Improvement of Seafloor Positioning Through Correction of Sound Speed Profile Temporal Variation

Dear Editor,This letter proposes a high-precision seafloor transponder positioning method based on the correction of sound speed profile(SSP)temporal variation.In the proposed method,the ocean sound speed error is modeled as the temporal variation of a background SSP,and the linearized expression of the acoustic travel time with respect to the sound speed coefficient is derived based on the ray acoustic model.Moreover,the proposed method introduces the constraint of acoustic ranging observations between seafloor transponders and determines the weights of travel time and ranging observations using Akaike’s Bayesian information criterion(ABIC)to reduce the positioning error caused by the correlation between sound speed and position parameters.The experimental results in the South China Sea show that the proposed method performs better than the global navigation satellite system-acoustic ranging combined positioning solver(GARPOS)[1],in terms of rigid distance errors and long baseline positioning accuracy.

A Block Parallel l_0-Norm Penalized Shrinkage and Widely Linear Affine Projection Algorithm for Adaptive Filter

To improve the identification capability of AP algorithm in time-varying sparse system, we propose a block parallel l_0-SWL-DCD-AP algorithm in this paper. In the proposed algorithm, we first introduce the l_0-norm constraint to promote its application for sparse system. Second, we use the shrinkage denoising method to improve its track ability. Third, we adopt the widely linear processing to take advantage of the non-circular properties of communication signals. Last, to reduce the high computational complexity and make it easy to implemented, we utilize the dichotomous coordinate descent(DCD) iterations and the parallel processing to deal with the tapweight update in the proposed algorithm. To verify the convergence condition of the proposed algorithm, we also analyze its steadystate behavior. Several simulation are done and results show that the proposed algorithm can achieve a faster convergence speed and a lower steady-state misalignment than similar APA-type algorithm. When apply the proposed algorithm in the decision feedback equalizer(DFE), the bite error rate(BER) decreases obviously.

水下传感器网络定位技术发展现状及若干前沿问题

由于海洋环境中温度、压力、波浪、海洋生物等因素的影响,致使绝大部分陆地无线传感器网络定位技术无法直接应用于水下传感器网络,需要结合其独特的海洋声传播环境进行研究.近十年来,水下传感器网络定位技术取得了巨大的进步,本文综述了水下传感器网络定位技术的研究现状,探讨了水下传感器网络定位技术中的若干前沿问题,并展望了水下传感器节点定位技术在近几年内预期能够解决的现实问题.

Seafloor geodetic network establishment and key technologies

Seafloor geodetic network construction involves the development of geodetic station shelter, network configuration design, location selection and layout, surveying strategy, observation model establishment and optimization, data processing strategy and so on. This paper tries to present main technological problems involved in the seafloor geodetic network construction, and seek the technically feasible solutions. Basic conceptions of developing seafloor geodetic station shelters for shallow sea and deep-sea are described respectively. The overall criteria of seafloor geodetic network construction for submarine navigation and those of network design for crustal motion monitoring are both proposed. In order to enhance application performances of the seafloor geodetic network, the seafloor network configuration should prefer a symmetrical network structure. The sea surface tracking line measurements for determining the seafloor geodetic station position should also adopt an approximately symmetrical configuration, and we recommend circle tracking line observations combined with cross-shaped line(or double cross-shape line) observations for the seafloor positioning mode. As to the offset correction between the Global Navigation Satellite System antenna phase center and the acoustic transducer, it is recommended to combine the calibration through external measurements and model parameter estimation. Besides, it is suggested to correct the sound speed error with a combination of observation value correction and parameterized model correction, and to mainly use the model correction to reduce the influence of acoustic ray error on the seafloor positioning. Following the proposed basic designs, experiments are performed in shallow sea area and deep-sea area respectively. Based on the developed seafloor geodetic shelter and sufficient verification in the shallow sea experiment, a long-term seafloor geodetic station in the deep-sea area of 3000 m depth was established for the first time, and the preliminary positioning result shows that the internal precision of this station is better than 5 cm.

High-resolution topography measurement of PACMANUS and DESMOS hydrothermal fields using a ROV in Manus basin

In China,the lack of high-resolution topographical data from small target areas limits our understanding of deep sea phenomena.Here,the high-resolution topography of the PACMANUS hydrothermal field and the DESMOS hydrothermal field were measured using a remotely operated underwater vehicle(ROV)with a multibeam system.A composition positioning system on the ROV provided high positioning accuracy(greater than 0.5 m).The data show that four knolls develop in the PACMANUS field on the crest of the Pual ridge.The

A Symbol-Based Passband Doppler Tracking and Compensation Algorithm for Underwater Acoustic DSSS Communications

In this paper,we consider the problem of Doppler tracking and compensation for a direct sequence spread spectrum(DSSS)signal in underwater acoustic(UWA)communication.Since the dynamic property of the UWA channel and the long duration of DSSS signals result in significant Doppler spread that severely distorts the propagated signal,Doppler tracking and compensation are required.Based on the ultra-wideband property of UWA signal,the Doppler spread not only results in the frequency shift,but also changes the signal duration.Therefore,the accurate estimation of the signal expansion/compression in the time domain can reflect the Doppler spread.Accordingly,we present a Doppler tracking and compensation algorithm for a DSSS signal operating on the correlation output of passband signal at a symbol-by-symbol basis.Note that the carrier frequency of UWA communication is around several kilohertz,and thus the time delay estimation can be performed on the passband to improve the accuracy.Furthermore,the prior information of Doppler limit is used to refine the resolution of delay estimation and achieve sequential estimation.To compensate the correlation magnitude distortion induced by the velocity variation,the local reference signal is selected adaptively based on the filtered Doppler factor.Simulation results demonstrate that the proposed passband Doppler tracking algorithm achieves a superior performance compared with the conventional receiver.