## 1 Introduction  
With the growing exploitation of the Arctic, extensive research into Arctic acoustics has been carried out in contemporary marine science and engineering fields [1]. Due to the seasonal existence of ice in most of the Arctic Ocean, it causes an effect on the propagation of acoustic waves [2]. Consequently, having a further understanding about sea ice models is essential. Arctic ice has a complicated structure because of the changeable environmental condition [3, 4], which makes it challenging to establish a plausible model. When it comes to sea ice modeling, scholars conducted a study concentrating mainly on its three characteristics: layered, porous and rough surface. [PERSON] [5] simplified the ice model by ignoring the surface roughness and regarded acoustic reflection from sea ice as from flat plate. What is more, they deduced the reflection coefficient in detail and analyzed the sound field propagation loss using the Bellhop simulation model. [PERSON] [6] put forward the multilayered ice model and extended the impedance transfer method to calculate the reflection coefficient at a water-ice interface, and then they determined the effects of the physical parameters and layering of ice and snow cover on reflections. Based on the layered model, [PERSON] [7] assumed that the water-ice and ice-air interfaces are rough and used the self-consistent perturbation method proposed by [PERSON] [8] to obtain the boundary conditions of rough surfaces to calculate the reflection coefficient. Then, a numerical analysis was conducted about the relations between reflection coefficients and ice thickness, grazing angle and frequency of acoustic wave. [PERSON] treated rough surfaces with a Gaussian distribution rather than concentrating on the specific scale of ridges generated by collisions of large packs of floating ice floes [9]. Nevertheless, [PERSON] [10] calculated the reflectivity from ridges based on the Burke-Twersky model [11], in which ridges are considered as elliptical half-cylinders situated at the bottom surface of ice. Besides the layering and rough surface of ice, scholars took porosity into account in the process of modeling sea ice. [PERSON] [12] modeled sea ice as a transversely isotropic brine-saturated porous medium, and the cylindrical pores align themselves vertically. In accordance with the model, [PERSON] [13] studied the reflection and refraction of waves at the interface of water and porous sea ice and the effect of ice thickness and porosity of the skeleton layer on reflection.  
Comparing these models, it can be found that most models are established based on one of the three characteristics, deviating from the actual condition of ice. Therefore, in an attempt to obtain precise results during analyses of transmission of acoustic signals in ice, a more comprehensive model is needed to incorporate those characteristics as much as possible.  
Based on this situation, a multilayered porous sea ice model which combines the layered characteristic and porous structure is proposed in this paper. Due to the difference of the formed time of ice layers, the density and sound velocity vary in each layer [14], which has a different effect on the propagation waves. Moreover, when the plane wave propagates into pores within ice, it gives rise to vibration of the fluid trapped in pores, and thus its energy is dissipated on account of the friction between the fluid and ice frame [15]. Hence, it is reasonable to model sea ice as multilayered and porous.