Distance [ml

Distance [ml

Fig. 7. Propagation characteristics of electromagnetic waves in seawater in the ELF band (left) and the HF band (right).

JAMSTEC has been developing a new communication tool that uses electromagnetic waves. This method is used for mutual communication between vehicles at up to 50 m distance. A prototype transmitter, a receiver, and antennas were made. An NTSC camera for underwater use was connected to the transmitter. The transmitter encodes and modulates the image data and then supplies power of 17 Watts to a multi-turn coil antenna. A high sensitivity search coil antenna receives the modulated data. The receiver demodulates, decodes, and outputs the image in QVGA format. In the tank test, QVGA images were transmitted to the receiver set 30 m away from the transmitter. e. Satellite Communication system

Most satellite communications from the ocean use an earth orbiter satellite, for example Argos satellites and Iridium satellites, rather than a geostationary satellite because the latter needs a large sized antenna such as a parabolic antenna. However, a geostationary satellite can provide full real-time communication and a large coverage area. The Eighth

Engineering Test Satellite, ETS-VIII has as its main purpose, dealing with the increasing demand for digital communications, such as mobile phones and other mobile devices. The satellite (weight of 3 tons and diameter of 40 m) has two Large Deployable Antenna Reflectors (LDARs). Table 2 lists specifications of the ETS-VIII.

Fig. 8. Picture of ELF wave transceiver tested in tap water and a received image.

Figure 9 shows the concept of this project. Devices or facilities on the ocean are able to communicate with land stations via a satellite with a large capacity wireless network. This enables us to remotely control these devices or facilities, resulting in effective research in marine-earth science. By using the ETS-VIII, remote control of an underwater vehicle from a land station at JAMSTEC as shown in Figure 9 will be possible. For this purpose development of a satellite communication system with help from the Japan Aerospace Exploration Agency and National Institute of Information and Communications Technology was started since 2003.





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