Remote sensing of coastal habitats: Challenges: Adjacency effects Atmospheric correction (no null...
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Transcript of Remote sensing of coastal habitats: Challenges: Adjacency effects Atmospheric correction (no null...
![Page 1: Remote sensing of coastal habitats: Challenges: Adjacency effects Atmospheric correction (no null NIR band) Currently addressed by Europeans (e.g. Belcolour)](https://reader035.fdocuments.in/reader035/viewer/2022062905/5a4d1acf7f8b9ab059970b5a/html5/thumbnails/1.jpg)
Remote sensing of coastal habitats:
Challenges: Adjacency effects Atmospheric correction (no null NIR band)
Currently addressed by Europeans (e.g. Belcolour)Atmospheric correction – similarity spectra (Rudick),
Doron & Babin).
Use of Red & NIR bands to obtain [chl]Development of algorithms for [Sediment]In-situ validation
Impetus for European effort: cross-EU litigation.
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Related contributions:
Linking in-situ optical properties and coral-reef biogeochemistry (see below).
Linking in-situ optical properties to particle composition and dynamics in coastal environments (resuspension-aggregation-settling) - OOXIX
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Optical properties related to biogeochemistry:
DOM, Hydrocarbons – fluorescence (UV-ex, VIS-em), absorption.
TSS, TSM, POC – attenuation, scattering, ocean color.
Phytoplankton pigments – fluorescence, absorption, ocean color.
Particulate size distribution – spectrum of attenuation, near forward scattering, ocean color.
Particulate composition (index of refraction) – back-scattering to scattering ratio, degree of polarization.
Temperature –NIR radiance.
Nitrate, sulphides – UV absorption.
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The effect of bottom substrate on inherent optical properties: Evidence of biogeochemical processes.
Emmanuel Boss (U. Of Maine) & Ron Zaneveld (Oregon State U.)
Special thanks to: Jim Washburn, Francois Baratange, Dick Zimmerman, Dave Burdige, and Rob Wheatcroft. Funded by ONR.
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Biogeochemical processes near coral reefs:
• Sediment resuspension by currents.
• Removal of selected particulate material from the water column by benthic filter feeders such as corals and sponges.
• Emergence/disappearance of organisms (‘particulate material’) from the sediment into/outoff the water column.
• Mechanical resuspension of sediment by benthic organisms and water column organisms such as fish.
• Release of colored particulate and dissolved waste products into the water by in-water organisms (e.g. zooplankton and fish) and by release of dissolved waste products by organisms (e.g. coral and sponges).
• Diffusive and advective (when sediment is resuspended) flux of colored dissolved material released from sediment pore water.
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Using optics for studying biogeochemical processes
Advantages:
• In-situ.• Non-invasive.
Disadvantages:
• Only net effect of by all processes can be measured. • ‘bulk’ analysis: all particles of given sizes (as determined by pre-
filters) are measured together.
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Methods:
CTDac-9
inlet
Data loggers
Human Sea-Sore
Can sample very close to the bottom.
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Optical properties and their relation to biogeochemical parameters:
Attenuation at a red wavelength: (c(660)):
•Indicator of total suspended particulate mass (volume or concentration. CDM absorption at this wavelength is negligible).
•In the oceanic environment found to correlate well with POC.
•To a lesser degree it also varies with size distribution and composition.
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Optical properties and their relation to biogeochemical parameters:
CDM absorption and ‘flavor’:
•In the coastal ocean CDM absorption is an indicator of the concentration of dissolved organic carbon, though the exact relationship varies between environments.
• Exponential slope of ag, indicator of CDM “flavor”. A steep slope (~0.02) represents “fulvic”-like or low molecular weight material, while a smaller slope (~0.01) represents “humic”-like or high molecular weight material (Carder et al., 1989, Blough and Del Vecchio, 2002).ag= ag(0)*exp(s( - 0))
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Optical properties and their relation to biogeochemical parameters:
Chlorophyll absorption:
•[chl][apg(676)-apg(650)]/0.014
•indicator, at a given light level, of phytoplankton biomass.
•Note: can be affected by non pigmented material (organic detritus and inorganic particles) when [chl] is low, since for it apg(676)<apg(650).
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Optical properties and their relation to biogeochemical parameters:
– exponent of cp, indicator of tendencies of the particulate size distribution. The parameter will be larger when the sample is dominated by small particles.
cp= cp(0) (0-
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Sampling site:
Lee stocking Isl.Bahamas:
Fringe reefs
Seagrass beds (dark)
Narrow outlets, characterized by ooids sediments in shallow areas (bright).
Bahamas banks
Exuma Sound
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Results: Horizontal gradients in optical properties across coral-sand boundaries (N=15):
The variability in all properties was higher above the reef.
Attenuation was larger over sand (13/2).
Attenuation slope was larger over reef (12/3).
CDM absorption was larger over reef (13/2).
[chl] was larger over sand (11/4).
Implications: Reef is patchy. Reef filters [chl] containing large particles and produces CDM.
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The variability in all properties was higher above the reef
Attenuation was larger over sand
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CDM absorption was larger over reefAttenuation was larger over sandAttenuation slope was larger over reef
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CDM absorption was larger over reefAttenuation was larger over sandNote: gradient in physical properties less than 0.01kg/m3
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Results: Vertical gradients in optical properties above reef and sand: (N=11, Nreef=6, Nsand=5):
The variability at 10cm was higher than at any depth further away from bottom.
Attenuation increased away from reef (7/4).
Attenuation spectral slope decreased away from bottom substrate (9/2).
CDM absorption was largest near substrate (11/0).
CDM spectral slope increased away from substrate (11/0).
[chl] increased away from bottom substrate (7/4).
Implications: ‘bottom’ filters out large, [chl] containing particles. CDM with low spectral slope is produced in/on substrate.
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Particle settling and resuspension
The vertical distribution of particles above the reef is opposite what is observed in a typical BBL.
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Results:Role of bottom substrate in vertical gradient between pore waters and overlying bank waters:
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Results:Role of Bahamas banks in export of DOC to Exuma Sound, time series of ~36hrs:
Inverted s-ag relationship relative to continental coast.DOC fluxed has higher spectral slope.
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Conclusions:
Bottom processes affect optical properties.
Optical measurements are sensitive enough to infer biogeochemical processes associated with bottom substrates.
Local benthic processes can result in large-scale gradients between environments as observed in CDM absorption between the bank waters and the adjacent Exuma Sound.
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ac-9 based :
Coulter counter based :
N=N(D0)D- dD
cp= cp(0) (0-
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y = 1.0926x - 0.1271R2 = 0.9898
0
4
8
12
0 5 10
measured Chl (g/L)
estim
ated
chl
((a
676-
a 650
)/0.0
14)
Karp-Boss,2001, data from Oregon coast (N=25)
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The variability at 10cm was higher than at any depth further away from bottom:
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Blough and Green (1995)
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Gradients in CDM between pore waters and overlying waters:
First generation sampling method…
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Spinrad et al. (1983): Bishop (1999):
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Example of a measurement series of pore waters:
Taken during ebbing tideDefinition of salinity may change in pore water (Hales).