AIR OUTLET 



SAMPLE JARS 



Figure Al6. Nielsen self -siphoning suspended sediment sampler 

 (from Nielsen 1983) 



Instantaneous . 



(1) Optical 



(a) Transmissometers 



Transmissometers , nephelometers , and almometers 

 measure the concentration of suspended sediment by 

 means of transmitted light over a fixed path length. 

 The instruments usually consist of a light source and 

 sensor on separate mounts; as sediment passes between 

 the mounts, an attenuation in light is detected and 

 can be calibrated to indicate the concentration of 

 material in suspension. The amount of light trans- 

 mitted through sediment-laden water depends on the 

 distance between the source and sensor, sediment grain 

 size and shape, fluid opacity, amount of organic 

 material in suspension, amount of natural light, and 

 quantity of air entrained in the fluid. The instru- 

 ments can be calibrated for the source-to-sensor 

 distance and grain size expected in the field; 

 however, the degree to which the other variables will 

 enter cannot be predicted. Hom-ma, Horikawa, and 



A27 



