Operational chlorophyll-a monitoring within the North Sea using integrated multi-temporal MODIS and SeaWiFS L2 imagery

Mark Slater, Robin Vaughan
University of Dundee, Dundee, DD1 4HN, Scotland
m.t.slater@dundee.ac.uk

ABSTRACT

The production of accurate level 2 and 3 chlorophyll-a products for Case 2 waters from space born remote sensing data presents a common problem associated with the top of atmosphere mixed pixel contributions of aerosols and turbid water suspended sediment. However, with the availability of SeaDAS 4.6 and collectively up to three nadir suitable daylight MODIS (Terra/Aqua) and SeaWiFS passes per day a standard atmospheric correction model with data fusion offers potentially reduced errors within Chlorophyll-a Case 2 monitoring. The approach undertaken here has two key aspects. Firstly, the application of a standard coastal aerosol model but with local ancillary humidity adjustments. Secondly, the fusion L2 SeaWiFS OC-4 and MODIS OC3 Chlorophyll- a to produce a Common Ocean Colour Chlorophyll-a (COCC_a) L3 product. For the sample studies with near coincident DONAR ship borne observations correlations of approximately y = 1.05 and r²=0.91 were demonstrated for spring-summer observations. The derivation of COCC_a products required only minimal modification of the SeaDAS 4.6 program, namely the local humidity adjustment (away from the default 70%) and per sensor product threshold masking of artificially high (>64mgm³) chlorophyll-a artefacts. When available multi-temporal products (2-3 days) can be merged to produce cloud/haze infill and further Chlorophyll-a data fusion. The above approach has the advantage of being a relatively simple approach to the monitoring of Case 2 chlorophyll-a with potential to provide a low-cost synoptic monitoring tool as a supplement to expensive point-sample field observations.

Last Update: 2005-03-15