NASA Technical Memorandum 104566, Vol. 14

SeaWiFS Technical Report Series

Stanford B. Hooker and

Elaine R. Firestone, Editors

Volume 14, The First SeaWiFS Intercalibration

Round-Robin Experiment, SIRREX, July 1992

James L. Mueller

September 1993
NASA Technical Memorandum 104566, Vol. 14

SeaWiFS Technical Report Series

Stanford B. Hooker, Editor

NASA Goddard Space Flight Center

Greenbelt, Maryland

Elaine R. Firestone, Technical Editor

General Sciences Corporation

Laurel, Maryland

Volume 14, The First SeaWiFS Intercalibration

Round-Robin Experiment, SIRREX, July 1992

James L. Mueller

Center for Hydro-Optics and Remote Sensing

San Diego State University

San Diego, California

National Aeronautics and

Space Administration

Goddard Space Flight Center

Greenbelt, Maryland 20771

1993
James L. Mueller

Abstract

This report presents the results of the first Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Intercalibration

Round-Robin Experiment (SIRREX-1), which was held at the Center for Hydro-Optics and Remote Sensing

(CHORS) at San Diego State University (SDSU) on 27–31 July 1992. Oceanographic radiometers to be used

in the SeaWiFS Calibration and Validation Program will be calibrated by individuals from the National Aeronautics and Space Administration’s (NASA) Goddard Space Flight Center (GSFC), CHORS, and seven other

laboratories. The purpose of the SIRREX experiments is to assure the radiometric standards used in all of these

laboratories are referenced to the same scales of spectral irradiance and radiance, which will be maintained by

GSFC and periodically recalibrated by the National Institute of Standards and Technology (NIST). The spectral

irradiance scale of GSFC’s FEL lampnumber F269 (recalibrated by NIST in October 1992) was transferred to

lamps belonging to the 9 participating laboratories; 1 set of lamp transfer measurements (involving 4 of the

lamps) was precise to within less than 1% and meets SeaWiFS goals, but a second set (involving another 14

lamps) did not. The spectral radiance scale of the GSFC 40-inch integrating sphere source was transferred to

integrating sphere radiance sources belonging to four of the other laboratories. Reflectance plaques, used for

irradiance-to-radiance transfer by five of the laboratories, were compared, but spectral bidirectional reflectance

distribution functions (BRDFs) were not determined quantitatively. Also reported here are results of similar

comparisons (in October 1992) between the GSFC scales of spectral irradiance and radiance and those used

by the Hughes/Santa Barbara Research Center (SBRC) to calibrate and characterize the SeaWiFS instrument.

This first set of intercalibration round-robin experiments was a valuable learning experience for all participants,

and led to several important procedural changes, which will be implemented in the second SIRREX, to be held

at CHORS in June 1993.

1. INTRODUCTION

The Sea-viewing Wide Field-of-view Sensor (SeaWiFS)

ocean color radiometer is scheduled to be launched in early

1994. It will operate in a sun-synchronous orbit with an

expected lifetime of 5 years. The National Aeronautics

and Space Administration (NASA) will carry out a program to acquire the global SeaWiFS data set, validate and

monitor its accuracy and quality, process the radiometric

data into geophysical units, and distribute it to the scientific community in the US and abroad. The SeaWiFS

data products figure as prominent components of major

scientific programs studying global change, including the

Joint Global Ocean Flux Study (JGOFS) and the Global

Ecosystem (GLOBEC) programs.

Two important goals of the SeaWiFS Project are to

determine from the radiance measurements, 1) normalized water-leaving radiance with an accuracy of 5%, and

2) chlorophyll a concentration with an accuracy of 30%

(Hooker et al. 1992). These are ambitious goals, and can

only be achieved by augmenting the SeaWiFS measurements with a program of ongoing validation measurements

to verify the radiometric precision and long-term stability

of the SeaWiFS instrument’s radiance responsivities, and

to validate the atmospheric correction models and algorithms used to convert SeaWiFS radiances to normalized

water-leaving radiances. One of the principal approaches

to this critical aspect of validation will be frequent direct comparisons between SeaWiFS estimates and in situ

measurements of water-leaving radiance collected during

cruises and from a marine optical buoy (MOBY). Because

the desired result is to validate normalized water-leaving

radiances derived from SeaWiFS data to within 5%, the

comparative in situ radiometric measurements must be

calibrated to be accurate within less than 5%.

The only economically feasible approach for acquiring

a large and globally distributed sample of in situ radiometric measurements for SeaWiFS validation is to solicit

contributions of data from the oceanographic community

at large, and to somehow provide assurance that the aggregate data set will be of uniform quality and accuracy

to within 5% (or at least be internally consistent to that

level of precision). The SeaWiFS Project, located at the

NASA Goddard Space Flight Center (GSFC), is addressing this problem through the SeaWiFS Calibration and

Validation Program (McClain et al. 1992). At the outset,

the Project sponsored a workshop to draft protocols for

ocean optics measurements to support SeaWiFS validation

(Mueller and Austin 1992), which included instrument performance specifications and requirements for instrument

characterization and calibration.

Of the oceanographers and institutions expected to contribute oceanic radiometer measurements to the SeaWiFS

validation database, only a small number are equipped

to calibrate and characterize radiometric instruments, and

fewer still are able to meet the exacting standards recommended for the Project. Currently, the laboratories which

engage in at least some aspects of the characterization and

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The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

calibration of oceanographic radiometers include the following:

GSFC,

the Center for Hydro-Optics and Remote Sensing (CHORS) located at San Diego State University (SDSU),

the Department of Physics at the University of

Miami (UM),

the University of California at Santa Barbara

(UCSB), and

the Moss Landing Marine Laboratory (MLML)

at San Jose State University (SJSU) in cooperation with Dennis Clark at the National Oceanic

and Atmospheric Administration (NOAA).

Several manufacturers of instruments engage in instrument

characterization and calibration including, for example,

Biospherical Instruments, Inc. (BSI) in San Diego, California, and

Satlantic, Inc. in Halifax, Nova Scotia, Canada.

The strategy adopted for SeaWiFS validation is to calibrate all involved instruments within the network consisting of these, and possibly a few additional, laboratories. In recognition of the need to maintain internal consistency between calibrations of in situ instruments and that

of the SeaWiFS instrument itself, the SeaWiFS Project,

under the Calibration and Validation element, has implemented an ongoing series of SeaWiFS Intercalibration

Round-Robin Experiments (SIRREXs). The purpose of

the SIRREX program is to transfer the National Institute

of Standards and Technology (NIST) scales of spectral irradiance and radiance through GSFC to 1) all participating

laboratories in the SeaWiFS ocean color community, and

2) to the calibration standards used to calibrate the SeaWiFS instrument for radiance responsivity. This process

is illustrated schematically in Fig. 1.

The first round-robin, SIRREX-1, was carried out from

27–31 July 1992 at CHORS. The objectives were as follows:

a) To intercalibrate FEL lampworking standards

of spectral irradiance used at the participating

laboratories and to reference each to the NIST

scale of spectral irradiance via a secondary standard to be maintained at GSFC;

b) To intercalibrate the integrating sphere sources

of spectral radiance used by the participants;

c) To intercompare plaques used to transfer the

scale of spectral irradiance from an FEL lamp

to a scale of spectral radiance; and

d) To intercompare transfer radiometers and other

support electronics (most critically shunts and

voltmeters) used to support radiometric calibrations at each laboratory.

The participants in SIRREX-1, and the sources and radiometers each contributed to the experiments, are listed

in Table 1.

This report describes the methods and results of the

first SIRREX (July 1992), discusses the significance of the

results in terms of the relative readiness of the calibration community to meet the SeaWiFS radiometric goals,

and recommends specific procedural guidelines for the next

SIRREX. In addition, this report describes subsequent activities to:

i) Determine the temporal stability of the Optronics 746/Integrating Sphere Irradiance Collector

(ISIC) spectroradiometer, used as a transfer radiometer for lampintercomparisons (Fig. 1);

ii) Intercalibrate the GSFC spectral irradiance and

radiance scales with those at the Hughes/Santa

Barbara Research Center (SBRC), which have

been used to calibrate the SeaWiFS instrument;

and

iii) Modify equipment and procedures to overcome

deficiencies noted during SIRREX-1.

2. METHODS

This section briefly describes methods for transferring

NIST-traceable scales of spectral irradiance and radiance

to the laboratories participating in SIRREX-1. The results

of the tests are presented in Section 3.

2.1 Irradiance: Standard Lamps

All of the participating laboratories base their absolute calibrations of irradiance and radiance responsivities

on the NIST scale of spectral irradiance, which is transferred to the American scientific and engineering community via calibrated tungsten-halogen lamps, usually FEL

lamps and less frequently DXW lamps (Walker et al. 1987).

Some laboratories acquire a calibrated FEL lampstandard

of spectral irradiance directly from NIST, but more typically, a laboratory will base its irradiance scale on a lamp

which has been calibrated and certified as traceable to

the NIST scale by a commercial standardizing laboratory.

This transfer is illustrated schematically in the upper-left

portion of Fig. 1. The transfer begins with NIST, and

propagates to laboratories either directly or through commercial providers of lamps; occasionally a user will have a

lamprecalibrated by NIST. In all cases, a laboratory will

purchase additional seasoned, but uncalibrated lamps, and

transfer the spectral irradiance scale from their calibrated

lampusing a transfer radiometer. These less expensive

working standards are then used for actual calibration experiments to avoid aging and, thus, expending the useful

working life of, their primary local scale reference lamp.

A laboratory will periodically intercompare all of their

working standard lamps and their primary reference lamp

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James L. Mueller

3
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Table 1. Participants in the July 1992 SIRREX and their intercalibration and radiometric sources (see Appendix D). All lamps are FEL lamps except those designated by the † symbol, which are DXW lamps.

Organization Contact Lamps Sphere Plaque Radiometer

BSI R. Booth F310 20 inch Spectralon BSI 6-channel radiometer

G. Adelman F321 and QED200

91453

CHORS J. Mueller 90572 40 inch Spectralon QED200

R. Austin 91348

C. Titus 91534

GSFC J. McLean F268 42 inch Optronics 746A

J. Cooper F269

MLML M. Yarbrough

M. Feinholz

W. Broenkow

NCCOSC/NRaD R. Howarth F265

NIST C. Johnson PR714 and NIST CaliC. Cromer brated Photodetectors

NOAA D. Clark F307 Optronics 420M Spectralon

F308

Satlantic S. McLean S724† Satlantic 7-channel

S721† radiometer and QED200

SRT D. Goebel

SIO/MPL R. Johnson F12L

UCSB R. Smith F219 20 inch Spectralon

D. Menzies F303

UM K. Voss F12G

F12H

†DXW lamps.

to maintain an internally consistent scale of spectral irradiance, and to detect cases when a lampbegins to either

become unstable, or to otherwise fail in a subtle way (a

lampusually becomes an unreliable source of spectral irradiance long before it burns out). The SIRREX program

extends this internal consistency maintenance throughout

the several laboratories participating in calibration of instruments for SeaWiFS validation.

During SIRREX-1, the spectral irradiance scale of

GSFC FEL lampF269 was transferred to 17 other lamps

belonging to the various participating laboratories as summarized in Table 1. The F269 irradiance scale was recalibrated by NIST in October 1992, to provide a fresh standard, traceable to NIST, as the basis for intercalibration of

all radiometers involved in SeaWiFS validation. Another

GSFC FEL lamp, F268, was also recalibrated by NIST to

provide a working reference to verify the long-term stability of F269 as the primary tie to the NIST scale of spectral

irradiance.

Transfer of the F269 scale of spectral irradiance to other

lamps follows the procedures for spectral irradiance calibrations described in Walker et al. (1987) and shown in

Fig. 1. A small ISIC is attached (at its exit port) to the entrance slit of an Optronics 746 spectroradiometer (a singlemonochromator radiometer system, with a 750 nm blaze

grating and a silicon detector). LampF269 was mounted

to illuminate the entrance port of the 746/ISIC, which was

placed perpendicular to the center of the lamp filament at

a distance of 50 cm (by convention, measured to the front

surface of the lampelectrical connection posts).

The calibration procedure used during SIRREX-1 was

as follows:

1. The lampand 746/ISIC were both powered on

and warmed up for approximately 20 minutes.

2. The irradiance responsivity of the 746/ISIC was

then determined by measuring the known spectral irradiance output from lamp F269.

3. The calibrated responsivity of the 746/ISIC was

used to measure the spectral irradiance emitted

by each of the other lamps. (The first measurement is always made immediately on the reference lamp, F269, to provide an initial measure

of the transfer precision.)

4. Each lampwas then powered down and replaced

by the next lampto be calibrated, which was allowed to warm up for approximately 15 minutes

before its spectral irradiance output was measured with the 746/ISIC.

5. The above procedure was repeated until all of

the lamps were calibrated.

4
James L. Mueller

6. At, or near, the end of a transfer session, the reference lamp(F269) was measured once again to

test the stability of the radiometer’s calibration

through the duration of the entire procedure;

this final precision test on F269 was not performed on 30 July, but it was during the session

of 31 July (Section 3.2).

2.2 Lamps, Spheres, and Plaques

Transfer of the NIST scale of spectral irradiance to a

scale of spectral radiance is accomplished by one of three

methods. In the method used at GSFC, known irradiance

from an FEL lampstandard of spectral irradiance is first

measured by the 746/ISIC, in a setupidentical to that described in Section 2.1 for lamptransfer. The responsivity

of the 746/ISIC to spectral irradiance is thus determined.

The entrance port of the 746/ISIC is then positioned at a

known distance from the exit port of a larger integrating

sphere, which is illuminated by stable lamp sources. The

apertures of the two spheres must be parallel and aligned

on the common perpendicular joining their two centers.

From the distance between the ports of the two spheres

and their respective areas, it is possible to calculate from

the measured irradiance, the radiance in the exit port of

the integrating sphere radiance source, and thus to transfer the scale of spectral irradiance from the lamp to a scale

of spectral radiance for the sphere.

In the second approach, the spectral irradiance from

a calibrated lampis directed at normal incidence onto a

plaque for which the bidirectional reflectance distribution

function (BRDF) is accurately known for at least one viewing angle. The spectral radiance reflected from the plaque

is calculated as the product of the BRDF and the known

incident spectral irradiance from the lamp. The spectral

responsivity of a radiance sensor is then calibrated by measuring the spectral radiance reflected from the plaque at

the viewing angle for which the BRDF is known. This technique may be used to calibrate an instrument directly, by

viewing the plaque, or to determine the spectral radiance

scale of an integrating sphere source, by using a transfer

radiometer.

A third approach, which was used during SIRREX-1, is

to use the first method to determine the spectral radiance

scale of one reference sphere source (in this case, the GSFC

42-inch integrating sphere), and to then use that source to

calibrate a narrow field-of-view transfer spectroradiometer.

During SIRREX, the radiance scale of the GSFC 42-inch

sphere was transferred to several other spheres, using a

commercial Photo Research PR714 Spectrascan spectroradiometer provided by NIST.

3. RESULTS

This section summarizes the results for spectral irradiance scale transfer and comparisons for lamp sources (Section 3.1) and integrating spheres (Section 3.2), reflectance

plaque intercomparisons (Section 3.3), shunt and voltmeter

tests (Section 3.4), stability tests of the Optronics 746 spectrophotometer (Section 3.5), and GSFC and SBRC spectral irradiance and radiance source comparisons during October 1992 (Section 3.6).

3.1 Lamp Sources

The NIST (October 1992) calibrated scale of spectral

irradiance of FEL lampF269 was transferred, by postcalculation from measurements on 30 and 31 July 1992,

to the other 17 lamps listed in Table 1. GSFC FEL lamp

F269, originally calibrated by its manufacturer (Optronics)

and subsequently recalibrated by NIST in October 1992,

provided the reference scale of spectral irradiance for all

round-robins between participating laboratories. GSFC

FEL lampF268 was recalibrated by NIST in October 1992,

and will provide a comparison benchmark against which

F269 will be periodically tested for possible drift.

Transfer of the (NIST October 1992) F269 spectral irradiance scale to the other lamps was done in two separate sessions, using the equipment and procedures described in Section 2.1, on 30 and 31 July 1992. On 30 July,

The GSFC Optronics 746/ISIC spectroradiometer was calibrated against lampF269 at 2015 PDT, and that calibration was then used to measure the irradiance spectra of

lamps F269 (as a test of transfer precision at the beginning

of the procedure), F268, F307, and F308; a post-session

test measurement of F269 was not performed. The results

of the transfer precision test of F269 and comparisons to

its NIST and original Optronics calibration, together with

similar results for the other 3 lamps, are given in Table 2

and illustrated in Figs. 2–5, respectively. The transfer procedure began at 2015 PDT and was completed for the 4

lamps at 2216 PDT.

On 31 July 1992, the Optronics 746/ISIC and lamp

F269 were powered on, and both were warmed up for approximately 20 minutes. The spectroradiometer was then

calibrated with F269, and then a precision test measurement of F269 was repeated at 0800 PDT. Between 0800

and 1807 PDT, the spectral irradiance output of the remaining 14 lamps were measured with the 746/ISIC using the responsivity table derived from the initialization

measurements of F269. A second stability and precision

test was made by remeasuring the output of lamp F269

at 1430 PDT. The F269 spectra measured at 0800 and

1430 PDT (31 July 1992) are listed and compared in Table 3, and the apparent change (0800 relative to 1430) is

illustrated in Fig. 6.

On the assumption that the 746/ISIC was not warmed

upadequately at 0800, the radiometer’s responsivity was

recalculated based on the F269 measurements at 1430 PDT

and calculated the irradiance scale transfers on that basis.

The results of these scale transfers, and comparisons to

previous calibration scales, are given in Tables 4 (F321,

91453, and F310), 5 (90572, 91348, and 91534), 6 (F219,

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The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Table 2. Irradiance scale transfer from GSFC lampF269 on 30 July 1992 to lamps: F268 (GSFC), F307 (NOAA),

and F308 (NOAA). (Irradiances under each lampcolumn are in units of μW cm−2 nm−1.)

λ F269 F268 F307 F308

[nm] RR NIST OI RR NIST OI RR OI RR NIST

400 2.3119 2.3410 2.3000 2.2986 2.2770 2.2300 2.2603 2.2800 2.3340 2.3530

405 2.4995 2.5380 2.4936 2.4009 2.3850 2.5056

410 2.7431 2.7430 2.6962 2.7410 2.7504 2.7873

415 2.9504 2.9570 2.9070 2.8837 2.9273 2.9521

420 3.2290 3.1790 3.1260 3.1007 3.1863 3.2576

425 3.3978 3.4090 3.3530 3.4039 3.4161 3.4770

430 3.6451 3.6450 3.5877 3.5520 3.6244 3.6968

435 3.8957 3.8900 3.8300 3.8199 3.8601 3.9314

440 4.1215 4.1410 4.0796 4.0753 4.0907 4.1986

445 4.4010 4.4000 4.3359 4.3211 4.3836 4.4461

450 4.6835 4.6650 4.6000 4.5945 4.5580 4.4700 4.6422 4.5700 4.7247 4.6870

455 4.9248 4.9390 4.8732 4.8367 4.8925 4.9806

460 5.2315 5.2190 5.1535 5.1267 5.1709 5.2812

465 5.4865 5.5050 5.4393 5.4040 5.4504 5.5458

470 5.7888 5.7960 5.7306 5.6686 5.7431 5.8345

475 6.0797 6.0930 6.0269 5.9896 6.0459 6.1607

480 6.4082 6.3940 6.3278 6.2953 6.3613 6.4571

485 6.6974 6.6990 6.6330 6.5799 6.6407 6.7621

490 7.0173 7.0090 6.9421 6.9077 6.9711 7.0750

495 7.3187 7.3220 7.2534 7.1928 7.2468 7.3906

500 7.6381 7.6380 7.5700 7.5035 7.4830 7.3800 7.6045 7.5200 7.7391 7.6720

505 7.9593 7.9570 7.8962 7.8325 7.9276 8.0386

510 8.2606 8.2790 8.2262 8.1409 8.2307 8.3354

515 8.6215 8.6030 8.5558 8.4918 8.5639 8.6792

520 8.9435 8.9280 8.8851 8.7895 8.8875 9.0135

525 9.2591 9.2560 9.2131 9.1085 9.1769 9.3413

530 9.5865 9.5840 9.5388 9.4254 9.5328 9.6671

535 9.9107 9.9130 9.8613 9.7533 9.8451 9.9893

540 10.2280 10.2430 10.1797 10.0879 10.1644 10.3172

545 10.5759 10.5720 10.4919 10.4029 10.5264 10.6624

550 10.9210 10.9010 10.8000 10.7303 10.6000 10.8376 10.8000 10.9807

555 11.2367 11.2290 11.1030 11.0514 11.0100 10.9000 11.1440 11.1000 11.3062 11.2700

560 10.8083 11.5560 11.4076 10.6374 10.7335 10.8937

565 11.9086 11.8820 11.7216 11.7021 11.8168 11.9775

570 12.2094 12.2060 12.0408 12.0098 12.1154 12.2915

575 12.5370 12.5280 12.3640 12.3287 12.4267 12.5983

580 12.8425 12.8480 12.6902 12.6345 12.7515 12.9204

585 13.1751 13.1660 13.0180 12.9530 13.0640 13.2306

590 13.4947 13.4810 13.3464 13.2720 13.3908 13.5689

595 13.7966 13.7920 13.6735 13.5766 13.7180 13.8752

RR: Round-robin transfer on 31 July 1992.

NIST: Calibration by NIST in October 1992.

OI: Original irradiance scale calibration by Optronics, Inc.

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James L. Mueller

Table 2. (cont.) Irradiance scale transfer from GSFC lampF269 on 30 July 1992 to lamps: F268 (GSFC), F307

(NOAA), and F308 (NOAA). (Irradiances under each lampcolumn are in units of μW cm−2 nm−1.)

λ F269 F268 F307 F308

[nm] RR NIST OI RR NIST OI RR OI RR NIST

600 14.0809 14.1000 14.0000 13.8502 13.8400 13.7000 13.9784 13.9000 14.1493 14.1500

605 14.4067 14.4020 14.3271 14.1829 14.3108 14.4947

610 14.7102 14.7000 14.6509 14.4799 14.6181 14.7947

615 15.0132 14.9930 14.9683 14.7886 14.9383 15.1105

620 15.3003 15.2830 15.2783 15.0583 15.2270 15.3956

625 15.5711 15.5680 15.5794 15.3329 15.5061 15.6649

630 15.8544 15.8490 15.8702 15.6126 15.7833 15.9539

635 16.1330 16.1270 16.1492 15.8959 16.0842 16.2516

640 16.3984 16.3990 16.4148 16.1412 16.3198 16.4841

645 16.6636 16.6680 16.6636 16.4026 16.5816 16.7605

650 16.9338 16.9310 16.9000 16.6716 16.5000 16.8413 16.8000 17.0263

655 17.1917 17.1910 17.1232 16.9336 17.1448 17.3169

660 17.4652 17.4450 17.3456 17.2006 17.4030 17.5820

665 17.6946 17.6950 17.5814 17.4419 17.6410 17.8171

670 17.9557 17.9400 17.8235 17.7078 17.8956 18.0759

675 18.1782 18.1790 18.0698 17.9204 18.1193 18.3108

680 18.4029 18.4150 18.3185 18.1347 18.3594 18.5406

685 18.6421 18.6450 18.5678 18.3913 18.5991 18.7854

690 18.8722 18.8700 18.8157 18.6095 18.8225 19.0213

695 19.0764 19.0880 19.0644 18.8085 19.0412 19.2244

700 19.3070 19.3000 19.3000 19.0330 18.9700 18.9000 19.2649 19.1000 19.4475 19.3600

705 19.5109 19.5040 19.5039 19.2304 19.4618 19.6511

710 19.6998 19.7010 19.6928 19.4194 19.6507 19.8399

715 19.8912 19.8920 19.8783 19.6171 19.8631 20.0457

720 20.0841 20.0770 20.0570 19.8022 20.0418 20.2392

725 20.2281 20.2550 20.2291 19.9593 20.2069 20.3909

730 20.4072 20.4290 20.3949 20.1152 20.3644 20.5710

735 20.5453 20.5960 20.5546 20.2862 20.5165 20.7253

740 20.6989 20.7580 20.7085 20.4364 20.6916 20.8739

745 20.8896 20.9140 20.8564 20.6109 20.8603 21.0583

750 21.0189 21.0650 21.0000 20.7472 20.6000 21.0116 20.9000 21.1952

RR: Round-robin transfer on 31 July 1992.

NIST: Calibration by NIST in October 1992.

OI: Original irradiance scale calibration by Optronics, Inc.

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The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Fig. 2. Apparent spectral irradiance of lamp F269 (top panel, solid line) using scale transfer from the

NIST October 1992 F269 scale, during SIRREX-1 on 30 July 1992, compared to the NIST October 1992

calibrated irradiance scale (O), and original calibration by Optronics (+), of FEL lampF269. The bottom

panel illustrates the differences between the NIST (O) and Optronics (+) irradiance scales, relative to

the SIRREX-1 30 July 1992 scale transfer from F269.

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James L. Mueller

Fig. 3. Spectral irradiance of lampF268 (toppanel, solid line) using scale transfer from the NIST

October 1992 F269 scale, during the SIRREX-1 lamptransfer on 30 July 1992, compared to the NIST

October 1992 calibrated irradiance scale (*), and original calibration by Optronics (+), of FEL lamp

F268. The bottom panel illustrates the differences between the NIST (O) and Optronics (+) irradiance

scales, relative to the SIRREX-1 30 July 1992 scale transfer from F269.

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The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Fig. 4. Spectral irradiance of lampF307 (toppanel, solid line) using scale transfer from the NIST

October 1992 F269 scale, during the SIRREX-1 lamptransfer on 30 July 1992, compared to the original calibration by Optronics (+). The bottom panel illustrates the differences between the Optronics

irradiance scale (+) relative to that of SIRREX-1.

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James L. Mueller

Fig. 5. Spectral irradiance of lampF308 (toppanel, solid line) using scale transfer from the NIST

October 1992 F269 scale, during the SIRREX-1 lamptransfer on 30 July 1992, compared to the October

1992 calibration of F308 by NIST (O). The bottom panel illustrates the differences between the NIST

irradiance scale (O) relative to that of SIRREX-1.

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The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Table 3. Comparison of GSFC reference lamp (F269) transfer values for the beginning and ending of runs on 31 July

1992. (Irradiances, E, under each lampcolumn are in units of μW cm−2 nm−1.)

λ Ebeg Eend Ratio λ Ebeg Eend Ratio

[nm] 0805 PST 1430 PST Eend/Ebeg [nm] 0805 PST 1430 PST Eend/Ebeg

400 2.3662 2.3662 1.0000 580 12.6530 11.9714 0.9461

405 2.4454 2.5021 1.0232 585 12.9650 12.2896 0.9479

410 2.6910 2.6755 0.9942 590 13.3038 12.5947 0.9467

415 2.9352 2.9284 0.9977 595 13.5834 12.9072 0.9502

420 3.1330 3.0631 0.9777 600 13.9427 13.1813 0.9454

425 3.3767 3.3292 0.9859 605 14.2578 13.5572 0.9509

430 3.5978 3.5070 0.9748 610 14.5915 13.9306 0.9547

435 3.8256 3.7520 0.9807 615 14.9030 14.2362 0.9553

440 4.0572 3.9528 0.9743 620 15.2284 14.5725 0.9569

445 4.3393 4.2016 0.9683 625 15.5162 14.8352 0.9561

450 4.5939 4.4590 0.9706 630 15.7872 15.1161 0.9575

455 4.8476 4.7050 0.9706 635 16.1084 15.4151 0.9570

460 5.1562 4.9824 0.9663 640 16.3456 15.5436 0.9509

465 5.4143 5.2543 0.9705 645 16.5771 15.7698 0.9513

470 5.7236 5.5255 0.9654 650 16.8254 16.0274 0.9526

475 6.0094 5.8089 0.9666 655 17.0401 16.2841 0.9556

480 6.3134 6.0913 0.9648 660 17.3080 16.5479 0.9561

485 6.6291 6.3820 0.9627 665 17.5444 16.7816 0.9565

490 6.9383 6.6938 0.9648 670 17.7872 17.0176 0.9567

495 7.2886 7.0598 0.9686 675 18.0341 17.2637 0.9573

500 7.5700 7.3084 0.9654 680 18.2483 17.5105 0.9596

505 7.8808 7.5889 0.9630 685 18.4637 17.7143 0.9594

510 8.2117 7.8774 0.9593 690 18.5335 17.9483 0.9684

515 8.5418 8.1929 0.9592 695 18.7220 18.1879 0.9715

520 8.8715 8.4787 0.9557 700 18.8973 18.3855 0.9729

525 9.2131 8.8148 0.9568 705 19.1091 18.5781 0.9722

530 9.4998 9.0970 0.9576 710 19.2982 18.7540 0.9718

535 9.8233 9.3918 0.9561 715 19.4967 18.9379 0.9713

540 10.1550 9.7350 0.9586 720 19.6881 19.1006 0.9702

545 10.4325 9.9923 0.9578 725 19.8721 19.2678 0.9696

550 10.7656 10.2835 0.9552 730 20.0009 19.4342 0.9717

555 11.0584 10.5684 0.9557 735 20.1427 19.5562 0.9709

560 11.3529 10.8279 0.9538 740 20.3120 19.7386 0.9718

565 11.6450 11.1093 0.9540 745 20.4504 19.9090 0.9735

570 11.9960 11.4023 0.9505 750 20.5221 20.0441 0.9767

575 12.3173 11.6746 0.9478

12
James L. Mueller

Fig. 6. Apparent drift in FEL lamp F269 between 0800 and 1430 PDT during the SIRREX-1 on 31 July

1992. F269 was the reference irradiance scale used during this transfer. The change is a clear symptom

of drift in responsivity of the transfer radiometer during the comparisons.

13
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Table 4. Irradiance scale transfer from GSFC lampF269 on 31 July 1992 to lamps: F321, 91453, and F310 (all BSI).

(Irradiances under each lampcolumn are in units of μW cm−2 nm−1.)

λ F321 91453 F310

[nm] RR BSI NIST RR BSI RR

400 1.9896 2.0541 2.0470 1.7438 1.8762 1.7918

405 2.1028 2.2280 1.9389 2.0369 2.0429

410 2.3927 2.4101 2.1003 2.2053 2.3048

415 2.5211 2.6002 2.3304 2.3812 2.3563

420 2.7584 2.7982 2.5073 2.5647 2.6648

425 2.9230 3.0040 2.6738 2.7556 2.8501

430 3.1666 3.2174 2.8678 2.9537 3.0565

435 3.3292 3.4383 3.0686 3.1588 3.2259

440 3.5876 3.6664 3.3062 3.3709 3.4665

445 3.8259 3.9014 3.5340 3.5897 3.7134

450 4.0583 4.1432 4.1420 3.7409 3.8150 3.9429

455 4.3354 4.3916 3.9941 4.0465 4.1977

460 4.8071 4.9066 4.4613 4.5272 4.6787

470 5.0824 5.1727 4.7255 4.7760 4.9431

475 5.3573 5.4442 4.9617 5.0298 5.1972

480 5.6333 5.7206 5.2316 5.2886 5.4649

485 5.9083 6.0018 5.4984 5.5520 5.7559

490 6.1934 6.2873 5.7537 5.8196 6.0312

495 6.4611 6.5768 6.0083 6.0912 6.3041

500 6.7659 6.8700 6.8940 6.3285 6.3665 6.6241

505 7.0583 7.1665 6.6071 6.6451 6.9133

510 7.3626 7.4660 6.8738 6.9267 7.2099

515 7.6353 7.7681 7.1517 7.2110 7.4741

520 7.9583 8.0726 7.4448 7.4976 7.8014

525 8.2519 8.3790 7.7362 7.7863 8.0707

530 8.5746 8.6870 8.0267 8.0768 8.3828

535 8.8991 8.9963 8.3362 8.3686 8.7115

540 9.1755 9.3066 8.5906 8.6616 8.9675

545 9.4643 9.6175 8.8854 8.9554 9.2756

550 9.7813 9.9288 9.1973 9.2496 9.5988

555 10.0860 10.2400 10.2800 9.4941 9.5441 9.8966

560 10.4097 10.5510 9.7795 9.8385 10.2230

565 10.7052 10.8614 10.0851 10.1326 10.5297

570 11.0020 11.1709 10.3788 10.4260 10.8222

575 11.3230 11.4792 10.6835 10.7185 11.1349

580 11.6220 11.7861 10.9837 11.0098 11.4358

585 11.9141 12.0913 11.2758 11.2998 11.7155

590 12.2319 12.3946 11.5641 11.5881 12.0346

595 12.5128 12.6957 11.8542 11.8745 12.3361

RR: Round-robin transfer on 31 July 1992.

NIST: Calibration by NIST on February 1991.

BSI: In-house transfer or interpolation at BSI.

14
James L. Mueller

Table 4. (cont.) Irradiance scale transfer from GSFC lampF269 on 31 July 1992 to lamps: F321, 91453, and F310

(all BSI). (Irradiances under each lampcolumn are in units of μW cm−2 nm−1.)

λ F321 91453 F310

[nm] RR BSI NIST RR BSI RR

600 12.8162 12.9944 13.0300 12.1329 12.1588 12.6147

605 13.0896 13.2905 12.3865 12.4407 12.8852

610 13.3493 13.5837 12.6051 12.7202 13.1143

615 13.6397 13.8739 12.8841 12.9969 13.4107

620 13.9179 14.1608 13.1551 13.2706 13.6711

625 14.1923 14.4442 13.4116 13.5413 13.9345

630 14.4642 14.7241 13.6594 13.8088 14.1959

635 14.7236 15.0002 13.9061 14.0728 14.4606

640 15.0125 15.2724 14.2392 14.3332 14.7644

645 15.2670 15.5405 14.4823 14.5899 15.0232

650 15.4994 15.8044 14.7119 14.8428 15.2632

655 15.7510 16.0640 14.9367 15.0917 15.4956

660 15.9980 16.3191 15.1414 15.3365 15.7204

665 16.2203 16.5697 15.3539 15.5771 15.9393

670 16.4520 16.8156 15.5950 15.8134 16.1766

675 16.6913 17.0568 15.8199 16.0453 16.4284

680 16.9130 17.2931 16.0260 16.2728 16.6543

685 17.1481 17.5246 16.2640 16.4956 16.8778

690 17.3658 17.7511 16.4758 16.7139 17.0764

695 17.5562 17.9725 16.6726 16.9275 17.2760

700 17.8071 18.1889 18.1000 16.9114 17.1364 17.5133

705 17.9916 18.4001 17.0909 17.3404 17.6985

710 18.1775 18.6062 17.2633 17.5397 17.8776

715 18.3607 18.8071 17.4520 17.7340 18.0745

720 18.5455 19.0027 17.6695 17.9235 18.2583

725 18.7277 19.1932 17.8039 18.1081 18.4318

730 18.8855 19.3783 17.9485 18.2878 18.5877

735 19.0782 19.5582 18.1592 18.4625 18.7914

740 19.2381 19.7328 18.3072 18.6322 18.9551

745 19.3787 19.9022 18.4438 18.7970 19.1095

750 19.5145 20.0663 18.5849 18.9569 19.2222

RR: Round-robin transfer on 31 July 1992.

NIST: Calibration by NIST on February 1991.

BSI: In-house transfer or interpolation at BSI.

15
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Table 5. Irradiance scale transfer from GSFC lampF269 on 31 July 1992 to lamps: 90572, 91348, and 91534 (all

CHORS). (Irradiances under each lampcolumn are in units of μW cm−2 nm−1.)

λ 90572 91348 91534 λ 90572 91348 91534

[nm] RR HEI RR CHORS RR [nm] RR HEI RR CHORS RR

400 0.7854 0.7416 1.6638 1.5670 2.0580 580 5.8775 6.0110 10.2523 10.1900 12.1804

405 0.8282 0.8162 1.8056 1.7160 2.2839 585 6.0705 6.2010 10.5241 10.4700 12.4814

410 0.9283 0.8946 2.0240 1.8720 2.5601 590 6.2525 6.3900 10.8053 10.7500 12.8086

415 1.0198 0.9749 2.1294 2.0340 2.7411 595 6.4572 6.5900 11.0832 11.0300 13.1071

420 1.0910 1.0620 2.3461 2.2040 2.9689 600 6.6578 6.7910 11.3270 11.3100 13.4032

425 1.1710 1.1530 2.4733 2.3810 3.1357 605 6.8351 6.9770 11.5934 11.5800 13.6946

430 1.2798 1.2510 2.6528 2.5650 3.3764 610 7.0115 7.1690 11.8373 11.8600 13.9604

435 1.3851 1.3510 2.8260 2.7550 3.5628 615 7.2053 7.3540 12.1055 12.1300 14.2808

440 1.4694 1.4550 3.0600 2.9520 3.8455 620 7.3815 7.5440 12.3549 12.3900 14.5536

445 1.5859 1.5660 3.2422 3.1560 4.0931 625 7.5564 7.7330 12.6088 12.6600 14.8330

450 1.6861 1.7210 3.4460 3.3660 4.3019 630 7.7360 7.9140 12.8619 12.9200 15.1094

455 1.8533 1.8410 3.6917 3.5810 4.5959 635 7.9199 8.1060 13.1098 13.1800 15.3777

460 1.9460 1.9650 3.9089 3.8030 4.8581 640 8.1117 8.2850 13.3785 13.4400 15.6544

465 2.0722 2.1060 4.1076 4.0300 5.1214 645 8.2887 8.4740 13.6214 13.6900 15.9221

470 2.2075 2.2370 4.3539 4.2620 5.3904 650 8.4585 8.7050 13.8613 13.9500 16.1925

475 2.3505 2.3760 4.5844 4.5000 5.6637 655 8.6379 8.8760 14.0825 14.1900 16.4456

480 2.4883 2.5010 4.8298 4.7430 5.9617 660 8.8040 9.0480 14.3006 14.4400 16.6880

485 2.6360 2.6770 5.0886 4.9900 6.2604 665 8.9610 9.2340 14.5187 14.6800 16.9306

490 2.7870 2.8280 5.3277 5.2410 6.5413 670 9.1366 9.4200 14.7456 14.9100 17.1713

495 2.9357 2.9810 5.5847 5.4970 6.8372 675 9.2997 9.5860 14.9636 15.1400 17.4124

500 3.0959 3.1460 5.8672 5.7560 7.1589 680 9.4618 9.7580 15.1685 15.3700 17.6374

505 3.2601 3.3030 6.0914 6.0190 7.4612 685 9.6298 9.9250 15.4019 15.5900 17.8787

510 3.4354 3.4680 6.3545 6.2860 7.7598 690 9.7900 10.1000 15.6075 15.8100 18.0966

515 3.5934 3.6420 6.6241 6.5550 8.0750 695 9.9490 10.2700 15.7891 16.0300 18.3033

520 3.7695 3.8110 6.9314 6.8270 8.3861 700 10.1182 10.4200 16.0228 16.2400 18.5524

525 3.9280 3.9930 7.1786 7.1010 8.6980 705 10.2646 10.5800 16.2046 16.4500 18.7350

530 4.1079 4.1630 7.4514 7.3770 9.0129 710 10.4137 10.7600 16.3776 16.6500 18.9132

535 4.2901 4.3450 7.7465 7.6550 9.3548 715 10.5613 10.9200 16.5575 16.8500 19.1049

540 4.4578 4.5200 7.9928 7.9350 9.6563 720 10.6979 11.0700 16.7433 17.0400 19.2993

545 4.6441 4.7060 8.2813 8.2160 9.9678 725 10.8541 11.2300 16.9091 17.2300 19.4855

550 4.7933 4.8890 8.5647 8.4970 10.2923 730 10.9826 11.3900 17.0696 17.4100 19.6554

555 4.9720 5.0760 8.8548 8.7800 10.6187 735 11.1308 11.5300 17.2476 17.5900 19.8354

560 5.1582 5.2580 9.1493 9.0630 10.9349 740 11.2688 11.6700 17.4059 17.7600 20.0053

565 5.3351 5.4480 9.4066 9.3450 11.2317 745 11.3834 11.8000 17.5388 17.9300 20.1491

570 5.5130 5.6390 9.6837 9.6280 11.5533 750 11.5153 11.9700 17.6778 18.1000 20.3092

575 5.7179 5.8240 9.9813 9.9110 11.8748

RR: Round-robin transfer on 31 July 1992.

CHORS: In-house transfer from lamp 90572.

HEI: Original irradiance scale calibration by HEI.

16
James L. Mueller

Table 6. Irradiance scale transfer from GSFC lampF269 on 31 July 1992 to lamps: F219 and F303 (UCSB), and to

lamps F12G and F12H (UM). (Irradiances under each lamp column are in units of μW cm−2 nm−1.)

λ F219 F303 F12G F12H

[nm] RR OI RR OI RR UM RR UM

400 2.2776 2.2500 2.2907 2.3100 2.0013 2.0670 2.0420 2.1310

405 2.4747 2.4478 2.1750 2.2594

410 2.7721 2.7668 2.4521 2.4240 2.5209 2.5060

415 2.9085 2.9300 2.6462 2.6945

420 3.2012 3.2230 2.9036 2.8190 2.9544 2.9050

425 3.3909 3.3848 3.0688 3.1418

430 3.6804 3.6490 3.2872 3.2390 3.3921 3.3420

435 3.8818 3.8818 3.4999 3.5808

440 4.1582 4.1660 3.7400 3.6950 3.8182 3.8090

445 4.4272 4.4413 3.9947 4.0791

450 4.6866 4.5200 4.6641 4.6200 4.2218 4.1580 4.3115 4.2990

455 5.0031 4.9612 4.4881 4.6019

460 5.2753 5.2501 4.7517 4.6590 4.8609 4.8040

465 5.5354 5.5196 5.0088 5.1136

470 5.8353 5.8011 5.2877 5.2060 5.3758 5.3720

475 6.1370 6.1095 5.5516 5.6660

480 6.4455 6.4088 5.8342 5.7610 5.9401 5.9220

485 6.7546 6.7217 6.1327 6.2419

490 7.0788 7.0299 6.4202 6.3010 6.5452 6.4940

495 7.3392 7.3210 6.7057 6.8353

500 7.7056 7.4400 7.6544 7.5800 7.0222 6.8750 7.1589 7.0770

505 8.0252 7.9930 7.3162 7.4451

510 8.3708 8.3097 7.6223 7.4700 7.7445 7.6930

515 8.7051 8.6465 7.9137 8.0603

520 9.0422 8.9709 8.2435 8.0840 8.3719 8.3050

525 9.3392 9.2834 8.5307 8.6701

530 9.6978 9.6156 8.8485 8.6780 8.9992 8.9230

535 10.0517 9.9713 9.1806 9.3280

540 10.3581 10.2802 9.4744 9.3040 9.6173 9.5520

545 10.6726 10.5970 9.7916 9.9174

550 11.0344 10.7000 10.9492 10.8000 10.0976 9.9070 10.2436 10.1800

555 11.3645 11.0000 11.2816 11.2000 10.4174 10.5832

560 11.7168 11.6234 10.7365 10.5500 10.8999 10.8300

565 12.0390 11.9337 11.0328 11.2083

570 12.3683 12.2724 11.3496 11.1500 11.5054 11.4400

575 12.6898 12.6020 11.6616 11.8371

580 13.0315 12.9118 11.9677 11.7600 12.1538 12.0800

585 13.3324 13.2331 12.2545 12.4247

590 13.6888 13.5674 12.5657 12.3700 12.7327 12.6900

595 14.0066 13.8781 12.8822 13.0429

RR: Round-robin transfer on 31 July 1992.

UM: In-house calibration at University of Miami.

OI: Original irradiance scale calibration by Optronics, Inc.

17
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Table 6. (cont.) Irradiance scale transfer from GSFC lampF269 on 31 July 1992 to lamps: F219 and F303 (UCSB),

and to lamps F12G and F12H (UM). (Irradiances under each lamp column are in units of μW cm−2 nm−1.)

λ F219 F303 F12G F12H

[nm] RR OI RR OI RR UM RR UM

600 14.2617 13.8000 14.1565 14.1000 13.1666 12.8000 13.3331 13.3300

605 14.6022 14.4714 13.4330 13.6374

610 14.8848 14.7438 13.7097 13.4600 13.9055 13.8600

615 15.2120 15.0518 14.0137 14.1969

620 15.5034 15.3464 14.2918 14.0000 14.4788 14.3100

625 15.7831 15.6284 14.5531 14.7446

630 16.0737 15.9070 14.8122 14.4800 15.0225 14.8000

635 16.3517 16.1811 15.0791 15.2853

640 16.6465 16.4714 15.3845 15.0100 15.5669 15.3200

645 16.9277 16.7601 15.6479 15.8307

650 17.1927 16.7000 17.0116 16.9000 15.8932 15.4900 16.0822 15.8000

655 17.4674 17.2679 16.1422 16.3338

660 17.7033 17.5129 16.3707 15.9900 16.5690 16.3100

665 17.9376 17.7503 16.6028 16.7980

670 18.1891 17.9901 16.8499 16.4700 17.0412 16.8000

675 18.4416 18.2312 17.0819 17.2772

680 18.6723 18.4654 17.2900 16.9700 17.4970 17.3100

685 18.9162 18.7044 17.5353 17.7399

690 19.1458 18.9360 17.7493 17.4200 17.9592 17.7500

695 19.3449 19.1294 17.9513 18.1596

700 19.5914 19.1000 19.3836 19.3000 18.1726 17.8900 18.4019 18.2200

705 19.7857 19.5641 18.3633 18.5706

710 19.9846 19.7560 18.5418 18.7704

715 20.1853 19.9563 18.7399 18.9689

720 20.3763 20.1394 18.9332 19.1414

725 20.5608 20.3226 19.1030 19.3123

730 20.7159 20.4617 19.2632 19.4811

735 20.9161 20.6588 19.4458 19.6663

740 21.0778 20.8246 19.6031 19.8191

745 21.2186 20.9643 19.7527 19.9696

750 21.3813 20.9000 21.1264 21.0000 19.9044 20.1218

RR: Round-robin transfer on 31 July 1992.

UM: In-house calibration at University of Miami.

OI: Original irradiance scale calibration by Optronics, Inc.

18
James L. Mueller

Table 7. Irradiance scale transfer from GSFC lampF269 on 31 July 1992 to lamps: F12L (SIO/MPL), F265 (NRaD),

and S271 and S272 (Satlantic). (Irradiances under each lampcolumn are in units of μW cm−2 nm−1.)

λ F12L F265 S721 S724 λ F12L F265 S721 S724

[nm] RR RR RR RR [nm] RR RR RR RR

400 2.1438 2.3474 2.5220 2.4478 580 12.4464 13.2176 14.6272 14.1485

405 2.3744 2.6142 2.8295 2.5995 585 12.7509 13.5452 14.9493 14.4954

410 2.5994 2.8749 3.0762 2.9406 590 13.0666 13.8861 15.3581 14.9029

415 2.7799 3.0741 3.3304 3.0871 595 13.3641 14.1994 15.7093 15.2113

420 3.0488 3.4045 3.6077 3.3900 600 13.6572 14.5157 16.1276 15.5669

425 3.2633 3.5550 3.8588 3.5732 605 13.9645 14.8311 16.4581 15.9103

430 3.4865 3.8167 4.1156 3.8849 610 14.2424 15.1277 16.7415 16.2088

435 3.6662 4.0256 4.3266 4.0975 615 14.5327 15.4486 17.0821 16.5554

440 3.9432 4.3184 4.6545 4.4044 620 14.8303 15.7427 17.4105 16.8870

445 4.2022 4.5819 4.9652 4.7120 625 15.1129 16.0335 17.7422 17.2119

450 4.4365 4.8276 5.2379 4.9783 630 15.3705 16.3130 18.0603 17.5165

455 4.7306 5.1259 5.5690 5.2995 635 15.6550 16.6005 18.3850 17.8447

460 4.9953 5.4237 5.8829 5.5973 640 15.9389 16.8726 18.7036 18.1857

465 5.2498 5.7083 6.1981 5.9021 645 16.2116 17.1487 19.0228 18.4895

470 5.5322 6.0065 6.5125 6.2045 650 16.4603 17.4211 19.3034 18.7915

475 5.8214 6.3130 6.8549 6.5303 655 16.7250 17.7069 19.6389 19.0801

480 6.1129 6.6162 7.1950 6.8840 660 16.9577 17.9650 19.9082 19.3530

485 6.4210 6.9338 7.5722 7.2221 665 17.1960 18.2030 20.1778 19.6236

490 6.7192 7.2547 7.9153 7.5439 670 17.4315 18.4492 20.4923 19.9567

495 6.9741 7.5401 8.2156 7.8504 675 17.6904 18.7045 20.7477 20.1918

500 7.3127 7.9277 8.6282 8.2353 680 17.9183 18.9311 20.9934 20.4538

505 7.6385 8.2347 9.0244 8.6215 685 18.1637 19.1720 21.2981 20.7209

510 7.9736 8.5541 9.3789 8.9818 690 18.3716 19.3918 21.5481 20.9837

515 8.2655 8.8956 9.7456 9.3499 695 18.5834 19.6106 21.7872 21.2197

520 8.6001 9.2419 10.1261 9.7268 700 18.8175 19.8637 22.0636 21.5047

525 8.8931 9.5343 10.4822 10.0640 705 19.0066 20.0574 22.2947 21.7228

530 9.2321 9.9032 10.8620 10.4374 710 19.2061 20.2417 22.5059 21.9488

535 9.5826 10.2662 11.2579 10.8290 715 19.3839 20.4358 22.7326 22.1602

540 9.8773 10.5791 11.6188 11.1769 720 19.5722 20.6276 22.9467 22.3795

545 10.1691 10.9243 11.9689 11.5535 725 19.7597 20.8134 23.1660 22.6031

550 10.5112 11.2655 12.3848 11.9225 730 19.9315 20.9847 23.3236 22.7933

555 10.8436 11.6012 12.7613 12.3115 735 20.1074 21.1735 23.5555 23.0114

560 11.1799 11.9502 13.1405 12.6737 740 20.2809 21.3534 23.7442 23.2005

565 11.4891 12.2613 13.5015 13.0335 745 20.4183 21.4953 23.9186 23.3502

570 11.7930 12.5840 13.8784 13.4110 750 20.5791 21.6512 24.0952 23.5404

575 12.1381 12.9155 14.2572 13.7933

19
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Fig. 7. Spectral irradiance of lampF321 (toppanel, solid line) using scale transfer from the NIST

October 1992 F269 scale, during the SIRREX-1 lamptransfer on 31 July 1992, compared to the February

1991 calibration of F321 by NIST (O) and blackbody interpolation of the original NIST scale by BSI

(×). The bottom panel illustrates the differences between the NIST (O) and BSI(×) scales relative to

the SIRREX-1 31 July 1992 scale transfer from F269.

20
James L. Mueller

Fig. 8. Spectral irradiance of lamp 91453 (top panel, solid line) using scale transfer from the NIST

October 1992 F269 scale, during the SIRREX-1 lamptransfer on 31 July 1992, compared to the in-house

calibration of 91453 by BSI (×). The bottom panel illustrates the differences between the BSI (×) scale

relative to the SIRREX-1 31 July 1992 scale transfer from F269.

21
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Fig. 9. Spectral irradiance of lamp 90572 (top panel, solid line) using scale transfer from the NIST

October 1992 F269 scale, during the SIRREX-1 lamptransfer on 31 July 1992, compared to the original

calibration by Hoffman Engineering, Inc., HEI (#). The bottom panel illustrates the differences between

the HEI (#) scale relative to the SIRREX-1 31 July 1992 scale transfer from F269.

22
James L. Mueller

Fig. 10. Spectral irradiance of lamp 91348 (top panel, solid line) using scale transfer from the NIST

October 1992 F269 scale, during the SIRREX-1 lamptransfer on 31 July 1992, compared to the in-house

CHORS (×) scale transfer from 90573. The bottom panel illustrates the differences between the CHORS

(×) scale relative to the SIRREX-1 31 July 1992 scale transfer from F269.

23
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Fig. 11. Spectral irradiance of lampF219 (toppanel, solid line) using scale transfer from the NIST

October 1992 F269 scale, during the SIRREX-1 lamptransfer on 31 July 1992, compared to the original

calibration of F219 by Optronics (+). The bottom panel illustrates the differences between the Optronics

(+) scale relative to the SIRREX-1 31 July 1992 scale transfer from F269.

24
James L. Mueller

Fig. 12. Spectral irradiance of lampF303 (toppanel, solid line) using scale transfer from the NIST

October 1992 F269 scale, during the SIRREX-1 lamptransfer on 31 July 1992, compared to the original

calibration of F303 by Optronics (+). The bottom panel illustrates the differences between the Optronics

(+) scale relative to the SIRREX-1 31 July 1992 scale transfer from F269.

25
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Fig. 13. Spectral irradiance of lamp F12G (top panel, solid line) using scale transfer from the NIST

October 1992 F269 scale, during the SIRREX-1 lamptransfer on 31 July 1992, compared to the in-house

calibration of F12G by UM (×). The bottom panel illustrates the differences between the UM (×) scale

relative to the SIRREX-1 31 July 1992 scale transfer from F269.

26
James L. Mueller

Fig. 14. Spectral irradiance of lamp F12H (top panel, solid line) using scale transfer from the NIST

October 1992 F269 scale, during the SIRREX-1 lamptransfer on 31 July 1992, compared to the in-house

calibration of F12H by UM (×). The bottom panel illustrates the differences between the UM (×) scale

relative to the SIRREX-1 31 July 1992 scale transfer from F269.

27
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

F303, F12G, and F12H), and 7 (F12L, F265, S721, and

S724). The results are illustrated in Figs. 7–14 for FEL

lamps F321, 91453, 90572, 91348, F219, F303, F12G, and

F12H, respectively. The currents (specified and measured)

applied to these lamps during this transfer process are

listed in Table 8.

Table 8. Lampoperating currents (in amps).

LampCurrent Date of Current

Number Measured Measurement Specified

F269 8.0009 30 July 1992 8.000

8.0000 31 July 1992

F268 8.0009 30 July 1992 8.000

F307 8.0009 30 July 1992 8.000

F308 8.0009 30 July 1992 8.000

F321 7.9005 31 July 1992 7.900

91453 7.9006 31 July 1992 7.900

F310 7.9007 31 July 1992 7.900

90572 7.1087 31 July 1992 7.108

91348 7.6565 31 July 1992 7.656

91534 8.0008 31 July 1992 8.000

F219 8.0007 31 July 1992 8.000

F303 8.0007 31 July 1992 8.000

F12G 8.0006 31 July 1992 8.000

F12H 7.9061 31 July 1992 7.906

F12L 7.8486 31 July 1992 7.849

F265 8.0000 31 July 1992 8.000

S271 8.0001 31 July 1992 8.000

S724 8.0002 31 July 1992 8.000

The irradiance scale transfers on 30 July 1992 from

lampF269 to lamps F269†, F268, F307, and F308 appear

to have been accurate to within less than 1%, except near

400 nm. The outlier at 560 nm in all spectra (Figs. 2–5)

obviously results from a single noise spike that occurred

during the initial calibration of the 746/ISIC at the outset

of the procedure; it should be edited out and filled in by

interpolation when applying these tables. The conclusion

about the accuracy of these transfers is based on the excellent agreement between the transferred F269 scales and

those determined in independent calibrations of three of

the four lamps by NIST in October 1992 (Figs. 2, 3, and

5). These results are clearly internally consistent and provide an acceptable basis for a common scale of spectral

irradiance within this subset of working standard lamps

(F269, F268, F307, and F308). This is mainly of benefit

for lampF307, since the other three were all recalibrated

by NIST in October 1992, and are in excellent agreement

with this transfer from F269.

The Optronics 746/ISIC transfer appears to have been

much less stable and precise during the sessions of 31 July

1992. The instrument’s spectral irradiance responsivity

appears to have drifted by as much as 5% between 0800

† An internal test of transfer precision.

and 1430 PDT on that date (Fig. 6). Moreover, the comparison between the 31 July 1992 transfer of the F269

spectral irradiance scale to lamp F321 differs from its original NIST (February 1991) calibration by as much as 3%

at 400 nm, although agreement is better at longer wavelengths (Fig. 7). It is possible that lamp F321 has decreased in brightness temperature through aging since its

original calibration, but this particular session of scale

transfers from lampF269 was not sufficiently precise to

support such a conclusion with any confidence. Many of

the other lamps to which the F269 scale was transferred

in the round-robin lamptransfer session of 31 July 1992

show similar, or larger, levels of disagreement (2–3%; Figs.

8–14), again with the largest discrepancies at wavelengths

near 400 nm (as large as 5–6%).

Although it is possible that the erratic precision of irradiance scale transfers on 31 July 1992 may be at least

partly due to responsivity drift in the Optronics 746 radiometer, subsequent stability tests of the instrument make

it seem unlikely to have been the only error contributor

(Section 3.5 below). It is also possible the lamp holder

used during these tests may have allowed a partial short

to the optical table, which would have caused the actual

lampcurrents to differ from those specified in Table 8.

A kinematic lamp holder was borrowed from the Scripps

Institution of Oceanography/Marine Physical Laboratory

(SIO/MPL) for use during these tests, and it was necessary

to mount it on posts compatible with the optical bench on

which the 746/ISIC was mounted.

After SIRREX-1, the post SIO/MPL provided with the

lampholder was discovered to have been ground down to

preclude any possibility of electrical contact with the lamp

holder’s spring-loaded contacts, as there was no insulating

material separating these components. When the holder

was mounted on an unmodified post, the clearance between the post and the spring-loaded contacts was small

enough (as was later discovered) that it was possible for

them to come into contact when a lampwas pushed down

into position. If this occurred during some or all of the

lampinsertions during the 31 July 1992 transfers, current

leaks to ground could easily account for many or all of the

observed inconsistencies.

Whatever the actual source of errors may have been,

the round-robin lampirradiance scale transfers of 31 July

1992 do not achieve the 1% precision required for SeaWiFS

validation intercalibrations. The resulting spectral irradiance scales in Tables 4–7 should be applied with skepticism, if at all.

3.2 Integrating Spheres

Integrating spheres are used as sources of spectral radiance for calibrating instruments at several of the participating laboratories. The spectral radiance levels of these

spheres were all measured using the NIST PR714 spectral

radiometer (Section 2.2). Based on post-calibration and

28
James L. Mueller

29
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

30
James L. Mueller

analyses of the PR714’s radiance responsivity at NIST, it

was decided the best approach would be to base the interpretation of the SIRREX-1 radiance source intercomparisons on the radiance scale of the GSFC 42-inch sphere.

The PR714 measured the spectral radiance of the GSFC

sphere (16 lamps at 6.5 A) in three trials on 28 July 1992

and one on 30 July 1992. The GSFC sphere radiance scale

and the PR714 readings from the four trials are listed in

Table 9 at 10 nm intervals. The conversion factors, F(λ),

required to adjust the PR714 readings to match the GSFC

scale are also listed in Table 9, together with the mean and

standard deviations from the four trials, and the departure

δ of each individual conversion factor from the mean. The

mean and individual scale factors F(λ), to convert PR714

readings to the GSFC sphere radiance scale, are illustrated

in Fig. 15.

Table 10 lists the mean scale factors F(λ), including

the units conversion factor of 100, at the 4 nm wavelength

intervals measured by the PR714. This table may be used

directly to convert PR714 data files to the GSFC sphere

radiance scale.

Radiance spectra were also measured with the PR714

(GSFC scale) for the spheres belonging to CHORS (40-inch

sphere illuminated through four 12-inch auxiliary spheres),

NOAA (Optronics 420M source), BSI (20-inch sphere with

one internal lamp), and UCSB (20-inch sphere illuminated

through an entrance port by FEL lamp F303 at a distance

of 50 cm). The spectral radiances measured during all trials for each of these spheres are listed, at 4 nm intervals,

in Tables 11–14, respectively. The maximum spectral radiance output of each sphere is illustrated in Fig. 16, and

representative ranges of radiance for spheres with variable

illumination schemes (not including the GSFC sphere) are

illustrated in Fig. 17.

NIST personnel (C. Johnson and C. Cromer) also measured the spectral radiance emission from several of the

spheres using well-calibrated, broad-band, filtered photodetectors. The results of these measurements are given in Appendix A. In summary, the measured photodetector currents were consistent with values predicted by integrating

the radiance spectra measured with the PR714, weighted

by the spectral response functions of the two photodetectors. For the GSFC sphere, agreement was within less than

1%, and less than 3% for the BSI 20-inch sphere. The

PR714 and photodetector measurements of the CHORS

40-inch sphere were made with different sphere illumination setups; the predicted and measured photodetector

currents differed by 30%.

The flux emitted by NOAA’s Optronics 420M was too

low to be accurately measured with the photodetectors.

With careful and systematic setups, these broad-band irradiance measurements can provide a valuable test of radiance scale transfer precision, e.g., with the PR714, and

they should be included in future SIRREXs.

Table 10. PR714 conversion to GSFC sphere radiance scales at PR714 wavelengths. (Includes a

factor of 100 for units conversion.)

λ [nm] F(λ) λ [nm] F(λ) λ [nm] F(λ)

380 106.241 556 102.668 732 106.852

384 105.791 560 102.617 736 106.186

388 105.340 564 103.132 740 105.521

392 105.057 568 103.647 744 105.444

396 104.942 572 103.921 748 105.368

400 104.826 576 103.956 752 105.411

404 104.799 580 103.991 756 105.576

408 104.771 584 103.390 760 105.740

412 104.494 588 102.789 764 106.078

416 103.968 592 102.588 768 106.415

420 103.441 596 102.785 772 106.768

424 103.551 600 102.983 776 107.136

428 103.662 604 103.813 780 107.504

432 103.233 608 104.642 784 107.824

436 102.266 612 105.235 788 108.144

440 101.298 616 105.591 792 108.403

444 102.186 620 105.946 796 108.600

448 103.074 624 105.638 800 108.798

452 103.414 628 105.330 804 108.509

456 103.206 632 105.049 808 108.220

460 102.998 636 104.797 812 108.018

464 102.609 640 104.544 816 107.903

468 102.220 644 104.761 820 107.788

472 102.580 648 104.977 824 107.822

476 103.688 652 105.122 828 107.857

480 104.795 656 105.195 832 108.139

484 103.931 660 105.269 836 108.668

488 103.066 664 105.146 840 109.198

492 102.791 668 105.023 844 109.655

496 103.105 672 104.831 848 110.112

500 103.419 676 104.569 852 110.583

504 103.523 680 104.308 856 111.069

508 103.627 684 104.565 860 111.554

512 103.532 688 104.823 864 111.372

516 103.237 692 105.339 868 111.190

520 102.943 696 106.112 872 110.972

524 103.340 700 106.885 876 110.717

528 103.738 704 107.438 880 110.462

532 104.138 708 107.990 884 110.249

536 104.541 712 108.307 888 110.035

540 104.943 716 108.389 892 109.807

544 104.063 720 108.470 896 109.562

548 103.184 724 107.956 900 109.318

552 102.719 728 107.442

3.3 Reflectance Plaque Intercomparisons

The reflectances of four Spectralon reflectance plaques,

which were all manufactured by Labsphere, Inc., were compared on 3 July 1992. Each plaque was mounted on a

photometric bar and illuminated at normal incidence by

31
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Fig. 15. Scale factors to adjust radiance measurements with the NIST PR714 spectroradiometer to the

spectral radiance scale of the GSFC 42-inch integrating sphere source (Table 9). The solid line illustrates

the average of four independent PR714 measurements of the spectral radiance output from the GSFC

sphere during SIRREX-1 and the points are the scale factors for each individual spectral measurement

on 28 July 1992 (+, O, and ×) and 30 July 1992 (O+).

32
James L. Mueller

Table 11. Radiance outputs of CHORS 40-inch integrating sphere, measured with the NIST PR714 radiometer, and

calibrated to the radiance scale of the GSFC sphere. (Radiances, Li(λ), are in units of μW cm−2 nm−1 sr−1.)

Run File Date Lamp Aperture Diameters [in.]

1 SCH3NF01.SCN 28 July 1992 1.250–1.250–1.250–1.250

2 SCH3NF02.SCN 28 July 1992 0.312–0.312–0.438–0.438

3 SCH3NF03.SCN 30 July 1992 1.250–1.250–1.250–1.250

4 S CHOR1.SCN 29 July 1992 1.250–1.250–1.250–1.250

5 S CHOR2.SCN 29 July 1992 0.875–0.875–1.080–1.080

6 S CHOR3.SCN 29 July 1992 0.628–0.628–0.766–0.766

7 S CHOR4.SCN 29 July 1992 0.438–0.438–0.531–0.531

8 S CHOR5.SCN 29 July 1992 0.312–0.312–0.438–0.438

9 S CHOR6.SCN 29 July 1992 0.000–0.312–0.000–0.438

10 S CHOR7.SCN 29 July 1992 0.312–0.000–0.438–0.000

λ [nm] L1(λ) L2(λ) L3(λ) L4(λ) L5(λ) L6(λ) L7(λ) L8(λ) L9(λ) L10(λ)

380 0.699 0.052 0.773 0.820 0.522 0.242 0.102 0.057 0.031 0.024

384 0.814 0.058 0.874 0.928 0.586 0.267 0.113 0.063 0.035 0.027

388 0.974 0.068 1.033 1.085 0.693 0.314 0.132 0.073 0.041 0.032

392 1.140 0.079 1.193 1.256 0.806 0.369 0.154 0.086 0.048 0.037

396 1.326 0.093 1.387 1.462 0.935 0.434 0.182 0.101 0.056 0.044

400 1.537 0.107 1.564 1.651 1.063 0.496 0.209 0.116 0.065 0.050

404 1.743 0.123 1.746 1.844 1.195 0.562 0.241 0.134 0.075 0.058

408 1.939 0.141 1.931 2.042 1.328 0.631 0.273 0.153 0.085 0.067

412 2.112 0.155 2.105 2.224 1.451 0.692 0.300 0.169 0.094 0.074

416 2.306 0.171 2.297 2.432 1.591 0.761 0.331 0.186 0.104 0.081

420 2.506 0.185 2.466 2.613 1.712 0.821 0.358 0.201 0.112 0.087

424 2.689 0.200 2.650 2.804 1.840 0.886 0.387 0.217 0.122 0.095

428 2.879 0.217 2.844 3.009 1.976 0.956 0.419 0.236 0.132 0.102

432 3.068 0.233 3.038 3.217 2.111 1.022 0.449 0.253 0.141 0.110

436 3.275 0.250 3.253 3.446 2.258 1.094 0.482 0.272 0.152 0.119

440 3.514 0.266 3.443 3.648 2.393 1.160 0.511 0.289 0.161 0.126

444 3.744 0.282 3.663 3.880 2.546 1.232 0.543 0.307 0.171 0.134

448 3.966 0.300 3.887 4.113 2.702 1.309 0.577 0.325 0.182 0.142

452 4.179 0.318 4.109 4.345 2.861 1.388 0.611 0.345 0.193 0.151

456 4.378 0.335 4.314 4.562 3.017 1.466 0.645 0.364 0.203 0.159

460 4.585 0.355 4.516 4.784 3.179 1.551 0.684 0.386 0.215 0.168

464 4.816 0.374 4.697 4.979 3.319 1.629 0.720 0.406 0.227 0.177

468 4.985 0.391 4.853 5.143 3.435 1.695 0.752 0.425 0.237 0.185

472 5.135 0.408 5.014 5.303 3.536 1.753 0.782 0.442 0.246 0.193

476 5.338 0.428 5.247 5.542 3.684 1.828 0.817 0.463 0.258 0.203

480 5.620 0.451 5.555 5.869 3.885 1.922 0.861 0.489 0.271 0.215

484 5.872 0.471 5.847 6.178 4.075 2.005 0.898 0.510 0.283 0.224

488 6.210 0.489 6.124 6.474 4.263 2.089 0.933 0.530 0.294 0.233

492 6.526 0.508 6.404 6.772 4.457 2.177 0.969 0.550 0.305 0.242

496 6.809 0.525 6.664 7.038 4.634 2.259 1.002 0.568 0.316 0.250

500 7.050 0.542 6.894 7.276 4.793 2.336 1.034 0.586 0.325 0.257

504 7.270 0.560 7.135 7.530 4.964 2.419 1.069 0.605 0.336 0.266

508 7.548 0.583 7.421 7.829 5.165 2.521 1.114 0.629 0.349 0.277

512 7.824 0.608 7.704 8.125 5.366 2.625 1.161 0.655 0.364 0.289

516 8.100 0.632 7.967 8.403 5.556 2.722 1.205 0.681 0.377 0.300

520 8.388 0.658 8.235 8.685 5.747 2.825 1.254 0.709 0.393 0.313

33
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Table 11. (cont.) Radiance outputs of CHORS 40-inch integrating sphere, measured with the NIST PR714 radiometer, and calibrated to the radiance scale of the GSFC sphere. (Radiances, Li(λ), are in units of μW cm−2 nm−1 sr−1.)

λ [nm] L1(λ) L2(λ) L3(λ) L4(λ) L5(λ) L6(λ) L7(λ) L8(λ) L9(λ) L10(λ)

524 8.724 0.685 8.518 8.980 5.944 2.928 1.303 0.738 0.408 0.326

528 8.986 0.708 8.763 9.235 6.111 3.014 1.344 0.762 0.421 0.338

532 9.209 0.732 9.028 9.501 6.291 3.105 1.387 0.787 0.434 0.350

536 9.474 0.757 9.317 9.806 6.485 3.202 1.432 0.813 0.448 0.361

540 9.779 0.781 9.627 10.128 6.695 3.305 1.478 0.839 0.462 0.373

544 9.978 0.800 9.872 10.385 6.862 3.384 1.513 0.859 0.473 0.382

548 10.279 0.822 10.142 10.680 7.048 3.475 1.554 0.883 0.486 0.393

552 10.621 0.842 10.405 10.950 7.230 3.562 1.592 0.904 0.497 0.402

556 10.873 0.862 10.657 11.201 7.399 3.643 1.628 0.925 0.509 0.412

560 11.103 0.879 10.857 11.411 7.538 3.713 1.659 0.943 0.519 0.420

564 11.365 0.901 11.107 11.664 7.710 3.801 1.699 0.965 0.531 0.430

568 11.588 0.923 11.360 11.930 7.893 3.894 1.740 0.988 0.543 0.439

572 11.847 0.948 11.618 12.200 8.082 3.992 1.785 1.014 0.558 0.451

576 12.059 0.972 11.872 12.454 8.269 4.089 1.830 1.039 0.572 0.463

580 12.323 0.997 12.146 12.749 8.470 4.194 1.878 1.067 0.587 0.475

584 12.541 1.018 12.324 12.944 8.613 4.275 1.917 1.089 0.599 0.485

588 12.766 1.036 12.489 13.116 8.742 4.343 1.950 1.108 0.609 0.494

592 12.947 1.055 12.649 13.275 8.865 4.411 1.983 1.127 0.620 0.502

596 13.115 1.072 12.776 13.413 8.968 4.474 2.014 1.146 0.630 0.511

600 13.213 1.085 12.873 13.511 9.047 4.520 2.037 1.160 0.637 0.517

604 13.381 1.104 13.029 13.672 9.174 4.590 2.070 1.178 0.648 0.525

608 13.520 1.122 13.185 13.834 9.295 4.657 2.102 1.198 0.658 0.534

612 13.617 1.135 13.291 13.933 9.385 4.709 2.127 1.212 0.666 0.540

616 13.716 1.151 13.421 14.065 9.492 4.768 2.154 1.228 0.675 0.547

620 13.826 1.168 13.550 14.207 9.609 4.836 2.186 1.246 0.685 0.555

624 13.881 1.177 13.585 14.240 9.662 4.871 2.201 1.255 0.690 0.559

628 13.935 1.187 13.609 14.272 9.715 4.914 2.220 1.266 0.696 0.564

632 14.003 1.200 13.656 14.318 9.776 4.958 2.243 1.278 0.702 0.570

636 14.011 1.210 13.645 14.305 9.813 4.995 2.262 1.290 0.707 0.575

640 13.988 1.220 13.580 14.228 9.819 5.024 2.280 1.299 0.712 0.581

644 13.954 1.234 13.525 14.164 9.826 5.061 2.303 1.314 0.719 0.588

648 13.899 1.246 13.437 14.067 9.812 5.085 2.321 1.326 0.725 0.595

652 13.760 1.258 13.329 13.950 9.786 5.108 2.338 1.337 0.730 0.601

656 13.633 1.271 13.170 13.781 9.728 5.130 2.358 1.351 0.736 0.608

664 13.269 1.292 12.838 13.448 9.598 5.144 2.389 1.373 0.746 0.620

668 13.065 1.305 12.697 13.317 9.543 5.160 2.409 1.386 0.752 0.627

672 12.915 1.317 12.475 13.062 9.429 5.150 2.424 1.398 0.757 0.634

676 12.726 1.319 12.203 12.789 9.279 5.113 2.422 1.401 0.757 0.637

680 12.402 1.318 11.912 12.475 9.105 5.062 2.415 1.400 0.755 0.638

684 12.140 1.320 11.607 12.161 8.925 5.013 2.409 1.401 0.754 0.640

688 11.803 1.311 11.164 11.698 8.650 4.912 2.384 1.391 0.747 0.638

692 11.419 1.302 10.755 11.271 8.398 4.817 2.356 1.381 0.739 0.635

696 10.972 1.295 10.324 10.823 8.145 4.724 2.333 1.372 0.732 0.633

700 10.447 1.278 9.777 10.263 7.813 4.592 2.292 1.355 0.721 0.628

704 9.872 1.251 9.132 9.590 7.401 4.420 2.233 1.327 0.703 0.617

708 9.296 1.229 8.581 9.016 7.044 4.273 2.181 1.303 0.688 0.608

712 8.647 1.200 8.013 8.424 6.657 4.105 2.120 1.273 0.669 0.596

34
James L. Mueller

Table 11. (cont.) Radiance outputs of CHORS 40-inch integrating sphere, measured with the NIST PR714 radiometer, and calibrated to the radiance scale of the GSFC sphere. (Radiances, Li(λ), are in units of μW cm−2 nm−1 sr−1.)

λ [nm] L1(λ) L2(λ) L3(λ) L4(λ) L5(λ) L6(λ) L7(λ) L8(λ) L9(λ) L10(λ)

716 8.001 1.158 7.360 7.747 6.183 3.886 2.033 1.228 0.643 0.578

720 7.400 1.118 6.808 7.166 5.761 3.685 1.952 1.187 0.618 0.562

724 6.855 1.073 6.301 6.638 5.356 3.476 1.865 1.139 0.591 0.541

728 6.286 1.022 5.839 6.155 4.967 3.259 1.768 1.085 0.562 0.517

732 5.792 0.958 5.364 5.656 4.545 3.006 1.651 1.018 0.526 0.486

736 5.384 0.901 5.017 5.287 4.222 2.795 1.548 0.957 0.495 0.457

740 5.052 0.848 4.743 4.995 3.959 2.608 1.453 0.899 0.467 0.428

744 4.764 0.801 4.557 4.797 3.763 2.462 1.373 0.850 0.443 0.402

748 4.615 0.755 4.400 4.630 3.592 2.327 1.293 0.799 0.421 0.375

752 4.492 0.713 4.272 4.491 3.456 2.214 1.224 0.754 0.402 0.350

756 4.363 0.674 4.153 4.363 3.337 2.113 1.159 0.712 0.383 0.326

760 4.200 0.644 4.088 4.293 3.257 2.042 1.111 0.679 0.370 0.307

764 4.170 0.628 4.099 4.300 3.240 2.011 1.087 0.661 0.364 0.295

768 4.188 0.617 4.118 4.314 3.235 1.994 1.069 0.648 0.359 0.287

772 4.199 0.606 4.129 4.319 3.224 1.975 1.054 0.637 0.355 0.281

776 4.207 0.597 4.140 4.332 3.213 1.956 1.040 0.627 0.351 0.275

780 4.215 0.589 4.160 4.347 3.206 1.942 1.027 0.618 0.347 0.270

784 4.235 0.584 4.207 4.387 3.217 1.933 1.019 0.612 0.344 0.266

788 4.285 0.581 4.253 4.439 3.236 1.934 1.015 0.609 0.343 0.265

792 4.331 0.578 4.307 4.491 3.259 1.933 1.011 0.605 0.341 0.262

796 4.370 0.574 4.362 4.550 3.282 1.932 1.005 0.600 0.340 0.259

800 4.445 0.573 4.437 4.620 3.322 1.941 1.005 0.599 0.340 0.258

804 4.522 0.572 4.503 4.688 3.363 1.950 1.005 0.598 0.340 0.257

808 4.571 0.569 4.558 4.742 3.389 1.954 1.001 0.594 0.339 0.254

812 4.630 0.568 4.623 4.804 3.425 1.965 1.001 0.592 0.339 0.252

816 4.710 0.569 4.683 4.862 3.467 1.979 1.004 0.593 0.340 0.252

820 4.779 0.570 4.749 4.929 3.515 1.997 1.008 0.594 0.342 0.252

824 4.851 0.574 4.824 5.009 3.572 2.024 1.018 0.598 0.345 0.252

828 4.928 0.579 4.891 5.078 3.628 2.053 1.028 0.604 0.349 0.254

832 4.972 0.585 4.941 5.129 3.671 2.077 1.038 0.609 0.351 0.256

836 5.017 0.590 4.985 5.175 3.713 2.101 1.049 0.614 0.354 0.259

840 5.049 0.595 5.018 5.208 3.743 2.121 1.058 0.619 0.357 0.261

844 5.064 0.600 5.029 5.223 3.761 2.138 1.067 0.625 0.360 0.264

848 5.049 0.605 5.028 5.222 3.772 2.152 1.074 0.629 0.362 0.266

852 5.067 0.610 5.039 5.232 3.792 2.166 1.083 0.636 0.364 0.270

856 5.074 0.616 5.041 5.234 3.797 2.178 1.092 0.641 0.367 0.273

860 5.062 0.620 5.028 5.217 3.800 2.188 1.099 0.646 0.369 0.276

864 5.037 0.623 5.006 5.197 3.794 2.191 1.102 0.649 0.370 0.278

868 5.015 0.625 4.971 5.161 3.778 2.188 1.104 0.651 0.370 0.279

872 4.954 0.623 4.919 5.110 3.742 2.174 1.099 0.649 0.368 0.279

876 4.884 0.620 4.854 5.048 3.702 2.158 1.094 0.647 0.366 0.279

880 4.845 0.619 4.811 4.995 3.666 2.143 1.090 0.645 0.364 0.279

884 4.805 0.615 4.751 4.930 3.627 2.123 1.082 0.641 0.362 0.277

888 4.719 0.606 4.652 4.836 3.560 2.090 1.066 0.632 0.356 0.274

892 4.599 0.590 4.504 4.685 3.445 2.028 1.037 0.615 0.347 0.267

896 4.422 0.569 4.322 4.491 3.305 1.948 0.999 0.593 0.334 0.257

900 4.203 0.546 4.139 4.299 3.169 1.866 0.959 0.570 0.321 0.247

35
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Fig. 16. Maximum levels of spectral radiance output compared for integrating sphere sources tested

during SIRREX-1.

36
James L. Mueller

Fig. 17. Varying levels of spectral radiance output compared for integrating sphere sources tested

during SIRREX-1.

37
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Table 12. Radiance output of the NOAA Optronics 420M (S/N 92106057), measured with the NIST PR714 radiometer, and calibrated to the GSFC 42-inch sphere radiance scale. (Radiances, Li(λ), are in units of μW cm−2 nm−1 sr−1.)

Run File Date Optronics 420M Settings

1 SOP1NF02.SCN 28 July 1992 Slide=3, Wheel=5, and Distance=100

2 SOP1NF03.SCN 28 July 1992 Slide=3, Wheel=6, and Distance=100

λ [nm] L1(λ) L2(λ) λ [nm] L1(λ) L2(λ) λ [nm] L1(λ) L2(λ)

380 0.01661 0.05015 556 0.15185 0.45502 732 0.30966 0.92480

384 0.01776 0.05355 560 0.15516 0.46455 736 0.31272 0.93337

388 0.01911 0.05755 564 0.15903 0.47606 740 0.31456 0.93903

392 0.02082 0.06257 568 0.16283 0.48787 744 0.31686 0.94604

396 0.02274 0.06816 572 0.16752 0.50173 748 0.31874 0.95063

400 0.02431 0.07325 576 0.17174 0.51458 752 0.32013 0.95481

404 0.02625 0.07857 580 0.17626 0.52848 756 0.32222 0.96138

408 0.02823 0.08452 584 0.18052 0.54063 760 0.32589 0.97143

412 0.03020 0.09065 588 0.18420 0.55187 764 0.32948 0.98175

416 0.03274 0.09797 592 0.18794 0.56290 768 0.33201 0.98945

420 0.03476 0.10448 596 0.19190 0.57457 772 0.33472 0.99668

424 0.03719 0.11152 600 0.19515 0.58433 776 0.33684 1.00236

428 0.03985 0.11921 604 0.19911 0.59682 780 0.33842 1.00677

432 0.04222 0.12667 608 0.20384 0.61048 784 0.34083 1.01462

436 0.04501 0.13499 612 0.20794 0.62341 788 0.34401 1.02272

440 0.04759 0.14273 616 0.21213 0.63619 792 0.34570 1.02820

444 0.05044 0.15124 620 0.21719 0.65104 796 0.34709 1.03279

448 0.05355 0.16028 624 0.22047 0.66119 800 0.35011 1.04109

452 0.05675 0.16991 628 0.22425 0.67243 804 0.35233 1.04700

456 0.05966 0.17886 632 0.22785 0.68324 808 0.35236 1.04800

460 0.06310 0.18931 636 0.23076 0.69187 812 0.35343 1.05123

464 0.06633 0.19875 640 0.23345 0.70024 816 0.35489 1.05508

468 0.06910 0.20720 644 0.23749 0.71164 820 0.35548 1.05751

472 0.07193 0.21562 648 0.24071 0.72130 824 0.35657 1.06118

476 0.07554 0.22614 652 0.24346 0.72986 828 0.35873 1.06563

480 0.07969 0.23883 656 0.24721 0.74078 832 0.35956 1.06863

484 0.08344 0.24995 660 0.25075 0.75099 836 0.36034 1.07190

488 0.08711 0.26086 664 0.25361 0.75957 840 0.36188 1.07680

492 0.09076 0.27198 668 0.25720 0.77076 844 0.36362 1.08032

496 0.09429 0.28251 672 0.26155 0.78330 848 0.36469 1.08361

500 0.09756 0.29226 676 0.26404 0.79180 852 0.36647 1.08902

504 0.10090 0.30239 680 0.26651 0.79931 856 0.36786 1.09247

508 0.10487 0.31451 684 0.27009 0.80954 860 0.36835 1.09434

512 0.10912 0.32685 688 0.27285 0.81710 864 0.36864 1.09557

516 0.11273 0.33789 692 0.27493 0.82438 868 0.36982 1.09856

520 0.11663 0.34959 696 0.27886 0.83584 872 0.37042 1.10029

524 0.12080 0.36200 700 0.28271 0.84653 876 0.37090 1.10152

528 0.12428 0.37242 704 0.28525 0.85467 880 0.37148 1.10329

532 0.12830 0.38448 708 0.28909 0.86554 884 0.37165 1.10469

536 0.13266 0.39715 712 0.29265 0.87620 888 0.37181 1.10585

540 0.13695 0.41022 716 0.29579 0.88532 892 0.37236 1.10576

544 0.14049 0.42073 720 0.30046 0.89889 896 0.37273 1.10767

548 0.14446 0.43275 724 0.30346 0.90759 900 0.37223 1.10520

552 0.14802 0.44375 728 0.30621 0.91541

38
James L. Mueller

Table 13. Radiance output of Biospherical Instruments, Inc., 20-inch integrating sphere (manufactured by Labsphere,

Inc.) measured using the NIST PR714 radiometer, and calibrated to the radiance scale of the GSFC 42-inch sphere.

(Radiances, Li(λ), are in units of μW cm−2 nm−1 sr−1.)

Run File Date

1 SBS1NF02.SCN 28 July 1992

2 SBS1NF03.SCN 28 July 1992

3 SBS1NF04.SCN 30 July 1992

λ [nm] L1(λ) L2(λ) L3(λ) λ [nm] L1(λ) L2(λ) L3(λ) λ [nm] L1(λ) L2(λ) L3(λ)

380 0.09064 0.09148 0.09283 556 1.08623 1.08520 1.09855 732 2.13170 2.13170 2.15627

384 0.09731 0.09756 0.09794 560 1.10929 1.10929 1.12160 736 2.14496 2.14390 2.16938

388 0.10525 0.10462 0.10660 564 1.13755 1.13755 1.15095 740 2.15157 2.15052 2.17690

392 0.11556 0.11504 0.11630 568 1.16707 1.16707 1.18054 744 2.16055 2.15949 2.18585

396 0.12635 0.12719 0.12813 572 1.19925 1.20029 1.21380 748 2.16215 2.16110 2.18744

400 0.13743 0.13795 0.13984 576 1.23084 1.23084 1.24539 752 2.16198 2.16093 2.18833

404 0.15018 0.14997 0.15227 580 1.26557 1.26557 1.28013 756 2.16325 2.16325 2.19176

408 0.16355 0.16397 0.16596 584 1.29444 1.29444 1.30892 760 2.17613 2.17613 2.20468

412 0.17754 0.17743 0.17983 588 1.32084 1.31981 1.33523 764 2.19475 2.19475 2.22339

416 0.19484 0.19504 0.19764 592 1.34698 1.34698 1.36237 768 2.20705 2.20598 2.23472

420 0.21061 0.21071 0.21309 596 1.37424 1.37424 1.39068 772 2.21544 2.21437 2.24213

424 0.22823 0.22792 0.23102 600 1.39748 1.39748 1.41396 776 2.21879 2.21772 2.24557

428 0.24713 0.24734 0.25034 604 1.42743 1.42743 1.44404 780 2.21996 2.21888 2.24791

432 0.26531 0.26510 0.26923 608 1.45976 1.45976 1.47650 784 2.22657 2.22549 2.25460

436 0.28604 0.28604 0.28992 612 1.49013 1.48908 1.50697 788 2.23317 2.23317 2.26345

440 0.30481 0.30511 0.30886 616 1.52051 1.51945 1.53740 792 2.23635 2.23527 2.26562

444 0.32597 0.32608 0.33016 620 1.55423 1.55317 1.57224 796 2.23716 2.23607 2.26540

448 0.34849 0.34880 0.35293 624 1.57823 1.57718 1.59619 800 2.24450 2.24341 2.27388

452 0.37136 0.37146 0.37663 628 1.60418 1.60418 1.62208 804 2.24831 2.24722 2.27760

456 0.39352 0.39373 0.39899 632 1.62826 1.62826 1.64822 808 2.24124 2.24015 2.27154

460 0.41900 0.41900 0.42435 636 1.64846 1.64846 1.66837 812 2.23597 2.23489 2.26622

464 0.44255 0.44235 0.44799 640 1.66539 1.66643 1.68629 816 2.23251 2.23036 2.26273

468 0.46326 0.46357 0.46960 644 1.69084 1.69084 1.71075 820 2.22582 2.22582 2.25708

472 0.48459 0.48479 0.49105 648 1.71217 1.71217 1.73212 824 2.22545 2.22437 2.25564

476 0.51056 0.51046 0.51740 652 1.73241 1.73241 1.75238 828 2.22293 2.22185 2.25313

480 0.54179 0.54158 0.54871 656 1.75570 1.75570 1.77569 832 2.21793 2.21685 2.24821

484 0.57027 0.57027 0.57734 660 1.77694 1.77799 1.79694 836 2.21574 2.21465 2.24617

488 0.59706 0.59696 0.60489 664 1.79484 1.79484 1.81587 840 2.21454 2.21344 2.24620

492 0.62497 0.62538 0.63330 668 1.82005 1.82005 1.84105 844 2.21284 2.21064 2.24354

496 0.65131 0.65173 0.65998 672 1.84817 1.84607 1.86809 848 2.20885 2.20775 2.24078

500 0.67595 0.67626 0.68453 676 1.86551 1.86447 1.88642 852 2.21055 2.21055 2.24152

504 0.70147 0.70199 0.71037 680 1.88172 1.88172 1.90258 856 2.20916 2.20805 2.24026

508 0.73264 0.73264 0.74197 684 1.90413 1.90517 1.92609 860 2.20542 2.20319 2.23554

512 0.76376 0.76365 0.77307 688 1.92141 1.92141 1.94237 864 2.19960 2.19737 2.22967

516 0.79172 0.79193 0.80195 692 1.93718 1.93613 1.95825 868 2.19823 2.19600 2.22825

520 0.82138 0.82138 0.83147 696 1.96201 1.96095 1.98323 872 2.19281 2.19059 2.22388

524 0.85245 0.85276 0.86299 700 1.98379 1.98379 2.00623 876 2.18666 2.18445 2.21766

528 0.87918 0.87949 0.89038 704 1.99942 2.00050 2.02198 880 2.18273 2.18052 2.21366

532 0.90944 0.90985 0.92068 708 2.02265 2.02265 2.04533 884 2.17742 2.17411 2.20829

536 0.94129 0.94160 0.95247 712 2.04375 2.04375 2.06650 888 2.17209 2.16879 2.20180

540 0.97450 0.97450 0.98625 716 2.06047 2.06047 2.08324 892 2.16430 2.16210 2.19614

544 1.00057 1.00088 1.01316 720 2.08588 2.08588 2.11083 896 2.15618 2.15508 2.19014

548 1.03060 1.03081 1.04216 724 2.10190 2.10190 2.12673 900 2.14482 2.14482 2.17761

552 1.05801 1.05801 1.07033 728 2.11553 2.11553 2.14132

39
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Table 14. Radiance output of the UCSB 20-inch integrating sphere illuminated with lamp F303 at a distance of

50 cm, measured using the NIST PR714 radiometer, and calibrated to the radiance scale of the GSFC 42-inch sphere.

(Radiances, Li(λ), are in units of μW cm−2 nm−1 sr−1.)

Run File Date Configuration

1 SUC1NF01.SCN 29 July 1992 1-inch Entrance Aperture

2 SUC1NF02.SCN 29 July 1992 1-inch Entrance Aperture

3 SUC1NF03.SCN 29 July 1992 5-inch Entrance Aperture

4 SUC1NF04.SCN 29 July 1992 2-inch Entrance Aperture

λ [nm] L1(λ) L2(λ) L3(λ) L4(λ) λ [nm] L1(λ) L2(λ) L3(λ) L4(λ)

380 0.00803 0.00805 0.14385 0.03033 556 0.05819 0.05826 1.01744 0.21889

384 0.00854 0.00859 0.15149 0.03234 560 0.05922 0.05925 1.03335 0.22258

388 0.00923 0.00923 0.16296 0.03467 564 0.06041 0.06045 1.05504 0.22710

392 0.01005 0.01004 0.17713 0.03782 568 0.06154 0.06158 1.07689 0.23134

396 0.01089 0.01095 0.19267 0.04112 572 0.06296 0.06302 1.10052 0.23663

400 0.01158 0.01164 0.20556 0.04387 576 0.06422 0.06427 1.12480 0.24159

404 0.01243 0.01246 0.21955 0.04680 580 0.06550 0.06554 1.15118 0.24687

408 0.01327 0.01328 0.23343 0.05001 584 0.06681 0.06686 1.17244 0.25165

412 0.01408 0.01411 0.24828 0.05307 588 0.06792 0.06796 1.19132 0.25553

416 0.01514 0.01517 0.26605 0.05704 592 0.06894 0.06899 1.21054 0.25934

420 0.01600 0.01602 0.28146 0.06039 596 0.07013 0.07017 1.22931 0.26364

424 0.01702 0.01704 0.29874 0.06418 600 0.07094 0.07102 1.24506 0.26693

428 0.01815 0.01818 0.31710 0.06830 604 0.07209 0.07216 1.26859 0.27126

432 0.01913 0.01914 0.33499 0.07206 608 0.07356 0.07362 1.29233 0.27646

436 0.02024 0.02027 0.35466 0.07638 612 0.07463 0.07469 1.31333 0.28045

440 0.02137 0.02138 0.37257 0.08041 616 0.07569 0.07575 1.33573 0.28499

444 0.02253 0.02255 0.39291 0.08478 620 0.07717 0.07722 1.36141 0.29082

448 0.02375 0.02376 0.41364 0.08937 624 0.07803 0.07807 1.37858 0.29399

452 0.02506 0.02509 0.43589 0.09414 628 0.07900 0.07910 1.39562 0.29766

456 0.02619 0.02621 0.45679 0.09859 632 0.07994 0.08006 1.41396 0.30128

460 0.02750 0.02752 0.47987 0.10351 636 0.08059 0.08071 1.42629 0.30370

464 0.02877 0.02879 0.50145 0.10825 640 0.08122 0.08128 1.43748 0.30600

468 0.02986 0.02988 0.51979 0.11214 644 0.08223 0.08232 1.45408 0.30988

472 0.03089 0.03092 0.53721 0.11592 648 0.08306 0.08319 1.46863 0.31283

476 0.03226 0.03227 0.56002 0.12111 652 0.08371 0.08382 1.48222 0.31537

480 0.03379 0.03381 0.58821 0.12701 656 0.08449 0.08466 1.49798 0.31864

484 0.03515 0.03518 0.61278 0.13230 660 0.08545 0.08556 1.51272 0.32191

488 0.03657 0.03659 0.63612 0.13739 664 0.08600 0.08610 1.52567 0.32438

492 0.03793 0.03796 0.65951 0.14237 668 0.08691 0.08699 1.54489 0.32778

500 0.04031 0.04034 0.70066 0.15120 672 0.08811 0.08819 1.56303 0.33189

504 0.04147 0.04150 0.72135 0.15560 676 0.08864 0.08873 1.57481 0.33410

508 0.04284 0.04286 0.74632 0.16093 680 0.08903 0.08910 1.58548 0.33598

512 0.04434 0.04437 0.77162 0.16658 684 0.08998 0.09004 1.59984 0.33931

516 0.04553 0.04556 0.79400 0.17127 688 0.09057 0.09068 1.61008 0.34130

520 0.04685 0.04687 0.81706 0.17614 692 0.09089 0.09099 1.61906 0.34267

524 0.04830 0.04833 0.84181 0.18136 696 0.09191 0.09197 1.63625 0.34635

528 0.04941 0.04945 0.86206 0.18579 700 0.09279 0.09286 1.65030 0.34973

532 0.05075 0.05077 0.88476 0.19068 704 0.09317 0.09326 1.65992 0.35132

536 0.05224 0.05225 0.90972 0.19612 708 0.09405 0.09413 1.67600 0.35432

540 0.05358 0.05363 0.93525 0.20149 712 0.09479 0.09484 1.69067 0.35730

544 0.05459 0.05461 0.95436 0.20563 716 0.09519 0.09525 1.70062 0.35931

548 0.05592 0.05597 0.97674 0.21039 720 0.09634 0.09641 1.71925 0.36348

552 0.05705 0.05709 0.99781 0.21458 724 0.09699 0.09703 1.72946 0.36532

40
James L. Mueller

Table 14. (cont.) Radiance output of the UCSB 20-inch integrating sphere illuminated with lamp F303 at

a distance of 50 cm, measured using the NIST PR714 radiometer, and calibrated to the radiance scale of the

GSFC 42-inch sphere. (Radiances, Li(λ), are in units of μW cm−2 nm−1 sr−1.)

λ [nm] L1(λ) L2(λ) L3(λ) L4(λ) λ [nm] L1(λ) L2(λ) L3(λ) L4(λ)

728 0.09735 0.09741 1.73841 0.36691 816 0.10293 0.10296 1.85593 0.38802

732 0.09786 0.09792 1.74810 0.36907 820 0.10266 0.10269 1.85503 0.38728

736 0.09841 0.09843 1.75632 0.37091 824 0.10242 0.10251 1.85777 0.38719

740 0.09848 0.09855 1.76115 0.37122 828 0.10278 0.10283 1.86053 0.38796

744 0.09872 0.09881 1.76724 0.37211 832 0.10273 0.10281 1.85891 0.38779

748 0.09873 0.09882 1.76702 0.37216 836 0.10250 0.10253 1.86040 0.38718

752 0.09845 0.09856 1.76669 0.37178 840 0.10278 0.10280 1.86292 0.38765

756 0.09849 0.09856 1.76945 0.37194 844 0.10296 0.10301 1.86523 0.38818

760 0.09917 0.09924 1.77960 0.37390 848 0.10289 0.10295 1.86530 0.38781

764 0.09984 0.09991 1.79378 0.37679 852 0.10310 0.10317 1.86885 0.38859

768 0.10025 0.10032 1.80267 0.37852 856 0.10319 0.10323 1.87040 0.38885

772 0.10083 0.10089 1.81079 0.38031 860 0.10288 0.10290 1.86853 0.38798

776 0.10107 0.10111 1.81488 0.38108 864 0.10251 0.10252 1.86548 0.38713

780 0.10114 0.10120 1.81789 0.38142 868 0.10255 0.10262 1.86688 0.38727

784 0.10152 0.10157 1.82546 0.38278 872 0.10253 0.10260 1.86544 0.38663

788 0.10221 0.10225 1.83412 0.38488 876 0.10232 0.10242 1.86115 0.38596

792 0.10222 0.10229 1.83851 0.38559 880 0.10212 0.10219 1.86018 0.38540

796 0.10218 0.10226 1.84186 0.38575 884 0.10177 0.10184 1.85770 0.38433

800 0.10288 0.10297 1.85174 0.38776 888 0.10147 0.10152 1.85519 0.38336

804 0.10328 0.10334 1.85767 0.38890 892 0.10131 0.10141 1.85135 0.38257

808 0.10286 0.10295 1.85489 0.38786 896 0.10107 0.10117 1.84831 0.38171

812 0.10276 0.10277 1.85467 0.38757 900 0.10046 0.10056 1.84092 0.37977

FEL lamp91453 at a distance of 240 cm. Tabulations of

spectral irradiance emitted by lamp 91453 are given in Table 4, both as determined independently at BSI by in-house

transfer from a local working standard scale of spectral irradiance, and as determined during the transfer of 31 July

1992 from F269 (Section 3.1).

In principal, the measured radiances and calibrated irradiance of lamp91543 could be combined to calculate the

BRDF of each plaque for normal incident illumination and

reflectance at 45◦. In the present case, however, the absolute radiometer calibration scale of the PR714, as transferred from the GSFC 42-inch sphere, varied over a range

of 3% during SIRREX-1 (Fig. 15), and the accuracy of the

transfer of the F269 spectral irradiance scale to 91453 on

31 July 1992 (Section 3.1) is uncertain by greater than 5%

at 400 nm, and upto 2% at longer wavelengths (Fig. 8).

The spectral BRDF must be determined with an accuracy

of less than 1%, for a plaque to be used to transfer spectral irradiance to radiance for instrument calibration, and

this particular data will not support such a determination.

Therefore, BRDF calculations from the data acquired during the July 1992 comparisons are not presented.

In terms of relative BRDFs, the spectral irradiances

reflected at 45◦ from plaques belonging to NOAA, BSI,

and UCSB agreed within less than 1% at all wavelengths.

The spectral irradiances reflected from the CHORS plaque

were approximately 3.5% lower than those reflected from

the BSI plaque at 400 nm, with the discrepancy decreasing

monotonically to 1.5% at 700 nm; this difference suggests

that the CHORS plaque may have become contaminated

with dirt, and that it should be cleaned and retested.

3.4 Shunt and Voltmeter Tests

Current shunt resistors and 5 1

2 -digit voltmeters are used

to measure lamp currents at the participating laboratories.

Shunt resistors belonging to BSI, GSFC, UM, NOAA,

and CHORS were all connected in parallel to measure lamp

current supplied to an FEL lamp by an Optronics 83DS

current-regulated power supply, set to deliver 8.000 A at

a nominal 110 VDC. Assuming that the GSFC shunt was

calibrated exactly at 0.01 Ω, all of the other shunt resistances, as calculated from the voltage dropduring the test,

matched their independent calibration values within less

than 1.0 μΩ.

Precision voltmeters (5 1

2 -digit resolution or better) belonging to BSI, Satlantic, NIST, GSFC, UM, and CHORS

were compared by sequentially measuring the voltage drop

across one of the shunts during the above test. The meters belonging to BSI, Satlantic, NIST, and GSFC agreed

to within 3 μV; the CHORS meter read 69 μV low, and

the UM meter read 30 μV high compared to the average

of these four. While the CHORS and UM meter discrepancies are less than 0.1% of reading, and are more than

sufficiently accurate for lampcurrent determination, they

41
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

exceed the 5 1

2 -digit precision specification of the meters,

and should therefore, be recalibrated.

3.5 Optronics 746 Stability Tests

The GSFC Optronics 746 Spectroradiometer system,

configured with an ISIC as described in Section 2.1, was

tested for short-term stability in February 1993. These

tests were prompted by the apparent lack of stability in the

lampirradiance scale transfers, using this radiometer, on

31 July 1992 (Section 3.1). It is noteworthy, however, that

the 746/ISIC was refurbished by the manufacturer (Optronics, Inc.) immediately following SIRREX-1 and reconfigured with a grating extending from 350–1,100 nm. (During SIRREX-1, the 746/ISIC was equipped with a grating

designed to measure near-infrared spectral irradiance, with

its lower wavelength limit at 400 nm.) Moreover, the manufacturer recommended an operating procedure for manually setting the phase angle of the 746’s chopper system,

whereas the auto-phasing setting was employed by GSFC

personnel during the July 1992 lamp transfer measurements. The recommended phase angle operating procedure was used during the February 1993 stability tests.

The laboratory procedure consisted of a series of measurements of spectral irradiance emitted by a seasoned FEL

lampat one-half hour intervals, over a total duration of 4

hours. The 746/ISIC and lampsetupconfiguration was

identical to that described for irradiance scale transfer in

Section 2.1 above. The 746/ISIC system was powered on

and allowed to warm up for approximately one hour before commencement of the tests. The initial phase angle

was set manually and readjusted for peak output prior

to each lamprun (following the manufacturer’s recommended procedure). FEL lamp 89157 was warmed up for

approximately 10 minutes, and then its spectral irradiance

output (at 50 cm) was scanned from 350–1,100 nm, with

the 746/ISIC voltage responses recorded at 10 nm intervals. This procedure was repeated at one-half hour intervals, with the first run at 1230 PST and the final run at

1630 PST.

Lampvoltage and current were monitored throughout

each run, and the lampwas powered down at the end of

each test and warmed upfor 10 minutes before the start of

the next run. The 746/ISIC was kept powered up during

the wait between tests. The results of the 9 spectral irradiance measurements, expressed as percent variation from

the mean of the 9 runs at each wavelength, are illustrated

in Fig. 18. The 746/ISIC system drifted over a total range

of approximately 2%, with the largest responsivity changes

occurring during the first 1.5 hours of the test (2.5 hours of

operation, including the 1 hour warmup). Responses were

stable within a 1% range between 1400 and 1630 PST, with

the largest drift evidenced near 400 nm (Fig. 18). These results clearly suggest the GSFC Optronics 746/ISIC should

be warmed upfor at least 3 hours before commencing lamp

irradiance scale transfer measurements. For full-day test

sessions, like those described in Section 3.1 above, the system should probably be allowed to remain powered up

overnight so that measurements can begin at the start of

each workday.

3.6 GSFC and SBRC Source Comparisons

The GSFC 42-inch sphere, Optronics 746/ISIC, and

FEL lamps were transported to SBRC in October 1992

for intercomparison with the radiometric sources used by

SBRC to calibrate the SeaWiFS instrument. These intercomparisons, which were performed on 26–28 October

1992, are reported here in Appendix B. The spectral radiance scales of the SBRC and GSFC integrating sphere

sources were found to agree to within less than 3%. The

GSFC sphere radiance scale was checked by transfer from

FEL lampF269 using the 746/ISIC (Section 2.2). The

radiance scale of the SBRC sphere had been determined

at some previous time (the date is not specified in Appendix B) and was not checked independently against the

SBRC working standard of spectral irradiance (DXW lamp

SS27) during the experiment. SBRC did transfer the irradiance scale of lampSS27 to the GSFC sphere, using a

Halon reflectance plaque and a Cary 14 spectrophotometer,

which had been modified to function as a transfer radiometer (Appendix B). The results of this transfer yielded a

scale of spectral irradiance which disagreed with the GSFC

scale by greater than 25% at 400 nm and by approximately

10% at all wavelengths greater than 500 nm.

Intercomparisons were also made between the spectral

irradiance scales of FEL lampF269 and DXW lampSS27,

first using the GSFC 746/ISIC setupto transfer the F269

scale to SS27, and then using the SBRC Cary 14 for the reverse transfer. The GSFC 746/ISIC transfer of the (NIST

October 1992) spectral irradiance scale of F269 to SS27

was higher than the SBRC SS27 scale by about 2–6%. On

the other hand, the SBRC Cary 14 transfer of the SS27

scale to F269 was higher than the NIST October 1992 calibrated scale of F269, by upto 10%. The discrepancies

in these two scale comparisons are not internally consistent, i.e., they are in opposite directions and cannot be

reconciled by assuming that one or the other scales was in

error. At this writing, GSFC’s lampF269 has been sent

to SBRC for a repeat comparison between its irradiance

scale and that of SS27 using the SBRC equipment. The

forthcoming results of those tests will indicate the direction further follow-upactions, if any, should take to assure

internal consistency between the calibrations of in situ radiometers and the SeaWiFS instrument itself.

The SDSU CHORS prototype QED-200 filter wheel

transfer radiometer was also used to compare the GSFC

and SBRC spheres on 28 October 1992. The measurements

with this system were not internally consistent within 4%

in most cases, and were significantly worse in some channels. After careful analyses of these data and subsequent

42
James L. Mueller

43
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

measurements at CHORS, it was determined that the design and fabrication of the Gershun tube and filter assembly, and internal baffling, were not adequate for this version of the instrument to be used for reliable transfers, and

therefore, these data are not presented here. A revised design of this instrument will be fabricated to correct these

deficiencies in time for testing during the next SIRREX in

June 1993.

4. DISCUSSION AND CONCLUSIONS

The first SIRREX experiment in July 1992 was an extremely valuable exercise for the participating community,

albeit more as a learning experience than as a fully successful intercalibration. Although some results of the intercalibration meet accuracies which will support the SeaWiFS

validation requirements, the majority of intercomparisons

fall short of that standard.

The 30 July 1992 transfers of the NIST (October 1992

through post-calculation) F269 irradiance scale to lamps

F268, F307, and F308 are thought to be accurate within

1%. The resulting scales for those lamps (Table 2) are

internally consistent and meet SeaWiFS goals.

The 31 July 1992 transfers of the F269 scale to the

other lamps (Tables 4–7) were not sufficiently precise to

meet SeaWiFS standards. In the majority of cases, therefore, improved transfers must be effected during future intercalibrations. During the next SIRREX, the 746/ISIC

will be allowed to warm upfor several hours before commencement of lamptransfer measurements. Also, a subset

of the lampscales will be independently checked with a different transfer radiometer setupto assure that the desired

precision is attained.

As an additional stepto improve our intercalibration of

irradiance scales, a series of blind tests has been initiated.

GSFC has transferred the F269 irradiance scale (NIST October 1992) to another FEL lamp, and then it in turn, was

used to transfer the scale from that lampto a small sample of other FEL lamps provided by other participating

laboratories (so far BSI and CHORS). The GSFC reference FEL lampand its irradiance scale are then mailed

sequentially to the other laboratories, where it will be independently transferred to the same small sample of FEL

lamps in a blind test. After several laboratories have performed these blind transfers, the resulting independently

transferred irradiance scales will be intercompared to determine the precision of scale transfers at, and between,

the various laboratories. Improved procedures can then be

implemented where warranted.

Based on multiple measurements with the PR714, the

spectral radiance scale of the GSFC sphere appears to be

stable to within less than 3%. Possible sources of this variability are short-term instabilities in the PR714 radiometer, variability in the lampillumination of the sphere, and

spatial inhomogeneity in the radiance distribution in the

sphere’s exit port. Based on repeated 746/ISIC measurements of the sphere’s irradiance scale by GSFC, the scale

appears to be repeatable within less than 2% over periods of many months. No information is currently available

on the short-term stability of the PR714 Spectrascan radiometer’s spectral responsivity; nor has the radiance distribution of the sphere’s exit port been mapped. Both of

these possible sources of apparent scale variability should

be investigated, and a better error budget developed, either before, or during, the next SIRREX.

For the present, it would seem appropriate for BSI,

UCSB, and NOAA to apply the spectral radiance scales

given in Tables 12–14. It would also be appropriate, however, to independently test the long term stability of these

radiance scales, either using built-in photodiode detectors

(BSI), or external radiometers, and make appropriate adjustments. The radiance scales of these sources will be

retested during the next SIRREX exercise.

Radiance scale measurements on the CHORS sphere

point out the need to re-lamp it to achieve a better graybody radiance spectrum, i.e., by eliminating the dichroic

reflectors in the original lampconfiguration. This has been

accomplished; the sphere is now lamped with four 150 W

tungsten-halogen lamps mounted in aluminum parabolic

reflectors to illuminate the entrance ports of the vestibule

spheres, which in turn illuminate the main 40-inch sphere

with diffuse radiance. The radiance scales listed in Table 11 for this sphere no longer apply and this sphere will

be recharacterized during the next SIRREX in June 1993.

The results, and shortcomings, associated with the first

SIRREX in July 1992, suggest many procedural modifications which should be implemented before, and during, the

next SIRREX in June 1993:

1. One week is an insufficient amount of time to

carry out such a broad experimental program of

radiometric intercomparisons involving so many

different groups. Two weeks have been scheduled for the June 1993 SIRREX.

2. Software and data formats should be organized

to facilitate near-real time analyses of all measurements made during future SIRREXs. The

SeaWiFS Project will provide assistance in database management (see Appendix C). In addition, software and format conversions should be

organized to put all data into a pre-established

framework of tables and graphs within a few

hours of data acquisition.

3. Detailed experimental procedure check lists and

log forms should be developed in advance of, and

used during, each future SIRREX. During the

July 1992 exercise, the participants depended

solely on records documented in notebooks by

the participating scientists and engineers. Furthermore, many procedural details, e.g., source

and detector placements and distances, were established on a purely ad hoc basis and were

recorded in a relatively uncontrolled way. In

44
James L. Mueller

retrospect, many of these details can be anticipated. To ensure an orderly implementation,

they should be itemized on detailed experiment

check list forms, which can then be filled out

during each experiment by a designated lead scientist or engineer.

4. The procedure for propagating the NIST scale

of spectral radiance through GSFC to the SeaWiFS community should be strengthened. Prior

to the next SIRREX, the calibration of transfer radiometers and their relationships to the

NIST and GSFC sphere scales of spectral radiance should be reconsidered to determine any

needed changes. During the next SIRREX, the

new SeaWiFS transfer radiometer, which NIST

is building for the Project, will be employed.

More systematic radiance scale verification tests

should be coordinated and planned using the

NIST calibrated broad-band photodetectors

(Appendix A). Each participant should also provide, in advance, data sheets detailing precise

dimensions and areas of exit and entrance ports

of any integrating sphere sources to be characterized during the round-robin.

5. Each integrating sphere source of spectral radiance should be mapped to determine the variability of radiance distribution over its exit port.

There is unlikely to be sufficient time available

to attempt this mapping during the round-robin,

and it would be better if each participant did

this independently and provided the results at

the outset of the experiment.

6. Spectral BRDFs of reflectance plaques used to

transfer spectral irradiance scales to radiance

scales should be measured with an accuracy to

within 1%. NIST will provide reflectance standards for this purpose during the June 1993 SIRREX, but detailed laboratory procedures for the

BRDF determinations have yet to be specified

and scheduled.

At this time, the relationshipbetween the SBRC radiometric scales used to calibrate the SeaWiFS instrument,

and the GSFC/NIST scales have not been determined with

sufficient precision. The principal uncertainty appears to

be associated with the lack of a proven internal consistency between the underlying spectral irradiance scales of

lamps F269 (GSFC) and SS27 (SBRC); this uncertainty

may be resolved by tests presently in progress. In addition, however, the pathway from the irradiance scale of

SS27 to the SBRC sphere has not been adequately documented within the SeaWiFS Project, and it should be. The

radiance scales of the SBRC and GSFC spheres do appear

to agree within 3%, which is approximately the same repeatability obtained with PR714 spectral measurements of

the GSFC sphere.

This consistency between the two spheres will provide

the primary linkage between SeaWiFS radiance responsivity calibration and the SIRREX intercalibration process,

but it is important that the heritage of the SBRC sphere

radiance scale is better understood. Even with improved

repeatability of the GSFC sphere scale, e.g., through mapping of radiance variability, any improvement of the 3%

level of precision in comparison to the SBRC sphere would

require a similar mapping of radiance variability in its exit

port. These questions should continue to be developed

and considered as SIRREX activities proceed through the

summer of 1993.

Acknowledgments

In addition to some of the participants, several people contributed to the preparation of this document. In particular,

the author thanks Carol Johnson, James McLean, and Robert

Woodward for the material presented in Appendices A, B, and

C, respectively.

Appendices

A. NIST Photodetector Results

B. Radiometric Source Comparison at SBRC

C. Intercalibration Data Archive

D. Attendees to SIRREX-1

Appendix A

NIST Photodetector Results

Spectral radiance measurements were made at CHORS of

the GSFC sphere, the CHORS sphere, the BSI sphere, and

the NOAA (Optronics) sphere usinga commercial, imaging

monochromator that has a single grating and a linear diode

array (the PR714).

Usingthis device, NIST recorded the spectral radiance of

a calibrated sphere source (the FASCAL sphere source with

a 1 in. aperture) before and after SIRREX-1. The best data

are those from the measurements after the CHORS visit; the

current set at the calibration value was available for these runs.

It appears that the PR714 measurements at CHORS should be

low by several percent, except below 400 nm, where the PR714

appears to measure high (Fig. A1, derived from files ISS5.SCN

and SSCALSUM.WQ1). This is noted in passing, as the calibration

of the NASA sphere will be used as the reference.

GSFC brought their 42-inch sphere source with accompanyingcalibration data. Duringthe round-robin, C. Cromer

referenced the scans of the spheres taken with the PR714 to

the GSFC sphere calibration data (Fig. A2), and took the average of two PR714 scans on the sphere (files SGD2NF01.SCN

and SGD2NF02.SCN on 28 July 1992) for the measured spectral

radiance for the GSFC sphere at CHORS usingthe PR714.

Fig. A2 shows the following interpolated onto the wavelength grid of the PR714 and referenced to the GSFC sphere:

the reference spectral radiance from GSFC for their sphere; corrected data for CHORS (file SCH3NF01.SCN on 28 July 1992);

corrected PR714 data for BSI (file SBS1NF02.SCN); and corrected PR714 data for the NOAA sphere (file SOP1NF02.SCN).

Usingcalibrated filter-radiometers, NIST measured the integrated spectral radiance for the GSFC, CHORS, and BSI

45
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Fig. A1. Spectrum of differences in calibration of the PR714 Spectrascan imaging monochromator after

SIRREX-1, relative to the previous calibration.

Fig. A2. Comparison of the spectral radiances of the GSFC, CHORS, and BSI spheres measured during

SIRREX-1 (see also Section 3.2), and the spectral response functions of NIST filter radiometers.

46
James L. Mueller

spheres. Last July, predicted signal values were calculated by

integrating the PR714 data and then weighting them by the

spectral response functions of the two radiometers (Fig. A2).

More recently, NIST calculated what the signals should have

been based on the GSFC sphere calibration data. The GSFC

photodetector measurements were made on 28 July immediately after the files SGD2NF01 and SGD2NF02 were recorded. The

CHORS measurements were made on the morningof 29 July.

The BSI measurements were made on 28 July 1992 immediately

after SBS1NF03 was recorded. The NOAA sphere was too weak

for photodetector measurements. The results (in current) are

given in Table A1.

Table A1. Photodetector measurements.

Group Measured Calculated Agreement

Filter Radiometer at ∼550 nm

BSI 1.757 × 10−8 11.806 × 10−8 2.8 %

CHORS 7.340 × 10−8 9.690 × 10−8 32.0

GSFC 2.649 × 10−7 2.641 × 10−6 −0.3†

Filter Radiometer at ∼720 nm

BSI 2.877 × 10−9 2.927 × 10−9 1.7 %

CHORS 3.171 × 10−9 4.111 × 10−9 29.6

GSFC 4.578 × 10−7 4.538 × 10−7 −0.9

†Assumes the gain was (as is believed) written down incorrectly.

The conclusions from the NIST photodetector results are as

follows:

1. The NIST photodetectors, and the ancillary data on

the PR714 and the NIST sphere, support the conclusion that the calibration assigned to the GSFC sphere

is closer to the truth than the radiometric scale on

the PR714.

2. The CHORS sphere was not set to the same level on

the two different days, so a comparison of the photodetector and PR714 results is not consistent. The

other possibility is that the separation between the

CHORS sphere and the photodetectors was recorded

incorrectly. Also, the sphere aperture could have

been measured incorrectly.

3. When used correctly, the photodetectors provide independent confirmation of the spectral radiance (or

irradiance) scales.

Appendix B

Radiometric Source Comparison at SBRC

The GSFC scales of spectral irradiance and radiance were

compared with those of SBRC on 26–28 October 1992. These

comparisons at SBRC were part of the overall SIRREX effort to

provide traceability between data sets obtained by different researchers performing in situ optical measurements. These data

are to be used for SeaWiFS baseline algorithm development and

system validation.

The primary goal of the tests at SBRC was to compare the

radiance output of the SeaWiFS flight instrument calibrator

at SBRC with that of the 42-inch integrating sphere supplied

by GSFC. This comparison procedure transfers the radiation

scale used by SBRC to calibrate the SeaWiFS instrument to

the GSFC sphere. The GSFC sphere will be maintained as a

reference scale to which the individual laboratories can relate.

Direct comparisons of the radiance output of the GSFC sphere

and the SBRC sphere were made.

Additional experiments involved the comparison of irradiance standard lamps from SBRC and GSFC, as well as absolute

detector measurements conducted by J. Mueller and C. Titus.

The personnel and test equipment involved were as follows:

GSFC

Personnel: J. McLean, J. Cooper, and R. Barnes.

Sphere: 107 cm diameter with 16–45 lamps.

Spectrometer: Optronic 746 with a 350–1,000 nm range

in 5 nm steps.

SBRC

Personnel: L. Fulton and F. Domingue.

Sphere: 100 cm diameter with lamp level designation N5–N45–N200, where, N5, N45, and

N200 are the number of 5W, 45W, and

200W lamps, respectively.

Spectrometer: A modified Cary 14 with a 380–940 nm

range in 20 nm steps.

CHORS

Personnel: J. Mueller, C. Titus, and R. Austin.

A matrix of tests performed was established by GSFC and

SBRC personnel and is shown in Table B1.

System Setup and Calibration

Functional checks were made on the Optronics 746 spectroradiometer system, which was initially configured with an

ISIC. This included visual inspection for damage during shippingand handling. Some connections and circuit boards inside

the radiometer’s electronic control unit were loose. Repairs

were made and the system calibration test proceeded.

The system calibration procedure involves usingan irradiance standard lamp to establish instrument irradiance responsivity constants. This procedure transfers the standard lamp

calibration values to the spectrometer. Fig. B1 shows the setup

for this test. The radiance of the 42-inch sphere is determined

by comparingthe irradiance of the standard lamp at 50 cm from

the spectrometer, to the irradiance produced by the radiance of

the aperture of the integrating sphere at some selected distance

(66.6 cm in this case). The setup for the laboratory is shown in

Fig. B2.

Fig. B3 shows the irradiance calculation geometry. The radiance is then calculated from the equation:

E(λ) = πr2

1

d2 + r2

1 + r22

L(λ) (B1)

where E(λ) is the spectral irradiance, L(λ) is the spectral radiance, r2

1 is the radius of source aperture, r22 is the radius of

detector aperture, and d is the distance between the two apertures.

The radiance values obtained at SBRC are given in Table B2. Also shown are calibration values acquired at GSFC

just prior to the SBRC trip.

Calibration of SBRC Sphere by GSFC Techniques

The SBRC sphere (with a 100 cm diameter) was calibrated

usingthe 746/ISIC at the 0–0–11 and 0–0–5 levels (see above

for nomenclature) over the spectral range of 350–1,000 nm in

5 nm steps with a spectral bandpass of 4 nm. The laboratory

setup was the same as shown in Fig. B2 with the SBRC sphere

replacingthe GSFC sphere. The distance was set to 78.3 cm

to allow the viewinggeometry to be the same as used with the

GSFC sphere.

47
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Fig. B1. System calibration test setup.

Fig. B2. Sphere calibration setup (GSFC).

48
James L. Mueller

Table B1. A matrix of equipment and tests involved in SIRREX-1.

Sources Transfer Test Data

12345 Radiometers Configuration Format

××× SBRC Modified Cary 14 350–1,000 nm, ∆λ=20 nm Detector Output and Radiance

(with halon plate) Hard Copy

× × CHORS QED Radiometer 10 Discrete filters ASCII MS/DOS

(no information)

××××× GSFC 746 350–1,000 nm, ∆λ=5 nm Irradiance (μW cm−2 nm−1)

(with input sphere) Irradiance Transfer ASCII MS/DOS

× × GSFC 746 350–1,000 nm, ∆λ=5 nm Radiance (μW cm−2 nm−1 sr−1)

(with telescope) Radiance Transfer ASCII MS/DOS

Sources: 1=FEL source for system calibration; 2=FEL irradiance source; 3=DXW lamp viewed directly; 4=GSFC 42-inch sphere;

and 5=SBRC SIS(100) sphere.

Table B2. Comparison of 42-inch sphere calibration

values. All dates are for 1992.

λ [nm] 7 July 14 Oct. 27 Oct. Average % Diff.

380 1.901 2.042 1.972 5.0572

400 2.841 2.849 2.894 2.861 0.9985

420 4.237 4.292 4.250 4.260 0.6748

440 5.879 5.845 5.894 5.873 0.4275

460 7.774 7.651 7.759 7.728 0.8683

480 9.893 9.731 9.821 9.815 0.8270

500 12.246 11.960 12.030 12.079 1.2343

520 14.642 14.410 14.540 14.531 0.8002

540 17.172 16.980 17.050 17.067 0.5693

560 19.595 19.510 19.620 19.575 0.2946

580 22.168 22.090 22.220 22.159 0.2953

600 24.715 24.630 24.630 24.658 0.1990

620 27.407 26.840 27.080 27.109 1.0499

640 29.775 29.130 29.400 29.435 1.1005

660 31.847 31.320 31.630 31.599 0.8382

680 33.947 33.350 33.780 33.692 0.9142

700 36.114 35.360 35.700 35.725 1.0570

720 37.837 37.050 37.360 37.416 1.0596

740 39.527 38.640 39.170 39.112 1.1411

760 40.592 39.720 40.050 40.121 1.0974

780 42.220 41.330 41.700 41.750 1.0709

800 43.228 42.550 42.700 42.826 0.8316

820 43.998 43.370 43.500 43.623 0.7599

840 44.802 44.180 43.990 44.324 0.9582

860 45.216 44.700 44.390 44.769 0.9320

880 45.474 45.120 44.770 45.121 0.7801

900 45.486 45.160 44.650 45.099 0.9343

920 45.480 45.340 44.670 45.163 0.9586

940 44.839 44.890 44.160 44.630 0.9132

960 44.866 44.960 44.030 44.619 1.1474

980 44.794 44.780 43.850 44.475 1.2165

1000 44.485 44.380 43.760 44.208 0.8863

The SBRC sphere was reset to the 0–0–11 level. Radiance

values were measured at four wavelengths: 450 nm, 550 nm,

650 nm, and 750 nm for lamp levels 0–0–11, 0–0–10, 0–0–9, 0–

0–8, 0–0–7, 0–0–6, 0–0–5, 0–0–4, 0–0–3, 0–0–2, and 0–0–1. The

results of these measurements are given in Tables B3 and B4.

Irradiance Standard Measurement by GSFC

The SBRC irradiance standard (SS27), a 1,000W DXWtype quartz halogen lamp, was measured using the 746/ISIC

in the same lab setup configuration (Fig. B1). The lamp-tocollector aperture distance was 110 cm. The data obtained in

the first test was repeated the followingmorning. Care was

taken to reduce stray light, to verify the distance, and to recalibrate the spectral radiometer (746/ISIC). The results are

listed in Table B5 and illustrated in Fig. B4.

Table B3. SBRC sphere (200W lamps) radiances in

μW cm−2 nm−1 sr−1.

λ Number of Lamps λ Number of Lamps

[nm] 11 5 [nm] 11 5

380 5.124 2.355 700 80.445 37.068

400 7.465 3.453 720 84.028 38.729

420 10.176 4.758 740 87.380 40.208

440 13.996 6.464 760 89.087 40.980

460 18.115 8.377 780 91.472 42.166

480 22.767 10.522 800 93.023 42.783

500 28.018 12.933 820 93.710 43.107

520 33.457 15.533 840 94.567 43.326

540 39.115 18.203 860 94.836 43.504

560 44.902 20.834 880 94.931 43.594

580 50.453 23.523 900 94.991 43.741

600 55.988 26.002 920 95.253 43.842

620 61.680 28.405 940 94.876 43.736

640 66.822 30.793 960 95.036 43.860

660 71.645 33.004 980 95.414 43.958

680 76.138 35.158 1000 95.982 44.141

Calibration of the GSFC Sphere by SBRC Techniques

SBRC personnel calibrated the GSFC sphere usinglamp

SS27 and the Cary 14 spectrophotometer (see Fig. B5). The

technique used consists of comparingthe calculated radiance

reflected from a halon plate illuminated by SBRC lamp SS27

to the radiance of the aperture of the integrating sphere. The

results of that calibration are given in Table B6.

Fig. B6 shows that the SBRC measured values are about

10% smaller than those obtained by GSFC. (Note: the SBRC

sphere was not recalibrated duringthis intercomparison.)

Calibration of GSFC Lamp F269 by SBRC Techniques

The laboratory measurement setup was configured as shown

in Fig. B7. A test consists of the following sequence of steps:

1. The Cary 14 system essentially stops at one wavelength and records 10 samples.

2. The average and standard deviation are computed

and then recorded for a given source.

3. A rotatable mirror directs the output of the unknown

source into the Cary 14 system.

49
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Fig. B3. Irradiance calibration geometry.

Fig. B4. Lamp SS27 irradiance at 50 cm.

50
James L. Mueller

Fig. B5. Sphere calibration setup (SBRC).

Fig. B6. Radiance of GSFC sphere at SBRC.

51
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Table B4. SBRC sphere radiance comparison at selected wavelengths in units of μW cm−2 nm−1 sr−1.

λ Measure- Lamp Level (Number of 200W Lamps On)

[nm] ment 11 10 9 8 7 6 5 4 3 2 1

GSFC 15.880 14.319 13.055 11.661 10.320 8.785 7.327 5.766 4.403 2.891 1.441

450 SBRC 16.070 14.500 13.115 11.835 10.376 8.906 7.406 5.922 4.430 2.907 1.435

Ratio 0.988 0.987 0.995 0.985 0.995 0.986 0.989 0.974 0.994 0.994 1.004

GSFC 41.799 37.731 34.141 30.791 27.034 23.173 19.312 15.340 11.471 7.562 3.725

550 SBRC 41.275 37.310 33.570 30.280 26.545 22.790 18.980 15.155 11.335 7.459 3.692

Ratio 1.013 1.011 1.017 1.017 1.018 1.017 1.017 1.012 1.012 1.014 1.009

GSFC 68.847 62.397 56.508 50.619 44.309 37.859 31.479 25.309 18.859 12.451 6.128

650 SBRC 68.270 61.785 55.545 49.965 43.860 37.595 31.310 25.025 18.740 12.340 6.099

Ratio 1.008 1.010 1.017 1.013 1.010 1.007 1.005 1.011 1.006 1.009 1.005

GSFC 88.374 80.008 72.223 64.686 56.486 48.452 40.418 32.136 24.152 15.927 7.860

750 SBRC 87.330 79.070 71.055 63.810 55.945 48.000 40.000 31.955 23.905 15.795 7.802

Ratio 1.012 1.012 1.016 1.014 1.010 1.009 1.010 1.006 1.010 1.008 1.007

Average of Ratios 1.005 1.005 1.012 1.007 1.008 1.005 1.006 1.001 1.006 1.006 1.006

Standard Deviation 0.010 0.010 0.009 0.013 0.009 0.011 0.010 0.016 0.007 0.007 0.002

Table B5. SBRC DXW lamp SS27 irradiance at 50 cm in units of μW cm−2 nm−1.

λ Baffled Unbaffled Average Precision λ Baffled Unbaffled Average Precision

[nm] 27 Oct. 28 Oct. 28 Oct. Irradiance [%] [nm] 27 Oct. 28 Oct. 28 Oct. Irradiance [%]

380 1.54 1.64 1.39 1.53 0.0682 700 18.94 19.04 18.96 18.98 0.0022

400 2.10 2.14 2.05 2.10 0.0187 720 19.74 19.90 19.82 19.82 0.0033

420 2.76 2.94 2.76 2.82 0.0307 740 20.53 20.67 20.61 20.61 0.0029

440 3.63 3.70 3.64 3.66 0.0087 760 21.13 21.30 21.21 21.21 0.0032

460 4.62 4.64 4.66 4.64 0.0035 780 21.67 21.82 21.84 21.78 0.0035

480 5.70 5.79 5.77 5.75 0.0068 800 22.20 22.36 22.33 22.30 0.0031

500 6.98 6.97 6.97 6.97 0.0008 820 22.63 22.78 22.80 22.74 0.0034

520 8.21 8.24 8.21 8.22 0.0015 840 22.97 23.07 23.03 23.02 0.0017

540 9.56 9.56 9.52 9.54 0.0020 860 23.17 23.32 23.32 23.27 0.0030

560 10.79 10.88 10.84 10.84 0.0034 880 23.32 23.52 23.48 23.44 0.0036

580 12.10 12.21 12.16 12.16 0.0038 900 23.47 23.55 23.54 23.52 0.0016

600 13.39 13.44 13.37 13.40 0.0022 920 23.49 23.62 23.56 23.56 0.0022

620 14.65 14.75 14.71 14.70 0.0027 940 23.45 23.55 23.55 23.52 0.0022

640 15.84 15.90 15.89 15.88 0.0016 960 23.36 23.49 23.51 23.45 0.0029

660 17.01 17.06 16.98 17.01 0.0019 980 23.18 23.44 23.42 23.34 0.0051

680 18.01 18.11 18.02 18.05 0.0024 1000 23.02 23.31 23.30 23.21 0.0058

Table B6. Radiance of GSFC sphere (SBRC measurement) in units of μW cm−2 nm−1 sr−1.

λ Data Source: λ Data Source:

[nm] GSFC SBRC [nm] GSFC SBRC

380 2.040 1.309 680 33.780 30.630

400 2.894 2.142 700 35.700 32.510

420 4.250 3.398 720 37.360 34.000

440 5.894 4.883 740 39.170 35.570

460 7.759 6.735 760 40.050 36.760

480 9.821 8.781 780 41.700 37.710

500 12.030 10.820 800 42.700 38.540

520 14.540 13.040 820 43.500 39.150

540 17.050 15.250 840 43.990 39.480

560 19.620 17.640 860 44.390 39.720

580 22.220 20.060 880 44.770 40.080

600 24.630 22.500 900 44.650 40.410

620 27.080 24.630 920 44.670 40.150

640 29.400 26.770 940 44.160 39.740

660 31.630 28.770

4. The data for the unknown source is then recorded.

5. This process continues until the chosen wavelength

range has been scanned.

The results of this test are given in Table B7, and the plot in

Fig. B8 compares two SBRC measurements to the irradiance

scale of F269 as calibrated by NIST in October 1992. The

laboratory setup for this test was done in a hurried, makeshift

arrangement and the SBRC measurements are not necessarily

reliable in this instance.

Relative Radiance Checks Using the 746 with Telescope

The reflex telescope replaced the ISIC on the 746 and was

used to scan both the SBRC and GSFC spheres. The 746/T

laboratory setup is shown in Fig. B9. The telescope focus was

set at infinity (defocused) and the distance was 141 cm for the

GSFC sphere and 145 cm for the SBRC sphere. The field-ofview was 1.5◦. Scans were made from 350–1,000 nm in steps of

5 nm. Output levels 0–0–11, 0–0–5, 0–0–3, 6–2–0, and 0–0–1

were measured on the SBRC sphere. The GSFC sphere was

measured with all 16 lamps lit. This level is roughly equivalent

52
James L. Mueller

Fig. B7. Lamp calibration setup (SBRC).

Fig. B8. Irradiance measurements of lamp F269.

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The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

54
James L. Mueller

Table B7. Irradiance lamp F269 calibrated at SBRC in units of μW cm−2 nm−1.

λ NIST SBRC Ratio of λ NIST SBRC Ratio of

[nm] Data Data1 Data2 SBRC/NIST [nm] Data Data1 Data2 SBRC/NIST

380 1.653 1.921 1.937 1.162 680 18.410 19.406 19.528 1.054

400 2.341 2.616 2.678 1.117 700 19.300 20.380 20.502 1.056

420 3.179 3.607 3.679 1.134 720 20.080 21.124 21.237 1.052

440 4.142 4.584 4.653 1.107 740 20.760 21.878 21.988 1.054

460 5.219 5.671 5.781 1.087 760 21.350 22.447 22.563 1.051

480 6.394 6.943 7.015 1.086 780 21.850 22.887 22.996 1.047

500 7.638 8.178 8.291 1.071 800 22.270 23.352 23.452 1.049

520 8.928 9.535 9.651 1.068 820 22.600 23.487 23.597 1.039

560 11.560 12.205 12.353 1.056 840 22.860 23.609 23.703 1.033

580 12.850 13.628 13.738 1.061 860 23.040 23.728 23.813 1.030

600 14.100 15.014 15.146 1.065 880 23.160 23.879 23.955 1.031

620 15.280 16.192 16.314 1.060 900 23.210 24.077 24.134 1.037

640 16.400 17.348 17.489 1.058 920 23.200 23.933 23.983 1.032

660 17.450 18.425 18.561 1.056 940 23.130 23.848 23.889 1.031

Table B8. SBRC sphere measurements from October 1992 usingthe 746 with telescope optics. Values are in units of

μW cm−2 nm−1 sr−1.

λ 200W Lamps Six 5W and λ 200W Lamps Six 5W and

[nm] 11 5 3 Two 45W One 45W [nm] 11 5 3 Two 45W One 45W

380 5.510 2.549 1.522 0.274 0.134 700 83.976 38.264 23.004 4.334 1.967

400 7.544 3.478 2.067 0.374 0.180 720 87.926 40.074 24.086 4.542 2.058

420 10.559 4.878 2.895 0.527 0.251 740 91.584 41.766 25.087 4.750 2.147

440 14.435 6.637 3.959 0.719 0.342 760 93.261 42.653 25.537 4.841 2.182

460 18.781 8.636 5.131 0.935 0.441 780 96.080 43.766 26.304 4.996 2.249

480 23.643 10.878 6.459 1.183 0.555 800 97.520 44.458 26.690 5.083 2.280

500 28.715 13.255 7.886 1.447 0.678 820 98.454 44.844 26.923 5.125 2.298

520 34.520 15.973 9.502 1.751 0.816 840 98.636 44.919 27.002 5.143 2.303

540 40.500 18.685 11.126 2.053 0.954 860 99.183 45.201 27.137 5.187 2.310

560 46.535 21.451 12.767 2.369 1.096 880 99.775 45.456 27.304 5.226 2.326

580 52.510 24.244 14.432 2.684 1.238 900 99.748 45.366 27.248 5.238 2.321

600 59.159 27.042 16.225 3.007 1.387 920 100.160 45.558 27.129 5.261 2.329

620 64.526 29.421 17.658 3.293 1.512 940 99.644 45.392 26.990 5.248 2.323

640 69.771 31.776 19.122 3.573 1.635 960 99.465 45.248 26.905 5.245 2.313

660 74.818 34.083 20.485 3.840 1.753 980 99.264 45.133 26.851 5.242 2.307

680 79.640 36.344 21.855 4.104 1.867 1000 99.956 45.457 26.967 5.280 2.324

to the 0–0–5 level of the SBRC sphere. The data given in

Table B8 is considered relative radiance, since the use of the

telescope in this transfer is still beingevaluated.

CHORS QED Radiometer Measurements

CHORS personnel used a filtered radiometer to measure

output of both the SBRC and GSFC spheres. The GSFC sphere

was measured with 16 lamps lit, as well as with 4 lamps lit. The

SBRC sphere was measured at five levels, namely: 0–0–11, 0–

0–5, 0–0–3, 6–2–0, and 0–0–1. The raw data obtained is given

in Table B9. Spectral calibration constants for the CHORS

radiometer have not yet been made available.

Observations and Conclusions

One of the purposes of SIRREX-1 was to determine and

resolve any problem areas involved in relatingdata obtained

by researchers making in situ optical measurements. These

measurements have succeeded in pinpointingareas that need

improvement. In summary, there is a need for:

a) Well defined and controlled experimental techniques

in measurements,

b) An improvement in performance of laboratory and

field optical measuringequipment,

c) Independent means for verifyingthe validity of each

measurement procedure and results, and

d) Real-time assessment of critical test results (tests

with results that influence subsequent measurements

or analyses).

The tests at SBRC provided instances of data which was

consistent with SBRC’s results, as well as data which was inconsistent:

1. The GSFC measurement of the SBRC sphere produced values that agreed with SBRC data to within

2–3%.

2. The SBRC measurement of the GSFC sphere differed

by about 10% (below) with respect to the GSFC

data.

55
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Table B9. CHORS QED filter radiometer (output in volts).

Filter GSFC SBRC

No. 16 Lamps1 16 Lamps2 4 Lamps 4 Gain 10 0–0–11 0–0–5 0–0–3 6–2–0 0–1–0

f0 −0.003517 −0.003466 −0.000908 −0.008741 −0.009387 −0.004367 −0.002638 −0.005041 −0.002586

f1 −1.168189 −1.168254 −1.168186 −1.167163 −1.168203 −1.168187 −1.168189 −1.167153 −1.167231

f2 −0.196693 −0.203744 −0.048600 −0.498981 −0.468297 −0.213149 −0.125810 −0.245612 −0.112980

f3 −0.135841 −0.140254 −0.034848 −0.350364 −0.326341 −0.149405 −0.090253 −0.169211 −0.077407

f4 −0.081303 −0.083192 −0.020943 −0.191009 −0.193980 −0.091559 −0.054962 −0.102837 −0.041497

f5 −0.075136 −0.078216 −0.019542 −0.196656 −0.183058 −0.086134 −0.049347 −0.096849 −0.044247

f6 −0.067072 −0.070157 −0.017220 −0.167580 −0.165884 −0.076129 −0.045552 −0.084676 −0.040100

f7 −0.046341 −0.050157 −0.012283 −0.124569 −0.118150 −0.055241 −0.033016 −0.061248 −0.028088

f8 −0.028182 −0.029460 −0.007285 −0.073411 −0.069386 −0.032618 −0.019477 −0.035893 −0.016343

f9 −0.019709 −0.020510 −0.005033 −0.050783 −0.048354 −0.022554 −0.013501 −0.025229 −0.011645

f10 −0.038875 −0.061576 −0.011572 −0.122711 −0.141077 −0.058019 −0.034322 −0.051110 −0.029186

f11 −0.008850 −0.009195 −0.002211 −0.022232 −0.022494 −0.010359 −0.006191 −0.011129 −0.005891

f0 −0.003500 −0.003597 −0.000906 −0.009141 −0.009433 −0.004385 −0.002623 −0.005053 −0.002811

f1 −1.168188 −1.168224 −1.167169 −1.168204 −1.168164 −1.168192 −1.167165 −1.167018

f2 −0.196787 −0.204084 −0.492756 −0.468861 −0.213136 −0.125907 −0.244585 −0.112142

f3 −0.135833 −0.140717 −0.349807 −0.326169 −0.151141 −0.090757 −0.169857 −0.078108

f4 −0.081377 −0.084890 −0.210041 −0.198057 −0.091898 −0.054879 −0.103036 −0.047446

f5 −0.074915 −0.078120 −0.196930 −0.164220 −0.086245 −0.049909 −0.096560 −0.043978

f6 −0.066952 −0.070085 −0.173530 −0.164150 −0.076202 −0.045450 −0.085150 −0.039159

f7 −0.048395 −0.048747 −0.124690 −0.118042 −0.055256 −0.032975 −0.060531 −0.025334

f8 −0.028377 −0.029483 −0.073148 −0.069348 −0.032631 −0.019420 −0.036220 −0.016340

f9 −0.019722 −0.020397 −0.050601 −0.048648 −0.022568 −0.013565 −0.024896 −0.011099

f10 −0.039295 −0.041515 −0.128689 −0.096752 −0.056662 −0.029032 −0.062016 −0.023348

f11 −0.008845 −0.009222 −0.022356 −0.022397 −0.010379 −0.006170 −0.011292 −0.005856

f0 −0.003444 −0.004081 −0.009127 −0.009362 −0.004386 −0.005070 −0.002769

f1 −1.168182 −1.168172 −1.166920

1= Run number 1.

2 = Run number 2.

3. The GSFC measurement of the SBRC lamp produced

values higher than the values furnished by SBRC.

4. The SBRC measurement of the GSFC (NIST) lamp

produced higher values than those furnished by NIST.

Appendix C

Intercalibration Data Archive

SIRREX activities are beingrecorded usingthe Sybase relational database utility on the Calibration/Validation UNIX

workstation (CALVAL) at GSFC. A duplicate database has

also been implemented on a 486 PC (WIFS) usingthe FoxPro

database package. The SIRREX database provides a means of

ensuringdata integrity and availability. The database is designed to hold descriptive data (meta-data) on calibration files

and accompanyingnotes obtained duringSIRREX activities.

The actual calibration data and the additional descriptive text

are stored in on-line ASCII files outside the database on both

CALVAL and WIFS within identical directory structures. The

information stored within the database is used to locate and

describe these intercalibration files.

The database layout was implemented usinga two-table design for storing the meta-data. General information on the

SIRREX data sets are provided in the data set table, and specific information on the data are provided in the data table.

Both tables use the data set field as the primary key for accessingthe meta-data. Tables C1 and C2 show the design of

the database tables alongwith typical entries for the data set

fields (columns). Information was stored in either text (character) format or integer format. Blanks may appear in the

table for columns in which NULL ALLOWED is set to YES. The

DATA SET DESC field in the DATA SET table provides the name

of on-line ASCII files that contain additional descriptive information. The followingtext is the contents of the descriptive

ASCII file referenced in Table C1:

Irradiance file for Hoffman 90572 lamp obtained

on the second day at the first SeaWiFS round robin

lamp intercomparison trials at CHORS. Lamp modes

are shown in the radiometric source column in the

"data" table. Data in ∼/cooper3/pp08-15.

Routines for accessingthe meta-data in the SIRREX database on CALVAL have been implemented usingthe Sequential

Query Language (SQL). With these routines, it is possible to

obtain information on a file, information on the data within the

file, or both. Plans have been made to link the database with

the Interactive Data Language (IDL) thus providing a graphical user interface and a means for analyzingand displaying

the data. This implementation will also provide a more robust

scheme for selectinginformation. A link between the database

and IDL has been successfully implemented for other applications on CALVAL.

56
James L. Mueller

Table C1. Design of the data set table.

Column Data Type Nulls Allowed Example Entry

DATA SET character NO ir90572a.dat

DATA SET DESC character NO ir90572a.meta

ORIGINAL NAME character YES ir90572a.dat

SOURCE character YES NASA

Table C2. Design of the data table.

Field Data Type Nulls Allowed Example Entry

DATA SET character NO ir90572a.dat

DATA character NO Irradiance

DATA DESC character NO Irradiance as a function of wavelength

FORMAT character NO ASCII

UNITS character NO W/cm2nm

LOCATION character YES Santa Barbara, CA

DATE character YES 7/31/92

IDATE integer YES 920731

TIME character YES 1055

INVESTIGATOR character YES J. Cooper, J. McLean

RADIOMETRIC SOU character YES Irradiance lamp standard-Hoffman 90572

INSTRUMENT character YES 746 monochrometer system

CAL SOURCE character YES NULL

PROCESS LEVEL integer YES 0

SPECTRAL RES character YES 400nm to 750nm at 5nm intervals

BANDPASS character YES 2nm

DATA TYPE character YES Lamp

Appendix D

Attendees to SIRREX-1

Gregg Adelman

Biospherical Instruments

5340 Riley Street

San Diego, CA 92110

Voice: 602–686–1888

Fax: 602–686–1887

Ros Austin

SDSU/CHORS/Suite 206

6505 Alvarado Road

San Diego, CA 92120–5005

Voice: 619–594–2244

Fax: 619–594–4570

Internet: raustin@chors.sdsu.edu

Rocky Booth

Biospherical Instruments

5340 Riley Street

San Diego, CA 92110

Voice: 602–686–1888

Fax: 602–686–1887

Internet: booth@ssurf.ucsd.edu

Bill Broenkow

Moss LandingMarine Laboratory

PO Box 450

Moss Landing, CA 95039

Voice: 408–755–8675

Fax: 408–755–8686

Dennis Clark

NOAA/NESDIS

E/RA 28, WWB, Rm. 104

Washington, DC 20233

Voice: 301–763–8102

Fax: 301–763–8020

Omnet: d.clark.noaa

John Cooper

NASA/GSFC/Code 925

Greenbelt, MD 20771

Voice: 301–286–1210

Fax: 301–286–1616

Internet: cooper@toms.dnet.gsfc.nasa.gov

Chris Cromer

NIST/Bldg. 221, Room A221

Gaithersburg, MD 20899

Voice: 301–975–3216

Fax: 301–840–8551

Internet: cromer@garnet.nist.gov

Mike Feinholz

Moss LandingMarine Laboratory

PO Box 450

Moss Landing, CA 95039

Voice: 408–755–8675

Fax: 408–753–2826

Internet: feinholz@nsf.mlml.sdsu.calstate.edu

Dave Goebel

Sigma Research Technologies, Inc.

1851 Woodbine Ct.

Marco Island, FL 33937

Voice: 813–394–9138

57
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Bob Howarth

NCCOSC/NRaD/Code 844

271 Catalina Blvd.

San Diego, CA 92152

Voice: 619–553–3717

Lab: 619–553–5189

Carol Johnson

NIST/Bldg. 221, Room A221

Gaithersburg, MD 20899

Voice: 301–975–2322

Fax: 301–840–8551

Internet: cjohnson@enh.nist.gov

Richard Johnson

UCSD/MPL/Mail Code 0701

9500 Gilman Drive

La Jolla, CA 92093-0701

Voice: 619–534–1772

Fax: 619–553–0764

Internet: monette@mpl.ucsd.edu

Jim McLean

NASA/GSFC/Code 925

Greenbelt, MD 20771

Voice: 301–286–8134

Fax: 301–286–1616

GSFCmail: jmclean

Scott McLean

Satlantic Inc.

Richmond Terminal Pier 9

3295 Barrington Street

Halifax, B3K5X8

Nova Scotia

Voice: 902–492–4780

Fax: 902–492–4781

Internet: scott@predator.ocean.dal.ca

Dave Menzies

CRSEO/UCSB

Santa Barbara, CA 93106

Voice: 805–893–8496

Fax: 805–893–2578

Internet: davem@crseo.ucsb.edu

James Mueller

SDSU/CHORS/Suite 206

6505 Alvarado Road

San Diego, CA 92120–5005

Voice: 619–594–2230

Fax: 619–594–4570

Omnet: j.mueller

Internet: jmueller@chors.sdsu.edu

Raymond Smith

CRSEO/UCSB

Santa Barbara, CA 93106

Voice: 805–893–4709

Fax: 805–893–2578

Omnet: r.smith.ucsb

Internet: ray@crseo.ucsb.edu

Clay Titus

SDSU/CHORS/Suite 206

6505 Alvarado Road

San Diego, CA 92120–5005

Voice: 619–594–2244

Lab: 619–594–4830

Fax: 619–594–4570

Internet: ctitus@chors.sdsu.edu

Ken Voss

UM/Dept. of Physics

Coral Gables, FL 33124

Voice: 305–284–2323

Fax: 305–284–4222

Omnet: k.voss

Internet: kvoss@umiami.miami.edu

Mark Yarbrough

Moss LandingMarine Laboratory

PO Box 450

Moss Landing, CA 95039

Voice: 408–755–8685

Fax: 408–755–8686

Internet: yarbrough@nsf.mlml.sdsu.calstate.edu

Glossary

ASCII American Standard Code for Information Interchange

BRDF Bidirectional Reflectance Distribution Function

BSI Biospherical Instruments, Incorporated

CALVAL Calibration and Validation

CHORS Center for Hydro-Optics and Remote Sensing

DXW Not an acronym, but a lamp designator.

FASCAL Fast Calibration (Facility)

FEL Not an acronym, but a lamp designator.

GLOBEC Global Ecosystem

GSFC Goddard Space Flight Center

HEI Hoffman Engineering, Incorporated

IBM International Business Machines

IDL Interactive Data Language

ISIC Integrating Sphere Irradiance Collector

JGOFS Joint Global Ocean Flux Study

MLML Moss LandingMarine Laboratory

MOBY Marine Optical Buoy

MS/DOS MicroSoft/Disk OperatingSystem

NASA National Aeronautics and Space Administration

NCCOSC Navy Command, Control, and Ocean Surveillance

Center

NIST National Institute of Standards and Technology

NOAA National Oceanic and Atmospheric Administration

NRaD Naval Research and Development

OI Original Irradiance

PC (IBM) Personal Computer

PDT Pacific Daylight Time

PR Photo Research

PST Pacific Standard Time

RR Round-Robin

58
James L. Mueller

SBRC (Hughes) Santa Barbara Research Center

SDSU San Diego State University

SeaWiFS Sea-viewingWide Field-of-view Sensor

SIO/MPL Scripps Institution of Oceanography/Marine

Physical Laboratory

SIRREX SeaWiFS Intercalibration Round-Robin Experiment

SIRREX-1 The First SIRREX (July 1992)

SIS Spherical Integrating Source

SJSU San Jose State University

S/N Serial Number

SQL Sequential Query Language

SRT Sigma Research Technology, Incorporated

UCSB University of California at Santa Barbara

UM University of Miami

VDC Volts Direct Current

Symbols

d The distance between source and detector apertures.

E(λ) Spectral irradiance.

Ebeg Beginning irradiance value.

Eend Endingirradiance value.

fi Filter number, i=0–11.

F(λ) A conversion factor to convert PR714 readings to

the GSFC sphere radiance scale.

F(λ) A mean conversion factor.

L(λ) Spectral radiance.

Li(λ) Spectral radiance for run number i.

r1 The radius of source aperture.

r2 The radius of detector aperture.

δ The departure of each individual conversion factor

from the mean.

∆λ An interval in wavelength.

λ Wavelength.

References

Hooker, S.B., W.E. Esaias, G.C. Feldman, W.W. Gregg, and

C.R. McClain, 1992: An Overview of SeaWiFS and Ocean

Color. NASA Tech. Memo. 104566, Vol. 1, S.B. Hooker

and E.R. Firestone, Eds., NASA Goddard Space Flight

Center, Greenbelt, Maryland, 24 pp.

McClain, C.R., W.E. Esaias, W. Barnes, B. Guenther, D. Endres, S.B. Hooker, G. Mitchell, and R. Barnes, 1992: Calibration and Validation Plan for SeaWiFS. NASA Tech.

Memo. 104566, Vol. 3, S.B. Hooker and E.R. Firestone,

Eds., NASA Goddard Space Flight Center, Greenbelt,

Maryland, 41 pp.

Mueller, J.L., and R.W. Austin, 1992: Ocean Optics Protocols

for SeaWiFS Validation. NASA Tech. Memo. 104566, Vol.

5, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard

Space Flight Center, Greenbelt, Maryland, 45 pp.

Walker, J.H., R.D. Saunders, J.K. Jackson, and D.A. McSparron, 1987: Spectral Irradiance Calibrations. NBS Special Publication 250–20, U.S. Dept. of Commerce, National Bureau of

Standards, Washington, D.C., 37 pp. plus appendices.

SeaWiFS Technical Report Series

Vol. 1

Hooker, S.B., W.E. Esaias, G.C. Feldman, W.W. Gregg, and

C.R. McClain, 1992: An Overview of SeaWiFS and Ocean

Color. NASA Tech. Memo. 104566, Vol. 1, S.B. Hooker

and E.R. Firestone, Eds., 24 pp.

Vol. 2

W. Gregg, 1992: Analysis of Orbit Selection for SeaWiFS:

Ascendingvs. DescendingNode. NASA Tech. Memo.

104566, Vol. 2, S.B. Hooker and E.R. Firestone, Eds.,

16 pp.

Vol. 3

McClain, C.R., W.E. Esaias, W. Barnes, B. Guenther, D. Endres, S. Hooker, G. Mitchell, and R. Barnes, 1992: Calibration and Validation Plan for SeaWiFS. NASA Tech.

Memo. 104566, Vol. 3, S.B. Hooker and E.R. Firestone,

Eds., 41 pp.

Vol. 4

McClain, C.R., E. Yeh, and G. Fu, 1992: An Analysis of GAC

SamplingAlgorithms: A Case Study. NASA Tech. Memo.

104566, Vol. 4, S.B. Hooker and E.R. Firestone, Eds.,

22 pp.

Vol. 5

Mueller, J.L., and R.W. Austin, 1992: Ocean Optics Protocols.

NASA Tech. Memo. 104566, Vol. 5, S.B. Hooker and E.R.

Firestone, Eds., 43 pp.

Vol. 6

Firestone, E.R., and S.B. Hooker, 1992: SeaWiFS Technical

Report Series Summary Index: Volumes 1–5. NASA Tech.

Memo. 104566, Vol. 6, S.B. Hooker and E.R. Firestone,

Eds., 9 pp.

Vol. 7

Darzi, M., 1992: Cloud Screeningfor Polar OrbitingVisible

and IR Satellite Sensors. NASA Tech. Memo. 104566, Vol.

7, S.B. Hooker and E.R. Firestone, Eds., 7 pp.

Vol. 8

Hooker, S.B., W.E. Esaias, and L.A. Rexrode, 1993: Proceedings of the First SeaWiFS Science Team Meeting. NASA

Tech. Memo. 104566, Vol. 8, S.B. Hooker and E.R. Firestone, Eds., 61 pp.

Vol. 9

Gregg, W.W., F.C. Chen, A.L. Mezaache, J.D. Chen, J.A.

Whiting, 1993: The Simulated SeaWiFS Data Set, Version 1. NASA Tech. Memo. 104566, Vol. 9, S.B. Hooker

and E.R. Firestone, Eds.,17 pp.

Vol. 10

Woodward, R.H., R.A. Barnes, C.R. McClain, W.E. Esaias,

W.L. Barnes, and A.T. Mecherikunnel, 1993: Modelingof

the SeaWiFS Solar and Lunar Observations. NASA Tech.

Memo. 104566, Vol. 10, S.B. Hooker and E.R. Firestone,

Eds., 26 pp.

Vol. 11

Patt, F.S., C.M. Hoisington, W.W. Gregg, and P.L. Coronado,

1993: Analysis of Selected Orbit Propagation Models for

the SeaWiFS Mission. NASA Tech. Memo. 104566, Vol.

11, S.B. Hooker, E.R. Firestone, and A.W. Indest, Eds.,

16 pp.

59
The First SeaWiFS Intercalibration Round-Robin Experiment, SIRREX-1, July 1992

Vol. 12

E.R. Firestone and S.B. Hooker, 1993: SeaWiFS Technical Report Series Summary Index: Volumes 1–11. NASA Tech.

Memo. 104566, Vol. 12, S.B. Hooker and E.R. Firestone,

Eds., 28 pp.

Vol. 13

McClain, C.R., K.R. Arrigo, J. Comiso, R. Fraser, M. Darzi,

J.K. Firestone, B. Schieber, E-n. Yeh, and C.W. Sullivan,

1993: Case Studies for SeaWiFS Calibration and Validation, Part 1. NASA Tech. Memo. 104566, Vol. 13, S.B.

Hooker and E.R. Firestone, Eds., 52 pp., plus color plates.

Vol. 14

Mueller, J.L., 1993: The First SeaWiFS Intercalibration RoundRobin Experiment, SIRREX-1, July 1992. NASA Tech.

Memo. 104566, Vol. 14, S.B. Hooker and E.R. Firestone,

Eds., NASA Goddard Space Flight Center, Greenbelt,

Maryland, 60 pp.

60
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 September 1993 Technical Memorandum

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 SeaWiFS Technical Report Series

 Volume 14, The First SeaWiFS Intercalibration Round-Robin Experiment,

 SIRREX-1, July 1992 Code 900

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17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT

 Unclassified Unclassified Unclassified UL

 SeaWiFS, Oceanography, Round-Robin, SIRREX, Intercalibration, Spectral Irradiance, 65

 Spectral Radiance Calibration, Lamps, Scale, Transfer, Sphere

James L. Mueller: CHORS San Diego State University, San Diego California

Elaine R. Firestone: General Sciences Corporation, Laurel, Maryland

Unclassified–Unlimited

Subject Category 48

13. ABSTRACT (Maximum 200 words)

This report presents the results of the first Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Intercalibration Round-Robin

Experiement (SIRREX-1), which was held at the Center for Hydro-Optics and Remote Sensing (CHORS) at San Diego State University (SDSU) on 27-31 July 1992. Oceanographic radiometers to be used in the SeaWiFS Calibration and Validation Program will be

calibrated by individuals from the National Aeronautics and Space Administration’s (NASA’s) Goddard Space Flight Center (GSFC),

CHORS, and seven other laboratories. The purpose of the SIRREX experiments is to assure the radiometric stadards used in all of

these laboratories are referenced to the same scales of spectral irradance and radiance, which will be maintained by GSFC and

periodically recalibrated by the National Institute of Standards and Technology (NIST). The spectral irradiance scale of GFSC’s FEL

lamp numbrt F269 (recalibrated by NIST in October 1992) was transferred to lamps belonging to the 9 participating laboratories; 1 set

of lamp trsansfer measurements (involving 4 of the lamps) was precise to within less that 1% and meets SeaWiFS goals, but a second

set (involving another 14 lamps) did not. The spectral radiance scale of the GSFC 40-inch integrating sphere source was transferred to

integrating sphere radiance sources belonging to four of the other laboratories. Reflectance plaques, used for irradiance-to-radiance

transfer by five of the laboratories, were compared but spectral bidirectional reflectance distribution functions (BRDFs) were not

determined quantitatively. Also reported here are results of similar comparisons (in October 1992) between the GSFC scales of

spectral irradiance and radiance and those used by the Hughes/Santa Barbara Research Center (SBRC) to calibrate and characterize the

SeaWiFS instruments. This first set intercalibration round-robin experiments was a valuable learning experience for all participants,

and led to several importnt procedural changes, which will be implemented in the second SIRREX, to be held at CHORS in June 1993.

National Aeronautics and Space Administration

Washington, D.C. 20546–0001 NASA TM–104566, Vol. 14

Laboratory for Hydrospheric Processes

Goddard Space Flight Center 93B00117

Greenbelt, Maryland 20771

6. AUTHOR(S)

 James L. Mueller

Series Editors: Stanford B. Hooker and Elaine R. Firestone

Report is available from the Center for AeroSpace Information (CASI),

7121 Standard Drive, Hanover, MD 21076–1320; (301)621-0390