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 JohnsonNIST
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
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
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
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
MOBY Radiometric Calibration Flow Diagram
NISTStandards
NISTStandards
Correction for temperature
and stray light
Correction for temperature
and stray light
Uncertainty
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Primary Calibration Sources
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
How well can you do?Uncertainties in Irradiance Standards from NIST
Irradiance Standard Lamps (FEL), typical expanded uncertainties in spectral irradiance Source of Uncertainty Relative Expanded Uncertainties [%] (k=2) 250 350 655 900 1600 2000 2300 2400 HTBB temperature 0.57 0.41 0.22 0.16 0.09 0.08 0.07 0.07 HTBB emittance 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
HTBB uniformity 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
HTBB stability 0.07 0.05 0.03 0.02 0.01 0.01 0.01 0.01 Geometric factors 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
SR stability (HTBB) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.5
Wavelength accuracy 0.58 0.38 0.18 0.005 0.011 0.013 0.011 0.011 SR stability (lamp) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Current stability (lamp) 0.08 0.06 0.03 0.02 0.02 0.01 0.01 0.01 Unc. of PWS (k=2) 0.85 0.60 0.36 0.28 0.24 0.24 0.23 0.54 Lamp-to-lamp transfer 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
Long term stability of PWS 1.31 0.94 0.50 0.36 0.20 0.16 0.14 0.14 Unc. of issued lamps (k=2) 1.56 1.12 0.63 0.47 0.33 0.31 0.29 0.57
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
How well can you do?Uncertainties in Radiance Standards from NIST
“Land-level” integrating sphere source, expanded uncertainties in spectral radiance Source of Uncertainty Relative Expanded Uncertainties [%] (k=2) 300 400 500 600 700 800 900 1000 Blackbody quality 0.12 0.07 0.03 0.01 0.00 0.01 0.03 0.04 Calibration of pyrometer lamp 0.33 0.27 0.22 0.18 0.15 0.12 0.11 0.10 BB temperature determination and transfer to lamp 1.02 0.21 0.36 0.16 0.37 0.31 0.31 0.55 Wavelength accuracy 0.12 0.10 0.07 0.06 0.05 0.04 0.04 0.03 Temperature scale (thermodynamic vs ITS-90) 0.58 0.46 0.37 0.30 0.27 0.24 0.20 0.19 Unc. for NPR (4 lamps) (k=2) 1.23 0.59 0.57 0.39 0.48 0.41 0.39 0.59
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Uncertainties from Transfer of Scales
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
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 %
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Calibration Stability & Repeatability
0.020
0.022
0.024
0.026
0.028
0.030
1996 1997 1998 1999 2000 2001 2002
Optronics Calibration
Calibration Series 1
Calibration Series 2
Calibration Series 3
Calibration Series 4
SLM412
Ra
dia
nce
(W
cm
-2 s
r-1 n
m-1
)Date
OL420 and SLM412 Radiances at 411.8 nm
a
OL Calibration History
within the calibration uncertainty Stability ~ 0.5 % (SLM)
OL420 and SLM RadianceAt 412 nm
(870 nm results similar)
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Uncertainties Associated with the Deployments
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%
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.
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
0 5 10 15 20 25 30 350.98
1
1.02
1.04
1.06
1.08
Deployment Number
Lu
To
p S
yste
m R
esp
on
se R
atio
(P
reC
al/P
ost
Ca
l)
411.8 nm442.1 nm546.8 nm665.6 nm
411.8 442.1 546.8 665.6-0.01
0
0.01
0.02
0.03
0.04
0.05
0.06
Wavelength (nm)
Pre
/ P
ost S
yste
m R
espo
nse
Sta
bilit
y
LuTopLuMidLuBot
Averaged over deployments by wavelength
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
In Situ Wavelength Calibration with Spectral Features
Red Spectrograph2.5 years
Approx. +/- 1 nm
Blue Spectrograph2.5 years
Approx. +/- 0.6 nm
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Uncertainties Associated with Systematic Effects
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).
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Impact of Stray Light or Spectral out-of-band
-200 -100 0 100 200 300 400 500 600 7001E-6
1E-5
1E-4
1E-3
0.01
0.1
1
Re
lativ
e S
pe
ctra
l Re
spo
nsi
vity
(a
u)
Relative Wavelength (nm)
Band 8, 411.8 nm Band 9, 442.1 nm Band 12, 546.8 nm
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.
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Stray Light in MOBYStray light correction to MODIS BandsImages of Laser Lines
Correction to Responsivity Multiple Deployment Time Series
Single Deployment
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 Lu
There are a number of parameters that go into the model; each has an uncertaintyWe 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.
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
MOBY Radiometric UncertaintyMOBY WorkshopPreliminary Results
Uncertainty Component Value [%]
Calibration Source Radiance 3% to 5% (Comm. Lab); 0.5% (NIST)
Source stability between calibrations ~3% to ~4% (Repeat Cals.); ~0.5% (SLMs)
Responsivity during deployment ~0.6%
Wavelength Within 1 Pixel
Temperature ~ Negligible
Stray light <~ 0.25%
Combined Standard Uncertainty [%] 3.2% to 5.1%
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
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
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Primary Calibration Sources
350 400 450 500 550 600 650
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Lu(
) [
W/c
m2 /s
r/nm
]
Wavelength [nm]
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Measured Source
Calibration Source
Lca
l()
[W
/cm
2 /sr/
nm]
Source Spectral Power Distributions
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
LED Sources
12 mm12 mm
Fiber-coupled Spectroradiometer
Multiple Channel Power Supply
Data Acquisition & Control
Realized Spectrum
Target Spectrum
L()
Integrating Sphere
LED Heads
Photometer
Fiber-coupled Spectroradiometer
Multiple Channel Power Supply
Multiple Channel Power Supply
Data Acquisition & Control
Realized Spectrum
Target Spectrum
L()
L()
Integrating Sphere
LED Heads
Photometer
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
LED Source: Field Tests
LED source MOS204 23 degC sets
0
2
4
6
8
10
12
300 400 500 600 700
Wavelength
AD
U/p
xl/s
ec
0
0.01
0.02
0.03
0.04
0.05
mean
stdev/mean
OL420 source MOS204 13 degC sets
0
10
20
30
40
50
60
300 400 500 600 700
Wavelength
AD
U/p
xl/s
ec
0
0.01
0.02
0.03
0.04
0.05
mean
stdev/mean
More flux in the blue;Better matched to the ocean’s spectral distribution
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Spectrally Tunable, Detector-based Source
Under development using GOES-R funding
Dispersing element Spatial Light Modulator(SLM)
Recombine the Light
SLM Light Guide
• New Technology: SLM– Digital micromirror devices (DMDs)
– Liquid crystal on silicon arrays (LCOS arrays)
375 425 475 525 575 625 675 725
Wavelength (nm)In
tens
ity
(a. u
.)
Target
Output
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
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
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.