Velocity is vital information for navigation and oceanic engineering. Coherent Doppler sonar is an accurate tool for velocity measurement, but its use is limited due to velocity ambiguity. Velocity ...measured by frequency shift has no velocity ambiguity, yet its measurement error is larger than that of coherent Doppler sonar. Therefore, coherent Doppler sonar assisted by frequency shift is used to accurately measure velocity without velocity ambiguity. However, the velocity measured by coherent Doppler sonar assisted by frequency shift is affected by impulsive noise. To decrease the impulsive noise, Kalman filter and linear prediction are proposed to improve the velocity sensing accuracy. In this method, the Kalman filter is used to decrease measurement error of velocity measured by frequency shift, and linear prediction is used to remove the impulsive noise generated by a wrong estimate of the integer ambiguity. Lab-based experiments were carried, and the results have shown that coherent Doppler sonar assisted by frequency shift, Kalman filter and linear prediction can provide accurate and precise velocity with short time delay in a large range of signal to noise ratio.
With high accuracy and resolution Pulse-to-Pulse coherent Doppler sonar is wildly used in both laboratory and field application. However, the occurrence of range and velocity ambiguities brings ...serious limitations on the more general application of the technique. One method to deal with speed ambiguities is to import a dual pulse repetition interval which can provide acceptable speed ambiguities and requires uncomplicated equipment. The experiments are carried out under the frequency of 200KHz with 40ms and 60ms pulse intervals in a water tank. The results show that this method is efficient and produces high quality velocity data to track the velocity of an object in a limited range in water.
Generally, in-depth knowledge is required of all huge plant operators in order to continuously keep the plant in a good condition. Ship engineers have the same work as huge plant operators except for ...the conditions of self-reliance and self-sufficiency at sea. On the basis of the cognitive process of human activities, Rasmussen proposed three different modes, such as the knowledge-based mode, the rule-based mode, and the skill-based mode. An important but complex feature is to understand how to accomplish the plant operator shift between each mode. In this paper, the authors focus on improving the proficiency of ship engineers. Some experiments were carried out on the training ship of the National Institute for Sea Training, Japan.
This paper presents a measurement method combining conventional and coherent Doppler sonar using an adaptive algorithm to reduce measurement error at a wide range of SNRs. In our previous paper, we ...proposed a combined method to provide accurate and precise velocity using a fixed range of ambiguity velocity. The combined method worked well at high SNRs, but at low SNRs it was not as accurate. In order to provide accurate velocity at a wide range of SNRs, an adaptive algorithm for the range of ambiguity velocity is proposed at navigators' request. The results of theoretical and numerical error analyses showed that the combined method using the adaptive algorithm provides accurate and precise velocities at a wide range of SNRs.
Pulse-to-pulse coherent Doppler sonar is an autonomous and powerful tool for velocity measurement in laboratory and field applications. However, coherent Doppler sonar has velocity ambiguity that ...limits measureable velocity. Some techniques have been developed to extend the ambiguity velocity, but they are not yet enough to eliminate it completely. On the other hand, conventional Doppler sonar, while it does not have velocity ambiguity, has larger velocity error than coherent Doppler sonar. In our research, we combine conventional and coherent Doppler sonars in a method to provide accurate and precise velocity without ambiguity. Three kinds of sonar are introduced: conventional, coherent and combined Doppler. Theoretical errors of conventional and coherent Doppler sonars are explained, and the measurement error of combined Doppler sonar is obtained theoretically. From results based on a simulation, it is clear that under certain conditions, the combined Doppler sonar can provide accurate and precise velocities without velocity ambiguity.
Conventional (usually used) Doppler sonar, though unlimited by velocity range ambiguity, takes seconds to return valuable velocity readings. Coherent Doppler sonar has been proposed to provide ...accurate velocity with short time lag for current or turbulent. However the velocity ambiguity seriously limits its general application. In this paper, combined Doppler sonar is proposed to overcome the disadvantages of both conventional and coherent Doppler sonars. An adaptive algorithm is used for combined Doppler sonar to provide accurate and precise velocity information at a wide range of SNRs. Experiments are carried out to evaluate the performance of combined Doppler sonar proposed. Based on experimental results, with suitable ambiguity velocities, combined Doppler sonar can provide accurate and precise velocity information at a wide range of SNRs.
Pulse-to-Pulse coherent Doppler sonar has the advantages of quick-response and high accuracy when compared with the conventional Doppler sonar and has become widely used in laboratories and for ...commercial products. However, this system has the limited range and ambiguity velocity, which limits more general applications. Multi-frequency and dual time intervals have been proposed to enlarge the ambiguity velocity, but it is still in adequate. Conventional Doppler sonar has no ambiguity velocity and its velocity range is virtually unlimited as we had expected, but the accuracy of conventional Doppler sonar is not good with short time lags. In this paper, the symbiotic combination method is introduced to take advantage of both conventional and coherent Doppler sonar. The symbiotic combination method can provide accurate velocity without ambiguity velocity and has a much shorter time lag compared to the conventional method. A simulation using symbiotic combination method was carried out with different SNR, and the results indicate that this method can be used to provide highly accurate velocity information with a short time lag.
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