MODISTerra crosscalibration for ocean color bands Ewa Kwiatkowska
MODIS-Terra cross-calibration for ocean color bands Ewa Kwiatkowska Bryan Franz, Gerhard Meister, Gene Eplee OBPG 30 January 2008
MODIS calibration changes since launch band 8 412 nm SD – Solar Diffuser frame 979, mirror AOI 50. 30 SV – Space View frame 23, mirror AOI 11. 40 MS 1 – Mirror Side 1 MS 2 – Mirror Side 2 Terra pre-launch damage to mirror coating, MS 2 B side electronics A side electronics SD door permanently opened
MODIS trends in ocean color products Terra/Aqua ratios normalized water-leaving radiances Lwn(412 nm) band 8 Lwn(443 nm) band 9 Lwn(488 nm) band 10 Lwn(531 nm) band 11 Lwn(551 nm) band 12
MODIS-Terra ocean color RVS band 8 412 nm Terra response versus scan angle (RVS) +10% in terms of normalized water-leaving radiances Lwn(412 nm) band 8 Mirror side 1 MS 1 Mirror side 2 MS 2 -10%
TOA sensor cross-calibration Goal • Extract MODIS-Terra – RVS, and – polarization sensitivity • For all ocean-color bands, per mirror side and detector • Through the entire Terra mission • Optionally, derive temporal calibration change Approach • Vicarious calibration / cross-calibration using Sea. Wi. FS • Sea. Wi. FS – stable spatially and temporally • Sea. Wi. FS – insensitive to polarization
TOA sensor cross-calibration MODIS – measured TOA radiance Lt( ) MODIS – vicarious L’t( ) = [ Lr( ) + La( ) + t. Lf( ) + TLg( ) + td( )Lw( ) ] · tg( ) · fp( ) ’ (fit in the ln-ln space) AOT( ’) ’ (fit based on bio-optical models) Sea. Wi. FS n. Lw( ’)
Current implementation MODIS – vicarious L’t( ) = [ Lr( ) + La( ) + t. Lf( ) + TLg( ) + td( )Lw( ) ] · tg( ) · fp( ) MODIS operational assuming accuracy of MODIS NIR band calibration Sea. Wi. FS ’ (fit based on bio-optical models) n. Lw( ’)
Polarization fp • Polarization correction fp = Im / I t Im = M 11 It + M 12(Qtcos 2 – Utsin 2 ) + M 13(Qtsin 2 + Utcos 2 ) • • It – Stokes vector exiting the TOA Mueller matrix M – instrument characterization, including polarization - rotation angle Im – Stokes vector measured by a sensor Im = M R( ) It Im = M 11 … M 14 M 21 … M 24 M 31 … M 34 M 41 … M 44 1 0 0 cos 2 -sin 2 0 0 sin 2 cos 2 0 0 1 It Qt Ut 0
Polarization of the atmosphere degree of atmospheric polarization dp air molecule (Rayleigh) and glint scattering MODIS Terra swath 412 nm band 8 2 2 dp = Q + U I polarization correction fp pre-launch MODIS characterization
Time series and global optimization • Global time series throughout the entire Terra mission – MODIS Terra – one day a month global set of granules (90 days) – Sea. Wi. FS – 9 -day global L 3 s centered on each month’s day from MODIS – Strict screening criteria for Sea. Wi. FS L 3 bins and MODIS L 2 pixels Lt = M 11 L’t + M 12(Qtcos 2 – Utsin 2 ) + M 13(Qtsin 2 + Utcos 2 ) Known: • Lt – MODIS-measured • L’t – MODIS-vicarious • Qt and Ut – atmospheric molecular and glint polarization, Rayleigh tables, glint derivation • – theoretical calculation Unknown: • M 11 – RVS and absolute calibration • M 12 and M 13 – polarization sensitivity • Global optimization for each day to derive M 11, M 12, and M 13 • M 11, M 12, M 13 = fn(mirror AOI)
412 nm 1. 0 1 -1. 5% 0. 99 6 March 2000 0. 98 443 nm 1. 01 1. 0 1 -2% 0. 99 488 nm 1. 01 polynomial across scan 2% 1. 0 RVS M 12 M 13 linear 0. 99 531 nm 1. 02 3 -rd degree 2% 1. 01 1. 0 551 nm 1. 02 1. 5% 1. 01 667 nm 1. 014 1% 1. 01 Detector 4 1. 006 678 nm 1. 015 1% 1. 005 Mirror side 1 Mirror side 2
412 nm 1. 05 0. 95 0. 85 443 nm 15% 16 October 2007 1. 02 0. 98 7% polynomial across scan 0. 94 488 nm 1. 02 6% RVS M 12 M 13 linear 0. 98 531 nm 1. 04 1. 02 3 -rd degree 3% 1. 0 551 nm 1. 02 2% 1. 0 667 nm 1. 02 1. 3% 1. 01 678 nm 1. 025 1. 015 1. 005 1. 4% Detector 4 Mirror side 1 Mirror side 2
Blue band temporal trends Mirror side 1 Mirror side 2 RVS Detector 4 Space View (lunar) frame Nadir frame Solar Diffuser frame
Blue band temporal trends Mirror side 1 Mirror side 2 M 12 Detector 4 Space View (lunar) frame Nadir frame Solar Diffuser frame
412 nm 1. 08 1. 04 1. 00 0. 96 443 nm Temporal trends 1. 08 1. 04 1. 00 0. 96 488 nm RVS M 12 M 13 1. 08 1. 04 1. 00 0. 96 531 nm 1. 08 1. 04 1. 00 0. 96 551 nm 1. 08 Mirror side 2 Detector 4 1. 00 0. 96 667 nm 1. 08 1. 04 1. 00 0. 96 678 nm 1. 08 1. 04 1. 00 0. 96 Space View (lunar) frame Nadir frame Solar Diffuser frame
Pre-launch M 13 RVS M 12 M 13
Temporal smoothing Polynomial fit through time into derived RVS and M 12 per individual frame
412 nm Smoothed results 443 nm Mirror side 1 Detector 4 488 nm RVS M 12 531 nm October 2007 Daily RVS and M 12 use temporally smoothed values for all frames 551 nm 667 nm 678 nm March 2000
412 nm Smoothed results 443 nm Mirror side 1 Detector 4 488 nm RVS M 12 531 nm October 2007 Daily RVS and M 12 use temporally smoothed values for all frames 551 nm 667 nm 678 nm March 2000
Verification of the vicarious cross-calibration with lunar measurements band 8 412 nm Terra detector ratios detector 10 / detector 1 • lunar measurements — vicarious cross-cal 412 nm band 8 Mirror side 1 MS 1 Mirror side 2 MS 2
Future plans • Why seasonality in M 13? • Is extracted polarization sensitivity too large? RVS? • Global time-series testing for water-leaving radiances • Validation of RVS and detector calibration • Application of the cross-calibration to Aqua
- Slides: 21