Richard W. Spinrad

A Low Power, High Resolution, In Situ Fluorometer For Profiling And Moored Applications In Water

Sea Tech Inc. has developed an in situ fluorometer to measure chlorophyll a fluorescence in aquatic environments. The instrument has been developed within stringent constraints of size, weight and power consumption. The use of custom-designed components, including the flashlamp, excitation and emission filters, and energy storage capacitor for the light source has permitted optimal mechanical, optical and electrical design of the instrument. This new design results in efficient stimulation and detection of chlorophyll a fluorescence. The instrument is not sensitive to ambient light and has excellent stability over time and temperature. Chlorophyll a concentration is measurable on three selectable ranges of approximately 3, 10 or 30 µg/1 full scale with a minimum detectable signal of <0.02 gg/1. Time constants of 0.1, 1, 3 and 10 seconds are selectable to smooth the output data. Power requirements are nominally 12 VDC at 150 mA, and output signal is 0 to 5 VDC. These power requirements and signal levels make the fluorometer compatible with most oceanographic moored and profiling data acquisition systems. Operating depth for the instrument is rated at 500 meters with a plastic housing or 3000 meters with a stainless steel pressure housing.

Volume scattering function of suspended particulate matter at near-forward angles: a comparison of experimental and theoretical values

Narrow angle light scattering measurements were made for various sizes of spherical particles suspended in water. These were compared to calculated theoretical scattering values as derived from the theory of Mie (1908). Through measurements with different particle concentrations at angles between 0.2 degrees and 0.7 degrees the effect of the unscattered main beam light was removed. Results agreed well with Mie theory for these angles.

Optical Properties Of Turbidity Standards

Measurements of light scattering and light attenuation were made for suspensions of formazin and diatomaceous earth. Light scattering was measured for light of wavelength 632.8 nm at angles from 0.1° to 1.0° and for light of wavelengths 400, 500, 550, 600, 650, and 700 nm at 45°. Light attenuation was measured over a 25 cm pathlength for light of 660 nm. These measurements were made for suspensions which varied from 0 to 40 Jackson Turbidity Units of formazin and 0 to 40 mg/1 of diatomaceous earth. The results indicate the necessity for multiple optical measurements for determinations of turbidity of water. In addition the tables and curves presented may be used in the calibration of light scattering meters and transmissometers which are used for turbidity studies.

Measurements Of The Volume Scattering Function At Near Forward Angles For Suspended Oceanic Particulates

Measurements of the volume scattering function were made from 0.1° to 1.0° from the main beam for two types of phytoplankton (Amphidinium C. and Thalassiosira F.) and one quartz suspension. The functions obtained were quite flat within that angular range as predicted by theory. Using particle size distribution measurements and tables of theoretical scattering values the theoretical volume scattering functions of the samples used were also determined. The theoretical volume scattering functions for particulate indices of refraction of 1.02 and 1.15 were close in value to the obtained functions for the phyto-plankton but the measured scattering function of the quartz particles was much higher than the theoretical prediction. The explanation for this probably lies in the fact that the quartz particles have a significantly higher composite index of refraction than either of the phytoplankton. The results of this experiment are part of a system of experiments that will be made to be able to determine the index of refraction distribution of oceanic particulate matter.