高分七号激光测高中全波形回波数据的EMD降噪

针对具有多个高度层的复杂场景，全波形激光测高系统记录的回波信号中往往带有较高的噪声，采用合适的降噪方法将有助于提高计算激光测距的精确性、反演地物垂直结构和构建目标特征参数的准确性。根据高分七号激光测高在轨探测的低信噪比全波形数据的特性，采用经验模态分解（Empirical mode decomposition，EMD）方法来构建典型的本征模函数（Intrinsic mode function, IMF），对于分解出多个不同尺度IMF的筛选，比较了使用去除高频分量，阈值选取、Wavelet选取和去趋势波动分析（Detrended fluctuation analysis, DFA）等方法与策略，通过降噪效果及定量评价，测试结果表明EMD-DFA1与EMD-1IMF对高分七号激光测高的全波形数据具有较好的降噪效果，其次为EMD-Wavelet和EMD-Threshold。另外通过EMD-DFA1对单个波峰、混叠波峰、多个波峰等不同情况的全波形数据测试，结果表明该方法具有较好的自适应性。

Noise reduction based on empirical mode decomposition for full waveforms data of GaoFen-7 laser altimetry

The complex full waveforms from laser altimetry, mixed with high noise, are usually reflected by the object with multiple height elevations. To accurately analyze the decomposition, vertical structure and characteristic parameters from these waveforms, a noise reduction method based on empirical mode decomposition (EMD) was investigated and tested with the full waveform of nonlinear and nonstationary signals obtained by GaoFen-7 space-borne laser altimetry. The reconstruction of an effective waveform signal was implemented through reverse superimposition of its intrinsic mode functions (IMFs) and the residual. And then different selection methods for these IMFs were compared, such as removed high frequency, threshold, wavelet and detrended fluctuation analysis (DFA). The results show that EMD-DFA1 and EMD-1 IMF have a higher noise reduction effect on these full waveforms, followed by EMD-Wavelet and EMD-Threshold. Finally, EMD-DFA1 was performed on the full waveforms with single peak, mixed peaks and multiple peaks. And the results show that EMD-DFA1 does well adaptability.