The MEMS (Micro-Electro-Mechanical System) Sensor Network used on submarine hydrate mounds deformation monitoring is proposed, which consists of horizontal array (up to 21 m) and vertical array (up to 3 m) and can realize synchronous monitoring of the seabed and shallow strata deformation. The deployment mechanism of the vertical monitoring array is analyzed. The self-capacitive monitoring network has low power consumption and is easy to achieve long-term in-situ monitoring.
Gas hydrate is a solid phase comprised of water and low-molecular-weight gases, usually methane, that forms within sediments under conditions of low temperature, high pressure and adequate gas concentration (Ruppel and Waite, 2020). The submarine hydrate mound is a common micro-topography in the submarine gas hydrate occurrence area or the natural gas seepage region (Mackay, 1998), the shape of which is similar to the pingo-like feature in the permafrost region, therefore, also called submarine hydrate pingo (Paull et al., 2007). Studying on the seafloor hydrate mounds is crucial since they are important indicators of submarine methane seepages, shallow gas hydrate, hydrocarbon reservoirs and seabed instability. The exposed hydrates above and inside hydrate mounds is in a critical equilibrium state. Once the seabed temperature increases, pressure or the gas flux decreases, the near-seabed gas hydrate will decompose, reducing the strength of sediments, causing the collapse and instability of the seabed, and even large-scale disasters in landslide areas (Loher et al., 2018).
The geophysical instrument and vessel-based equipment enables in-situ observation the morphology of submarine hydrate mounds. However, these instruments need to be equipped with scientific ships, having a long observation period, preventing long-term continuous in-situ monitoring from being realized. The existing self-capacitive sensor systems can realize in-situ continuous monitoring of seabed temperature (Macdonald et al., 1994; Vardaro et al., 2006), pore water pressure (Liu et al., 2015) and topography changes (Saito and Yokoyama, 2008; Yokoyama et al., 2012), but the single monitoring node and limited monitoring range make. The submarine cabled observatory can achieve long-term, in-situ and real-time monitoring, but in fact, the monitoring location of which is relatively fixed and poor mobility, the cost is high, and the placement technique is difficult, making it not suitable for submarine hydrate mound monitoring. Therefore, in order to deeply study the evolution processes and its mechanism of hydrate mounds and carry out long-term in-situ monitoring, long-term in-situ device based on MEMS sensor network is developed in this paper.
