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Preliminary After-launch GOCI Characterization: Inter-slot radiance discrepancy issue

Preliminary After-launch GOCI Characterization: Inter-slot radiance discrepancy issue. Young-Je Park*, Hee-Jeong Han, Seongick Cho, Joo-Hyung Ryu , Jae-Hyun Ahn and Yu- Whan Ahn Korea Ocean Satellite Center, Korea Ocean Research and Development Institute

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Preliminary After-launch GOCI Characterization: Inter-slot radiance discrepancy issue

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  1. Preliminary After-launch GOCI Characterization: Inter-slot radiance discrepancy issue Young-Je Park*, Hee-Jeong Han, Seongick Cho, Joo-HyungRyu, Jae-Hyun Ahnand Yu-WhanAhn Korea Ocean Satellite Center, Korea Ocean Research and Development Institute Presented at IGARSS 2011, Vancouver, Canada

  2. Objectives • To understand the inter-slot radiance discrepancy issue • To seek ideas/suggestions on how to approach this GOCI specific issue

  3. Sensors have specific issues • MODIS stripe noise • detector calibration • difference in mirror side characteristics • Sensitivity to polarization state • MERIS • SMILE effects: wavelength variation • Discontinuity at some camera interface

  4. Outline • Overview of the GOCI optical system and image acquisition sequence • Inter-slot discrepancy: • variability within a slot • variability across different slot boundaries • variability with observation hours (0, 3, 7 hours) • How RT simulations show • Image smoothing technique • Future directions

  5. GOCI sensor

  6. GOCI optical layout Three Mirror Anastigmatic Telescope

  7. GOCI slots imaging sequence 1 2 3 4 8 7 6 5 9 10 11 12 16 15 14 13

  8. Imaging procedure for a GOCI slot

  9. Nominal time intervals for GOCI operation • Interval between bands = ~ 8 seconds • Interval between consecutive L1a slots = ~ 103 seconds • Duration for acquiring one GOCI image = ~ 103*16 seconds = 27 minutes • Interval between consecutive GOCI images = one hour • Interval between the adjacent slots in L1B scene = up to ~103*7 seconds or 12 minutes => sun angle difference??

  10. Requirements for comparing radiances from two slots • Accurate geometric registration • Spatially homogenous conditions for the atmosphere and water are preferred, which is to avoid seeing different air/water mass from two different slots

  11. Inter-slot discrepancy

  12. Variability within a slot • 20110330_0h image: slot 3-6 border

  13. Variability across different slot boundaries • 20110330-3h

  14. Inter-slot discrepancy: spectral aspect(033003) • Slot #2-7 border

  15. Inter-slot discrepancy: spectral aspect(033003) • Slot #3-6 border

  16. Slot #4-5 border

  17. Slot #5-12 border

  18. Slot #6-11 border

  19. Slot #7-10 border

  20. Slot #8-9 border

  21. Slot #9-16 border

  22. Slot #10-15 border

  23. Variability with observation hour

  24. Slot border reflectance change • Within a slot border: moderately variable with consistent difference spectra • For different slot borders: variable magnitude, moderately variable spectra • For different observation hours: larger difference (lower reflectance for the upper slot) in the 7h image • Bands 7 & 8 reflectance ratio changes significantly, which has a serious effect on atmospheric correction that uses those bands.

  25. How does RT code simulate the discrepancies? uslot=3,lslot=6: 3099,1584 3099,1585 lat,lon= 41.0020866 131.8832245 sunz= 54.8425102 54.0042229 suna= 121.0095673 122.2263718 senz= 47.5428658 47.5378571 sena= 185.6037445 185.6040649 • 0h: 9hr local time uslot=3,lslot=6: 3099,1592 3099,1593 lat,lon= 40.9659882 131.8822021 sunz= 37.4894829 37.5132179 suna= 180.6660614 182.7969666 senz= 47.5027428 47.4977188 sena= 185.6062317 185.6065369 • 3h: 12hr local time uslot=3,lslot=6: 3099,1597 3099,1598 lat,lon= 40.9434242 131.8815613 sunz= 65.5979691 66.5323486 suna= 252.3380127 253.3214874 senz= 47.4776611 47.4726372 sena= 185.6077881 185.6080933 • 7h: 17hr local time

  26. Simulation with AOT550=0.1

  27. Simulation with AOT550=0.5

  28. GOCI data

  29. An image smoothing technique • Distance-to-border weighted average • Applied to overlapped area • Simple and good for image generation • Smoothing the TOA reflectance data will not be good for downstream data processingincluding the atmospheric correction. • Smoothing the geophysical parameters would make sense.

  30. Distance-to-border weighted average Slot i Slot j Slot i d1 wi d4 d2 wj d3 wi= min(d1,d2,d3,d4) where is number of pixels to the k-th border N’=∑(wiⅹNi)/∑wi N’: weighted average Ni: reading from the ith slot

  31. Example 1 (original)GOCI 20110412-07h, South Japan

  32. Example 1 (weighted average)GOCI 20110412-07h, South Japan

  33. Future work • Clarify questions of • Is it an issue of the GOCI radiometric calibration? • Is it an issue of the band filter properties? • Is it an issue of the ghost image? • Develop a scientifically based model to correct the inter-slot discrepancy. Bands6,7,8 are critical for atmospheric correction.

  34. Thank you!Please contact us if you have any idea on this issue.youngjepark@kordi.re.kr

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