Striping Noise Analysis and Mitigation for Microwave Temperature Sounder-2 Observations

The Microwave Temperature Sounder (MWTS)-2 has a total of 13 temperature-sounding channels with the capability of observing radiance emissions from near the surface to the stratosphere. Similar to the Advanced Technology Microwave Sounder (ATMS), striping pattern noise, primarily in the cross-track direction, exists in MWTS-2 radiance observations. In this study, an algorithm based on principal component analysis (PCA) combined with ensemble empirical mode decomposition (EEMD) is described and applied to MWTS-2 brightness temperature observations. It is arguably necessary to smooth the first three principal component (PC) coefficients by removing the first four intrinsic mode functions (IMFs) using the EEMD method (denoted as PC3/IMF4). After the PC3/IMF4 noise mitigation, the striping pattern noise is effectively removed from the brightness temperature observations. The noise level in MWTS-2 observations is significantly higher than that detected in ATMS observations. In May 2014, the scanning profile of MWTS-2 was adjusted from varying-speed scanning to constantspeed scanning. The impact on striping noise levels brought on by this scan profile change is also analyzed here. The striping noise in brightness temperature observations worsened after the profile change. Regardless of the scan profile change, the striping noise mitigation method reported in this study can more or less suppress the noise levels in MWTS-2 observations.摘要第二代微波温度探测 (MWTS-2) 仪共有13个温度探测通道, 这些通道具有观测从地面到平流层大气放射的辐射量的能力. 然后, 与ATMS仪器类似, MWTS-2 观测中被发现有主要分布在垂直于扫描线方向的带状噪音. 此研究提出一个以结合经验证交分解(PCA) 与集合经验模态分解 (EEMD)为基础的算法并应用于MWTS-2观测中. 研究中论证了PCA中前三个分量有必要以EEMD算法去掉前四个模态以达到平滑的作用(文中表示为PC3/IMF4). 经过PC3/IMF4 降噪以后, 亮温观测中的带状噪音可以被有效的去除. MWTS-2观测中探测到的带状噪音显著高于ATMS仪器中的噪音. MWTS-2的扫描设置在2014年5月从变速扫描被调整到了恒定速度扫描. 本次研究对此调整对带状噪音的影响也作出了分析. 所得结果显示扫描设置调整以后带状噪音变得相较调整前更大. 不论观测来自扫描设置调整前或者调整后, 本文中描述的去除带状噪音的算法均可适用.