Abstract: The application of an hand-held fluorometer used to monitor algal growth on stone surfaces is reported. The system is based on a modulated ultra-bright blue LED, used to induce chlorophyll-a fluorescence, as well as that of accessory pigments. With the addition of an encoding wheel and when linked to computer this system can produce real time map of the algae population on solid surface. The system has been shown to have a linear response to algal concentration, making it a viable tool for algal monitoring. The hand-held system is relatively immune to ambient light allowing it to be used on-site in various daylight conditions. Results from field and laboratory tests of the system on historically important sites and test samples are presented.!5
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