The optical properties of both phytoplankton and zooplankton were investigated in this study. The absorption spectrums of planktons were measured using an UV-visible spectrophotometer. An absorption peak was found at 670 nm for the phytoplankton. A particle detecting system for an optical plankton counter (OPC) was designed and built with a red LED as a light source based on the optical characteristics of plankton. In order to observe underwater environment, the embedded system was developed. The autonomous float is controlled by embedded system composed of field-programmable gate array (FPGA) and CPU to perform image signal processing, data compression, power management and satellite communication. Embedded system acquires high-resolution particle image using a linear-CCD for counting particles in underwater environment. On-board signal processing reduces amount of particle image data for good performance in satellite communication. Using OPC and the embedded system, scanning images of brine shrimp was acquired.