*Article* **Pressure Sensing Technique for Observing Seabed Deformation Caused by Submarine Sand Wave Migration**

#### **Xiaolei Liu 1,2,\* , Xiaoquan Zheng <sup>1</sup> , Zhuangcai Tian <sup>1</sup> , Hong Zhang <sup>1</sup> and Tian Chen <sup>1</sup>**


Received: 12 April 2020; Accepted: 28 April 2020; Published: 30 April 2020

**Abstract:** Long-term, continuous in-situ observation of seabed deformation plays an important role in studying the mechanisms of sand wave migration and engineering early warning methods. Research on pressure sensing techniques has examined the possibility of using the temporal characteristics of the vertical deformation of the seafloor to identify important factors (e.g., wave height and migration rate) of submarine sand wave migration. Two pressure sensing tools were developed in this study to observe the seabed deformation caused by submarine sand wave migration (a fixed-depth total pressure recorder (TPRFD) and a surface synchronous bottom pressure recorder (BPRSS)), based on the principle that as a sand wave migrates under hydrodynamic forcing, the near-bottom water pressure, bottom pressure and total fixed pressure synchronously change with time. Laboratory flume experiments were performed, using natural sandy sediments taken from the beach of Qingdao, China, to better present and discuss the feasibility and limitations of using these two pressure sensing methods to acquire continuous observations of seabed deformation. The results illustrate that the proposed pressure sensor techniques can be effectively applied in reflecting elevation caused by submarine sand wave migration (the accuracy of the two methods in observing the experimental bed morphology was more than 90%). However, an unexpected step-like process of the change in sand wave height observed by BPRSS is presented to show that the sensor states can be easily disturbed by submarine environments, and thus throw the validity of BPRSS into question. Therefore, the TPRFD technique is more worthy of further study for observing submarine sand wave migration continuously and in real-time.

**Keywords:** sand wave; pressure sensing technique; physical model test; field application
