Use of a ship-borne laser fluorosensor for remote sensing of chlorophyll a in a coastal environment

In vivo fluorescence of chlorophyll a (chl a) was measured, with a ship-borne lidar (light detecting and ranging) system and with an in situ fluoroineter and a laboratory spectrofluoronwter, in a frontal region separating the runoff plume of the Gripe Current and marine waters of the Anticosti Gyre in the St. Lawrence Estuary, during daytime and nighttime. These fluorescence measurements were compared with extracted chl a concentrations from water samples. The results showed that lidar can. produce accurate synoptic estimates of surface chl a concentrations. The lidar instrument measured a variable fluorescence intensity F, which lies between the ground (F0) and maximum (Fm) fluorescence intensity of chl a.8 The slope of the linear regression of lidar F against extracted chl a was steeper and less variable during the night than during the day. Monitoring of all variables over a 24-h period showed that photosynthetically available radiation (PAR) up to 100 W m−2 did not significantly reduce lidar fluorescence-that is, up to 90 min after sunrise tinder cloud free conditions. In the context of lidar remote sensing from an. aircraft, dawn flights will allow measurements of F that lie close to dark-adapted values and that are little affected by PAR. At this time of day, light conditions would be adequate for safe low-attitude flights.