My thesis research is on individual particle and bulk optical properties as a doctoral student in the MIT/WHOI Joint Program in Oceanography with Heidi Sosik (principle advisor) and Rob Olson. The title of my thesis proposal is "Interpretation of Variability in Water Column Optical Properties through Individual Particle Analysis". The aim of this study is to develop methods for the derivation of bulk optical properties from single particle measurements and to apply these methods to the study of optical variability in the ocean.
Variability in the magnitude and spectral shape of bulk optical properties in the ocean are significantly affected by changes in the properties of single particles. Recent advances in measurement techniques make it possible to use concurrent measurements of single particle and bulk optical properties in order to resolve sources of bulk optical variability. My research has involved significant development of single particle analyses for flow cytometric data. I am applying these techniques to understanding optical variability in field measurements collected at oceanic sites off the northeastern coast of the U.S.
The focus of this research is on determining the properties of "optically important" particles including phytoplankton, bacteria, organic detritus, and inorganic particles to describe variability in bulk optical properties. Determinations of particle type, concentration, size, and refractive index are made from a combination of flow cytometric measurements and Mie theory modeling. Bulk inherent optical properties, including absorption and backscattering, are calculated as a sum over all particles and compared to in situ bulk measurements in order to validate single particle methods. The goal is to determine what types of changes in particle properties account for variability seen in inherent and apparent optical properties. As the calculation of apparent optical properties is dependent on ambient light fields, a radiative transfer program will be used to study the effects of single particles on bulk apparent optical properties. I will apply single particle and bulk optical measurements to a study of chlorophyll-based bio-optical models and physical factors which force changes in optical properties.
This research will enhance our ability
to use ocean color for studying the role of the ocean in the global carbon
cycle. Currently, methods in optical oceanography are limited by a simplistic
treatment of diverse marine particles, i.e. consideration of limited types
of particles and/or making assumptions regarding particle properties. This
research will contribute a comprehensive assessment of the role of particles
by considering numerous particle types including a variety of phytoplankton
species, heterotrophic bacteria, organic detrital particles, and inorganic
particles, in addition to dissolved material. This is made possible by
recent developments in flow cytometric methods which allow numerous types
of particles to be studied in detail. The combination of extensive single
particle and bulk measurements presents a unique opportunity to study the
role of particles in ocean color variability. This work will contribute
to an understanding of which environmental factors are important in forcing
changes in upper ocean optical properties, knowledge which is necessary
for modeling ecosystem processes.
EDUCATION
Ph.D. candidate, MIT/WHOI Joint Program in Oceanography, expected degree
in 7/2001.
B.S. (Independent Studies Program in Physics and Biology) Caltech (Pasadena,
CA), 1994.
EXPERIENCE
Graduate Research Assistant in Ocean Optics, WHOI, 7/96-present.
Volunteer Acoustics Technician, Southwest Marine Fisheries Science
Center (La Jolla, CA), 8/95 - 9/95.
Research Assistant in Environmental Engineering Sciences, Caltech,
5/95 - 6/96.
Volunteer Physics Teacher, United States Peace Corps, Fiji, 10/1994
- 1/1995.
Research Assistant in Microbiology, Caltech, 9/1993 - 12/1993.
Research Intern in Astronomy, UC-Berkeley, 6/1992 - 9/1992.
Research Intern in Biomedicine, Nicolet Instrument Corp. (Madison,
WI), 6/1993 - 9/1993.
Research Intern in Sleep Disorders, Nicolet Instrument Corp., 6/1991
- 9/1991.
Research Intern in Fiber Optics, Nicolet Instrument Corp., 6/1990 -
9/1990.
Research Intern in Spectroscopy, Nicolet Instrument Corp., 6/1989 -
9/1989.
AWARDS and Grants
ONR Grant to H.M. Sosik, R.E. Green and R.J. Olson, 2000.
NASA Earth System Science Fellowship, 1999.
TEACHING
Teaching Assistant for Satellite Remote Sensing course, Shoals Marine Lab, Summer 1999 & 2000.
OCEANOGRAPHIC CRUISES
R/V McArthur, Whale Habitat and Prey Study, August 1 - 31, 1995.
R/V Oceanus, Coastal Mixing and Optics Experiment, January 5-8, 1997.
R/V Knorr, Coastal Mixing and Optics Experiments, April 23 - May 13,
1997.
R/V Cape Hatteras, Gulf of Maine cruise, June 19 - July 4, 1998.
R/V Oceanus, GLOBEC Gulf of Maine process cruise, October 19 - 28,
1998.
R/V Oceanus, GLOBEC Gulf of Maine process cruise, December 3 - 13,
1998.
PUBLICATIONS
Sosik, H.M., R.E. Green, W.S. Pegau and C. S. Roesler, Temporal and
vertical variability in optical properties of
New England shelf waters during late summer and
spring, submitted to JGR CMO special issue in May, 1999.
ABSTRACTS
Green, R.E., H.M. Sosik, R.J. Olson and M.D. DuRand (2000) Comparison
of refractive index estimated from
single-cell and bulk optical properties. In: Ocean
Optics XV (submitted).
Green, R.E., H.M. Sosik, M.D. DuRand and R.J. Olson (2000)
Toward closure between single particle and bulk
optical properties during the coastal mixing and
optics Experiment. EOS, 80, 118.
Green, R.E. and H.M. Sosik (1998) Vertical and temporal variability
in apparent optical properties during the
Coastal Mixing and Optics experiment. EOS,
79, 120.
Sosik, H. M., R. E. Green and R. J. Olson (1998) Optical variability
in coastal waters of the Northwest Atlantic.
In: Ocean Optics XIV, S. G. Ackleson (ed.). 14 pp.
Fuller, M., S. Lowry, R. Green (1992) The use of a novel fiber optic
based ATR accessory for structural and
quantitative analysis. Pittsburgh Conference on
Analytical Chemistry and Spectroscopy.