Level 2 scatterometer processing
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Level 2 Scatterometer Processing. Alex Fore Julian Chaubell Adam Freedman Simon Yueh. L2 Processing Flow. L1B geolocated, calibrated TOI σ 0. Average over block; filter by L1B Qual. Flags. L2 (lon, lat) L2 σ TOI + KPC. Ancillary Data: ρ HHVV, f HHHV , f VVHV Θ F (from rad or IONEX).

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Level 2 Scatterometer Processing

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Level 2 scatterometer processing

Level 2 Scatterometer Processing

Alex Fore

Julian Chaubell

Adam Freedman

Simon Yueh


L2 processing flow

L2 Processing Flow

L1B geolocated, calibrated TOI σ0

Average over block; filter by L1B Qual. Flags

L2 (lon, lat)

L2 σTOI + KPC

  • Ancillary Data:

  • ρHHVV, fHHHV, fVVHV

  • ΘF (from rad or IONEX)

L2 σTOA + KPC

Cross-Talk +

Faraday Rotation

Wind Retrieval

L2 wind + σwind

  • Ancillary Data:

  • -PALS HIGHWINDS 2009 data

  • Ancillary Data:

  • NCEP wind dir.

ΔTB retrieval

L2 ΔTB+ σΔTB


Level 2 scatterometer cross talk and faraday rotation mitigation strategy

Level 2 Scatterometer Cross-Talk and Faraday Rotation Mitigation Strategy

Alex Fore

Adam Freedman

Simon Yueh


Forward beam integration

Forward Beam Integration

  • We use Mueller matrix formalism

  • Mtot gives transformation from transmitted signal to received signal.

  • Model Srx for transmit H (SrxH) and transmit V (SrxV).

  • Received power for (H or V) is modeled as appropriate element of SrxH + that fromSrxV times instrument gain + noise.


Simulated total 0 performance

Simulated Total σ0 Performance

  • Total σ0 performance is independent of any Faraday rotation corrections or cross-talk removal.

  • De-biased RMSE will be below 0.1 dB for high σ0 for all beams.

  • Total L2 σ0 as compared to a area-weighted 3 dB footprint model function σ0 computed in forward simulation.

  • Total is σ0 wind retrieval is our baseline algorithm.

  • In future we may use the area-gain weighted model function σ0


L2 faraday and cross talk mitigation process flow

L2 Faraday and Cross-Talk Mitigation Process Flow

TOI:

(σHH, σHV, σVV)

Explicit fit trained on scale -model antenna patterns

Cross-Talk Correction

Cross-Talk Corrected:

(σHH, σHV, σVV)

2d non-linear minimization problem

Ancillary Inputs:

Faraday rotation angle

-radiometer

-IONEX

TOA:

(σHH, σHV, σVV)

Faraday Rotation Correction

Assumptions:

(ρHHVV, fHHHV, fVVHV ) per beam.

PALS HIGHWINDS

data


Cross talk correction

Cross-Talk Correction

  • Training data:

    • Forward simulated data with nominal antenna model.

    • Forward simulated data where cross-talk explicitly set to zero in beam integration. (This was done in a way to conserve total σ0 at level 2).

  • Computing the Fit:

    • Perform a least-squares fit of the HV σ0 in the absence of cross-talk to a simple distortion model.

    • Perform a second least-squares fit to determine how to distribute the remaining σ0 into the co-polarized channels.

    • Yields an explicit 3 parameter (α, β, γ) fit for each beam

Simplified Distortion Model:


Cross talk correction beam 1

Cross-Talk Correction - Beam 1

No cross-talk correction

With cross-talk correction

nesz≈-26.5


Cross talk correction beam 2

Cross-Talk Correction – Beam 2

With correction

No correction

nesz≈-25.5


Cross talk correction beam 3

Cross-Talk Correction - Beam 3

No correction

With correction

nesz≈-24


Faraday rotation correction

Faraday Rotation Correction

  • Inputs:

    • Faraday rotation angle.

    • Observed HH, HV, VV σ0. (symmetrized cross-pol)

    • HH-VV correlation; ratio of HV to both HH and VV channels. This factor may need to be tuned depending on if cross-talk removal is or is not performed before Faraday rotation correction.

  • Method:

    • Non-linear measurement model.

    • Minimize cost function to solve for Faraday rotation corrected σ0 HH and σ0 VV. (called sigma true below).

    • Obtain σ0 HV via conservation of total σ0.

Measurement Model:

Cost Function


Faraday rotation correction beam 1

Faraday Rotation Correction – Beam 1

No correction

With correction

No correction

With correction


Faraday rotation correction beam 2

Faraday Rotation Correction – Beam 2

With correction

No correction

With correction

No correction


Faraday rotation correction beam 3

Faraday Rotation Correction – Beam 3

No correction

With correction

No correction

With correction


Open issues future work

Open Issues / Future Work

  • Antenna patterns:

    • The cross-talk from the theory and scale-model antenna patterns seems to be significantly different.

    • Will the cross-talk in the as-flown configuration differ from both the theory and scale-model patterns?

  • The error estimate for Faraday rotation correction needs to be analyzed for nominal ionospheric TEC, not worst case.

  • We need to develop a strategy to determine antenna patterns post-launch.


Level 2 scatterometer wind retrieval

Level 2 Scatterometer Wind Retrieval

Alex Fore

Julian Chaubell

Adam Freedman

Simon Yueh


L2 wind retrieval process flow

L2 Wind Retrieval Process Flow

Baseline algorithm:

-total σ0 approach.

-Faraday rotation and cross-talk has no effect on total σ0 approach.

Ancillary Inputs:

-NCEP wind direction

Inputs:

-Total σ0

-antenna azimuth

-Kpc estimate

L2 Scat wind speed + error

Solve for wind speed

Newton’s Method:

1d root-finding problem

Newton’s Method

Wind Model Function

-input: wind speed, relative azimuth angle, incidence angle (or beam #)

-output: total sigma-0


L2 wind retrieval

L2 Wind Retrieval

  • We also compute a wind speed error due to the uncertainty in the scatterometer σ0,tot.

    • From the estimated kpc we have the variance of the observed σ0,tot.

    • We numerically compute dw/dσ0tot and propagate the error to a variance for wind.


Simulated total 0 wind retrieval performance

Simulated Total σ0 Wind Retrieval Performance

  • Total σ0 performance is independent of any Faraday rotation corrections or cross-talk removal.

  • As compared to beam-center NCEP wind speed:

    • B1 total std: 0.205 m/s

    • B2 total std: 0.186 m/s

    • B3 total std: 0.226 m/s

  • By construction, when we derive the model function from the data there will be no bias.


Wind speed retrievals

Wind Speed Retrievals


Open issues future work1

Open Issues / Future Work

  • Derivation of model function from the data.

  • Re-perform the analysis using averaged wind over 3-dB footprint as the truth for training

  • Comparison of predicted σwind to observed RMSE of retrieved wind as compared to beam center wind.

  • Use individual polarizations to retrieve winds after calibration of individual channels.


Level 2 scatterometer delta tb estimation

Level 2 Scatterometer Delta TB Estimation

Alex Fore

Adam Freedman

Simon Yueh


Pals highwinds 2009 campaign

PALS HIGHWINDS 2009 Campaign

  • NASA/JPL conducted HIGHWINDS 2009 campaign with following instruments:

    • POLSCAT, a Ku band scatterometer.

    • PALS, a L-band scatterometer and radiometer.

  • From POLSCAT we determine the wind speed, and then we consider the relationship to the observed L-band active and passive observations

    • From this data we can show the high correlation between radar σ0 and excess TB due to wind speed.

    • We also can derive the wind speed - radar σ0 model function as well as the wind speed – ΔTB model function.


Pals highwinds results

PALS HIGHWINDS Results

  • We find very high correlation between wind speed and TB( > 0.95 ).

  • We also find a similarly high correlation between radar backscatter and TB.

    • Suggests radar σ0 is a very good indicator of excess TB due to wind speed.

    • Caveat: we need ancillary wind direction information for Aquarius: PALS results show a significant dependence on relative angle between the wind and antenna azimuth.


Pals highwinds results 2

PALS HIGHWINDS Results (2)


Pals highwinds results 3

PALS HIGHWINDS Results (3)

  • From all of the data we derived a fit of the excess TB wind speed slope as a function of Θinc.


L2 t b

L2 ΔTB

  • L2 ΔTB will be the scatterometer wind speed times the PALS dTB/dw. (Note: not included in v1 delivery)

    • We estimate the ΔTB errors due to the wind RMSE numbers on previous slide.

PALS Tb relation:


Comparison with previous measurements

Comparison with Previous Measurements

  • Horizontal polarization has very good agreement with the measurements from WISE ground-based campaign.

  • Large discrepancy for vertical polarization

    • Cause is uncertain

    • Wave effects?

  • WISE – Camps et al., TGRS 2004

  • Hollinger – TGE, 1971

  • Swift – Swift, Radio Science, 1974


L2 t b1

L2 ΔTB


Open issues future work2

Open Issues / Future Work

  • The wind speed - ΔTB coefficients will be updated with Aquarius data after launch.


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