Lisl Robertson, University of Cape Town, RSA with assistance from Stewart Bernard Christo Whittle GOOS AFRICA.
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Lisl Robertson, University of Cape Town, RSAwith assistance from
Stewart BernardChristo Whittle
GOOS AFRICA
Preliminary Validation and Application of the Globcolour Products in the Benguela System
• HABs in the Southern Benguela: in situ and satellite monitoring activities
• Preliminary Qualitative Globcolour spectral validation
• Globcolour Regional experiments: Benguela System and Subtropical Convergence
• Marine Remote Sensing Unit: data provision to Africa
HABs and the Southern Benguela
BOB: HAB Monitoring Buoy
Moorings: multi-sensor lightweight coastal buoys allowing high frequency point sampling with real time data on demand. Mooring system supplied real time data from January 2005 until April 2007.
BOB Instrumentation• Two hyperspectral radiometers• 30 m digital thermistor chain• Fluorometer• ADCP
Satellite Monitoring
Satellites:• Near real time reception of daily 1 km MERIS data directly from ESA via local DDS• Archived reception of 250 m MERIS data on request• Locally processed AVHRR sea surface temperature and MODIS data through UCT Remote Sensing Unit
A
B
CMarch 30th: small Prorocentrum triestinum dominated assemblage
April 2nd: low biomass waters
April 5th : large Ceratium furca dominated assemblage
Multi-Scale Observation of HAB Events: Summer 2005
Remote Sensing Reflectance Spectra: BOB vs Globcolour
050201: high biomass diatoms, Chlorophyll a ~ 10
050428: chlorophyll a estimated 5 – 10Typical “background” signal in bloom season
050422: massive dinoflagellate bloom,Chlorophyll a ~ 50
050517: very odd spectrum…
Remote Sensing Reflectance Spectra: BOB vs Globcolour: focus on 531 nm band
050227 050508 050510 060309
531 may be problematic in high biomass, but could also be sensitive to phycoerythrin peak –
further investigation required
060312 060319
Remote Sensing Reflectance Spectra: BOB vs Globcolour: focus on 510 nm band
Little mystery: one week in 2006 – 510 nm band failed.But look how well Globcolour performs in the blue …
Globcolour, BOB Remote Sensing Reflectance Comparisons
• 412 nm expected to perform worst
• 531 nm has some accurate matches but many outliers as has been seen
• Best performing bands at 620, 670 and 709 nm, with a slight general overestimation by Globcolour (also by MERIS). But Globcolour not fully normalised at 709 … unclear effect on RRS?
GlobColourWeighted Chl 1
SeaWiFSOC4 Chl
GlobColourGSM Chl 1
GlobColourExperimentalBenguelaChl
GlobColour Comparative Products: Southern Africa and Southern Ocean
Analytical reflectance algorithms: size distributions of two layered spheres
Chloroplast Cytoplasm
The analytical reflectance algorithm is based on the representation of the optical properties of algal cells using two layered spheres, using Standard particle size distributions to simulate polydispersednatural algal populations.
This allows better estimates of algal biomass (Chl a), and biomass independent assemblage descriptors: mean algal size (Deff) and physiological/algal group proxies (fluorescence quantum yield). An analytical algorithm also allows analogous application to both buoy and satellite ocean colour measurements.
Simulated effects of changing chlorophyll concentration, effective algal diameter, and assemblage type on the reflectance spectrum
Algal Fluorescence Line Height
Non Algal BackscatteringAlgal Fluorescence Quantum Yield
Algal Effective Diameter
GSM Particulate Backscattering
GlobColour Experimental Products: Southern Africa and Southern Ocean
Experimental reflectance/fluorescence inversion algorithms
Fluorescence line height and quantum yield products allow some assessment of algal biomass and physiological variability.
Algal effective diameter is used to assess biomass specific assemblage variability e.g. HABs in the Benguela, carbon export in the sub-tropical convergence zone
Near Real Time:MODIS variousMERIS variousAVHRR SSTMSG-2 SST
Archive/Climate10 yr colour,15 yr altimetry,20 yr+ winds,20 yr+ temperature
Higher LevelInteroperable with other sites for integrated products
New MRSU and GEO/GOOS ChloroGIN site to be launched November 2007
Marine Remote Sensing: Developing an Operational Capability
• Validation and protocols for high biomass studies
• Algorithm validation and development
• Ecological use of Globcolour in regional systems
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