Skip to main content

Full text of "Bio-Optical Measurement and Modeling of the California Current and Polar Oceans"

See other formats


Final Report 

Performance Period 8/18/97 - 1 1/30/00 



Bio-Optical measurement and modeling of the California 

Current and Polar Oceans 

B. Greg Mitchell, Principal Investigator 

Scripps Institution of Oceanography 

University of California San Diego 

LaJolla,CA 92093-0218 

Email: gmitchell@ucsd.edu 

Phone: (858)534-2687 

Contract number: NAS5-97130 



Table of Contents 

Overview 1 

Year End Technical Memorandum 2000 2 

Introduction 2 

Research Activities: Field methods and data 2 

Research Results 3 

Future Plans 4 

References 4 

Year End Technical Memorandum 1999 9 

Introduction 9 

Research Activities: Field methods and data 9 

Research Results 10 

Lwn match-ups 10 

Work plan for next period 1 1 

References 13 

Year End Technical Memorandum 1998 14 

Introduction 14 

Research Activities: Field methods and data 14 

Research Results 15 

Work plan for next period 16 

References 16 

Publications 19 

Conference Abstracts 20 



Overview 

This report summarizes our 3-year effort for our NASA SIMBIOS Contract: 

Bio-Optical measurement and modeling of the 

California Current and Polar Oceans 

NAS5-97130 

The principal goals of our research are to validate standard or experimental products through 
detailed bio-optical and biogeochemical measurements, and to combine ocean optical 
observations with advanced radiative transfer modeling to contribute to satellite vicarious 
radiometric calibration and advanced algorithm development. To achieve our goals requires 
continued efforts to execute complex field programs globally, as well as development of 
advanced ocean optical measurement protocols. We completed a comprehensive set of ocean 
optical observations in the California Current, Southern Ocean, Indian Ocean requiring a large 
commitment to instrument calibration, measurement protocols, data processing and data merger. 
We augmented separately funded projects of our own, as well as others, to acquire in situ data 
sets we have collected on various global cruises supported by separate grants or contracts. In 
collaboration with major oceanographic ship-based observation programs funded by various 
agencies (CalCOFI, US JGOFS, NOAA AMLR, INDOEX and Japan/East Sea) our SIMBIOS 
effort has resulted in data from diverse bio-optical provinces. For these global deployments we 
generate a high-quality, methodologically consistent, data set encompassing a wide-range of 
oceanic conditions. Global data collected in recent years have been integrated with our on-going 
CalCOFI database and have been used to evaluate SeaWiFS algorithms and to carry out 
validation studies. The combined database we have assembled now comprises more than 700 
stations and includes observations for the clearest oligotrophic waters, highly eutrophic blooms, 
red-tides and coastal case 2 conditions. The data has been used to validate water-leaving radiance 
estimated with SeaWiFS as well as bio-optical algorithms for chlorophyll pigments. The 
comprehensive data is utilized for development of experimental algorithms (e.g. high-low 
latitude pigment transition, phytoplankton absorption, and cDOM). During this period we 
completed 9 peer-reviewed publications in high quality journals, and presented aspects of our 
work at more than 10 scientific conferences. 



Year End Technical Memorandum 2000 

Bio-Optical measurement and modeling of the California Current and Polar Oceans 

B. Greg Mitchell, Principal Investigator 

Scripps Institution of Oceanography 

University of California San Diego 

LaJoIla.CA 92093-0218 

Email: gmitchell@ucsd.edu, Phone: (858)534-2687 

Contract number: NAS5-97130 



Introduction 

This SIMBIOS project contract supports in situ ocean optical observations in the California 
Current, Southern Ocean, Indian Ocean as well as merger of other in situ data sets we have 
collected on various global cruises supported by separate grants or contracts. The principal goals 
of our research are to validate standard or experimental products through detailed bio-optical and 
biogeochemical measurements, and to combine ocean optical observations with advanced 
radiative transfer modeling to contribute to satellite vicarious radiometric calibration and 
advanced algorithm development. 

In collaboration with major oceanographic ship-based observation programs funded by 
various agencies (CalCOFI, US JGOFS, NOAA AMLR, INDOEX and Japan/East Sea) our 
SIMBIOS effort has resulted in data from diverse bio-optical provinces. For these global 
deployments we generate a high-quality, methodologically consistent, data set encompassing a 
wide-range of oceanic conditions. Global data collected in recent years have been integrated 
with our on-going CalCOFI database and have been used to evaluate SeaWiFS algorithms and to 
carry out validation studies. The combined database we have assembled now comprises more 
than 700 stations and includes observations for the clearest oligotrophic waters, highly eutrophic 
blooms, red-tides and coastal case 2 conditions. The data has been used to validate water-leaving 
radiance estimated with SeaWiFS as well as bio-optical algorithms for chlorophyll pigments. 
The comprehensive data is utilized for development of experimental algorithms (e.g. high-low 
latitude pigment transition, phytoplankton absorption, and cDOM). 

Research Activities: Field methods and data 

A key element of our program includes on-going deployment on CalCOFI cruises to the 
California Current System (CCS) for which we have a 7-year time-series. This region 
experiences a large dynamic range of coastal and open ocean trophic structure and has 
experienced strong interannual forcing associated with the El Nino - La Nina cycle from 1997- 
2000 (Kahru and Mitchell, 2000; Kahru and Mitchell, in press). CalCOFI data provides an 
excellent reference for evaluating our other global data sets. 

During the third year of our contract, we participated in 3 CalCOFI cruises, one cruise in 
collaboration with NOAA AMLR to the Southern Ocean, three cruises in East Asian marginal 
seas, and one cruise off the west coast of Mexico with colleagues from CICESE in Ensenada, 
Mexico. The global distribution of our present data set is shown in Figure 1. On all cruises, an 
integrated underwater profiling system was used to collect optical data and to characterize the 
water column. The system included an underwater radiometer (Biospherical Instruments MER- 
2040 or MER-2048) measuring depth, downwelling spectral irradiance (Ed) and upwelling 
radiance (L u ) in 13 spectral bands. A MER-2041 deck-mounted reference radiometer 
(Biospherical Instruments Inc) provided simultaneous measurements of above-surface 
downwelling irradiance. Details of the profiling procedures, characterization and calibration of 



the radiometers, data processing and quality control are described in Mitchell and Kahru (1998). 
The underwater radiometer was also interfaced with 25 cm transmissometers (SeaTech or 
WetLabs), a fluorometer, and SeaBird conductivity and temperature probes. When available, 
additional instrumentation integrated onto the profiling package included AC9 absorption and 
attenuation meters (WetLabs Inc.), and a Hydroscat-6 backscattering meter (HobiLabs). 

In conjunction with in situ optical measurements, discrete water samples were collected from 
a CTD-Rosette immediately before or after each profile for additional optical and 
biogeochemical analyses. Pigment concentrations were determined fluorometrically and with 
HPLC. Spectral absorption coefficients (300-800 nm) of particulate material were estimated by 
scanning particles concentrated onto Whatman GF/F filters (Mitchell 1990) in a dual-beam 
spectrophotometer (Varian Cary 1). Absorption of soluble material was measured in 10 cm 
cuvettes after filtering seawater samples through 0.2 urn pore size polycarbonate filters. 
Absorption methods are described in more detail in Mitchell et al. (2000). We have also been 
collecting detailed measurements of other optical and phytoplankton properties including 
phycoerythrin pigment, size distribution using flow cytometry and a Coulter Multisizer, 
photosynthesis, and particulate organic matter (carbon and nitrogen). 

Research Results 

Our normalized water leaving radiances (L wn ) at SeaWiFS bands for the global data set are 
plotted against surface chl-a in Figure 2. Our original CalCOFI data represented approximately 
30% of the data used by O'Reilly et al. (1998) for development of the SeaWiFS OC2v2 and 
approximately 25% of the updated OC 4 algorithm (O'Reilly et al., 2000). Previously we used 
SeaDAS v3.0 to evaluate OC2v2 estimates of chl-a compared to a CalCOFI-specific regional 
algorithm (CAL-P6) using match-ups collected during CalCOFI cruises (Kahru and Mitchell, 
1999). Here we compare retrievals for SeaDAS v4.0, which has updated atmospheric and bio- 
optical algorithms (Figures 3 and 4). Whereas OC2v2 in SeaDAS 3.0 tended to overestimate in 
situ chl-a at high values and underestimate at low values (Kahru and Mitchell, 1999), we find 
that OC4 in SeaDAS 4.0 tends to underestimate chl-a at high values, but is very good at low 
chlorophyll (Figure 3). Even after processing with the new atmospheric algorithm that 
eliminates the assumption that L wn in the near infrared is zero (Siegel et al., 2000), SeaDAS 
v4.0 still has significant underestimates of L wn at 412 for all our match-ups (chl-a range 0.1- 
10.0) with worse performance at high chl-a (Figure 4). Even L wn 443 tends to be 
underestimated over most the range, but not as severely as L wn 412. Continued effort is still 
required to improve the accuracy of L wn if we are to be able to apply multi-wavelength bio- 
optical retrieval algorithms that require accurate estimates of L wn at 412 and 443 (e.g. Garver 
and Siegel, 1997; Carder et al., 1999). 

For the Southern Ocean data (red crosses in Figure 2), there is a strong deviation from our 
other global data sets, and much greater variance in the scatter plots. This region has been 
shown to have bio-optical algorithms that are different than low latitude regions such as 
CalCOFI (Mitchell and Holm-Hansen, 1991; Mitchell, 1992). The large variance in the L w n- 
chl-a scatter plots may be attributable in part to very different community types (e.g. prymnesio- 
phytes, diatoms, cryptophytes as discussed in Arrigo et al., 1998). Our results underscore the 
need for more data to serve as a basis for regional algorithms to improve estimates of chl-a from 
ocean color remote sensing. Regional algorithms will require procedures to allow transition 
from low latitude to high latitude without introducing errors at the lower latitudes. More data 
and advanced models are required to resolve issues regarding Southern Ocean bio-optical 
algorithms, and the causes of observed differentiation within the region as well as differences 
between the Southern Ocean and lower latitudes. For a better understanding, it is essential to 
determine not only reflectance and chlorophyll, but also inherent optical properties including 
absorption and backscattering as reported by Reynolds et al. (In press). Generally, there are few 
observations in the Southern Ocean, and even fewer with detailed observations including 
inherent optical properties. We lack combined pigment and optical observations in the extremely 
low chlorophyll regions that can be observed in the SeaWiFS images for the southern Pacific 
Ocean sector west of the Drake Passage, and the southern Indian Ocean sector west of Kerguelan 



Island. These two regions represent very low satellite-derived chlorophyll, which never exceed 
values of 0.2 mg chl-a m . 

A significant issue that has arisen within the SIMBIOS community is the fidelity of chl-a 
estimates using either HPLC or fluorometric methods. We have completed analysis and quality 
control for more than 800 samples taken from the same water sampling bottles during CalCOFI 
cruises (Figure 5). The fluorometric method is described in Venrick, et al., (1984) and the HPLC 
method is described in Goericke and Repeta (1993). We find that there is excellent overall 
agreement with a nearly 1:1 relationship, however individual samples routinely differ by up 
to30-40%. For the JGOFS Southern Ocean Polar Front cruises, the discrepancies were much 
larger and are still unresolved. A high priority for SIMBIOS should be to ensure the highest 
possible quality of pigment estimates, which will require consistent implementation of rigorous 
protocols. As a contribution to this effort, we participated in the SIMBIOS pigment round robin 
experiment during the past year. 

Future Plans 

With renewal of our SIMBIOS contract, we will continue our approach of acquiring detailed, 
high quality data sets at the global scale. We will continue to participate in CalCOFI cruises. In 
2001 we will also participate in the NOAA AMLR cruise to the Southern Ocean and the NOAA 
ACE-Asia cruise to the western sub-tropical Pacific, East China Sea, and Yellow Sea. A detailed 
set of spectral reflectance, absorption, backscattering, pigment, and particle size structure will be 
determined on most cruises. A new free-fall radiometer will be acquired with 19 channels (310- 
700 nm) for determining both downwelling and upwelling irradiance, and upwelling radiance for 
all spectral bands. We have shown that measuring these three radiometric geometries with our 
MER 2048 allowed us to retrieve backscatter and absorption coefficients (Stramska et al., 2000). 
We will continue our modeling efforts to improve our understanding of regional bio-optical 
properties and their relationship to biogeochemical parameters (e.g. Reynolds et al, in press; 
Loisel et al., submitted). Our goal is to develop appropriate regional parameterizations for semi- 
analytical inversion models for the retrieval of inherent optical properties as well as 
biogeochemical properties besides chl-a in addition to continuing our validation work for 
standard ocean color satellite algorithms. 

References 

Arrigo, K.R., D.H. Robinson, D.L. Worthen, B. Schieber and M.P. Lizotte (1998) Bio-optical 

properties of the southwestern Ross Sea. Journal of Geophysical Research. 103(00): 

21,683-21,695 
Carder, K.L., F.R. Chen, Z.P. Lee and S.K. Hawes (1999) Semianalytic moderate-resolution 

imaging spectrometer algorithms for chlorophyll a and absorption with bio-optical domains 

based on nitrate-depletion temperatures. Journal of Geophysical Research. 104(C3): 5,403- 

5,421 
Garver, S.A. and D.A. Siegel (1997) Inherent Optical Property Inversion of Ocean Color Spectra 

and its Biogeochemical Interpretation: 1. Time series from the Sargasso Sea. Journal of 

Geophysical Research. 102(C8): 18,607-18,625 
Goericke, R. and D.J. Repeta (1993) Chlorophylls a and b and di vinyl chlorophylls a and b in the 

open subtropical North Atlantic Ocean. Marine Ecology Progress Series. 101: 307-313 
Kahru, M. and B.G. Mitchell (1999) Empirical chlorophyll algorithm and preliminary SeaWiFS 

validation for the California Current. International Journal of Remote Sensing. 20(17): 

3,423-3,430 
Kahru, M. and B.G. Mitchell (2000) Influence of the 1997-98 El Nino on the surface chlorophyll 

in the California Current. Geophysical Research Letters. 27(18): 2,937-2,940 



Kahru, M. and B.G. Mitchell (2000) Seasonal and non-seasonal variability of satellite-derived 

chlorophyll and CDOM concentration in the California Current. Journal of Geophysical 

Research. (In Press) 
Loisel, H. and D. Stramski (2000) Estimation of the inherent optical properties of natural waters 

from the irradiance attenuation coefficient and reflectance in the presence of Raman 

scattering. Applied Optics. 39(18): 3,001-3,011 
Mitchell, B.G. (1990) Algorithms for determining the absorption coefficient of aquatic 

particulates using the quantitative filter technique (QFT). In: Spinrad, R., ed., Ocean Optics 

X, Bellingham, Washington, SPIE, pp. 137-148 
Mitchell, B.G. (1992) Predictive bio-optical relationships for polar oceans and marginal ice 

zones. Journal of Marine Systems. 3: 91-105 
Mitchell, B.G. and M. Kahru (1998) Algorithms for SeaWiFS standard products developed with 

the CalCOFI bio-optical data set. Cal.Coop.Ocean.Fish.Invest.R. 39: 133-147 
Mitchell, B.G. and O. Holm-Hansen (1991) Bio-optical properties of Antarctic Peninsula waters: 

Differentiation from temperate ocean models. Deep-Sea Research I. 38(8/9): 1,009-1,028 
Mitchell, B.G., A. Bricaud, K.L. Carder, J.S. Cleveland, G.M. Ferrari, R. Gould, M. Kahru, et al. 

(2000) Determination of spectral absorption coefficients of particles, dissolved material and 

phytoplankton for discrete water samples. In: NASA, Ocean Optics Protocols for Satellite 

Ocean Color Sensor Validation. 
O'Reilly, J.E., S. Maritorena, B.G. Mitchell, D.A. Siegel, K.L. Carder, S.A. Garver, M. Kahru 

and C. McClain (1998) Ocean color chlorophyll algorithms for SeaWiFS. Journal of 

Geophysical Research. 103(C11): 24,937-24,953 
O'Reilly, J.E., S. Maritorena, D.A. Siegel, M.C. O'Brien, D.A. Toole, B.G. Mitchell, M. Kahru, 

et al. (2000) Ocean color chlorophyll a algorithms for SeaWiFS, OC2 and OC4: Version 4. 

In: NASA, SeaWiFS Postlaunch Calibration and Validation Analyses. 
Reynolds, R.A., D. Stramski and B.G. Mitchell (2000) A chlorophyll-dependent semi analytical 

reflectance model from derived from field measurements of absorption and back scattering 

coefficients within the Southern Ocean. Journal of Geophysical Research. (In Press) 
Siegel, D.A., M. Wang, S. Maritorena and W. Robinson (2000) Atmospheric correction of 

satellite ocean color imagery: The black pixel assumption. Appl.Opt. 39(21): 3,582-3,591 
Stramska, M, D. Stramski, B.G. Mitchell and CD. Mobley (2000) Estimation of the absorption 

and backscattering coefficients from in-water radiometric measurements. Limnology and 

Oceanography. 45(3): 628-641 
Venrick, E.L. and T.L. Hayward (1984) Determining chlorophyll on the 1984 CalCOFI surveys. 

CalCOFI Reports. XXV: 74-79 




45 90 13! 180 -135 -90 -45 

Figure 1. Distribution of in situ optical stations available for algorithm development. 



10.0 



S 1.0 



412 nm 



o N =[-0.227,-0.279, 0.067,-0 057]. 
N - 457, RMS1 - 0.078 
+ 




10.00 



1.00 



10.10 



0.01 



^ 443 nm 

H =[-0.'l 95,-0.293, 0.057,-0.024Jf 
N = 457, RMS1 = 0.074 




0.1 1— 
0.01 0.10 1.00 10.00 100.00 0.01 0.10 1.00 10.00 100. 

490 nm ._ _ 510 nm 



10.0 



o 



(J N =[-0. 144,-0.211, 0.014, 0.005] 
N - 457, RMS1 = 0.070 




10.0 



o 

m 



1.0 



0.1 



o„=[*-0.200,-0.086,-0.016, 0.014]: 
N = 461, RMS1 = 0.072 




XX 



0.1 
0.01 0.10 1.00 10.00 100.00 0.01 0.10 1.00 10.00 100. 

555 nm 665 nm 



10.0 



o K =[-0.354, 0.161, 0.002, 0.014] 
N = 462, RMS1 = 0.083 



IT) 

m 
£.1.0 



0.1 




1.000 



t^O-100^ 
-J0.010 



o M -[-1.572, 0.612, 0.077.-0.042] 
N - 459, RMS1 = 0.1 61 




0.001 

0.01 0.10 1.00 10.00 100.00 0.01 0.10 1.00 10.00 100. 
Chl-a, mg m Chl-a, mg m~ 3 

Figure 2. Normalized water leaving radiance at SeaWiFS bands plotted against 

chlorophyll for our global data set. Blue = CalCOFI, Green = Japan/East Sea; 

Black = INDOEX; Red = JGOFS Southern Ocean. 



10.0 



SZ 



on 1.0 
o 



0.1 



x' SeaDAS: r*=' 0.908 RMSE= 6.186 T N= 40 
CAL-P6: r*= 0.914 RMSE= 0.160 N= 40' 



V.--6 o 



O 



<>.■■ 

.*' 
X 

x£ 



OC4v4 : SeaWiFS CHLA= - 
0.124+ 0.779 in situ CHLA, 
CAL-P6: SeaWiFS CHLA= 
0.051+ 0.986 in situ CHLA 



0.1 1.0 10.0 

In situ Chi a, mg m" 3 

Figure 3. Chlorophyll-a estimates derived using SeaWiFS SeaDAS version 4.0 

compared to in situ estimates of chlorophyll-a for NASA's global processing 

version 3.0 OC4 algorithm, and our CAL-P6 algorithm. 




443 nm 




1.0 



10.0 



10.0 


510 nm 7' 


o 




* — 




if> 




c 




$ 




_i 




(n10 


x»ifc> 


u. 


Jm 


* 


W* 


o 




(D 




01 




0.1 





1.0 



10.0 



10.0 


555 nm 


m 
m 

c 

s 




(ol-O 




u. 


V'* 


o 

ID 


,# 


0.1 





1.000 


665 nm 


0.100 


#''' : 


0.010 


..•'X 


0.001 





0.1 1.0 10.0 0.001 0.010 0.100 1.000 

In Situ Lwn555 In Situ Lwn555 

Figure 4. Normalized water leaving radiance derived from 

SeaWiFS SeaDAS version 4.0 processing compared to in situ 

measurements at the 6 visible bands of SeaWiFS. 




0.01 0.10 1.00 10.00 

Chla Fluor, mg m~ 3 

Figure 5. CalCOFI HPLC total chlorophyll-a (mono-vinyl and di-vinyl chl-a, 

and closely related derivates) plotted against fluorometric chlorophyll-a. 

The 1 : 1 and regression fits are indicated by the solid and dashed lines, respectively. 



Year End Technical Memorandum 1999 

Bio-Optical measurement and modeling of the California Current and Polar Oceans 

B. Greg Mitchell, Principal Investigator 

Scripps Institution of Oceanography 

University of California San Diego 

LaJolla,CA 92093-0218 

Email: gmitchell@ucsd.edu, Phone: (858) 534-2687 

Contract number: NAS5-97130 



Introduction 

This SIMBIOS project contract supports in situ oceanic optical observations in the 
California Current and Southern Ocean. The principal objectives of this research are to validate 
standard or experimental products through detailed bio-optical and biogeochemical 
measurements, and to combine ocean optical observations with advanced radiative transfer 
modeling to contribute to satellite vicarious radiometric calibration and algorithm development. 

In collaboration with the CalCOFI and US JGOFS programs, our sampling efforts have 
been focused primarily on the California Current and Antarctic waters, with the purpose of 
generating a high-quality, methodologically consistent data set encompassing a wide-range of 
oceanic conditions. In the past year we have collaborated with other SIMBIOS Pis to collect 
data in the Atlantic and Indian Oceans and we are merging our ONR-sponsored Sea of Japan 
data set to the SIMBIOS database. The combined data base we have assembled includes stations 
which cover the clearest oligotrophic waters to highly eutrophic blooms and red-tides, and 
provides a coherent set of observations to validate bio-optical algorithms for pigments, inherent 
optical properties and primary production. This unique and comprehensive data is utilized for 
development of experimental algorithms (e.g. high-low latitude pigment transition, 
phytoplankton absorption, photosynthesis, and cDOM). 

Research Activities: Field methods and data 

The Southern California Bight region, from San Diego to just north of Point Conception, 
has one of the longest, most comprehensive time-series of marine observations; the California 
Cooperative Oceanic Fisheries Investigation (CalCOFI). This region experiences a large 
dynamic range of coastal and open ocean trophic structure, and has been extensively studied with 
respect to its regional optical properties in an effort to develop regional ocean color algorithms 
(e.g. Smith and Baker 1978, Mitchell and Kiefer 1988, Sosik and Mitchell 1995). During the 
second year of our contract, we participated in 3 CalCOFI cruises in the California Current 
region as part of the CalCOFI program. 

The Southern Ocean is a large, remote region, which plays a major role in global 
biogeochemical cycling. Despite evidence that bio-optical relationships in these waters can 
diverge significantly from lower-latitude waters (e.g. Mitchell and Holm-Hansen 1991), 
Antarctic waters have been under-represented in the databases (e.g. SeaBAM) used to formulate 
and test modern ocean color algorithms. During the past year, we have analyzed detailed 
observations collected in year 1 of our SIMBIOS project and have published novel algorithms 
for retrieval of particulate organic carbon (Stramski et al, 1999) and have submitted a detailed 
optical model for Southern Ocean waters (Reynolds et al., submitted). 

On all cruises, an integrated underwater profiling system was used to collect optical data 
and to characterize the water column. The system included an underwater radiometer 



(Biospherical Instruments MER-2040 or MER-2048) measuring depth, downwelling spectral 
irradiance (E d ) and upwelling radiance (L„) in 13 spectral bands. A MER-2041 deck-mounted 
reference radiometer (Biospherical Instruments Inc) provided simultaneous measurements of 
above-surface downwelling irradiance. Details of the profiling procedure, characterization and 
calibration of the radiometers, data processing and quality control are described in Mitchell and 
Kahru (1998). The underwater radiometer was also interfaced with 25 cm transmissometers 
(SeaTech or WetLabs), a fluorometer, and SeaBird conductivity and temperature probes. When 
available, additional instrumentation integrated onto the profiling package included AC9 
absorption and attenuation meters (WetLabs Inc.), and a Hydroscat-6 backscattering meter 
(HobiLabs). 

In conjunction with in situ optical measurements, discrete water samples were collected 
from a CTD-Rosette immediately before or after each profile for additional optical and 
biogeochemical analyses. Pigment concentrations were determined fluorometrically and with 
HPLC. Spectral absorption coefficients (300-800 nm) of particulate material were estimated by 
scanning particles concentrated onto Whatman GF/F (Mitchell 1990) in a dual-beam 
spectrophotometer (Varian Cary 1). Absorption of soluble material was measured in 10 cm 
cuvettes after filtering seawater samples through 0.2 urn pore size polycarbonate filters. We 
have also been collecting detailed measurements of other optical and phytoplankton properties 
including phycoerythrin pigment, size distribution using a Coulter Multisizer, photosynthesis, 
and particulate organic matter (carbon and nitrogen). 

Research Results 

A. Chi algorithms - CalCOFI data represents approximately 30% of the data used by 
O'Reilly et al. (1998) for development of the operational SeaWiFS Ocean Color 2 version 2 
algorithm (OC2v2). We have evaluated this algorithm compared to a CalCOFI-specific regional 
algorithm (CAL-P6) using match-ups collected during CalCOFI cruises (Kahru and Mitchell, in 
press). At this time the atmospheric correction or calibration errors in the retrieval of Lwn create 
larger errors in chl-a retrieval than differences between OC2v2 and CAL-P6. For the Southern 
Ocean, however, there is a significant bias in the OC2v2 algorithm, which warrants a focused 
effort - at low chl-a OC2v2 underestimates chl-a, and it overestimates at high chl-a. Figure 1 
illustrates the Lwn(490)/ Lwn(555) ratio plotted against chl-a for our combined RACER and 
JGOFS Southern Ocean data sets. This region has been shown to have bio-optical algorithms 
that are different than low latitude regions such as CalCOFI (Mitchell and Holm-Hansen, 1991; 
Mitchell, 1992; Arrigo et al., 1998). Our results underscore the eventual need for specific 
regional algorithms to obtain more accurate estimates of chl-a and primary production from 
ocean color remote sensing. Regional algorithms will require procedures to allow transition 
from low latitude to high latitude without introducing errors at the lower latitudes. 
Unfortunately, there is relatively little data in the polar front region; we have less than 20 
observations from JGOFS, and there are no reports of other data in this region. Also lacking in 
the polar Southern Ocean data sets are combined pigment and optical observations in the 
extremely low chlorophyll regions that can be observed in the SeaWiFS imager for the southern 
Pacific Ocean sector west of the Drake Passage, and the southern Indian Ocean sector west of 
Kerguelan Island. These two regions represent very low satellite-derived chlorophyll which 
never exceed values of 0.2 mg chl-a m . 

L WN match-ups 

In situ instrument intercomparison - During INDOEX, we deployed our Biospherical 
Instruments MER-2048 and the SMBIOS pool Satlantic SPMR radiometer at the same stations. 
The MER-2048 was deployed from the ship's stern A-frame, with potential contamination by 
ship's shadow, and the SPMR was deployed in free-fall mode, which would have no ship shadow 
artifacts. Figure 2A is a scatter plot for SeaWiFS channels of L WN derived from the two 
systems. Overall, the correspondence is excellent with no bias relative to the 1:1 relationship. 
Figure 2B is a plot of MER-2048 and SPMR derived spectral L WN compared to SeaWiFS 



10 



derived L^ N for a clear sky match-up. The issues of poor L WN retrieval reviewed by Kahru and 
Mitchell (in press) and Mitchell and Flatau, 1998 are evident. 

Evaluation of atmospheric correction schemes - The SIMBIOS Project has defined a 
need to evaluate the atmospheric correction algorithms for SeaWiFS, and convened a workshop 
which led to the proposal of 6 separate atmospheric correction schemes. We evaluated all 6 
schemes with our match-up data (25 match-ups, 17 of which are from CalCOFI). Evaluation of 
satellite-retrieved normalized water-leaving radiances (L WN ) was done by comparing SeaWiFS 
HRPT images with in situ data collected concurrently (± 4 hours). HRPT data were processed to 
Lwn using SeaDAS 3.3 software (Fu et al. 1998; update 004 released 9/1/99). The level 2 
generation atmospheric correction module of this version of SeaDAS was modified by the 
SIMBIOS project with 6 candidate codes to be evaluated. Satellite values were derived as 
averages over 3x3 pixel areas centered at the in situ measurement. In summary, these 
comparisons reveal under-estimation of the SeaWiFS-retrieved L WN using the "baseline" 
algorithm compared to in situ measurements; the discrepancies were larger for pooled data 
greater than 1 mg chl m" 3 . An example of the SeaWiFS retrieved problem is illustrated in Figure 
2B. The differences were generally smallest in the 555 nm band, and largest at shorter 
wavelengths. Some of the proposed atmospheric correction revisions improved the 
underestimation, but none of the candidate algorithms was capable of retrieving accurate L WN 
for SeaWiFS bands 1 and 2. Part of the problem at short wavelengths may be attributed to 
calibration errors rather than issues related to the zero water leaving radiance assumptions or 
aerosol models of the base line processing. 

Work plan for next period 

Our participation in the quarterly CalCOFI cruises in the California Current will continue 
throughout the next period. We also hope to carry out at least 1 cruise to the Southern Ocean as 
well as additional cruises in Korean waters. We will continue data processing from previous 
cruises, including CalCOFI, JGOFS, INDOEX and Japan/East Sea. Specific attention will be 
placed on developing routine processing schemes for our AC9 and Hydroscat data. We will 
continue our modeling efforts to improve our understanding of regional bio-optical properties 
and their relationship to biogeochemical parameters (e.g. Reynolds et al, submitted). Our goal is 
to develop appropriate regional parameterizations for semi-analytical inversion models for the 
retrieval of inherent optical properties as well as biogeochemical properties besides chl-a from 
satellite ocean color data. 



II 



u 

"2 
o 



-1 



-2 





1 1 1 1 
\OC2v2 


'■ 1 ' • 


1 1 


• 


I ,J T"""T 


. 


7 SPGANT 


5VVw 

^@V 

a> 










- 


- 








*pV 


H. M92 


- 


: r 2 = 0.844 










■ 


: RMSE1 = 


0.169 










- 


\ N = 181 

— 1 — * 1 1 


1 , , . 


. 1 . , 


> > 




1 1 1 


• 



■1.0 -0.5 0.0 0.5 

Log 10 (L wn 490/L wn 555) 



1.0 



Figure 1. The relationship between log transformed values of L WN (490)/L WN (555) versus 
chlorophyll a for Southern Ocean data. Curves represent the SeaWiFS OC2v2, Mitchell 1992, 
and our latest Southern Ocean algorithm SPGANT. 



2.50 



2.00 



c 



1.50 



1.00 



0.50 



0.00 




0.00 



0.50 



1.00 1.50 

SPMR-Lwn 



2.00 



1.80 
1.60 
1.40 
1.20 
1.00 - 
0.80 - 
0.60 - 
0.40 
0.20 • 
0.00 



2.50 



350 400 



Hi — Lwn1-412 

-*- - rYER2048/2041-Lwn2 

■x ■• snip 

- SeaWiFS S1999071075812.U 




450 500 550 

Wavelength, nm 



600 650 700 



Figure 2. A. Scatter plot of L W n estimates for several stations during INDOEX derived from 
data using our Biospherical Instruments MER 2048 and the SBVIBIOS pool Satlantic SPMR. 
B. Spectral plot of Ly^ derived from SeaWiFS and from two different in water profilers. 



12 



References 

Arrigo, K.R., D.H. Robinson, D.L. Worthen, B. Schieber and M.P. Lizotte (1998) Bio-optical 

properties of the southwestern Ross Sea. Journal of Geophysical Research. 103(00): 

21,683-21,695 
Fu, G., K. Settle and C.R. McClain (1998) SeaDAS: The SeaWiFS Data Analysis System. 

Proceedings of the Fourth Pacific Ocean Remote Sensing Conference, Qingdao, China73- 

77, July 28, 1998 
Kahru, M. and B.G. Mitchell (1999) Empirical chlorophyll algorithm and preliminary SeaWiFS 

validation for the California Current. International Journal of Remote Sensing. (In Press) 
Mitchell, B.G. (1990) Algorithms for determining the absorption coefficient of aquatic 

particulates using the quantitative filter technique (QFT). In: Ocean Optics X, Spinrad, 

R.,ed. 137-148 
Mitchell, B.G. and O. Holm-Hansen (1991) Bio-optical properties of Antarctic Peninsula waters: 

Differentiation from temperate ocean models. Deep-Sea Research I. 38(8/9): 1,009-1,028 
Mitchell, B.G. (1992) Predictive bio-optical relationships for polar oceans and marginal ice 

zones. Journal of Marine Systems. 3: 91-105 
Mitchell, B.G. and M. Kahru (1998) Algorithms for SeaWiFS standard products developed with 

the CalCOFI bio-optical data set. Cal.Coop.Ocean.Fish.Invest.R. 39: 133-147 
Mitchell, B.G. and D.A. Kiefer (1988) Variability in pigment specific particulate fluorescence 

and absorption spectra in the northeastern Pacific Ocean. Deep-Sea Research I. 35(5): 

665-689 
Mitchell, B.G. and P.J. Flatau (1998) Bio-Optical measurement and modeling of the California 

Current and Polar Oceans. In: SIMBIOS Year End Technical Memorandum, pp. 10 

[http://simbios.gsfc.nasa.gov/Documents/yrend/97 1 30_yr98.pdf] 
O'Reilly, J.E., S. Maritorena, B.G. Mitchell, D.A. Siegel, K.L. Carder, S.A. Garver, M. Kahru 

and C. McClain (1998) Ocean color chlorophyll algorithms for SeaWiFS. Journal of 

Geophysical Research. 103(01): 24,937-24,953 
Reynolds, R.A., D. Stramski and B.G. Mitchell (1999) A chlorophyll-dependent semi analytical 

reflectance model from derived from field measurements of absorption and back 

scattering coefficients within the Southern Ocean. Journal of Geophysical Research. (In 

Press) 
Smith, R.C. and K.S. Baker (1978) The bio-optical state of ocean waters and remote sensing. 

Limnology and Oceanography. 23: 247-259 
Sosik, H.M. and B.G. Mitchell (1995) Light absorption by phytoplankton, photosynthetic 

pigments, and detritus in the California Current System. Deep-Sea Research I. 42(10): 

1,717-1,748 
Stramski, D., R.A. Reynolds, M. Kahru and B.G. Mitchell (1999) Estimation of particulate 

organic carbon in the ocean from satellite remote sensing. Science. 285: 239-242 



13 



Year End Technical Memorandum 1998 

Bio-Optical measurement and modeling of the California Current and Polar Oceans 

B. Greg Mitchell, Principal Investigator 

Scripps Institution of Oceanography 

University of California San Diego 

LaJolla,CA 92093-0218 

Email: gmitchell@ucsd.edu, Phone: (858)534-2687 

Contract number: NAS5-97130 



Introduction 

This SIMBIOS project contract supports in situ oceanic optical observations in the 
California Current and Southern Ocean. The principal objectives of this research are to validate 
standard or experimental products through detailed bio-optical and biogeochemical 
measurements, and to combine ocean optical observations with advanced radiative transfer 
modeling to contribute to satellite vicarious radiometric calibration and algorithm development. 

Our sampling efforts have been directed towards obtaining measurements in both the 
California Current and Antarctic polar waters, with the purpose of generating a high-quality, 
methodologically consistent data set encompassing a wide-range of oceanic conditions. The 
combined data base includes stations which cover the clearest oligotrophic waters to highly 
eutrophic blooms and red-tides, and provides a coherent set of observations to validate bio- 
optical algorithms for pigments and primary production. This unique and comprehensive data is 
utilized for development of experimental algorithms (e.g. high-low latitude pigment transition; 
phytoplankton absorption, photosynthesis, cDOM. 

Research Activities: Field methods and data 

The Southern California Bight region, from San Diego to just north of Point Conception, 
has one of the longest, most comprehensive time-series of marine observations; the California 
Cooperative Oceanic Fisheries Investigation (CalCOFI). This region experiences a large 
dynamic range of coastal and open ocean trophic structure, and has been extensively studied with 
respect to its regional optical properties in an effort to develop regional ocean color algorithms 
(e.g. Smith and Baker 1978, Mitchell and Kiefer 1988, Sosik and Mitchell 1995). During the 
first year of our contract, we participated in 4 quarterly cruises in the California Current region 
as part of the CalCOFI program. 

The Southern Ocean is a large, remote region which plays a major role in global 
biogeochemical cycling. Despite evidence that bio-optical relationships in these waters can 
diverge significantly from lower-latitude waters (e.g. Mitchell and Holm-Hansen 1991), 
Antarctic waters have not been represented in the databases (e.g. SeaBAM) used to formulate 
and test modern ocean color algorithms. During the past year, we participated in 3 cruises to the 
Southern Ocean as part of the US JGOFS program. One cruise was located within the Ross Sea 
Polyna during the annual spring phytoplankton bloom, with 2 subsequent cruises covering the 
region of Antarctic Polar Front Zone along 170° W. 



14 



On all cruises, an integrated underwater profiling system was used to collect optical data 
and to characterize the water column. The system included an underwater radiometer 
(Biospherical Instruments MER-2040 or MER-2048) measuring depth, down welling spectral 
irradiance (E d ) and upwelling radiance (L„) in 13 spectral bands. A MER-2041 deck-mounted 
reference radiometer (Biospherical Instruments Inc) provided simultaneous measurements of 
above-surface downwelling irradiance. Details of the profiling procedure, characterization and 
calibration of the radiometers, data processing and quality control are described in Mitchell and 
Kahru (1998). The underwater radiometer was also interfaced with 25 cm transmissometers 
(SeaTech or WetLabs), a fluorometer, and SeaBird conductivity and temperature probes. When 
available, additional instrumentation integrated onto the profiling package included AC9 
absorption and attenuation meters (Wetlabs Inc.), and a Hydroscat-6 backscattering meter 
(HobiLabs). 

In conjuction with in situ optical measurements, discrete water samples were collected 
from a CTD-Rosette immediately before or after each profile for additional optical and 
biogeochemical analyses. Pigment concentrations were determined flurometrically and with 
HPLC. Spectral absorption coefficients (300-800 nm) of particulate material were estimated by 
scanning particles concentrated onto Whatman GF/F (Mitchell 1990) in a dual-beam 
spectrophotometer (Varian Cary 1). Absorption of soluble material was measured in 10cm 
cuvettes after filtering seawater samples through 0.2 um pore size polycarbonate filters. 

Research Results 

Lwn matchups- Validation of satellite-retrieved normalized water-leaving radiances 
(Lwn) was done by comparing SeaWiFS images with in situ data collected concurrently (± 4 
hours). Satellite data'received at the Monterey Bay Research Institute, the University of 
California Santa Barbara (CalCOFI region) and McMurdo Station, Antarctica (Southern Ocean 
region) were processed to Lwn using SeaDAS 3.2 software (Fu et al. 1998). A total of 16 
matching sets of Lwn were found between 2-Oct-1997 and 21-Apr-1998 for the CalCOFI region. 
Because of persistent cloud cover in the Southern Ocean, only 3 matchups were possible in the 
Ross Sea region (all on 1 -Dec- 1997). Satellite values were derived as averages over 3x3 pixel 
areas centered at the in situ measurement. 

In both regions, these comparisons reveal significant under-estimation of the SeaWiFS- 
retrieved Lwn compared to in situ measurements (Figure 1). The differences were generally 
smallest in the 555 nm band, and largest at shorter wavelengths. The magnitude of under- 
estimation in the shorter wavelength bands increases at high Chi concentration. 

Chi algorithms- O'Reilly et al. (1998) describe the Ocean Color 2 (OC2) chlorophyll 
algorithm that is used by NASA in the operational processing of SeaWiFS data (Fu et al. 1998). 
This algorithm uses the ratio of remote sensing reflectances (R re ) at 490 and 555 nm to estimate 
chlorophyll a concentration, with the coefficients derived by a statistical fit to a data set of 919 
bio-optical measurements comprising the SeaBAM data set. More recently (August 1998), 
NASA announced a revised version of the OC2 (OC2-v2) which was intended to reduce the 
drastic over-estimation of Chi in high biomass waters produced by the original OC2 algorithm. 

Figure 2 compares the performance of the OC2-v2 algorithm with our present data base 
of measurements from CalCOFI and the Southern Ocean. When applied to the CalCOFI data, 
this algorithm overestimates chl a at very high chl a and underestimates elsewhere (with the 
exception of the extreme low chl a). A similar pattern is seen with the Southern Ocean data, 
although in general the degree of underestimation is greater and the transition to overestimation 



15 



occurs at lower Chi. These results underscore the eventual need for specific regional empirical 
algorithms to obtain more accuate estimates of Chi and primary production from ocean color 
remote sensing. We have recently developed an improved empirical chlorophyll algorithm for 
the California Current (CAL-P6), which utilizes a sixth order polynomial of the ratio of L WN at 
490 and 555nm (Kahru and Mitchell, submitted). 

Work plan for next period 

Our participation in the quarterly CalCOFI cruises in the California Current will continue 
throughout the next period. We are also initiating field programs in the Indian Ocean (INDOEX) 
and the Sea of Japan (JES) to increase the regional scope of our data base. 

Modeling efforts include the pursuit of regional bio-optical algorithms for in water 
optical properties and their relationship to biogeochemical parameters, as well as the 
development of semi-analytical models for the retrieval of inherent optical properties from 
satellite data. We anticipate that these efforts will lead to an improved understanding of the 
variability observed in empirical satellite algorithms. We will also initiate analyses to determine 
the elements of the SeaWiFS processing that lead to the underestimates of L wn , which is of 
particular concern for high chlorophyll waters. 

References 

Fu, G., Settle, K., and McClain, C. R., (1998), SeaDAS: The SeaWiFS Data Analysis System. 

Proceedings of the Fourth Pacific Ocean Remote Sensing Conference. Qingdao, China, 

7/28/98, 73-77pp 
Kahru, M. and Mitchell, B. G., (1999), Empirical chlorophyll algorithm for the California 

Current, International Journal of Remote Sensing (In Press) 
Mitchell, B. G. (1990), Algorithms for determining the absorption coefficient of aquatic 

particulates using the quantitative filter technique (QFT). SPIE. Bellingham, Washington 

137-148. 
Mitchell, B. G. and O. Holm-Hansen (1991), Bio-optical properties of Antarctic Peninsula 

waters: Differentiation from temperate ocean models. Deep-Sea Research I, 38: 1,009- 

1,028. 
Mitchell, B. G. and M. Kahru (1998), Algorithms for SeaWiFS standard products developed with 

the CalCOFI bio-optical data set. Cal Coop Ocean Fish Invest R, 39: 133-147. 
Mitchell, B. G. and D. A. Kiefer (1988), Variability in pigment specific particulate fluorescence 

and absorption spectra in the northeastern Pacific Ocean. Deep-Sea Research /, 35: 665- 

689. 
O'Reilly, J. E., S. Maritorena, B. G. Mitchell, D. A. Siegel, K. L. Carder, S. A. Garver, M. 

Kahru, and C. McClain, (1998), Ocean color chlorophyll algorithms for SeaWiFS. 

Journal of Geophysical Research, 103: 24,937-24,953. 
Smith, R. C. and K. S. Baker, (1978), The bio-optical state of ocean waters and remote sensing. 

Limnology and Oceanography, 23: 247-259. 
Sosik, H. M. and B. G. Mitchell, (1995), Light absorption by phytoplankton, photosynthetic 

pigments, and detritus in the California Current System. Deep-Sea Research I, 42: 1,717- 

1,748. 



<* 



1.4 
1.2 
1.0 
0.8 



^ 0.6 



0.4 
0.2 



0.0 



chl= 0.13 




980131a. u02, 87.70 



400 450 500 

Wavelength, nm 



550 



1 



1.0 


- 


< > i . 
chl 


= 0.29 










0.8 


' + 


+ ""■ 


"■"-* 


0.6 




NX. 


0.4 








0.2 








0.0 




980209c. u 


02, 77.80 



400 450 500 

Wavelength nm 



B 



550 





' 


,,.<*,,, 


""■"'" T ~r~ 


0.8 


- 


chl= 1.05 


c 


0.6 


X 

'_ + 


+ \ 




1 

^ h 0.4 




^^ K ^. 


*Nv 


0.2 






?• 


0.0 




p971201e.d01, 423.04 
i . , 


i 



400 450 500 

Wavelength, nm 



550 



1 



0.50 


- 


11 ■ i ' 

chl= 4.65 


D 








.. -X 


0.40 


- x " 






0.30 








0.20 








0.10 






j 






980409a. uJM, 87.35 




0.00 




i / . . . i . . 


i 



400 450 500 

Wavelength, nm 



550 



Figure 1. Examples comparing SeaWiFS-derived normalized water-leaving spectral radiances 
(o, solid lines) with in situ measurements from CalCOFI (panels A, B, D) and the Southern 
Ocean (panel C). In situ values were calculated using in-water spectral measurements of E d and 
Lu (x, dashed lines) or using above surface measurements of E d (+). Surface chlorophyll a 
concentration at each station is also indicated. 



17 



20 
1.5 
1.0 
0.5 


' 1 ' | 1 1 1 |T"I 1 | 1 i t j t T T"T~T' t t | t t T" 

N. CalCOFI 


1 

e 
2 

2 
1 
s 

3 

5 


0.4 

0.2 

0.0 

-0.2 

-0.4 


1 1 l l | l l l 1 J 1 1 1 1 | 1 1 1 1 | 1 4 1 1 J l 1 I I | ( I 1 t- 

JC - 


0.0 
-0.5 

*r -i.o 


* K 


t 




1.0 

0.5 

0.0 

-0.5 

-1 




9 

g " 
I l0 

0.5 


\ Southern Ocean : 
: *♦ \ : 

* ■ i ■ ■ 1 1 ■ i 1 1 \i ~ 


t 


0.0 
-0.5 
-1.0 
-1,5 


Jill Mil 1 I ■ 1 1 1 1 i ■ 1 ■ i i • 1 ■ ■ . . 



-0.6 -0,4 -0.2 0.0 0.2 0.4 0.6 0.8 

Log(R rs (490yR„(555)) 



■1.5 -!0 -0.5 0.0 0.5 1.0 1.5 2.0 
Log (Chi observed) |mg ni^l 



Figure 2. A comparison of the OC2-v2 algorithm (solid line in left panels) with in situ 
measurements of chlorophyll a from CalCOFI and the Southern Ocean. The right panels 
illustrate quantile-quantile plots of the differences between modeled and measured chlorophyll a. 



Publications 

Gross, L., S. Thiria, R. Frouin, and B.G. Mitchell, 2000 Artificial neural networks for modeling 

the transfer function between marine reflectance and phytoplankton pigment concentration. 

Journal of Geophysical Research. 105(C2): 3,483-3,495. 
Kahru, M. and B.G. Mitchell, 1999: Empirical chlorophyll algorithm and preliminary SeaWiFS 

validation for the California Current, International Journal of Remote Sensing 20(17): 3,423- 

3,429. 
Kahru, M., and B.G. Mitchell, 2000. Seasonal and non-seasonal variability of satellite-derived 

chlorophyll and CDOM concentrations in the California Current. Journal of Geophysical 

Research. (In Press) 
Loisel, H., D. Stramski, B.G. Mitchell, F. Fell, V. Fournier, B. Lemasle and M. Babin (2000) 

Comparison of the ocean inherent optical properties obtained from measurements and inverse 

modeling. Submitted to Applied Optics. (In Press) 
Mitchell, B.G. and M. Kahru, 1998: Algorithms for SeaWiFS standard products developed with 

the CalCOFI bio-optical data set. CalCOFI Reports, Vol. 39: 133-147. 
Nakajima, T., A. Higurashi, K. Aoki, T. Endoh, H. Fukushima, M. Toratani, Y. Mitomi, B.G. 

Mitchell and R. Frouin, 1999: Early phase analysis of OCTS radiance data for aerosol remote 

sensing, IEEE Transactions, 37(3): 1,575-1,585. 
O'Reilly, J.E., S. Maritorena, B.G. Mitchell, D.A. Siegel, K.L. Carder, S.A. Garver, M. Kahru, C. 

McClain, 1998: Ocean Color Chlorophyll Algorithms for SeaWiFS, Journal of Geophysical 

Research, 103(01): 24,937-24,953. 
Reynolds, R.A., S. Stramski and B.G. Mitchell, 2000: A chlorophyll-dependent semianalytical 

reflectance model derived from field measurements of absorption and backscattering 

coefficient within the Southern Ocean. Journal of Geophysical Research. (In Press) 
Stramska, M., D. Stramski, B.G. Mitchell and C.Mobley, 2000: Estimation of the absorption and 

backscattering coefficients from in-water radiometric measurements, Limnology and 

Oceanography. 45(3): 628-641 



19 



Conference Abstracts 

Flatau, P.J., B.G. Mitchell, A. Subramaniam, J. Welton, K. Markowicz, J.K. Nolan, M. Kahru, 

K. Voss, M. Reynolds, T. Nakajima, M. Miller, J.D. Wieland 2000 Comprehensive ocean 

color measurements during the 1999 INDOEX project. AGU Ocean Sciences Meeting, San 

Antonio, TX 
Fougnie, B., P.-Y. Deschamps, R. Frouin, and B.G. Mitchell, 1998: Measuring Water-Leaving 

Radiance with a Polarization Radiometer: Theory and Experimental Verification, AGU 

Conference, San Diego. 
Kahru, M. and B.G. Mitchell, 1998: Empirical chlorophyll algorithm for the California Current, 

AGU, San Francisco. 
Kahru, M. and B.G. Mitchell, 2000, Seasonal and non-seasonal variability of satellite-derived 

chlorophyll and CDOM concentration in the California Current. AGU Ocean Sciences 

Meeting, San Antonio, TX 
Loisel, H., D. Stramski, M. Babin, F. Fell and B.G. Mitchell, 2000, An inverse model for the 

estimation of the inherent optical properties in presence of Raman scattering: description and 

validation. AGU Ocean Sciences Meeting, San Antonio, TX 
Mitchell, B.G., 2000, Global bio-optical algorithms and ocean color satellite validation for ocean 

color. August 21 - September 9, 2000. Satellite Oceanography 2000, Focus at the sea surface, 

Department of Physical Oceanography, CICESE, Ensenada B.C., MEXICO 
Mitchell, B.G., M. Kahru, R. Reynolds, J. Wieland, D. Stramski 2000 Satellite Estimation Of 

Seasonal Variations In Organic Carbon To Chlorophyll-A Ratios In The Southern Ocean 

And Interpretation Of Carbon Flux Dynamics. AGU Ocean Sciences Meeting, San Antonio, 

TX 
Mitchell, B.G., M. Kahru, R.A. Reynolds, J.D. Wieland and D. Stramski, 2000, Satellite 

Estimation Of Seasonal Variations In Organic Carbon To Chlorophyll-A Ratios In The 

Southern Ocean Oceans from Space Symposium. October 9-13, 2000, Venice, Italy 
Reynolds, R.A., M. Kahru, J.D. Wieland, D. Stramski and B.G. Mitchell, 1998: An evaluation of 

SeaWiFS ocean color chlorophyll algorithms within the Southern Ocean, AGU, San 

Francisco. 
Stramski, D., R.A. Reynolds, M. Kahru, J.D. Wieland and B.G. Mitchell 2000 Geographic 

distribution and seasonal variations in particulate organic carbon within the Southern Ocean 

as determined from satellite imagery of ocean color, AGU Ocean Sciences Meeting, San 

Antonio, TX 



20