Showing papers on "Secchi disk published in 1970"

The secchi disk in turbid coastal waters1

Abstract: Measurements of Secchi disk depth are correlated with beam transmittance (B) in turbid coastal water. Both k (the irradiance attenuation coefficient) and a! (the beam attenuante coefficient) can be estimated from the Secchi depth either on an empirical basis or by using the Duntley-Preisendorfer equation of contrast reduction, Such estimates possess relatively large standard errors of estimate. The effects of the size of Secchi disk and viewing techniques are discussed. An estimate of contrast threshold of the human eye under field conditions has been obtained. A modification of the factor in the Poole and Atkins equation for estimating k from Secchi depth is suggested.

Monitoring Of Coastal Waters Of The Baltic SeaBy Airborne Imaging Spectrometer AISA

Abstract: Aim of the present work is to test what parameters of coastal waters could be quantitatively and operatively monitored with passive optical sensors from airborne and/or satellite measurements. Airborne imaging spectrometer AISA was used for remote measurements. Flight campaign was carried out in the Archipelago Sea, south-western coast of Finland. Simultaneous in situ measurements were carried out onboard research vessel Muikku and two outboard work boats. Suitability of more than seventy retrieval variables, proposed by different authors, was tested in estimation of concentrations of chlorophyll a, suspended matter and pheophytin, as well as water turbidity and Secchi disk depth.

Estimation of suspended sediment concentrations in natural water bodies from Secchi disk measurements.

Abstract: The Secchi disk i s one of the simplest and l e a s t expensive instruments f o r measuring the rate of attenuation of l i g h t i n natural water bodies. Because t h i s rate of attenuation i s often c l o s e l y r e l a t e d to the concentration of suspended sediment i n the water, disk measurements may, i n some s i t u a t i o n s , provide a u s e f u l and inexpensive a l t e r n a t i v e to the standard gravimetric methods f o r determining sediment concentration. Published empirical .studies i n d i c a t e that s a t i s f a c t o r y r e l a t i o n ships between Secchi disk transparency and concentration can be establ i s h e d but that these r e l a t i o n s h i p s d i f f e r from area to area and become more complex as t u r b i d i t y increases. Results presented i n t h i s paper based on data from the Mackenzie d e l t a , N.W.T. support these conclusions. These r e s u l t s cover a range of t u r b i d i t i e s which extends w e l l above those previously examined. Phy s i c a l i n t e r p r e t a t i o n of these empirical r e s u l t s i s made d i f f i c u l t by the large number of uncontrolled variables associated with Secchi disk readings. This i n t e r p r e t a t i o n i s f a c i l i t a t e d by the i n t r o duction of objective attenuation c o e f f i c i e n t s (more variables controlled) as v a r i a b l e s intermediate between transparency and concentration. The two c o e f f i c i e n t s most commonly used are the volume attenuation c o e f f i c i e n t oc and the d i f f u s e attenuation c o e f f i c i e n t f o r downwelling i r r a d i a n c e K^. Empirical r e l a t i o n s h i p s between e i t h e r of these objective