Both the MODIS optical sensors on the NASA Aqua and Terra spacecraft and the MERIS instrument on the ESA Envisat measure spectral radiance in bands designed to allow detection of the fluorescence signal from surface chlorophyll in sea water, stimulated by ambient sun and sky light. We present images of fluorescence as derived from the level 1 MERIS data and compare the signal levels of the fluorescence with measurements of extracted chlorophyll from research cruises during 2002 to 2004, with satellite estimates of chlorophyll from the blue to green ratio observed by MERIS, and with fluorescence measurements made by MODIS. We show that the fluorescence signal is consistent between MERIS and MODIS, and that relation between fluorescence and chlorophyll concentration in surface waters is consistent with a simple model accounting for absorption of stimulating and emitted radiation by chlorophyll pigments. Considerable scatter is observed, suggesting variable fluorescence efficiency and effects of coloured dissolved organic matter