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Nares Strait Aug.-3, 2009

Nares Strait Aug.-3, 2009. Level-1B Band-1 @ 645nm. Infrared measurements of sea surface temperature (SST). Andreas Muenchow, University of Delaware, May-11, 2010. Nares Strait motivation Vertical and temporal temperature changes Sensor calibration Cloud detection Atmospheric correction

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Nares Strait Aug.-3, 2009

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  1. Nares Strait Aug.-3, 2009 Level-1B Band-1 @ 645nm

  2. Infrared measurements of sea surface temperature (SST) Andreas Muenchow, University of Delaware, May-11, 2010 • Nares Strait motivation • Vertical and temporal temperature changes • Sensor calibration • Cloud detection • Atmospheric correction • Validation References: 1. Robinson, I.S., 2004: Measuring the Oceans from Space, chapt.-7 2. Gumley, L., 2006: Modis Ocean Products, http://www.ssec.wisc.edu/library/coursefiles/SouthAfrica/Gumley_MODIS_Ocean.ppt 3. Vincent et al., 2008: Arctic waters and marginal ice zones, a composite Arctic sea surface temperature algorithm, J. Geophys. Res., 113, C04021, doi:10.1029/2007JC004353. 4. Luo, et al., 2008: Developing clear sky, cloud, and cloud shadow mask for producing clear-sky composites at 250-meter spatial resolution, Rem. Sens. Env., 112, 4167-4185. 5. Minnett, P.J., 2001: The marine-atmosphere emitted radiance interferometer, a high accuracy, seagoing infrared spectrometer, J, Atmos. Ocean. Tech., 18, 994-1013.

  3. Nares Strait Aug.-3, 2009 My first MODIS SST image (made 4 days ago): Pretty, but wrong on so many levels … What is SST?

  4. MODIS Ocean Standard Products (Level-2) [from Gumley, 2006]

  5. Planck’s Law: sst4 sst 2 bands used to estimate sst and sst4 sst4 usable only at night (solar contributions) sst usable day and night (negligible solar contributions) [from Robinson, 2004]

  6. sst4 sst [from Robinson, 2004]

  7. [from Robinson, 2004]

  8. [from Robinson, 2004]

  9. [from Robinson, 2004]

  10. [from Minnett et al., 2001]

  11. [from Robinson, 2004]

  12. Night Day [from Robinson, 2004]

  13. [from Robinson, 2004]

  14. [from Robinson, 2004]

  15. Sensor Calibration Band-integrated radiance as a function of temperature (Planck’s Law) at detector: L(Tb) = ∫ C1() / [5  exp(C2/ Tb)-1] d  where Tb blackbody temperature () detector response function (determined pre-launch) C1, C2 constants Calibration finds gain and offset to relate the digital output signal S to radiance at detector L: L = gain*S + offset or Tb = A + B ln(L) Need 2 known points to find gain and offset for each detector

  16. MODIS has 10 detectors scanned by 2 mirror-sides --> 20 calibrations SST Striping due to imperfect inter-detector calibrations [from Gumley, 2006]

  17. Chlor_a [from Gumley, 2006]

  18. MODIS Chlorophyll Algorithm Semi-analytical algorithm(1) Chl_a = 10**(0.283 - 2.753*R + 1.457*R2 + 0.659*R3 - 1.403*R4) where: R = log10((Rrs443 > Rrs488) / Rrs551) Rrs = nLw / F0; remote sensing reflectance F0 = extraterrestrial solar irradiance nLw = water leaving radiance at 443, 488, 551 (1) Performance of the MODIS Semi-analytical Ocean Color Algorithm for Chlorophyll-a Carder, K.L.; Chen, F.R.; Cannizzaro, J.P.; Campbell, J.W.; Mitchell, B.G. Advances in Space Research. Vol. 33, no. 7, pp. 1152-1159. 2004 [from Gumley, 2006]

  19. [from Robinson, 2004]

  20. Canadian Center for Remote Sensing Cloud Detection Standard NASA Cloud Detection [from Luo et al., 2008]

  21. This really is another full lecture [from Robinson, 2004]

  22. [from Robinson, 2004]

  23. 2008 [from Luo et al., 2008]

  24. Modis Bands Bi with i=1,2,3,6 [from Luo et al., 2008]

  25. [from Luo et al., 2008]

  26. [from Luo et al., 2008]

  27. [from Robinson, 2004]

  28. SST = a + b*T4 + c*(T4-T5) + d* (T4-T5)*(sec-1) Atmosphere-A: Atmosphere-B Tbi brightness temperature channel “i”, e.g, T4 (Band-31 in Modis) Tbj brightness temperature channel “j”, e.g, T5 (Band-32 in Modis) [from Robinson, 2004]

  29. Daytime Coefficients for NOAA-12 AVHRR SST algorithm(McClain et al., 1985) a=-263.006 b=0.963563 c=2.579211 d=0.242598  sensor zenith SST = a + b*T4 + c*(T4-T5) + d* (T4-T5)*(sec-1) SST4 SST [from Robinson, 2004]

  30. MODIS Longwave Infrared Sea Surface Temperature ---> SST dBT <= 0.5 sst = a00 + a01*BT11 + a02*dBT*bsst + a03*dBT*(sec() - 1.0) dBT >= 0.9 sst = a10 + a11*BT11 + a12*dBT*bsst + a13*dBT*(sec() - 1.0) 0.5 < dBt < 0.9 sstlo = a00 + a01*BT11 + a02*dBT*bsst + a03*dBT*(sec() - 1.0) ssthi = a10 + a11*BT11 + a12*dBT*bsst + a13*dBT*(sec() - 1.0) sst = sstlo + (dBT - 0.5)/(0.9 - 0.5)*(ssthi - sstlo) where: dBT = BT11 - BT12 BT11 = brightness temperature at 11 um, in deg-C BT12 = brightness temperature at 12 um, in deg-C bsst = Either sst4 (if valid) or sstref (from Reynolds OISST) sec() = 1/(cosine of sensor zenith angle) a00, a01, a02, a03, a10, a11, a12, a13 derived from match-ups [from Gumley, 2006]

  31. MODIS Shortwave Infrared Sea Surface Temperature --> SST4 sst4 = a0 + a1 * BT39 + a2 * dBT + a3 * (sec() - 1.0 ) where: dBT = BT39 - BT40 BT39 = brightness temperature at 3.959 um, in deg-C BT40 = brightness temperature at 4.050 um, in deg-C sec() = 1/(cosine of sensor zenith angle) a0, a1, a2, and a3 are time dependent coefficients derived from match-ups between observed MODIS brightness temperature and field measurements of SST. Note: sst4 is not valid during daytime because of solar reflection. [from Gumley, 2006]

  32. Measuring at-sea skin temperature for SST validation and algorithm development [from Minnett et al., 2001]

  33. Nares Strait Aug.-3, 2009 My first MODIS SST image (made 4 days ago): Pretty, but wrong on so many levels … What is SST?

  34. Standard SST algorithm Arctic SST algorithm [from Vincent et al., 2008]

  35. [from Vincent et al., 2008]

  36. [from Vincent et al., 2008]

  37. Is atmospheric correction always appropriate? SST = a + b*T4 + c*(T4-T5) + d* (T4-T5)*(sec-1) Is anything lost by applying atmospheric corrections?

  38. Is atmospheric correction always appropriate? SST = a + b*T4 + c*(T4-T5) + d* (T4-T5)*(sec-1) Is anything lost by applying atmospheric corrections? • Image noise may be enhanced • Includes noise from 2channels • Thermal gradients are modified

  39. Is atmospheric correction always appropriate? SST = a + b*T4 + c*(T4-T5) + d* (T4-T5)*(sec-1) Is anything lost by applying atmospheric corrections? • Image noise may be enhanced • Includes noise from 2channels • Thermal gradients are modified If spatial structures, patterns, fronts, eddies, plumes are studied Use brightness temperatures Ti, not SST

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