**5. Conclusions**

The application of pressure sensing technology in observing changes in the sea floor caused by the migration of submarine sand waves has been demonstrated in this paper. In studying the change law of the near-bottom water pressure, bottom pressure and total fixed pressure during sand wave migration, we propose two methods: BPRSS and TPRFD. Through a simulation experiment with an indoor water flume, the observation effects of the two methods were evaluated. Overall, the main conclusions of this study can be summarized as follows:

(1) Pressure sensor techniques can be used to observe seabed elevation changes (accuracy of above 90%), but for microtopography with severe terrain fluctuations (such as the sand wave crests considered in this experiment), their observation accuracy will decrease.

(2) Reflecting seabed elevation from the weight of overlying sand is feasible, but less accurate than using water pressure to reflect elevation.

(3) The use of a floating ball-mounted pressure sensor as a surface synchronous bottom pressure recorder (BPRSS) to observe sea floor elevation will affect sediment migration on the surface of a sand wave, causing the results to show a step-like change process not observed under real conditions.

(4) Considering the underflow velocity of a sand wave development area, and the actual size of sand waves during field observations, it is more effective to use a fixed-depth total pressure recorder (TPRFD) to observe a trough.

**Author Contributions:** Conceptualization, X.L.; Methodology, X.Z.; Project administration, X.L.; Resources, X.Z.; Supervision, X.L.; Writing–original draft, X.Z.; Writing–review & editing, X.L., Z.T., H.Z. and T.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the Fundamental Research Funds for the Central Universities (grant number 201822013), the National Natural Science Foundation of China (41877221), the Shandong Provincial Natural Science Foundation (ZR2019QD001), and the National Key Research and Development Plan of China (2016YFC0802301).

**Conflicts of Interest:** The authors declare no conflict of interest.
