Communication between remote instrumentation and buoy	The experimental modem controller	Raw bitmapped (no error correction) video signal as received over 2km

Communication with underwater remote operated vehicles (ROV), as well as underwater instrumentation, is usually done by using cables. These sometimes cause problems with the control of the ROV, as well as its use in areas where fouling of the cable can take place. This ultrasonic communications system can transmit colour, still and video, pictures from an ROV, as well as real-time or stored data from underwater instrumentation.

The system uses Multicarrier Modulation for underwater acoustic communications, and has been successfully tested at a data rate up to 10kbps over 1km. It is designed for operating in multipath fading environments. The transmitter and receiver use Digital Signal Processors which control the modulation and transmission, and synchronisation and demodulation, respectively.

The system algorithm generates 48 frequencies for transmitting 48 parallel bits of data in each packet. A long transmitted signal sequence is combined with synchronisation, zero gap and information packets. The long multi-frequency signal packets have been implemented to minimise the effect of multipath fading. To acquire the starting point of the transmitting sequence, the Linear Frequency Modulation (LFM) signal is used for synchronisation. In order to reduce noise, the adaptive threshold packets are used to set up a suitable signal.

Experimental results from sea-trials have shown that the system can cope with multipath fading environments and is characterised by its simplicity and robustness.

Low-cost underwater vehicle for environmental or security monitoring

The PRAWN is a low-cost six-legged remote operated vehicle designed for walking along the seabed, or inside pipes, and able to carry a low weight payload. This could be a camera, metal detector, or small instruments. It is radio controlled up to a distance of 200m and a depth of 10m.

Currently, PRAWN uses servo motors driving six legs. It is planned to modify this in the near future to use water muscles, driven from a small on-board compressor. This will allow greater depth, as well as lessen the magnetic footprint.

Pipe inspection robot

The legged Pipe Rover                                                                     The tracked Pipe Rover

This project was funded by the Department of Industry,  Hong Kong Government, via the Co-operative Applied Research and Development Scheme. A university-owned company - Pearl Technologies Ltd., - was set up to manage the project. All IPR belongs to that company.

This robot is designed to inspect the inside of full or partially filled pipes up to a diameter of 2m. Its is based around a waterproof chassis (operating at a depth of 25m) that contains the control electronics, communications, power supplies and sensors for an underwater inspection robot. The chassis is designed in such a way that it can take a number of propulsion mechanisms.

Initially, two propulsion mechanisms have been produced. First is a six-legged unit for walking in circular pipes, as well as for traversing rough terrain. The second is a tracked unit designed primarily for flat bottomed ducts.

The communications and control are designed so that in fully filled pipes/ducts or in still open water, an ultrasonic link can be used, thus obviating the need for an umbilical. In partially filled pipes or ducts, or in rough open water, environments, a light weight fibre-optic communications tether can be used.

The robot has an on-board high resolution video recorder which records the front camera picture as well as the attitude sensor data and time/distance information. A sampled, lower resolution, video signal is sent back to the control console. The robot is electrically powered, using on-board batteries, although the legs are powered by an in-house designed hydraulic system that makes use of the surrounding water.

The sensors included on the basic model include colour video inspection camera with pan and tilt and lights, ultrasonic obstacle detection and distance/depth/temperature/ heading/pitch and roll information. Owing to the modular design, it is possible to fit optional sensors such as ultrasonic pipe profiling for navigation and guidance use. This can also be recorded, along with the sensor data, at the control console. A small black and white navigation camera is built in to the rear of the robot to allow ease of extraction from the pipe or duct

Development of remote operated vehicles as platform for underwater instrumentation

Most of the monitoring of undersea living organisms is currently done by using human divers. This has many drawbacks, including potential danger to the divers as well as high costs and potential damage or disturbance to the environment under study. The use of remote operated vehicles (ROVs) for underwater surveying is a mature and widely adopted practice in harsh environments. However, most ROVs deployed today are remotely and/or semi-manually controlled. Relatively little work has been carried out in shallow water applications, and especially for an ROV that can provide minimum intrusion into the environment.

City University has recently taken possession of a Marine Science and Engineering Laboratory at Hoi Ha Wan Marine Park, in conjunction with the World Wide Fund (WWF). As part of the ongoing measurement of the underwater environment, and the monitoring of the coral reefs in the park, by colleagues in the Department of Biology and Chemistry at CityU, ROVs are to be used, initially, as instrumentation platforms. There is a strong need in this work for an ROV which can provide a highly stable instrument platform for many onboard instruments specially designed for marine biology.

This project aims to modify a commercially available ROV so that it can be used as a mobile platform for underwater instrumentation, as well as developing image scanning devices for remote sensing.

Instrumentation for marine environmental monitoring
 

Typical seabed in Hong Kong (taken with remote camera system)	Pipe discharging foul water into the environment

When monitoring a marine environment many types of sensors are needed. most have been designed to work in stand-alone systems, usually monitored via a control console or boat. Many of these were initially designed for use with divers and/or fixed positions on the sea-bed.

These commonly used sensors are being evaluated, such that their applicability for use, either on an ROV or as part of a wired or wireless underwater LAN. Some modifications, as well interface and communications circuitry, will be necessary.

The sensors that will be evaluated and used will initially be limited to those that will be used for the monitoring of coral reefs. This will include the stereoscopic video cameras, hyperspectral and possibly, spectroradiometer, as well as sensors for monitoring oxygen and pH levels. One possibility to be considered in some detail is the feasibility of using the ROV to collect water samples from various parts of the reef for further analysis on-shore.

Further applications include the laying of a network of sensors on the seabed, with constant or polled data acquistion. This may make use of the underwater acoustic modem. At the same time, image processing techniques are being used to allow the monitoring of the marine environment using fixed or mobile video cameras.

In the educational development area, along with colleagues from the Physics and Materials Science Department, she received HK$6.28 million (US$810,000) from the UGC's Teaching Development Grant for the establishment of an Integrated Teaching Studio. A further $500,000 (US$64,500) was later awarded from the same fund for the continuation of work in using multimedia to support first year EE laboratory work. This work is part of her doctoral studies.

Full details of research grants awarded since 1990.

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