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CALCON 2000 19-21 September
B. Carol Johnson, Steven W. Brown
and Howard W. Yoon
National Institute of Standards and Technology
Gaithersburg, MD
Radiometric Calibration History of MOBY/NIST Single Channel Dual Mode
Radiometers
CALCON 2000 19-21 September
Ocean Color Radiometry and Bio-Optics
MODIS & SeaWiFS: Global Exoatmospheric Radiances
Corrections for Atmospheric and Reflected Components
Water-leaving Radiance, Lw(,,)
Remote Sensing Reflectance Phytoplankton Carbon
Ground Truth using Buoy and Ship Deployments
CALCON 2000 19-21 September
Marine Optical Buoy (MOBY) & Marine Optical Characterization Experiments
• NOAA/NESDIS Program (D. K. Clark, PI)
• Methods– MOBY deployed off coast of
Lanai, Hawaii: 1994—present
– MOCE cruises
• Goals– daily values for Lw in SeaWiFS
and MODIS bands—need 5%
– bio-optical algorithm development
CALCON 2000 19-21 September
Field Radiometers in the NOAA Program
• Moss Landing Marine Laboratories—partner in instrument design, deployment, and calibration
• MOBY—dual spectrograph; 350nm to 950nm; rebuilt, recalibrated, and redeployed every three months at field laboratory (Honolulu, Hawaii)
• MOS—Marine Optical Spectrograph; a profiling version of the MOBY system
• Various other commercial radiometers for in-water and at surface measurements (filter radiometers and grating instruments)
CALCON 2000 19-21 September
Calibration of MOBY and MOS
• Spectral Radiance Responsivity– Integrating sphere source(s)
– Calibrated by commercial standards laboratory (1%-2%)
– Re-lamped every 50 h
– Calibrated twice—at the beginning and end of the 50 h
– Lamp current and voltage always recorded
– Used before and after field deployments
Sphere Sourcewith External 45 W Lamp
Schematic ofRadiance Inputon buoy arm(window, lens,and fiber optic)
Lcal()
CALCON 2000 19-21 September
Calibration of MOBY and MOS
• Spectral Irradiance Responsivity– 1000 W lamp standards of spectral
irradiance (m/n FEL)
– Calibrated by NIST (0.4%)
– Recalibrated every 50 h
– Lamp current and voltage recorded during radiometer calibrations
– Used before and after field deployments
Lamp Source withReference Plate
Schematic ofIrradiance Inputon buoy arm(diffuser and fiber optic)
FEL at 50 cmEcal()
CALCON 2000 19-21 September
Verification of Standard Sources
• NOAA required direct verification of Lcal() and Ecal() • NIST response—transfer radiometers
– Standard Lamp Monitors (SLMs)• Dual Mode (Irradiance and Radiance)• Interchange Fore Optics for E and L modes• Single Channel using Interference Filters• Temperature-controlled filter and detector• 7 decade custom preamp• Rugged design
• Recalibrated at NIST to verify stability of SLMs• Used in Comparisons at Snug Harbor with SXR and VXR (six channel
filter radiometers from NIST for SeaWiFS and EOS)
CALCON 2000 19-21 September
SLM Specifications
• Wavelength– 412 nm and 870 nm
– 10 nm bandpass
• Field-of-View– 5 (radiance)
– hemisphere (irradiance)
• Temperature-stabilized– 28 C
• Accuracy & Stability– > 0.985
VXR
Sphere Source
SLMs
Calibration Hut, Honolulu
CALCON 2000 19-21 September
Characterization and Calibrations at NIST
• Characterizations Performed:– Electronics
• Gain Range Factors
– Spatial • Cosine response (E mode)• Point Spread (L mode)
– Stability• Interchange Fore Optics• Repeat Absolute Calibrations
– Spectral• Relative (using
monochromator & lamp)• Absolute (using lasers)
• Calibrations Performed:– Radiance Mode
• NIST-calibrated sphere sources (in 1996, 1998, and 2000)
• SIRCUS Facility (2000)
– Irradiance Mode• NIST FELs (in 1996, 1998,
and 2000)
• SIRCUS Facility (2000)
CALCON 2000 19-21 September
Calibration Method 1—Broadband Source
• STEP 1– Determine the Relative
Spectral Responsivity of the SLMs in radiance and irradiance mode
• Visible Spectral Comparator Facility was used in 1996– could not fill SLM radiance
field of view
– finite bandwidth, ~ 1 nm
– low flux
0
3
6
9
120
36
912
mm
mm
0.9951.0001.0051.0101.015
0 3 6 9 12
0
3
6
9
12
mm
mm
0.995
1.000
1.005
1.010
1.015
Response Uniformity of Silicon Photodiode
0.2% Contours at 500 nm 1.1 mm resolution
Rel
ativ
e R
esp
ons
e
Rel
ativ
eR
esp
ons
e
So u rcesLig ht Tig ht Box
Mo nitorDe te c to r
B affle
Pris m - Gratin g Mono c hro m ato r
S h utte r
0.0
0.2
0.4
0.6
0.8
1.0
400 600 800 1000 1200 1400 1600 1800
Abs
olu
te R
esp
onse
(A
/W)
Wavelength (nm)
Absolute Spectral Response
0
3
6
9
120
36
912
mm
mm
0.9951.0001.0051.0101.015
0 3 6 9 12
0
3
6
9
12
mm
mm
0.995
1.000
1.005
1.010
1.015
Response Uniformity of Silicon Photodiode
0.2% Contours at 500 nm 1.1 mm resolution
Rel
ativ
e R
esp
ons
e
Rel
ativ
eR
esp
ons
e
So u rcesLig ht Tig ht Box
Mo nitorDe te c to r
B affle
Pris m - Gratin g Mono c hro m ato r
S h utte r
0.0
0.2
0.4
0.6
0.8
1.0
400 600 800 1000 1200 1400 1600 1800
Abs
olu
te R
esp
onse
(A
/W)
Wavelength (nm)
Absolute Spectral Response
SourcesA
lign
men
t Las
er
Wav
elen
gth
Dri
ve
Light Tight Box
Monitor Detector
ShutterBaffle
X/Y
sca
nnin
g de
tect
or c
arri
age
CALCON 2000 19-21 September
Calibration Method 1, continued
• STEP 2– Calibrate the NIST Sources
– FASCAL
• Spheres calibrated in radiance mode (shown)
• Irradiance scale is based on the radiance scale
• FASCAL supplies NIST-calibrated FEL Lamps (irradiance mode)
CALCON 2000 19-21 September
Calibration Method 1, continued
• STEP 3– Calibrate the SLM with the
broadband source
– r() = relative spectral responsivity
– S = net signal
– LNIST () = source radiance (or irradiance)
SLM Calibration
SLMNIST Sphere or FEL Lamp
dr
dLr
SDb
)(
)()( NIST
Channel Calibration Coefficient
CALCON 2000 19-21 September
Calibration Method 2—Tunable Lasers
Laser
Wavemeter
Motor- driven Rotating Mirror
Monitor Photodiode (output to stabilizer)
Integrating Sphere
Exit Port
Spectrum Analyzer
Lens
Detector Package
Computer
SIRCUS (Spectral Irradiance and Radiance response Calibrations using Uniform Sources)
Transfer standard
Intensity Stabilizer
=200 nm -10 m
• ONLY STEP– SIRCUS (Spectral Irradiance
and Radiance Responsivity using Uniform Sources)
– Determine the Absolute Spectral Radiance (Irradiance) Responsivity, R()
– Reduced Uncertainties
dRDd )(
Channel Calibration Coefficient
CALCON 2000 19-21 September
Spectral Response—Radiance Mode
300 400 500 600 700 800 900 1000 11001E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1SI
RC
US
Rad
ianc
e R
espo
nsiv
ity [
A m
m2 s
r W
-1]
Wavelength [nm]
SIRCUS
Vis/SCF
Vis
/SC
F R
elat
ive
Spec
tral
Res
pons
ivity
FAKE 870 Sircus data
CALCON 2000 19-21 September
Spectral Response: Irradiance Mode
300 400 500 600 700 800 900 1000 1100 12001E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0.01SI
RC
US
Irad
ianc
e R
espo
nsiv
ity [
A m
m2 s
r W
-1]
Wavelength [nm]
SIRCUS
Vis/SCF
Vis
/SC
F R
elat
ive
Spec
tral
Irr
adia
nce
Res
pons
ivity
CALCON 2000 19-21 September
History of SLM 412
4/27/96 11/13/96 6/1/97 12/18/97 7/6/98 1/22/99 8/10/99 2/26/000.340
0.345
0.350
0.355
0.360
Reference Gain: 108 []
SLM
412
Rad
ianc
e [V
cm
2 sr
nm W
-1]
Wavelength [nm]
OL420 NPR1234 NPRL1 Sircus
8/1/96 2/17/97 9/5/97 3/24/98 10/10/98 4/28/99 11/14/99 6/1/00
0.72
0.73
0.74
0.75
0.76
0.77 Reference Gain: 108 []
SLM
412
Irr
adia
nce
[V c
m2 s
r nm
W-1]
Wavelength [nm]
F423 F493 F332 E007 FAKEsircus
Radiance
Irradiance
CALCON 2000 19-21 September
History of SLM 870
Radiance
Irradiance
4/27/96 11/13/96 6/1/97 12/18/97 7/6/98 1/22/99 8/10/99 2/26/000.0600
0.0605
0.0610
0.0615
0.0620
0.0625
0.0630
0.0635
Reference Gain: 107 []
SLM
870
Rad
ianc
e [V
cm
2 sr
nm W
-1]
Wavelength [nm]
OL420 4 Lamps Lamp #1 FAKEsircus
6/1/96 12/18/96 7/6/97 1/22/98 8/10/98 2/26/99 9/14/99 4/1/00
0.562
0.564
0.566
0.568
0.570
0.572
0.574
0.576
0.578
0.580
Reference Gain: 107 []
SLM
870
Irr
adia
nce
[V c
m2 s
r nm
W-1]
Wavelength [nm]
F332 E007 F423 F493 FakeSIRCUS
CALCON 2000 19-21 September
Conclusions—SLMs for MOBY/MOS
• Traceability to NIST and EOS Calibration Program
• Continuous Monitoring of Standard Sources
• Verification of FEL-derived radiance scales from commercial standards laboratories
• Uncertainties of between 1.2% and 0.5% using broadband source calibration method
• Uncertainties of about 0.25% using tunable laser source