Sensoriamento remoto

int. j. remote sensing, 2001, vol. 22, no. 2 & 3, 359–368

On the calibration and use of in situ ocean colour measurements for monitoring algal blooms
D. G. BOWERS†, S. KRATZER¶, J. R. MORRISON‡, P. S. D. SMITH†, P. TETT§, A. W. WALNE d and K. WILD-ALLEN§
†University of Wales Bangor, Menai Bridge, Anglesey LL59 5EY, Wales, UK ‡Bermuda Biological Station for Research, Ferry Reach, St. George’s, GE01, Bermuda §Department of Biological Sciences, Napier University, 10 Colinton Road, Edinburgh EH10 5DT, Scotland, UK d Sir Alistair Hardy Foundation for Ocean Science, The Laboratory, Citadel Hill, Plymouth Pl1 2PB, England, UK ¶Department of Physical Geography, University of Stockholm, S-106 91, Stockholm, Sweden (Received 6 January 1999 ) Abstract. Simultaneous in situ measurements of chlorophyll concentration and water colour are reported at three diverse sites: a sea loch, the west Scottish shelf and the north Atlantic. A good (R2 5 0.97) log–log relation exists between the ratio, c, of the irradiance re ection coe cients at 490 and 570 nm and the chlorophyll concentration, C, over a range of chlorophyll concentrations from 0.01 to nearly 50 mg mÕ 3 . This relation can be expressed as C 5 1.87 cÕ 1 .8 1 . The equation is very similar to that used in remote sensing algorithms for the conversion of ocean colour data into chlorophyll concentrations. The root mean square (RMS) variation of observed chlorophyll about the values predicted by this equation is 33%. The robustness of this algorithm implies that this colour ratio can be used to monitor chlorophyll concentrations in case 1 waters with a minimum of additional calibration information. As an illustration, a time series is presented of colour-ratioderived chlorophyll concentration during the spring bloom in a Scottish sea loch in 1994. The data show reasonable agreement with the chlorophyll time series measured by a recording uorometer, and a comparison of the two time series serves to highlight the advantages