Sc. Knowles et Jt. Wells, In situ aggregate analysis camera (ISAAC): A quantitative tool for analyzing fine-grained suspended material, LIMN OCEAN, 43(8), 1998, pp. 1954-1962
The ISAAC tin situ aggregate analysis camera) system was developed to provi
de quantitative analysis of fine-grained suspended material in waters of in
ner-coastal, estuarine, fluvial, and lacustrine environments with suspended
sediment concentrations (SSC) up to 200 mg/liter. Light from strobes is co
llimated by physically treated Plexiglas prisms, producing a well-defined v
olume of illumination (VOI) in front of a 35-mm camera mounted in an underw
ater camera housing. Particles within the VOI are in focus. Using a measure
d scale factor, researchers can measure suspended particle number, size, sh
ape, and volume concentration. A submersible pump collects water from the d
epth of each photograph, allowing laboratory analysis of filtered suspensat
e. The present system, which is easily modified to meet specific field cond
itions, illuminates a 70.0 mm x 46.9 mm x 17.5 mm volume of water and docum
ents particles similar to 10 mu m in diameter and larger. We use a 2,700-do
t-per-inch scanner to convert photo negatives to digital 256-graytone image
s. In-house software is used to classify particle morphology within 1/4 phi
size classes, from similar to 20-4,000 mu m Conversion of the ISAAC system
to digital or video camera technology would allow Teal-time data collectio
n and analysis.
In situ photographic data from the Elbe, Hudson, and Columbia River estuari
es, as well as several coastal environments in North and South Carolina, il
lustrate the utility of the system for particulate concentrations ranging f
rom similar to 2 to 200 mg/liter. A random composite sample from these data
reveals that virtually all particles may form larger aggregates, character
ized by an average equivalent spherical diameter (ESD) of similar to 300 mu
m, with <10% of the aggregate volume in suspension contained within aggreg
ates <50 mu m in diameter. Aggregates larger than 2 mm ESD have been observ
ed in <1% of the over 1,000 photographs taken, supporting suggestions in th
e literature that the Kolmogorov microscale of turbulent eddies limits the
growth of suspended aggregates.