基于激光雷达夜间观测提取重力波方法的定量比较

以激光雷达夜间观测的温度数据的时空范围和时空分辨率作为参考，构造具有已知背景温度（由稳态背景、行星波和潮汐波组成）和重力波频谱分布的合成温度数据，针对合成温度数据，分别采用已有的夜间平均方法和时间滑动平均方法提取重力波.在此基础上，提出了用谐波函数近似表示背景大气变化的谐波拟合方法提取重力波.通过比较提取出的重力波与事先给定的重力波得到谱响应，利用谱响应定量分析各方法能够有效提取重力波的周期范围.研究结果表明:对背景温度成分敏感的夜间平均方法提取的重力波振幅易被严重高估；对半日潮汐比较敏感的时间滑动平均方法通常可以提取周期小于1.15倍窗口宽度的重力波；对背景温度成分不敏感的谐波拟合方法可用来提取周期小于0.4倍夜间时间长度的重力波.将各方法应用于Na激光雷达夜间观测的温度数据，从中提取重力波，结果表明时间滑动平均方法和谐波拟合方法可以得到较好的结果. 

Quantitative Estimations on the Gravity Wave Extraction Methods from Night-time Lidar Observation

According to temporal and spatial ranges and resolutions of night-time lidar observations, a synthetic data is constructed with known background temperature (consisting of constant background, planetary waves and tides) and gravity waves. The nightly mean method and the temporal running mean method are used to extract gravity waves from the synthetic data. Moreover, a harmonic fitting method is proposed, that uses a harmonic function to approximately represent the background changes and then to extract gravity waves. Based on the spectral response defined by the ratio between the extracted gravity waves and the known gravity waves, the reliable range of periods of gravity waves extracted by each method is quantitatively analyzed. Results show that: the nightly mean method always overestimates the amplitudes of gravity waves since it is particularly sensitive to background temperature components and the length of night time; the temporal running method is sensitive to semidiurnal tides and can be used to extract gravity waves with periods less than 1.15 times of the window width; the harmonic fitting method is not sensitive to background temperature components and can be used to extract gravity waves with periods less than 0.4 times of the night time. Finally, the temporal running mean method and the harmonic fitting method can get reliable gravity waves from the temperature data observed by Na lidar during nighttime.