火星稀薄大气环境下的声传播特性研究

China future missions to the planet Mars might include several acoustic probes to record ambient sounds, to measure the wind speed, and to assist the safety of future Landers. Acoustic waves that are being directly coupled to the medium can probe effectively planetary environments. Moreover, sound interacts with matter intimately, that in many ways exceeds the electromagnetic interactions conventionally used on the probes in extraterrestrial environments. Hence, recent years have seen a resurgence of acoustic sensing in Martian exploration. .The typical Martian atmosphere is quite different from that on earth. The atmospheric pressure is 150-1350 Pa, and the temperatures are expected to be around -130-25℃. Another critical factor which influences the wave-propagation characteristics is the chemical composition of the Marian atmosphere. The composition has been established by ground based observations in previous missions. That is, the dominant constituent is Carbon dioxide (about 95%) with a minor amount of Nitrogen and Argon and a smaller amount of water vapor. It is expected that characteristics of sound wave propagation in Mars are much different from that in earth..The investigation of wave propagation in Martian atmosphere is vital for applications of all the acoustic probes which need to be specially designed for the extraterrestrial Mars environment. However, very little work has been done to quantify acoustic wave propagation in Martian atmosphere based on experiments. .In this proposal, Institute of acoustics, Chinese Academy of Sciences will cooperate with Beijing Institute of Spacecraft Environment Engineering to characterize the atmospheric acoustics of Mars both experimentally and theoretically. The low pressure, low temperature, and complex chemical composition of tenuous Martian atmosphere will be simulated in the Beijing Institute of Spacecraft Environment Engineering. And we will carry out sets of experiments to identity the sensitivity of acoustic wave propagation to temperature, pressure, frequency, and chemical composition variations, respectively. And then, analytical expressions for sound speed and sound absorption in the Martian atmosphere will be developed in order to verify and to better understand the experimental results. The objective of this proposal is to explore the properties of acoustic wave propagation in Mars atmosphere, so that to design Martian-specific acoustic sensors in the future China Mars Landers.

火星探测作为我国深空探测战略的重磅任务已进入实施阶段，火星具有大气层是个有声世界，可利用声音记录和探测火星。但火星大气和地球相比具有150-1350Pa超低压、-130-25℃低温和二氧化碳气体为主等特点，目前尚未有关于火星上声音的有效记录和声传播特性的实验研究。本项目针对我国火星探测任务的迫切需求，两大研究机构联合，利用中国空间技术研究院的低温、低压、大型空间环境模拟设备，在地面模拟火星大气环境，设计不同频段的声传播实验，得到温度、气压和气体成分等参数相关的、全面系统的声传播特性。同时，根据火星特殊的大气参数，分别利用第一性原理分子动力学模型和高阶Boltzmann方程，模拟计算、实验数据和理论分析相结合，探索研究超低压、低温环境下的声波传播规律，丰富和发展基础声学理论。项目所得成果将直接应用于我国火星探测计划中，为火星环境声记录、风速测量和火星车障碍探测奠定坚实基础。

从人类未来移居前景来说，火星是太阳系中最值得研究的一颗行星。声探测是探索和认知火星环境的一个重要新手段，被动声传感器可监测火星上可能存在的声音、并反演声源特性。2021年NASA“毅力号”火星车携带了两套声学系统，同年我国“祝融号”火星车成功登陆火星，携带的光纤声传感器也记录到了火星声信号。为更好地分析火星车记录到的声信号，首先需要准确模拟声波在火星大气中的传播路径，进而反演声源类型、位置和强度，获取火星环境及气候参数等。火星大气与地球表面大气差异很大, 声音的传播与温度、气压、大气组分、湿度和频率等因素密切相关，因而火星低温、稀薄、二氧化碳为主的大气中声传播的特性与地球上存在巨大差异。本项目通过在深空环境模拟容器中模拟火星大气，开展了声传播特性实验、理论和数值模拟研究，掌握了低压、低温火星大气环境的地面模拟技术；模拟了低压（250 ～100000 Pa）、低温（-50 ～ 20℃）、纯氮气、纯二氧化碳气体和空气（室温）环境，开展了21∼40 kHz声波传播特性的实验研究，得到了不同频段声波在模拟火星大气环境下的传播规律；综合实验数据、理论推导和数值模拟，探索了极端环境下的声波传播理论，实验证实了火星稀薄低温大气中存在声频散的现象；为我国火星探测任务中的声学载荷提供了理论和技术基础。