We developed Autonomous Buoy, which is composed of embedded system, OPC (Optical Particle Counter) and CTD (Conductivity, Temperature, Depth) sensors, to observe underwater environment. The vehicle is an autonomous profiling float that uses a buoyancy engine to cycle horizontally while moving up and down. The autonomous buoy is controlled by embedded system composed of field-programmable gate array (FPGA) and high performance CPU, which is designated to perform image signal processing, data compression, power management and satellite communication. Embedded system acquires high-resolution particle image using linear-CCD for counting particle and CTD value and analyzes particle images in underwater environment. It reduces amount of particle image data using on-board processing that provides good performance when autonomous vehicle communicates with a satellite.