Page 1 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Development of New SSES for AATSR L2P Gary Corlett AATSR Validation Scientist

Page 2 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Content Reminder of current SSES scheme SSTs from AATSR What affects the quality of AATSR SSTs? An alternate scheme using view differences Examples Analysis of GHRSST-PP MDB Future work Summary & Conclusions

Page 3 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Revised (Realistic) Content Reminder of current SSES scheme SSTs from AATSR What affects the quality of AATSR SSTs? An alternate scheme using view differences Examples Analysis of GHRSST-PP MDB Future work Summary & Conclusions

Page 4 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 What Affects AATSR Data Quality?

Page 5 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 What Affects the Quality of AATSR SSTs? For December 2005 coefficients D2-D3 bias (the latitude dependent correction) owing to limited number of channels Small residual bias (~ 0.15 K at T < 280 K) most likely due to temperature dependent emissivity These issues are being addressed in (A)RC project Suspected 12 μm calibration error In process of analysing flight-spare FPA Clouds and aerosols (claerosols) AATSR cloud screening is over-zealous –AATSR is designed for climate SSTs –Much better during day owing to 1.6 µm channel –Observable edge effects at night Dual-view corrects for tropospheric aerosol –But not quite! –Being addressed in (A)RC project Relative alignment of nadir and forward views New results suggest systematic offset Currently being investigated by AATSR QWG

Page 6 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Suspected 12 μ m Error: Implication for SSTs Calibration offset seen between AATSR and ATSR-2 12 μm clear-sky SEA BTs ATS_MET_2P and AT2_MET_2P products analysed Validation results suggest AATSR is incorrect Results in increase in latitude dependent D2-D3 bias Effect on current D3 SSTs is ~ K Effect on current D2 SSTs is ~ K

Page 7 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Distribution of M-AERI Matchups Matchups Day; Overpass ± 60 min; 1x1 Block LEGEND All +ve D-N -ve D-N Bi-modal distribution of differences 1 distribution due to -ve dual-nadir SST differences 1 distribution due to +ve dual-nadir SST differences

Page 8 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Nov 2003 July 2003 The Affect of Saharan Dust on AATSR SSTs (30)

Page 9 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Caribbean SST differences for clean months – November to March Data is derived from 30 product Threshold = K Threshold = K Day D2-N2 Night D3-N3

Page 10 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Day D2-N2 Night D3-N3 Threshold = K Threshold = K Caribbean SST differences for clean months – November to March Data is derived from 1-km product

Page 11 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Pacific Ocean – clean months

Page 12 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 BT

Page 13 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Schematic of BT Effects

Page 14 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Relative alignment of forward and nadir views (1) Nadir View 3.7 micron Forward View 3.7 micron

Page 15 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Relative alignment of forward and nadir views (2) Forward minus Nadir View 3.7 micron Forward minus Nadir View 3.7 micron with shift

Page 16 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Basis of New SSES Scheme

Page 17 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Requirements for AATSR SSES Need, per pixel: Bias Retrieval bias, or Bias to a common standard – GHRSST match-up database Standard deviation What exactly is a single pixel standard deviation? Quality flag Scale of 1-5 agreed in Melbourne –1: Cloudy –2: Bad –3: Acceptable (defined by provider) –4: Good –5: Excellent

Page 18 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Updated QF Scheme – Theoretical Thresholds

Page 19 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Updated QF Scheme – Experimental Thresholds T2 U = ± 0.09 °C T2 L = ± 0.09 °C T3 U = ± 0.07 °C T3 L = ± 0.07 °C

Page 20 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Updated PCF Scheme - Stratification Stratification If 2-channel RetrievalIf 3-channel Retrieval TL 2 < D-N < TU 2 TL 3 < D-N < TU 3 D-N < TL 2 D-N < TL 3 D-N > TU 2 D-N > TU 3

Page 21 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Potential SSES Scheme: Summary Effect of clouds and aerosols can be accounted for using D-N SST differences Should get well-defined normal distribution Can set thresholds to remove data not in normal distribution Suspected alignment error between forward and nadir views will contribute to D-N differences Significant positive edge structures still seen after view-difference shift D-N test is designed for current AATSR data Will need revising if and when relative alignment is corrected 12 μm calibration error will contribute to D-N differences D-N test is designed for current AATSR data Will need revising if and when 12 μm calibration error is corrected

Page 22 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Examples

Page 23 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Example 1 AATSR Orbit: ATS_NR__2PNPDE _012117_ _ 00403_22000_0504.N1 Area of interest: 102 ºE to 118 ºE by 12 ºS to 4 ºS Day time descending node The day time example demonstrates the over-zealous cloud-screening, as the updated PCF mask is mainly indicating good data, while the larger-scale bad data is most likely affected by aerosol rather than cloud. The data are for 16th May 2006 over Indonesia, and it is noted that the volcano Mount Merapi, in central Java, was fairly active during May 2006.

Page 24 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Comparison of N1 and L2P SSTs

Page 25 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 L2P Quality Control

Page 26 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 N1 D-N & New QF

Page 27 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Change in QF

Page 28 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Summary of Main Changes Due to New Scheme Large number of pixels classified as QF 2 and QF 3 data are now classed as QF 5 Little change for QF 4 and QF 5 (except night time) A lot of pixels identified as bad (QF 2) by new scheme was previously classed as QF 3

Page 29 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Analysis of GHRSST-PP MDB

Page 30 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Definitions of SST Depth 10 m 1 mm 1 m 10 m (a)Night time situation, light wind AATSR 3 channel SSTskin – SST10m (K) Depth 10 m 1 mm 1 m 10 m SSTskin – SST10m (K) Infrared sensors ( T ~10s) Contact thermometers Ships/Buoys ( T ~minutes) (b) Day time situation, strong solar radiation and light winds AATSR 2-channel

Page 31 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Location of GHRSST-PP Match-ups (1)

Page 32 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Location of GHRSST-PP Match-ups (2) Drifting Buoys Others

Page 33 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Example: Day time Good data low wind speed

Page 34 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Example: Night time high data low wind speed

Page 35 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Statistics from GHRSST-PP MDB Analysis Stratification Statistics NumberBiassigma 2-channel, B, L channel, B, H channel, A, L channel, A, H channel, C, L channel, C, H channel, B, L channel, B, H channel, A, L channel, A, H channel, C, L channel, C, H A: Data below lower threshold B: Data within upper and lower thresholds C: Data above upper threshold

Page 36 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 New Confidence Values and Statistics Stratification CaseSummary of criteriaBiasSt. Dev. Confidence Value Case 1: 2-channel, Middle D-N, Low wind Case 2: 2-channel, Middle D-N, High wind Case 3: 2-channel, Low D-N, Low wind Case 4: 2-channel, Low D-N, High wind Case 5: 2-channel, High D-N, Low wind (or 4) Case 6: 2-channel, High D-N, High wind (or 4) Case 7: 3-channel, Middle D-N, Low wind Case 8: 3-channel, Middle D-N, High wind Case 9: 3-channel, Low D-N, Low wind (or 3) Case 10: 3-channel, Low D-N, High wind (or 3) Case 11: 3-channel, High D-N, Low wind Case 12: 3-channel, High D-N, High wind Biases have been converted to skin biases by adding 0.17 K

Page 37 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Summary & Conclusions (1) Current PCF scheme used in L2P applied to AATSR data is appropriate for nadir-only IR with poor cloud screening Does not account for over-zealous operational AATSR cloud screening Does not account for impact of claerosols on forward view Have developed improved quality flag for AATSR Use D-N SST difference to identify retrievals affected by claerosols Threshold = mode + 3 * sigma Also stratification according to wind speed Future scheme could take into account spatial and temporal variation in SST retrievals

Page 38 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Summary & Conclusions (2) Issues Data classed as others No day time wind speed dependence May imply no significant diurnal warming has started or diurnal warming cancels out cool-skin effect Night-time sub-skin correction No current agreement on how to correct (consistently) Would only recommend QF 5 data if using AATSR as reference Requires changes to L2P product Addition of nadir-only SST for each dual-view SST Addition of flag to identify 3-channel retrievals

Page 39 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Acknowledgements Defra, the UK Department of Environment, Food and Rural Affairs, who funded AATSR to support their programme of climate prediction and research, which in turn provides inputs to their policy-making processes Funding agencies in Australia who made significant contributions The European Space Agency This work was funded by ESA (ESA-NOCS Contract: AO/1-4362/03/I-LG) and Defra (Space ConneXions Contract: /CPEG10)

Page 40 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Current SSES Scheme

Page 41 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Current SSES scheme for AATSR L2P

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Page 47 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 AATSR SSTs

Page 48 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 What is AATSR? Imaging infrared and visible radiometer on ENVISAT Similar channels to AVHRR & MODIS. Dual view (nadir and 55° to nadir) Along-track scanning, two views of same scene at different angles, for better atmospheric correction On-board calibration 2 on-board black bodies for IR calibration VISCAL unit for visible channel calibration 500 km swath 1 km IFOV at nadir Stirling Cycle Coolers, cooling low noise detectors to 80K, for optimum signal-to-noise ratios

Page 49 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Nominal Channel CentrePrimary Application 0.55 m Chlorophyll 0.66 m Vegetation Index 0.87 m Vegetation 1.6 m Cloud Clearing 3.7 m SST Retrieval 11 m SST/LST Retrieval 12 m SST/LST Retrieval AATSR SST Retrievals Retrievals by radiative transfer modelling Usually of the form: where n is the number of channels For AATSR we have 2 channels during day and 3 during night 3.7 µm not used during day owing to solar contamination We have two views, so we have four SST retrievals in total We also have two product formats 1-km gridded (swath) Spatially –averaged (gridded) Four Possible Retrievals: Nadir 2-channel N2 Nadir 3-channel N3 Dual 2-channel D2 Dual 3-channel D3

Page 50 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Retrieval Coefficients: 1-km CoefficientN2N3D2D3 Constant Nadir 3.7 µm Nadir 11 µm Nadir 12 µm Forward 3.7 µm Forward 11 µm Forward 12 µm

Page 51 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Ongoing Work

Page 52 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Spatial Pattern of AR Differences to Buoys Data from Anne OCarroll (Met Office)

Page 53 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Further Refinement of SSES The (A)ATSR L2P project is aiming to make a few further improvement to the SSES The two main ones are To use high quality ICOADS in situ data Introduce spatial and temporal variation to bias and standard deviations

Page 54 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 L2P Reformatting (2) 10 degree 20 degree 45 degree

Page 55 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 L2P Reformatting (3) 10 degree 20 degree 45 degree

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Page 61 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Example 2 AATSR Orbit: ATS_NR__2PNPDE _012117_ _00403_22000_0504.N1 Area of interest: 70 ºW to 50 ºW by 25 ºN to 35 ºN Night time ascending node The night time example in Section clearly demonstrates the edge of pixel cloud contamination that affects AATSR data, and is clearly not picked up by the current PCF scheme. In addition, as for the day time data, there is no reason to suspect the rest of the SST data, which has been cloud screened twice and retrieved using two different SST retrievals. Therefore the data which passes the D-N test is set as good data and the PCF mask for these pixels is set to 5.

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Page 71 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 AATSR and ATSR-2 Simulated Bias: Centre of Swath From Owen Embury (University of Edinburgh)

Page 72 Medspiration/Globcolour, NIVA, Oslo, 20 th November 2007 Compare AATSR and ATSR-2 BTs: Case 1 Nadir View Forward View