The detection of sea water depth with the help of ultrasound Essay

One of the classical way to detect depth in sea water or in reservoirs is by using ultrasound devices which the ultrasound source acts as emitter and transducer as receiver. By knowing the time delay of the reflected signal and the speed of propagation in water which is approximately 1500m/s, the distance of water depth can be determined. An underwater ultrasonic transducer is an electromagnetic device which can convert electrical energy to mechanical energy (sound waves) and vice versa. By creating sound wave transmitting through water, it can intercept with objects within its path and hence, a portion of energy is reflected back to the transducer. The distance to the object can be measured by the time difference between transmitted pulse and received echo [6].

According to various researches, ultrasound sensors are very useful in distance measurement in air and underwater. C.C.Chang had studied the ultrasonic measurement system for underwater applications. It uses ultrasonic system, laser system and camera based system for 3D position control of underwater vehicles [3]. A performance study of distance measurement sensor with different object materials and properties was conducted by A.M. Kassim [7]. The distance was measured by using infrared sensor and ultrasonic sensor at three objects with different properties which were hard, soft and transparent and also two different conditions which were water and sound wave. The results showed that ultrasonic sensor gave more stable and accurate measurement compared to infrared sensor under those properties and conditions. When the experiment was conducted under water condition, distance measurement using infrared sensor was totally out of range while ultrasonic sensor provided stable and consistent readings [7].

As we know that sound can travel in the air, liquids and metal, so it is possible to use ultrasound for distance measurement in the environments. Ultrasound shows a better performance in distance measurement compared to light waves and electromagnetic waves. This is so because ultrasound has lower speed and shorter wavelength. Higher precision in measurement can be achieved due to longer measurement time because of its slower propagation velocity. Besides, better resolution is obtained because of its shorter wavelength as well. Therefore, it is more applicable and reliable for distance measurement in the liquids and solids which have lower light transmission rates [8].

Furthermore, there are two ways of measuring depth of liquid which are contact and noncontact methods. Contact methods are basically resistive method, inductive and capacitive methods. While the most common noncontact methods are optical method, radar and ultrasonic method. For water depth measurement, contactless methods are always more preferable to prevent the quality of water in tank being affected. All the noncontact methods are actually working on same principle which first transmitting a signal and measuring the time for the sent signal to come back [11].

After researching and reading on different type of papers and studies, ultrasonic sensing system is the most suitable approach to measure depth of sediment underwater. Hence, in this project, ultrasonic sensor will be used in implementing sedimentation sensing system.