## 3 Characteristics of the Waveforms
### Contrasts in the Parameters
#### 3.4.2 Analysis of the 20 Hz Data  
This study selected some visible and SAR data of the northern and southern polar regions to examine. Previously, [PERSON] [23] had used the pulse peak (PP) values of 1.8 to make distinctions between the diffused and quasi-specular echoes of ERS-1. He found the main source of the diffused echoes were seawater or ice floe surfaces. The quasi-specular echoes had originated from the sea surfaces in areas with high ice concentrations. In another related study, [PERSON] [28] believed that the threshold of 1.8 could be used to classify the two different surfaces. The pulse peak values were used in this study also. For the research of 1 Hz and above, the PP values were found to have high recognition. In the analysis of the 20 Hz data, a value of 3 was set as the threshold. The waveforms with PP values less than 3 were processed as a type of diffused waveform, and those with PP values greater than 3 were processed as quasi-specular waveforms. The average type of waveform with PP values greater than 3 were spike-like waveforms. Meanwhile, those with PP values less than 3 were \"ocean like\" waveforms. **The Antarctic regions:**  
The impacts of the orbit and clouds could not be ignored in this study. Therefore, the less visible remote sensing data from the HY-1C from November were selected. The data from the HY-1C are shown in Figures 10 and 11, in which the intervals between the HY-2A/B ALT were simultaneously less than 5 h.  
Figure 9: Cumulative probability distributions for the four cases (open ice, young ice, old ice, and ambiguous ice) for the four waveform parameters: AGC of the C Band; AGC of the Ku Band; PP of the C Band; PP of the Ku Band. Note: **A–D** are the results of the HY-2A; **E–H** are the results of the HY-2B. The PP values of the small pieces of ice were found to be greater than 3. Also, in the leads near shore and the large ice floe centers, there were some cases where the PP values were greater than 3. The two different types of waveforms were above the ice sheet. In Figure 11, the HY-2B had results similar to those of the HY-2A. The HY-2A ALT data had indicated PP values less than 3 in the regions of small contiguous ice floes. The data of these regions had displayed spike-like waveforms. In the centers of the large ice floes, \"ocean like\" waveforms had existed. Although the footprint of the C Band was larger than that of the Ku Band, the C band was also correctly flagged on the same larger ice floes which had been identified as the diffuse surfaces in the Ku Band. However, there were found to be small differences in the number of identifications. **The Arctic regions:**  
This study selected the altimeter data from the HY-2A/B for 15 November 2018 as an example. The data of the AARI ice charts were from 11-13 November 2018. The chart (Figure 12C) provided five types of ice as follows: 1--Nilas (ice rind); 2--Young ice; 3--First-year ice; 4--Old ice (had survived at least one summer melt). The old ice was found to be the very similar to the old ice which had been identified in the OSI-SAF ICETYPE dataset. Figure 11: Distributions of the classifications of the PP values of the HY-2B ALT data. Note: **A1–A4** indicate the Ku Band; **B1–B4** indicate the C Band. Figure 10: Distributions of classified PP values of the HY-2A ALT data. Note: **A1–A4** indicate the Ku Band; **B1–B4** indicate the C Band. It was determined in this study that the PP values were lower than 3 from the seawater areas not only in the C Band, but also in the Ku Band. The PP values from the young ice and first-year ice were found to be greater than 3. However, above the old ice, there were some places where the PP values were less than 3 (Figure 12A,B). In Figure 12D,E, the \"ocean like\" echoes of the band C and Band Ku had existed in the regions of old ice. But these echoes from different band in Arctic and Antarctic had a slight difference in position. In the edges of sea ice (Figure 12F,G), the PP values from some nilas were less than 3 whose waveform similar to seawater.