Transcript Document

Toward Closure of In Situ Upwelling Radiance in Coastal Waters
1
Chang ,
2
Boss ,
3
Mobley ,
Grace C.
Emmanuel
Curt
1
2
Tommy D. Dickey , and W. Scott Pegau
1Ocean
Physics Laboratory, University of California, Santa Barbara; 2Oregon State University, Corvallis, OR; 3Sequoia Scientific, Inc., Redmond, WA
Contact Information: [email protected]; http://www.opl.ucsb.edu/
Introduction
Methods
• Spectral radiance is one of the
fundamental quantities of interest in the field
of ocean optics (Kirk, 1989; Mobley, 1994).
(1) Satlantic, Inc. SeaWiFS Profiling Multichannel
Radiometer (SPMR) on the Suitcase package
(l = 412, 442, 490, 532, 555, 590, and 682 nm)
• Radiance, L(q,F,l, z), is defined as the
radiant flux at a specified point with units of
W (or quanta s-1) m-2 sr-1 nm-1.
• The spectral shape and magnitude of
radiance is dependent on the influx of solar
radiation at the sea surface and the optical
properties of the water column.
• Upwelling radiance, Lu(q,F,l, z), is the
radiance of an upwelling light field.
Importance
• Quantifying ocean color/remote sensing
(Lw(l,0+) is water-leaving radiance and
Ed(l,0+) is solar spectral irradiance)
• Chlorophyll concentration
(O’Reilly et al., 1998)
• Spectral backscattering coefficient
• Spectral absorption coefficient
• Subsurface features
(Barnard et al., 2000)
• Bottom type
• Bathymetry
• Water column visibility
• Photosynthesis
• Average Statistics
Lu(l,0.66m)
r2 = 0.96
Used to calculate:
l=412
TSRB and Hydrolight
442
490
532
555
590
682
Percent 14.70 12.16 11.92 15.93 18.83 27.93 41.04
Difference
Lw(l,0+m)
r2 = 0.95
for Lu(l,0.66m), Lu(l,0-m).
Lu(l,0.66m)
r2 = 0.99
(2) Satlantic, Inc. Hyperspectral
Tethered Spectral Radiometric
Buoy (HyperTSRB)
l = 400 – 800 nm
3.3 nm bandwidth
l=412
442
490
532
Percent 17.62 19.39 17.19 9.52
Difference
The n-squared law for transmittance across sea
surface used to calculate:
where t ~ 0.98 and
n ~ 1.34
l=412
555
590
682
11.33 19.97 12.11
Suitcase and Hydrolight
442
490
532
555
590
682
Percent 22.77 19.02 18.63 19.28 24.04 19.54 31.21
Difference
Comparisons between Suitcase, HyperTSRB, and Hydrolight-derived Lu(l,0.66m), Lu(l,0-m), and Lw(l,0+m)
for July 21 and 22, 2000 at locations 39.37oN, 74.21oW and 39.46oN, 74.26oW, left to right.
Lw(l,0+m)
r2 = 0.99
l=412
442
490
532
555
590
682
Percent 24.08 17.20 13.28 14.32 20.63 16.16 19.44
Difference
• Differences in Lw(l,0+m) due to n-squared law of transmittance
• Differences in blue wavelengths attributed to:
- Scattering correction for absorption
- Errors in VSF measurements (prototype instrument)
(3) Hydrolight 4.1 with measured absorption and
attenuation (ac-9); CDOM absorption (filtered
ac-9); chlorophyll a concentration (fluorometer);
and volume scattering function
• Differences in red wavelengths attributed to:
- Use of default chlorophyll-specific absorption coefficient in
Hydrolight modeling
Assumptions:
- No Raman scattering
- No bioluminescence
- Default a*ph(l)
- TSRB sky irradiance
- Optically deep waters
Problems
Remote sensing
• Atmospheric corrections, clouds
• Extrapolation of region-specific to global
ocean color algorithms
• Determination of water column vertical
structure
Conclusions
Results
• Spectral shape of L(q,F,l, z) changes from nearshore to
offshore due to changes in water type.
References
Barnard, A.H., A.D. Weidemann, W.S. Pegau, J.R.V. Zaneveld, J. W. Rhea, and C. O.
Davis, Hyperspectral remote sensing imagery and the detection of subsurface features,
Ocean Optics XV, 2000.
LEO-15 site
Comparisons between Suitcase, HyperTSRB, and Hydrolight-derived Lu(l,0.66m), Lu(l,0-m), and Lw(l,0+m)
for July 24 and 27, 2000 at locations 39.41oN, 74.20oW and 39.34oN, 74.08oW, left to right.
In situ measurements
• Measurements of Lu(l,z) rather than the
desired Lw(l,0+)
• Surface roughness effects
(Toole et al., 2000)
Remote Sensing Reflectance Closure
Cullen, J.J. and M.R. Lewis, Biological processes and optical measurements near the
sea surface: Some issues relevant to remote sensing, J. Geophys. Res., 100, 13,25513,266, 1995.
Gordon, H.R., Contribution of Raman scattering to water-leaving radiance: a
reexamination, Appl. Opt., 38, 3166-3174, 1999.
Kirk, J.T.O., The upwelling light stream in natural waters, Limnol. Oceanog., 34, 14101425, 1989.
Leathers, R.A., T.V. Downes, and C.D. Mobley, Self-shading correction for upwelling
sea-surface radiance measurements made with buoyed instruments, Opt. Exp., 8, 561570, 2001.
• Self-shading (Leathers et al., 2000)
• Surface biological effects
(Cullen and Lewis, 1995)
Mobley, C.D., Light and Water: Radiative Transfer in Natural Waters, Academic Press,
San Diego, 592 pages, 1994.
• Scattering phase functions
(Mobley et al., 2002)
Mobley, C.D., L.K. Sundman, and E. Boss, Phase function effects on oceanic light
fields, Appl. Opt., in press.
• Raman scattering (Gordon, 1999)
O’Reilly, J.E., S. Maritorena, B.G. Mitchell, D.A. Siegel, K.L. Carder, S.A. Garver, M.
Kahru, and C. McClain, Ocean color chlorophyll algorithms for SeaWiFS, J. Geophys.
Res., 103, 24,937-24,953, 1998.
Study Site
Sampling
Locations
Year 2000
Toole, D.A., D.A. Siegel, D.W. Menzies, M.J. Neumann, and R.C. Smith, Remotesensing reflectance determinations in the coastal ocean environment: impact of
instrumental characteristics and environmental variability, Appl. Opt., 39, 456-469,
2000.
• LEO-15 site on the New Jersey continental
shelf
• New York Bight and Middle Atlantic Bight
Acknowledgements
• Waters less than 25 m deep
• Physics characterized by upwelling, smallscale eddies, riverine and estuarine inputs,
fronts, coastal jets, tides, etc.
• Optics characterized by phytoplankton
blooms, turbidity fronts, terrestrial CDOM,
bottom resuspension, etc.
This work was supported by:
Comparisons between Suitcase, TSRB, and Hydrolight-derived Rrs(l) for July 24, 2000
at locations 39.49oN, 74.19oW and 39.41oN, 74.20oW, left to right.
Special thanks to Francois Baratange for engineering support
and data processing and Bob Arnone for remote sensing images.