DRAFT paper
19990509
by Wesley R. Elsberry
The biologist collecting data in the field requires reliable and rapid means of documenting specimens. The advent of low-cost video capture devices for computers makes videography a useful tool for this purpose. Videography is indicated when conventional still photography or digital still photography would be cost-prohibitive. Videography is counter-indicated if details requiring high resolution are at issue.
Let's say that I wish to perform an analysis of size distribution of the common coquina clam Donax variabilis over a section of shoreline. I would likely set up a sample grid such that I would collect a specified volume of material from each station. I would want to collect the sample material from all stations in as short a period of time as possible, since I would want to control for migration of the clams up and down the beach with the tides. Since my study concerns size information, I have no need to take and preserve the clams after measurement -- they can be returned to their original sample points alive. But if my measurement procedures take a long time, I will have significant mortality in the sample specimens anyway.
This is where the use of videography plays a part. I can set up my video camera to document the section of beach with the sample grid and precisely record the timing of sample acquisition at each point in the grid. Once all the sample material is acquired, I can then set the video camera for closeup work. By using a plastic sheet ruled with a grid of lines at the centimeter or millimeter level, I can place each clam on the grid in front of the camera for a period of two to five seconds, and then that clam is ready to be returned to its original location. Two rulers placed orthogonally to each other can substitute for gridding the plastic sheet. A china marker can be used to add labelling, such as the particular station in the grid each specimen is from.
After field data collection is done, analysis of the video data can begin. In this case, a frame from each display of a clam is captured onto computer. By using the grid or rulers in the frame, the size of the clam can be determined and entered into a spreadsheet or directly into a statistics package.