An Optical Instrument For Monitoring Suspended Particulates In Ocean And Laboratory

Abstract

An o p t i c a l s e n s o r and submersible e l e c t r o n i c s u n i t h a s b e e n d e v e l o p e d f o r m e a s u r i n g p a r t i c l e c o n c e n t r a t i o n s i n t h e o c e a n , r i v e r s a n d l a b o r a t o r y . P a r t i c l e s a r e d e t e c t e d w i t h a n i n t e g r a t i n g s c a t t e ro m e t e r w h i c h c o n s i s t s o f a m o d u l a t e d i nf r a r e d emitter and p h o t o v o l t a i c d e t e c t o r . The instrument has programmable sampling modes f o r m u l t i p l e a p p l i c a t i o n s a n d i n c o rp o r a t e s CMOS i n t e g r a t e d c i r c u i t s f o r low power consumption. For shipboard surveys, t h e i n s t r u m e n t c a n b e i n t e r f a c e d w i t h CTD p r o f i l i n g s y s t e m s a n d o p e r a t e d i n a cont i n u o u s s a m p l i n g mode o n r e c h a r g e a b l e NICAD b a t t e r i e s . The b u r s t mode i s s w i t c h s e l e c t e d t o s y n c h r o n i z e s a m p l i n g w i t h s e l fr e c o r d i n g i n s t r u m e n t a t i o n f o r l o n g -t e r m d e p l o y m e n t s o f t h e i n s t r u m e n t . W e have d e p l o y e d t h e s e i n s t r u m e n t s w i t h a c o u s t i c c u r r e n t meters i n i c e -i n f e s t e d w a t e r s t o m o n i t o r s e d i m e n t t r a n s p o r t ; t h e y h a v e a l s o b e e

Sediment Size Effects in Acoustic Doppler Velocimeter-Derived Estimates of Suspended Sediment Concentration

“…Applying Equations (10)-(12) without recalibration to this dataset resulted in RMS errors of 0.62, 0.62, and 0.51, comparable to when they were applied to the tests with the well-sorted construction sand. Repeating the regression process assuming the same form as Equations (11) and (12), to determine best-fit coefficients for the Folly Island sand, yielded Equations (19) and (20) …”

“…Equation (19) is preferred because it yields results nearly as good as those obtained using Equation (20), with fewer adjustable parameters. measured or included, such as sediment shape, plays a role.…”

“…Thus, there is an infinite number of possible grain size distributions for the suspended flow, even with a constant size distribution for the bed. Equations (11) and (19) have the same form and both represent best fits to well-sorted sediment fractions of similar sizes. One may question the suitability of the proposed form of the equation if different sediments require different best-fit coefficients.…”

“…Nephelometers measure light scattered by suspended particles rather than direct light transmissions. An optical backscatter sensor (OBS) is a type of nephelometer designed to measure backscattered infrared radiation from a small sampling volume, on the order of a few cm 3 [17][18][19]. Each of these examples results in single point measurements, and all can be severely impacted by biofouling.…”

Summary of sediment resuspension monitoring activities, Old Tampa Bay and Hillsborough Bay, Florida, 1988-91

“…The biaxial electromagnetic current meters measure water velocity using the Faraday principle of electromagnetic induction where a conductor (water) moving in a magnetic field (induced by the current sensor) produces a voltage that is proportional to the water velocity. The OBS sensors are thumb-size and have an optical window at the relative position of the thumbnail (Downing and others, 1981;Downing, 1983). The optical window is used to transmit an infrared pulse of light that is scattered or reflected by particles in the water to a distance of about 4 to 8 in.…”