September: Produce a subset of scenarios (L2 files)

– September-November: Analysis and assessment

– December: Operational Readiness Review (ORR)

419-21 July 2010


Scenario Flow Chart

Daily simulated files (RSS & JPL)

Mission Simulator

Daily Mission Simulator L1, L2, L3 files uploaded to

web site

Telemetry files to/from Cordoba

Level 1 > Level 2 > Level 3Routine Processing

Apply spurious signals for special case studies

Generate special case telemetry files

Level 1 > Level 2 > Level 3Special Case Processing

Special Case Simulator L1, L2, L3 files uploaded to

evaluation products web site with documentation

519-21 July 2010


Potential scenarios / rehearsals

Simulate certain special situations to test and analyze

Develop and test analysis tools

Demonstrate we can address these issues at ORR

1. Insert arbitrary biases in all channels

2. Simulate arbitrary drifts in all channels

3. Orbit harmonics calibration drifts (1-4 harmonics, e.g.)

4. Simulate a complete cold sky maneuver

5. Solar flare

6. RFI

7. Attitude offsets & time tag offsets

8. Channel failure

a. H or V channel

b. P or M channel

9. Other suggestions … lunar, bi-static solar reflection, diffuse galaxy refl.

619-21 July 2010


Arbitrary biases in all channels

Generate test data:

1. Select a 7-day segment from the mission simulator input.

2. Add an arbitrary bias to each of the radiometer and scatterometer channels on each horn.

3. Process to L2 science data files, L3 bin-average and L3 smooth files.

4. Place the modified L1A, L2 and L3 files in an evaluation folder.

Science Team Analysis:

1. Assess effects on L2 science data file TAs, U, Faraday, wind speed and SSS

2. Develop and evaluate bias detection/removal techniques, and assess uncertainties.

3. Inspect the impact on L3 files as a diagnostic tool.

4. Set up follow-on blind test with unknown biases.

719-21 July 2010


Linear 7-day calibration drifts

Generate test data:

1. Select a 7-day segment from the mission simulator input

2. Add arbitrary drift (~0.1K/ 7-days) to each of the radiometer and scatterometer channels on each horn.


4. Set aside the modified L1A, L2 and L3 files in a special folder.



2. Develop and evaluate drift detection/removal techniques, and assess uncertainties.


4. Set up follow-on blind test with unknown drifts.

819-21 July 2010


Harmonic orbital calibration drifts

Generate test data:

1. Select a 7-day segment from the mission simulator input

2. Add arbitrary harmonic to each of the radiometer and scatterometer channels on each horn. (N cycles per orbit, N=1..3, with amplitudes ~0.1K)


4. Set aside the modified L1A, L2 and L3 files in a special folder.



2. Develop and evaluate drift detection/removal techniques, and assess uncertainties.


4. Set up follow-on blind test with unknown drifts.

919-21 July 2010


Phase 2 – In Orbit Checkout

• Aquarius Commissioning phase timeline

• Science Commissioning approach

• Critical events and Science Tasks

• Preliminary Acceptance Criteria

1019-21 July 2010


Early Orbit and Commissioning

C-10

1119-21 July 2010


Aquarius Instrument Commissioning Timeline

DPU On

Verify S/Pconfig

Deply heaters on

Time from launch (days)

Ground Coverage

Mission Phase

NEN

Cordoba

Matera

AQ Activities

Mission Design Team Product

Post Launch Assessment Review PLAR

ICDS

ATC

Scatterometer

Radiometer

L+25

L+26

L+27

L+28

L+29

L+30

L+31

L+32

L+33

L+34

L+35

Antenna Deployment

Instrument preliminaryPerformance assessment

AQ Instrument Deployment & Checkout Phase SAC-D instruments on

ICDS ON

ConfigATC cntrlr

DPU off

Deply reflector

Deply Boom

DPU On

ATC On

Upload patches

DPU + RFEs + RBEs ON

SCAT Tx single beam

SCAT Rx only

SCAT Tx ALL beam

11 days L+451 2 3 4 5 6 7 8 9 10

1219-21 July 2010


• Post-launch in-orbit checkout simulation: During the period from launch to L+25 days, the science team will compute simulated Tb and σ0 based on the final orbit maneuvers (Science Task 1).

– These data will provide “Expected Values” for each beam along-track to compare quantitatively with observations for both the engineering and science acceptance analyses.

• The science team will carry out an analysis sequence (Science Tasks 2-7) at each stage of the instrument turn-on sequence.

• Acceptance criteria are limited:

– The timeline only allows for one 7-day cycle after the instrument is fully turned on.

– Assess whether the data are “as expected” in qualitative terms and the sensor is “calibrate-able”.

– Gross geographical and geophysical features are as expected, biases can be removed, stability is reasonable, polarization differences are appropriate, etc. (details below)

Science Commissioning Approach

1319-21 July 2010


Aquarius Commissioning Science Tasks

1419-21 July 2010


• Land versus ocean features are clearly evident, both in terms of brightness temperature (Tb) contrast and location.

• V-H polarization differences for each incidence angle are consistent with the emissivity model

• The 3rd Stokes is small.• Incidence angle effects such as the V-pol (H-pol) Tb increasing (decreasing) from the

inner to outer beams consistent with emissivity model.• Relative stability is seen over known Earth targets such as Antarctic ice, rain forests,

and ocean.

• Scat σ0 sensitivity to wind speed within expectations for each channel

• RFI detection and filtering are functional • No detectable scat-radiometer interference• No detectable radiometer interference from other SAC-D instruments• SSS biases will be removed via ground data matchups and crossover difference

analysis; initial “first-look” 7-day map will be produced• We will also look for any large anomalous features that cannot be easily explained by

expected calibration issues that usually occur early in a mission.

Preliminary Acceptance Criteria

1519-21 July 2010


Phase 3 - IOC + 6 months

Evaluate match-up data between Aquarius and in situ observing system•Provide preliminary SSS bias removal and un-validated science data•Monitor and analyze calibration drifts and biases•Asses systematic and geographically correlated errors•Analyze Scatterometer wind speed algorithm•Analyze roughness effects on TH, TV and salinity algorithm•And more…..

Plan a science meeting for approximately IOC + 6 months•Asses calibration and validation results•Approve algorithm updates•Reprocess the first six months of data.

1619-21 July 2010


Approaches to De-biasing

• Each radiometer needs to be independently calibrated• First try to remove the gross offsets in the initial retrieved SSS

– Use reference salinity field globally

– AVDS matchups – tabulate for each beam

– Cross-over analysis to remove residual inter-beam biases

• With time, work through the re-calibration of retrieval coefficients

Buoy Obs.

Buoy Obs.

Search Radius

Search Radius

Match-up processing• One match-up file per buoy observation contains all the satellite data in the search radius• Subsequent processing to generate the optimal weighted average satellite observation per buoy• Global tabulations

Match-up processing• One match-up file per buoy observation contains all the satellite data in the search radius• Subsequent processing to generate the optimal weighted average satellite observation per buoy• Global tabulations

1719-21 July 2010


Remove orbit errors and biases

Beam 2 SSS (with constant and harmonic errors added)

Adjusted Beam 2 SSS (with constant and harmonic errors removed)

Beam 1 SSS (with harmonic errors added)

Adjusted Beam 1 SSS (with harmonic errors removed)

Cross over difference analysis to remove systematic errors between different beams

1819-21 July 2010


Validation Working Group

• Review activities for these three phases– Pre-lauch

– IOC

– IOC + 6 months

• Focus in ideas of the third phase

1919-21 July 2010


Validation - Theory

The satellite salinity measurement SS and the in situ validation measurement SV are defined by:

SS = S ± εS

SV = S ± εV

where S is the true surface salinity averaged over the Aquarius footprint area and microwave optical depth in sea water (~ 1 cm). εS and εV are the respective satellite and in situ measurement errors

relative to S. The mean square of the difference ∆S between SS and SV is given by:

<∆S2> = <εS2> + <εV

2>

where < > denotes the average over a given set of paired satellite and in situ measurements, and

<εSεV> =0.

Our objective is to validate that

<εS2> = <∆S2> − <εV

2> ≤ εR2

where εR is the allocated rms error requirement. The satellite measurement error is the difference

between <∆S2> and mean square in situ error <εV2>.

2019-21 July 2010


Validation Errors

εV is the rss of several terms:

εP is the difference error between a point salinity measurement and the area average over the

instantaneous satellite footprint (log-normal distribution, median ~0.05 psu, extremes ~0.5).

εO is an error due to the temporal or spatial offset between the satellite and in situ samples (many

buoys surface once every 10 days and will be paired with the nearest satellite pass).

εZ is the difference error between the skin depth (~1-2 cm) salinity and in situ instrument measurement

generally at 0.5 m to 5 m depth (can be >1 psu in rain).

εC is the in situ sensor calibration error, usually very small (<0.05 psu)

εV is the rss of several terms:

εP is the difference error between a point salinity measurement and the area average over the

instantaneous satellite footprint (log-normal distribution, median ~0.05 psu, extremes ~0.5).

εO is an error due to the temporal or spatial offset between the satellite and in situ samples (many

buoys surface once every 10 days and will be paired with the nearest satellite pass).

εZ is the difference error between the skin depth (~1-2 cm) salinity and in situ instrument measurement

generally at 0.5 m to 5 m depth (can be >1 psu in rain).

εC is the in situ sensor calibration error, usually very small (<0.05 psu)

Error Source CBE (psu) Confidence Remarks

εP 0.05 High Our analysis

εO 0.20 Moderate Temporal offset TBD

εZ 0.10 Low Pending Argo experiments

εC 0.05 Moderate-High Argo results

Total RSS 0.23

0.5 - 1.0 Moderate-High Error Budget

0.17 - 0.46 Moderate-High Wentz Retreival Simulation

Validation Error Summary Table

Aquarius Error per 6-sec Observation

Error Source CBE (psu) Confidence Remarks

εP 0.05 High Our analysis

εO 0.20 Moderate Temporal offset TBD

εZ 0.10 Low Pending Argo experiments

εC 0.05 Moderate-High Argo results

Total RSS 0.23

0.5 - 1.0 Moderate-High Error Budget

0.17 - 0.46 Moderate-High Wentz Retreival Simulation

Validation Error Summary Table

Aquarius Error per 6-sec Observation

2119-21 July 2010


εP = difference error between a point measurement and the area average

Ship tracks spatially filtered and differenced with point measurementsShip tracks spatially filtered and differenced with point measurements

2219-21 July 2010


εP = difference error between a point measurement and the area average

Log normal

εP ~ 0.05 psu

Log normal

εP ~ 0.05 psu

2319-21 July 2010


εO = error due to temporal or spatial offset between the satellite and in situ samples

Spatial structure function from ship track dataSpatial structure function from ship track data

Distance from footprint center

Nominally ~0.2 psu

2419-21 July 2010


εZ = difference error between the skin depth (~1-2 cm) salinity and in situ instrument

TOGA/COARE

R/V Wecoma

Skin (2cm) vs 2m and 5m depths during heavy

rain

TOGA/COARE

R/V Wecoma

Skin (2cm) vs 2m and 5m depths during heavy

rain

100 km

2519-21 July 2010


Argo Enhanced SSS Float Trials

Purpose: To obtain “skin” salinity and upper 5m gradient statistics

• Argo CTD nominally shuts off at ~5m• Steve Riser and Gary Lagerloef are testing

experimental Argo floats each with a secondary CTD sensor to profile to the surface. The primary CTD will shut off at ~5 m per normal operations.

• Sea-Bird developed a specialized “Surface Temperature Salinity” (STS) sensor which is programmed to profile the upper ~30 m and is inter-calibrated with the primary CTD

• We deployed the first at the HOT site near Hawaii late summer 2007.

• 20 more have been funded by NASA and deployed in the past 2 years. (S.Riser)

• New version funded including acoustic rain and wind measurements (S.Riser)

2619-21 July 2010


Validation Approach

• Match co-located buoy and satellite observations globally.• Account for various surface measurement errors.• Sort match-ups by latitude (SST) zones.

– Validate that the error allocations are met for the appropriate mean number of samples within the zone, or

– Calculate global rms over monthly interval

The Current Best Estimate (CBE) includes instrument errors plus all geophysical corrections such as surface roughness, atmosphere, rain, galaxy, solar, …

The Current Best Estimate (CBE) includes instrument errors plus all geophysical corrections such as surface roughness, atmosphere, rain, galaxy, solar, …

2719-21 July 2010


Documents

Aquarius/SAC-D Mission Error Validation and Early Orbit Corrections Gary Lagerloef