PPT - Monterey Bay Aquarium Research Institute

Report
Second Generation Laser Raman
Spectrometer for the Deep Ocean
Alana Sherman1, Rachel M. Dunk1, Sheri N. White2, William Kirkwood1, Edward T. Peltzer1,
Peter Walz1, Farley Shane1, Richard Henthorn1, Karen A. Salamy1, Peter G. Brewer1
1
Monterey Bay Aquarium Research Institute, Moss Landing, CA
2 Woods Hole Oceanographic Institution, Woods Hole, MA
Raman Spectroscopy
• Vibrational spectroscopy
– Based on Raman scattering
• The inelastic scattering of
monochromatic radiation
– The shift in energy of the
scattered light is equal to the
change in the vibrational
energy of the molecule
– The Raman spectrum serves
as a fingerprint of a substance
based on molecular
composition and local
environment
Raman Spectroscopy in the
Ocean
• The technique provides the ability to make in situ
geochemical measurements in the deep ocean.
• Advantages of Raman Spectroscopy:
– Can analyze solids, liquids and gases
– Rapid analysis
– Can perform in situ analysis targets with
stability zones confined to the deep ocean
– Generally non-destructive, and requires little or
no sample preparation
Raman Spectroscopy in the
Ocean
• A number of oceanic targets are Raman active:
– Gases
• CO2, CH4, N2, O2, H2S, etc.
– Minerals
• Sulfides, anhydrite, calcium carbonates,
silicates, feldspars, magnetite, etc.
– CO2 and CH4 hydrates
DORISS 1
Deep Ocean Raman In Situ Spectrometer
40”
1
1
10”
2
3
3
2
15”
6”
20”
12”
Operations
ROV deployed instrument
Spectrum
Probe head
Doriss2
Intensity (Counts)
• The instrument housing is
mounted in the rear drawer of
the ROV
• The probe head is carried in
front of the ROV
• Communications between
Doriss and shipboard computer
via Ethernet
• Spectra of targets, video, and
environmental data are
transmitted back to the
operator
Raman Shift (cm-1)
DORISS1
• Scientific Successes
– First deep ocean Raman spectra
– 3 years of successful deployments
– Collected data from hydrothermal vents at Gorda Ridge,
natural hydrates from Hydrate Ridge
– Demonstrated worth of technique
– 8 papers published
• Technical Challenges
– Prototype instrument not suitable for routine
expeditionary use
• Weight and size
• Sensitivity
• Reliability and robustness
DORISS2
Laser
CCD camera
Power Supply
Spectrometer
(Kaiser Optical Systems
NXRN model)
Computer
DORISS2
• Improvements:
– U-shaped spectrometer simplifies
housings
– 90 lbs lighter than DORISS1
• Can be deployed on vehicles with
limited payload
– Increased sensitivity, due to new
back illuminated CCD camera
– More robust and reliable
12” diameter, 30” long
DORISS2 Data
CH4-H2S Fractionation
CH4-H2S Fractionation
Disappearance of the 2610 Δcm-1 H2S peak with time.
In Situ Calibration
• Would like a way to
calibrate intensity and
wavelength of the
instrument in situ.
NIST SRM2242
Acrylic
Polystyrene
• Calibration module
experiments:
– Relative intensity
correction standard:
NIST SRM 2242
luminescent glass
Calibration Module
Probe head
– Wavelength correction:
Acrylic and Polystyrene
Hydraulic Ram
• Less than 2% error
between white light
corrected and SRM
2242 corrected
spectra
• Difficulty extracting
water signal when
using stand-off optic
Intensity (Normalized)
Calibration Data
SRM2242 Corrected
WL Corrected
Raman Shift (cm-1)
Comparison of White Light corrected and
SRM 2242 corrected Acrylic spectra
Future Developments
• Improve fiber optic
cables
• Integrate new smaller
probe head
• Smaller positioner
Kaiser Optical Systems, MultiRxn Probe
Acknowledgements
• Crew of the R/V Western Flyer and R/V Point Lobos
• Pilots of the ROV Tiburon and ROV Ventana
• Technical support of John Ferreira, Larry Bird, Jim
Scholfield, Cheri Everlove
• Kaiser Optical Systems
• Steve Choquette at NIST
• David & Lucile Packard Foundation
Probe head

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