SCAT calibration TU-Wien

Transcription

1 SCAT calibration TU-Wien Presentation to SCIRoCCO project team ESA Presented by Christoph Reimer Vienna University of Technology

2 Outline Calibration methodology intra-calibration / inter-calibration Sensor intra-calibration Theoretical framework Results / Verification ERS-2 SCAT and MetOp-A ASCAT Sensor inter-calibration Theoretical framework Results / Verification ERS-2 SCAT MetOp-A ASCAT (MetOp-B ASCAT calibration)

3 Calibration methodology Stepwise relative calibration strategy Sensor intra-calibration Detect and correct for temporal inconsistencies of an individual mission Sensor inter-calibration Detect and correct for biases between SCAT missions Utilising a set of natural calibration targets over land Level 1 scatterometer data Instrument Spatial Resolution Temporal Coverage Spatial Coverage ERS- 2 SCAT 25 km May 1997 Feb Global MetOp-A ASCAT 25 km Jan Nov Global

4 Selection of calibration targets Level 1 AMI-WS / ASCAT data normalise backscatter σ 0 (L, 40, φ j ) azimuthal anisotropy parameter δ temporal variability parameter ν mean backscatter parameter σ 0 azim. isotropy / temp. stability mask spatial variability analysis Calibration Targets thresholds Parameter Azimuthal Anisotropy Temporal Variability Spatial Variability Threshold AMI ASCAT 0.3 db 0.2 db 0.4 db 0.25 db

5 Selected calibration targets Selection based on global backscatter analysis Azimuthal modulations Temporal variability Calibration Tar. Verification Tar. ERS-2 SCAT MetOp-A ASCAT

6 Sensor intra-calibration Measurement Model: σ 0 L T, t i, θ, φ j = σ 0 (L T, θ) + C intra (L T, t i, θ, φ j ) + ε meas. RCS true RCS calibration coeff. Estimate of σ 0 L T, θ Calibration Reference σ 0 (L T, θ): n obs n ac σ 0 1 (L T, θ) = σ 0 (L n obs n T, t i, θ, φ j ) C intra L T, t i, θ, φ j = 0 ac i=1 j=1 Cal. Ref. meas. RCS Perfectly calibrated Solve for calibration coefficient: Estimate calibration coefficient: C intra (t i, θ, φ j ) = 1 C intra (L T, t i, θ, φ j ) + ε = σ 0 (L T, t i, θ, φ j ) σ 0 (L T, θ) Intra-Cal. Coeff. n tar n tar (C intra (L T, t i, θ, φ j ) + ε) T=1 Sensor intra-calibration : 0 σ intra (L, t i, θ, φ j ) = σ 0 (L, t i, θ, φ j ) C intra (t i, θ, φ j ) calibrated RCS meas. RCS Intra-Cal. Coeff.

7 Calibration reference n obs σ 0 (L T, θ) = 1 σ 0 (L n T, t i, θ, φ j ) obs i=0 ESCAT data of year 1998 ASCAT data of year 2007 New Guinea Rainforest ERS-2 SCAT [ascending overpass] n poly =2 = B 0 (L T, 40 ) + B p (L T, 40 ) (θ 40 ) p p=1 Δ overpasses db [asc - desc] Calibration reference per overpass Amazon Rainforest MetOp-A ASCAT[ascending overpass]

8 Estimation of intra-calibration coeff. C intra (L T, t i, θ, φ j ) = σ 0 (L T, t i, θ, φ j ) σ 0 (L T, θ) C intra (L T, t i, θ, φ j ) modelled as 1-order polynomial centred at 40 per month Amazon Rainforest July 1999 ESCAT [Fore-beam / Right Swath] Amazon Rainforest July 2010 ASCAT [Fore-beam / Right Swath] Oscillating alterations?

9 Intra-Calibration anomalies ERS-2 SCAT Right Swath: Fore-/Mid-/Aft-beam Piloted in ZGM Mean over Calibration Targets C intra (t i, 40, φ j ) MetOp-A ASCAT Right Swath: Fore-/Mid-/Aft-beam Left Swath: Fore-/Mid-/Aft-beam Proc. Update New Cal. Table

10 Intra-Calibration verification ERS-2 SCAT Right Swath: Fore-/Mid-/Aft-beam Piloted in ZGM Mean over Verification Targets C intra (t i, 40, φ j ) MetOp-A ASCAT Right Swath: Fore-/Mid-/Aft-beam Left Swath: Fore-/Mid-/Aft-beam Proc. Update New Cal. Table

11 Sensor inter-calibration Measurement Model: 0 σ Ma L T, t i, θ, φ j = σ 0 Sl (L T, t i, θ, φ j ) + C inter (L T, θ, φ j ) master RCS slave RCS Inter-Cal. Coeff. Solve for calibration coefficient: C inter (L T, θ, φ j ) + ε = σ 0 Ma (L T, θ) σ Sl (L T, t i, θ, φ j ) σ Ma L T, θ = σ Ma L T, t i, θ, φ j Estimate calibration coefficient: Sensor intra-calibration : C inter θ, φ j = 1 Inter-Cal. Coeff. n tar n tar T=1 Calibration Reference C inter (L T, θ, φ j ) + ε 0 σ inter (L, t i, θ, φ j ) = σ 0 Ma (L, t i, θ, φ j ) = σ 0 Sl L, t i, θ, φ j C inter (θ, φ j ) calibrated RCS slave RCS Inter-Cal. Coeff.

12 Inter-calibration anomalies ESCAT is calibrated with respect ASCAT C inter (θ, φ j ) 1-order polynomial centred at 40 Antenna Beam C 0 [db] C 1 [db/deg] min(θ) [db] max(θ) [db] Right Fore Fore-beam Right Mid Right Aft Mid-beam Aft-beam

13 Inter-calibration verification ESCAT is calibrated with respect ASCAT C inter (θ, φ j ) 1-order polynomial centred at 40 Antenna Beam C 0 [db] C 1 [db/deg] min(θ) [db] max(θ) [db] Right Fore Fore-beam Right Mid Right Aft Mid-beam Aft-beam

14 Conclusion Simple and obvious SCAT calibration methodology Correct for biases with respect to calibration reference Utilising a set of calibration targets A robust estimation of calibration anomalies Calibration anomalies correspond to Main mission events On-ground processor updates Sensor inter-calibration Estimate and correct for biases between SCAT mission Merging of ERS SCAT and MetOp ASCAT

15 Calibration of MetOp-B ASCAT

16 MetOp-B calibration Objective: derive soil moisture from MetOp-B ASCAT Dedicated MetOp-B ASCAT model parameters not available Too short mission lifetime Current available model parameters are based on MetOp-A ASCAT Calibration methodology intra-calibration of MetOp-B ASCAT inter-calibration of MetOp-B ASCAT utilising MetOp-A ASCAT as calibration reference Investigated MetOp-B ASCAT data 06-Nov-2014 to 30-Jun-2014

17 Intra-Calibration MetOp-B ASCAT MetOp-B ASCAT Right Swath: Fore-/Mid-/Aft-beam Left Swath: Fore-/Mid-/Aft-beam Calibration Targets: Amazon Rainforest, Congo Rainforest and Indonesia Rainforest I Year 2013 as Calibration Reference Transponder cal. campaign Rainforest cal. to MetOp-A ASCAT

18 Intra-Calibration MetOp-B ASCAT MetOp-B ASCAT Right Swath: Fore-/Mid-/Aft-beam Left Swath: Fore-/Mid-/Aft-beam Verification Targets: Upper Guinean Forest, Indonesia Rainforest II Malaysian Rainforest and Laos Rainforest Transponder cal. campaign Rainforest cal. to MetOp-A ASCAT

19 Inter-Calibration ASCAT Left Swath Fore-beam Right Swath Fore-beam Differences less than 0.1 db Mid-beam Mid-beam Aft-beam Aft-beam

20 Inter-Calibration ASCAT verification Left Swath Fore-beam Right Swath Fore-beam Mid-beam Mid-beam Aft-beam Aft-beam

21 Thank you for your attention Questions / Comments are welcome