1. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Plan for calibration and maintenance of AHAB Uncertainty Budget: Laboratory Components Carol Johnson NIST

2. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 MOBY Uncertainties MOBY Calibration Workshop Nov 2003 to address uncertainties in measured water-leaving radiance –Radiometric components Uncertainty in the primary calibration sources Transfer uncertainty MOBY radiometric scale maintenance during deployment Systematic effects –Temperature –Stray light –Wavelength error –Environmental components (Ken’s Talk) Instrument self-shading Wave focusing: environmental ‘noise’ Polarization

3. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 MOBY Radiometric Uncertainties Established rigorous measurement protocols ensuring direct traceability to primary national radiometric standards Established radiometric uncertainty budget conforming with international recommendations Goal: uncertainty budget to be dominated by environmental factors. –Uncertainty goal: ~ 3 % (k=1) Radiometric calibration uncertainties of 4 % to 8 % (6 % > 400 nm) D. K. Clark, et al., Proc. SPIE 4483, 64-76 (2002) Satellite sensors uncertainty requirements: 5 % in water-leaving radiance

4. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 MOBY Uncertainties – Why do they matter? To evaluate what uncertainty components are important, it is important to understand how the MOBY data are used. SeaWiFS and MODIS: MOBY data are used to set the T=0 post-launch gains. In using a large number of MOBY matchups, random uncertainty components will be reduced, but systematic effects will not. For a large-enough data set, final uncertainty in gain coefficients will be dominated by systematic effects. SeaWiFS

5. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 MOBY Radiometric Calibration Flow Diagram NIST Standards NIST Standards Correction for temperature and stray light Correction for temperature and stray light Uncertainty

6. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Primary Calibration Sources

7. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 How well can you do? Uncertainties in Irradiance Standards from NIST

8. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 How well can you do? Uncertainties in Radiance Standards from NIST

9. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Uncertainties from Transfer of Scales

10. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 J. J. Butler, et al., J. Res. Natl. Inst. Stand. Technol. 108, 199-228 (2003). Results of measurements of Santa Barbara Remote Sensing SIS100 lamp-illuminated integrating sphere: sphere was used for MODIS and Landsat ETM+ pre-launch calibrations Transfer radiometers from NIST, NASA’s GSFC, and the University of Arizona measured the sphere radiance under different illumination conditions and compared their results with the SBRS-determined radiance. This +/- 2% agreement is good result, based on our experience. How well can you do? EOS Laboratory Intercomparison Experiments

11. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 MOBY Calibration Sources & Uncertainties Re-calibrated every 6 months or 50 H of use - Calibrated first with original lamps (1 % to 2% agreement) - Re-lamped and calibrated a second time Monitored during operation using NIST- calibrated filter radiometers called Standard Lamp Monitors (SLMs) Yearly NIST visits with transfer radiometers and sources to validate the MOBY radiance scales NIST-traceable calibration: 3-5 % uncertainties (secondary standards laboratory) NIST calibration unc (400 to 700 nm): < 1 %

12. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Calibration Stability & Repeatability OL Calibration History within the calibration uncertainty Stability ~ 0.5 % (SLM) OL420 and SLM Radiance At 412 nm (870 nm results similar)

13. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Uncertainties Associated with the Deployments

14. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Internal Reference Lamps - Stability QC Blue < 0.5 % Both + - 0.5% Red < 0.5%

15. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Diver Reference Lamp Calibrations The changes observed are well within the uncertainty of the method. Hence we cannot draw any useful conclusions.

16. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Pre to Post Deployment Calibrations Assume a rectangular probability distribution, the associated uncertainty is about 0.6% For top arm input and all deployments Averaged over deployments by wavelength

17. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 In Situ Wavelength Calibration with Spectral Features Red Spectrograph 2.5 years Approx. +/- 1 nm Blue Spectrograph 2.5 years Approx. +/- 0.6 nm

18. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Uncertainties Associated with Systematic Effects

19. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Temperature Affects the System Responsivity We measured and then applied a temperature correction to the pre- and post- deployment calibrations (as well as all MOBY data during deployments).

20. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Impact of Stray Light or Spectral out-of-band Spectral out-of-band of representative MODIS bands What is its magnitude? Does it impact the measurement requirements? No instrument is perfect: every instrument measures unwanted radiation Stray light causes systematic errors: that is, errors that don’t average to zero with repeat measurements.

21. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Stray Light in MOBY Stray light correction to MODIS Bands Images of Laser Lines Correction to Responsivity Multiple Deployment Time Series Single Deployment

22. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Evaluation of the uncertainties: Monte Carlo Uncertainty in SLC for in-water upwelling radiance L u There are a number of parameters that go into the model; each has an uncertainty We doubled the uncertainty in the fits to those parameters to account for drift, etc. Then ran a Monte Carlo simulation: for each component we used a Gaussian probability distribution. Simulations run a minimum of 100 times & uncertainties calculated.

23. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 MOBY Radiometric Uncertainty MOBY Workshop Preliminary Results Uncertainty ComponentValue [%] Calibration Source Radiance3% to 5% (Comm. Lab); 0.5% (NIST) Source stability between calibrations~3% to ~4% (Repeat Cals.); ~0.5% (SLMs) Responsivity during deployment~0.6% WavelengthWithin 1 Pixel Temperature~ Negligible Stray light<~ 0.25% Combined Standard Uncertainty [%] 3.2% to 5.1%

24. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 MOBY Summary: Lessons Learned for AHAB Traceability to primary national and international radiometric standards and the SI Good experiment design –multiple measurements (pre- & post- calibrations) –verify and validate –strict protocols –methods to monitor detectors and monitor sources Characterize instruments thoroughly

25. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 AHAB Implementations Primary Calibration Sources –Blue-rich, tailored for ocean color spectral distributions Transfer of Scales –Calibrate sources using NIST facilities –Expand SLM concept to hyperspectral (more spectral information) During deployment –Internal sources (LEDs) –System level stability monitoring –Improvements to diver calibration lamps Systematic –2-D stray light characterization at NIST SIRCUS facility

26. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Primary Calibration Sources Source Spectral Power Distributions

27. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 LED Sources

28. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 LED Source: Field Tests More flux in the blue; Better matched to the ocean’s spectral distribution

29. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Spectrally Tunable, Detector-based Source Under development using GOES-R funding

30. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 System Level Stability Monitoring Stable LED sources, as proven in MOBY (0.5% during deployments) Fiber-coupled to external optical input Allows Daily system level monitoring of AHAB responsivity Eliminates major source of unknown behavior for MOBY

31. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 AHAB Characterization Thermal characterizations at NIST –design for good thermal control and stability Detailed and thorough stray light characterization at NIST –spectral and spatial –smaller system means all tests can be done at NIST, resulting in full and dense wavelength coverage –Spatial effects have been dealt with under R&O work Excellent wavelength stability –Monitor using solar lines as with MOBY

32. NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006 Summary AHAB’s radiometric uncertainties will be the lowest possible for this type of field activities.