USE OF A SHIP-BORNE LASER FLUOROSENSOR FOR REMOTE-SENSING OF CHLOROPHYLL-A IN A COASTAL ENVIRONMENT

In vivo florescence of chlorophyll a (chl a) was measured, with a ship -borne lidar (light detecting and ranging) system and with an in situ fluorometer and a laboratory spectrofluorometer, in a frontal region s eparating the runoff plume of the Gaspe' Current and marine waters of the Anticosti Gyre in the St. Lawrence Estuary, during daytime and nig httime. These fluorescence measurements were compared with extracted c hl a concentrations from water samples. The results showed that lidar can produce accurate synoptic estimates of surface chl a concentration s. The lidar instrument measured a variable fluorescence intensity F, which lies between the ground (F-0) and maximum (F-m) fluorescence int ensity of chl a. The slope of the linear regression of lidar F against extracted chl a was steeper and less variable during the night than d uring the day. Monitoring of all variables over a 24-h period showed t hat photosynthetically available radiation (PAR) np to 100 W m(-2) did not significantly reduce lidar fluorescence-that is, up to 90 min aft er sunrise under cloud-free conditions. In the context of lidar remote sensing from an aircraft, dawn flights will allow measurements of F t hat lie close to dark-adapted values and that are little affected by P AR. At this time of day, light conditions would be adequate for safe l ow-altitude flights. (C) Elsevier Science Inc., 1997.