# Time-Frequency Attribute Analysis of Channel 1 Data of Lunar Penetrating Radar
## 2 Materials and Methods  
### Data Explanation and Preprocessing  
The YR launched by CE-3 was the first to land on the moon after the Soviet Union in 1976. Specifically, the YR used it to detect the surface of the landing site on the north side of the mare and several instruments in the ground. Its trajectory stretched to 114.8 m near the sinus (Figure 1). In this installment, the data description and pretreatment of the LPR CH-1 data will be introduced.  
The DFR on the YR offers a meaningful chance to map the underground structure about several hundred meters deep from the CH-1 (60 MHz) and its stratigraphic structure near the surface from the CH-2 (500 MHz). For the underground structure, the CH-1 data are selected. According to the recording parameters, real conditions, and data condition, a set of LPR data pretreatment procedures (Table 1) was projected. The data can be preprocessed to access the CH-1 image (Figure 2).  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Processing** & **Interpretative Statement** \\ \hline i & Data reading & The data is decomposed into 9 parts. According to their storage format (*-psd, which is the standard storage format for aerospace and aerospace), data and location information will be read one by one. \\ \hline ii & Data registration & The data is split into 9 parts and ought to be stitched together. \\ \hline iii & Time lag adjustment & The arrival time of the radar echo is delayed by 69.664 ns, which corresponds to the start time of the recorded data. \\ \hline iv & Deep useless data & As the SNRs of Part 1 and Part 2 are low and the rest of the data are not collected, the last 10,000 ns of data \\  & deleting & without the study value needs to be deleted. \\ \hline v & Low SNR traces & Some parts with low SNR should be removed. \\ \hline vi & Traces selecting & Rover patrols are uneven because the rover may stop at a waypoint to collect other scientific data, for example, APXS data, VINS data, and so forth. However, LPR never stops collecting data, which results in multiple acquisitions of multiple traces at the same place. The repeating traces are stacked and averaged. Two sets of data are obtained. One is all data without a copy track, and the other is a repeating track that has been stacked and averaged at the waypoint. \\ \hline vii & Location & Location information is added to the image. \\ \hline \hline \end{tabular}
\end{table}
Table 1: Data preprocessing instructions.  
Figure 1: Walking track of Yutu. This picture has come from the descent camera on the Chang’E-3 (CE-3) lander.  
There are many kinds of space electromagnetic waves on the moon; the terrain of the moon is very complex under the adverse circumstances, so the signal-to-noise ratio (SNR) of LPR data is low. The repeated gathers of each stop point are superimposed, the purpose of which is to improve the SNR of the single trace at the waypoint [24], and provide more accurate and reasonable one-dimensional data for the subsequent analysis of the frequency-domain (FD) and the time-frequency domain (TFD).  
In this paper, several analysis and processing methods are utilized, for example, the Fourier transform, short-time Fourier transform, CEEMD, and Hilbert transform. The Fourier transform (FT) and short-time Fourier transform (STFT) are commonly used as data analysis methods, the principle of which will not be repeated here. This section mainly introduces the CEEMD and Hilbert transform.