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DPGS OTT strategy analysis

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  1. DPGS OTT strategy analysis 4 February 2013 ARGANS

  2. Background • OTT are generated for DPGS monthly, using 10 ascending and 10 descending South Pacific operational L1c orbits • Use data from stable salinity regions • Reference TBs generated by forward model using climatology • Time series for salinity anomalies (SSS - climatology) for this region should be stable if OTT are correcting drift – but we see nearly ±1 psu. Why? • Alignment? OTT quality?

  3. South Pacific region Climatology for South Pacific test site 1: stable salinity (36.4 ±0.1 psu) www.argans.co.uk/smos/pages/regional/webform0.php

  4. OTT alignment in DPGS 3 27 3 27 20 orbits -> OTT1 20 orbits -> OTT2 1 6 12 18 24 30 1 6 12 18 24 30 OTT#1 in DPGS OTT#2 in DPGS Optimal OTT#2 validity OTTs made from orbits selected from first ~6 days Typically deployed around 12th of each month ~24 day delay compared to ideal validity

  5. Methodology • Select DPGS L1c orbits for 2012 with > 1000 grid points in South Pacific region 122 (as used in PPEP/PPSR & web time series) • longitude 120 to 130 west, latitude 15 to 25 south • 300 ascending & 300 descending orbits • Process with L2OS v550 and: • monthly OTT as used by DPGS (nominal reference) • same monthly OTT as used by DPGS with optimal temporal alignment (24 day shift) • weekly NIR aligned 2011 REPR OTT (optimal alignment) • MOTT for 2011 • Extract average filtered SSS1 time series for nGridPoints > 1000

  6. OTT strategy: ascending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.36 (filtered by quality)

  7. OTT strategy: ascending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.36 (filtered by quality) DPGS 9 day SSS1 anomaly (filtered by flags)

  8. OTT strategy: ascending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.36 (filtered by quality) OTT sun in EAFFOV

  9. OTT strategy: ascending orbits Monthly DPGS OTTs with optimal deployment SSS1 std = 0.24 (filtered by quality)

  10. OTT strategy: ascending orbits delta = optimal - monthly

  11. Ascending orbits • OTTs shifted by 24 days (optimal validity) give lower salinity anomalies in both ascending & descending (std decreases from 0.36 to 0.24) • TEC not a factor (low in ascending) • Looks like a sun effect • sun appears in EAFFOV May, disappears July • sun in back September/October? • Impact of filtering...

  12. OTT strategy: ascending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.36 (filtered by flags)

  13. OTT strategy: ascending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.36 (filtered by quality, > 1000 grid points)

  14. OTT strategy: ascending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.40 (filtered by quality, > 500 grid points)

  15. OTT strategy: ascending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.44 (filtered by quality, all grid points)

  16. Ascending orbits • OTTs shifted by 24 days (optimal validity) give lower salinity anomalies in both ascending & descending (std decreases from 0.36 to 0.24) • TEC not a factor (low in ascending) • Looks like a sun effect • sun appears in EAFFOV May, disappears July • sun in back September/October? • Filtering by poor flags impacted by galactic flag bug in v550 • Filtering by quality < 150 avoid this bug, but results are comparable • Fewer grid points in region => more noisy • L2OS product filtering needs further analysis

  17. OTT strategy: descending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.48 (filtered by flags, including GN bug)

  18. OTT strategy: descending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.48 (filtered by flags, including GN bug) Galactic noise September-October

  19. OTT strategy: descending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.41 (filtered by quality) Filtering by quality removes impact of galactic noise

  20. OTT strategy: descending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.41 (filtered by quality) DPGS 9 day SSS1 anomaly (filtered by flags)

  21. OTT strategy: descending orbits Monthly DPGS OTTs: 12 day delay SSS1 std = 0.41 (filtered by quality) OTT sun in EAFFOV OTT sun in EAFFOV

  22. OTT strategy: descending orbits DPGS OTTs with optimal deployment SSS1 std = 0.28 (filtered by quality)

  23. OTT strategy: descending orbits delta = shifted - DPGS

  24. Summary • OTTs shifted by 24 days (optimal validity) give lower salinity anomalies in both ascending (std 0.36 -> 0.24) & descending (std 0.41 -> 0.28) • TEC not a factor (low in ascending) • Low impact of galactic noise in September/October in descending orbits (GN bug reduces the number of valid points) • How can the ‘optimal’ OTTs be improved? • Delayed production • Increased OTT frequency

  25. Yin et al. IGARSS 2012 ξ Temporal evolution of OTT and galactic noise anomalies (averaged along dwell lines) across the satellite track, Ascending orbits 2K 20120501 Mean OTTs Along dwell lines 20100501 -2K ξ 2K 20120501 Galactic noise 20100501 -2K ξ No clear correlations between temporal across track variations in OTT and in galactic noise

  26. Yin et al. IGARSS 2012 Temporal evolution of OTT anomalies (averaged along dwell lines) across the satellite track, Descending orbits 20120501 2K Mean OTTs Along dwell lines 20100501 -2K 2K 20120501 Galactic noise 20100501 -2K No clear correlations between temporal across track variations in OTT and in galactic noise

  27. OTT strategy: DPGS

  28. Yin et al. IGARSS 2012 AF EAF Annual variations Descending orbits (Tx+Ty)/2 OTT means with Sun in FOV with Sun in FOV Physical temperature of the antenna patches Sun declination

  29. Yin et al. IGARSS 2012 Annual variations Ascending orbits (Tx+Ty)/2 OTT means with Sun in FOV with Sun in FOV Physical temperature of the antenna patches Sun declination

  30. Correlation coefficients between OTTs and <Tp7> and p-values for testing the hypothesis of no correlation (only p-values less than 0.05 correspond to significant R; other values are indicated in italics)

  31. OTT strategy: DPGS ascending descending

  32. OTT strategy: optimal ascending descending

  33. Way ahead • Delay DPGS salinity products? • Need a minimum of 24 days delay if OTT generated monthly • Generate OTT more frequently? • Additional work for preparation, ingestion & monitoring • Still not optimal (offset) • Implement an OTT post-processor? • L2OS can output data for OTT post-processing (AUX or in DAP) • OTTs can be generated as a running average daily (or less frequently) • Drift statistics available for monitoring • MOTT & drift correction derived from delta TBs?

  34. Work required • Repeat 2012 study with • v600 L2OS & monthly OTT • OTT made more frequently • OTT running average • different regions of interest • plot L1c TBs, forward model TBs/galactic noise, etc @ TOA • look for correlations with TP6/7... • Design system for automatically generating OTT within DPGS • Reprocessing?

  35. OTT strategy 2011 REPR OTTs (aligned with 2011 NIR events) ascending orbits, filtered by flags

  36. OTT strategy: ascending orbits 2011 MOTT (one OTT for all year) ascending orbits, filtered by flags