An assessment of validation techniques for estimating chlorophyll-alpha concentration from airborne multispectral imagery

Accurate estimates of chlorophyll-a levels in coastal waters are required for the assessment of waters potentially subject to eutrophication. Traditional laboratory analysis of water samples does not offer the required spatial or temporal density of sampling. Remote sensing methods have been suggested as a more appropriate representation of the variability in chlorophyll-a concentration encountered in UK coastal waters. This paper examines the use of two established techniques for the calibration of airborne multispectral imagery to determine chlorophyll-a concentration: the blue/green ratio and Fluorescence Line Height methods. These methods have been developed for use in oceanic or Canadian coastal waters. The errors incurred in the use of these techniques for calibration of data of UK coastal waters have not previously been addressed. This paper describes a rigorous assessment of the errors incurred, allowing the limitations of the techniques to be established. This has resulted in recommendations for chlorophyll-a measurement in the coastal zone.