Real-time size distribution, concentration, and biomass measurement of marine phytoplankton with a novel dual-beam laser fluorescence Doppler cytometer.

A novel cytometer is reported for measuring particle-size distribution, concentration, and biomass of marine phytoplankton containing chlorophyll a. The system utilizes optical fibers to carry light to and from a flow tube for measuring phytoplankton taken directly from the ocean. A unique feature of this system is in the simple optical detection scheme for which sample handling and preparation are not required. This simplicity makes the system especially suitable for field measurements. The system utilizes sophisticated digital signal processors to handle and reduce the large amount of data gathered. The signal-processing algorithms are vigorously streamlined to process the signals in real time, thus computing size and flow velocity information instead of logging the raw data. The high efficiency of the signal processors gives the system a performance throughput of ~250 particles/s. The system was tested both in the laboratory and in the field, yielding good discrimination of size distribution and sensitivity of concentration.