Miniature sensitive fluorometer for oceanographic tracer studies

Miniature fluorometers for sensing fluorescein in the ocean were developed and tested. The fluorometers were built into the trailing portion of an oceanographic chain fairing; they were roughly 10 cm square by 2 cm thick. Various developmental units had sensitivities (expressed as the rms noise equivalent weight fraction of dye in the water) between and in a 0-1 Hz bandpass. Baseline drift was of the order of per hour. The good drift and noise properties were achieved by a synchronous detector circuit operating at 16 Hz. A signal proportional to the magnitude of the excitation was used to normalize the signal from the GaAsP fluorescence sensor, thus reducing calibration errors and offset drifts caused by variations in the excitation.