Command, control and data transport for underwater robots using acoustic communications

Undersea robots are being used in environments where immediate supervision by human operators becomes ever more difficult and potentially dangerous. This necessitates the evolution toward autonomy in the robot, while at the same time maintaining some capability to provide a reduced level of supervision, and transmission of sensor data to the human observer. The US Navy´s Coastal Systems Station (CSS) is developing battery-powered robotic crawlers for mine countermeasures purposes in very shallow water. These machines carry a variety of sensors designed to detect the presence of underwater objects and to classify them as either man-made or natural, as well as camera systems to capture images of the objects. Benthos, Inc. is collaborating with CSS to provide acoustic communications (acomms) for both command and control and for transmission of images and sensor data. The University of California at San Diego is developing wavelet-based image compression to support the telemetry. Experimental results demonstrate that compression ratios of better than 100:1 provide acceptable visual representation to a human operator. The modem aboard the crawler provides robust acomms at rates up to 1200 bits per second at kilometer ranges. At this baud rate we can transmit a 320×240 pixel greyscale image compressed at 100:1, in in under 6 seconds. In the near term, the modems will provide the same image in under 2 seconds. Using existing capabilities, the acoustic transmission can be relayed via multiple modems for many kilometers, then via a Benthos gateway buoy, to the operator via a spread spectrum radio or cell phone link. Current efforts at CSS focus on the evolution of crawler autonomy with occasional supervision supplied via the acomms link. Sensors are being integrated with the vehicles to enable them to detect, locate, and image objects such as mines on the sea floor. The crawling robots have the distinct advantage of operating in the same plane as the targets, and can therefore exploit target features that cannot be used in other countermine approaches.