Underwater acoustic communication is a technology that uses sound or acoustic waves and water as its propagation medium. This technology has been used in various fields, such as underwater wireless sensor networks, underwater monitoring system, and surveillance systems. An acoustic modem is required to facilitate communication between nodes. In this paper, an underwater acoustic modem using Frequency Shift Keying (FSK) modulation has been designed. This modulation is widely used because of its reliability and simple design. FSK modem was designed using M=2 level or known as Binary FSK (BFSK) with 40 kHz mark frequency and 43 kHz space frequency. This study tested data packets sending and its error rate against the distance variation. Testing for 70-bit data resulted in 1% error at 100 cm distance and 37% error at 170 cm distance. When compared with the previous testing at 1200 bps which resulted in 0% and 35% error, it can be seen that error at 1200 bps is better than at 2400 bps, but the data transmission was better at 2400 bps. Addition to the number of bits sent and distance has an influence on the error value, i.e. the greater the distance and the amount of data sent, the greater the error value.

https://online.bpostel.com/index.php/bpostel/article/download/180102/426

Underwater Data Transmission Using Frequency Shift Keying (FSK) Modulation with Bit Rate of 2400 bps

A dense seismic reflection survey with a 400-m (1312-ft) line spacing has been conducted in a 14- by 16-km (9- by 10-mi) area offshore southwestern Taiwan where bottom-simulating reflectors (BSRs) are highly concentrated and geochemical signals for the presence of gas hydrate are strong. A complex interplay between north-south–trending thrust faults and northeast–southwest oblique ramps exist in this region, which impacts on the distribution and seismic characteristics of the BSR. A clear BSR is observed almost continuously in the southeastern half of the survey box, whereas BSRs either appear as small patches or are absent in the northwestern half. The reflection coefficient at the BSR presents abrupt lateral variations, with an average value of 0.094 or 32% of the reflection coefficient at the sea floor. A pattern of seismic blanking beneath the ridge crests overlying a high-amplitude BSR with bright reflections below the BSR in the slope basins reveals the significance of tectonics and sedimentation of the formation of BSRs. Local heat-flow values estimated from BSR subbottom depths show different ranges across the northeast–southwest-trending Yung-An lineament (YAL), with higher heat-flow values ranging from 55 to 70 mW/m2 in the southeastern half of the survey area, whereas the heat-flow values range from 45 to 55 mW/m2 to the northwest of the YAL. In the southeastern part of the survey area, an elongated diapiric feature deforms the sedimentary layers, BSRs occur shallower, and high heat-flow values are inferred. Furthermore, local dips of BSRs and sedimentary strata that crosscut the BSR at intersections of any two seismic profiles have been computed. A dominant N308 stratigraphic updip direction characterizes the anticlinal ridges; stratal dips fan out toward N285 south of the ridges and toward N330 north of the ridges. The concentric patterns of steep stratigraphic dips constitute favorable migration paths for the upward transport of fluids with significant dissolved-gas content across the BSR, which correlate well with the high gas volumes sampled in this area.

Structural Controls on the Formation of Bottom-simulating Reflectors Offshore Southwestern Taiwan from a Dense Seismic Reflection Survey

Underwater acoustic modems are commonly used to send and receive data in underwater communications, this device converts the digital data on the sending side into acoustic signals. The acoustic signal that is sent will then be received by another modem and the received acoustic signal will be converted back into digital data. In order to communicate between nodes in underwater communication, an acoustic modem is needed, where the implementation of its use is such as in underwater wireless sensor networks, underwater surveillance systems and underwater monitoring systems. Frequency Shift Keying (FSK) is a modulation scheme that is often applied in underwater communications. In this paper, we analyze the performance of an acoustic modem with a bitrate of 4800 bps implemented in the FSK modulation scheme. The size of the data packet sent is 7 bits. This proposed bitrate scheme of FSK modulation aims to test higher modulation speeds. The test results show that the measurement of the Bit Error Rate (BER) at a distance of 100cm is 0%, while at a distance of 160cm it has a BER value of 12%. 

Performance analysis of 4800bps FSK acoustic modem for short range underwater communication

With the depletion of land resources, marine resources development and utilization become increasingly apparent. Accompanied by the development of marine resources from nearshore extension to the deep ocean, Unmanned Underwater Vehicles (UUVs) become key instruments. Generally, UUVs include autonomous and tethered types; each has its advantages and disadvantages. Through the use of combined vehicle systems, we could take advantages of both systems. With the recent advent of seafloor observatories, deep submergence science is poised to enter a new research era where scientists will gain a more detailed understanding of various seafloor features. In this study, the Autonomous Underwater Vehicle (AUV) path planning in west Good Weather Ridge (119 55', 22 15') with the multi-beam echo sounder to obtain underwater topography. In order to observation the environment, the Remotely Operated Vehicle (ROV) is hired to carry out the terrain image at 1350m water depth in detailed. This experience will help to build future underwater investigation capabilities.

Shao-Yong Liu

Papers

Underwater topography measurement and observation in Southwest Taiwan using unmanned underwater vehicles