Photographic Counting of Duckweed and Fish Population by the Mixture-Gaussian Theory

This paper discusses the organism-counting ability of the Mixture-Gaussian theory on photograph analysis and video analysis.
The test samples of the photograph experiment were the duckweeds in Xin-Hai-Qiao Constructed Wetlands in Taipei County. The actual leaf-covering quantities of duckweeds on five photos were 336, 412, 1010, 1528 and 1928. Without overlapping of leaves, the counting accuracy rates were 95.7%, 76.8%, 68.2%, 82.1 % and 90%, respectively. The major cause of counting errors was water reflection.
The video experiment was done in the laboratory and in the field. In the laboratory, three fish sizes were mixed with three kinds of water turbidity in order to find out the counting variables. As a result, when fishes were smaller, the counting accuracy tended to be inaccurate, from 79.7% to 78.4% and 64.2%. Furthermore, the counting accuracy also decreased when water turbidity increased. In fact, the water turbidity was 2.9 NTU, 10 NTU and 15 NTU, and the counting accuracy was 78.4%, 60.4% and 45.5%.
In the field, the underwater video camera was placed into Jin-Gua-Liao River in Taipei County to videotape fishes at the riverbed. After the videotape was brought back to the laboratory, it was analysed by the Mixture-Gaussian theory. The counting result of fish-flux was 4.26fish/minm3. As a matter of fact, fish-overlapping and fish-shadows of close swimming at the riverbed truly affected the counting accuracy.
The study shows that it is possible to consider the Mixture-Gaussian theory as an evaluation method of organism-counting in the field of ecological engineering.