The method and equipment are described which allow remote measurements of the horizontal distributions of the phytoplankton photosynthetic activity to be carried out in situ aboard a moving vehicle (ship, plane, or helicopter). In the course of measurements the relative yield of the variable fluorescence of chlorophyll $a$ is determined, this quantity characterizing the efficiency of light utilization in the primary reactions of photosynthesis. It is shown that for the measurements to be correct, the photon fiux density of the activating pulse in the volume probed must be no smaller than $5 \times 10^{22} cm^{-2} s^{-1}$, that of the probing pulse must not exceed $10^{22} cm^{-2} s^{-1}$, and a time interval of 40-70 μs between these pulses must be ensured. The results of laser determinations of the photosynthetic activity of phytoplankton over extensive water areas of the North-West Atlantic are discussed.
Department of Quantum Radiophysics, Faculty of Physics, Moscow State University, Leninskie Gory, Moscow, 119992, Russia
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