ISO IEC 30140-1:2018 pdf free.Information technology – Underwater acoustic sensor network (UWASN) – Part 1: Overview and requirements.
5 UWASN overview and applications
5.1 Overview
Figure 1 shows the basic topology of UWASN. In a cluster-based network, the data sensed by underwater acoustic sensor nodes (UWA-SNodes) are transmitted via acoustic communication to an underwater acoustic gateway (UWA-GW) using an underwater acoustic cluster head (UWA-CH), unmanned underwater vehicle (UUV), or relay nodes. Users receive the transmitted data through various externally connected networks (e.g. radio frequency (RF) or satellite communication). During these processes, underwater communication is implemented by acoustic communication. In general, UWA-GWs are either moving nodes or fixed nodes. Topologies and communication configuration models could be adaptively modified according to the application domain’s needs at any given time.
RF communication systems are used in terrestrial sensor networks. The reasons for this are their high efficiency and low cost. Underwater RF communication is very difficult due to limited wave propagation characteristics that arise from the high attenuation due to the conductivity of water. Underwater communications can also be achieved by optical links employing lasers or LED light sources. Optical waves are still affected by attenuation, but can typically operate over longer ranges than RF.
Diode laser beams and low cost light sources such as LEDs can also be utilized. A light source for an underwater communications system is practicable using LEDs with an optical wavelength between 400 nm and 550 nm.[3]
Presently, underwater acoustic communication is the primary method for establishing wireless communication among UWA-SNodes, UUVs and UWA-GWs. This is because sound travels much further in water than RF radio signals. A UWASN consists of different types of UWA-SNodes and UUVs positioned so as to perform collective underwater monitoring. UWA-SNodes and UUVs are organized autonomously into a network that should adapt to changing ocean environments over time.[4]
UWA-SNodes are applicable to pollution monitoring, oceanographic information gathering, strategic observation, assisted navigation, offshore examination, and disaster prevention. Several UUVs with equipped sensors explore underwater resources and gather precise location information. To make this possible, reliable underwater communication between UWA-SNodes and UUVs is required.
UWA-SNodes and UUVs should have self-configuration capabilities that allow them to network themselves. They should manage the operations by sharing location information, configurations, and movements, in order to send monitored data to an on-shore location.
5.2 Application domain of UWASN
A UWASN can realize unexp’ored underwater applications, increasing the capacity for detecting and forecasting changes in time-varying oceanic environments. Table 1 shows the UWASN market segments and their current and future potential applications.
Annex A provides a description of the selected application of UWASN.
6 Characteristics of UWASN in terms of the effects of propagation variability
6.1 Underwater acoustic communication
Underwater acoustic communication method is used for underwater data transfer. It can establish acoustic communication with the help of transducers. Due to time variations of the channel, limited bandwidth, multipath propagation, and strong signal attenuation, underwater communication is difficult. Because of the high conductivity of seawater, acoustic communication works far better than the RF communication.
Concerns that should be examined while planning UWASN system are:
— attenuation of water limits sound’s propagation distance;
— path dependent, low propagation speeds of the sound, varying in the interval of (1500 ± 120) m/s;
— echoes and interferences caused by multipath(s) due to sea bottom and sea surface reflections, as well as between the layers of water body with different densities;
— acoustic signal disturbed by different characteristics of underwater channel and Doppler’s effect not only from motion of transmitter and receiver but also from time-variability of the surface and water column [5];
— noise level in underwater can corrupt or block parts of signal.
Sound is produced when an object vibrates and transmits motion to the surrounding physical medium. This results in the propagation of vibrations, where the particles in the medium oscillate in the same direction as the propagation.ISO IEC 30140-1 pdf download.