ISIIS uses a line-scan camera. It creates one single continuous image. As water flows freely in between the lower housings (the “optical pods”), organisms are scanned as they pass through the “viewing plane”. The vehicle’s fairing ensures the flow of water is turbulence free and organisms are undisturbed.
For ease of recording and processing, the image is recorded in sections. Every 2048 pixels, the file is cut and recorded as a 2048 x 2048 pixels. When played on a screen, the series of images appear to be a “video”.
ISIIS is based on back-illumination photography. It is a shadowgraphic system that captures silhouettes of plankton. As a pseudo collimated beam of light is projected throughout the scanning area, It ensures that the projections/shadows are telecentric (The size of an object is not dependent of its position within the field of view).
ISIIS effective Depth of Field is about 50cm. Its Effective Field of View is approximately 13 to 14cm (Lens diameter is 15cm). Therefore at 5 knots (2.5m/sec), ISIIS samples: