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