calcon 2000 19-21 september b. carol johnson, steven w. brown and howard w. yoon national institute...

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


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


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


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)


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()


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()


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)


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


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)


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


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)


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


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


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


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


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


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


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


SLM

870

Irr

adia

nce

[V c

m2 s

r nm

W-1]

Wavelength [nm]

F332 E007 F423 F493 FakeSIRCUS


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

calcon 2000 19-21 september b. carol johnson, steven w. brown and howard w. yoon national institute...

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