A new acoustic positioning method for Autonomous Underwater Vehicles (AUV) that uses a single underwater hydrophone is proposed in this paper to solve problems of Long Baseline (LBL) array laying and communication synchronisation problems among all hydrophones in the traditional method. The proposed system comprises a Strapdown Inertial Navigation System (SINS), a single hydrophone installed at the bottom of the AUV and a single underwater sound source that emits signals periodically. A matrix of several virtual hydrophones is formed with the movement of the AUV. In every virtual LBL window, the time difference from the transmitted sound source to each virtual hydrophone is obtained by means of a Smooth Coherent Transformation (SCOT) weighting cross-correlation in the frequency domain. Then, the recent location of the AUV can be calculated. Simulation results indicate that the proposed method can effectively compensate for the position error of SINS. Thus, the positioning accuracy can be confined to 2 m, and the method achieves good applicability. Compared with traditional underwater acoustic positioning systems, the proposed method can provide great convenience in engineering implementation and can reduce costs.

A diverse assemblage of Carboniferous plant fossils occurs in the upper Benxi Formation at the Kaihuagou Section near Taiyuan, Shanxi, China. It consists of impressions and fusain fragments, the latter revealing anatomical details. Unlike previously published assemblages from the Benxi Formation, there are no pteridosperms, but a predominance of noeggerathioids and fern fragments. There are three new species: Achlamydocarpon taiyuanensis, Conchophyllum suboblongifolium, and the first reported example of a Selaginella from the Carboniferous System of China, S. benxiensis. The arborescent lycophytes do not to belong to Lepidodendron, as previously claimed, but to Synchysidendron, and three new combinations are therefore proposed for species from the Benxi Formation: S. galeatum, S. subrhombicum and S. tripunctatum. The Benxi Formation flora represents a transition between the tropical swamp vegetation represented in the Westphalian floras of Europe and North America, and the Stephanian and Permian Cathaysian floras of China. It is evidence of an essential continuity between the Late Palaeozoic vegetation of the western and eastern tropics, which should be united as a single phytochorion, the Amerosinian Realm.