## 4 Results
### Waveform Parameter Statistics
Apart from the presented findings for different ice types, the following observations have been made for the discarded samples and are based on the comparison of the SAR images and the altimeter waveforms during the sampling process. FYI contains a large proportion of lead-like waveforms, i.e., waveforms with high PP, low SSD and high peak power that do not correspond to a recognizable lead in the SAR image. Therefore, more samples have been discarded over FYI because they could not be unambiguously attributed to FYI. Waveforms of mixtures of ice types within the altimeter footprint, e.g., transition from FYI to MYI at floe boundaries or small refrozen leads within MYI, resemble more the waveforms of FYI. More details can be found in Section 4.2. This holds also true for the transition from FYI to MYI areas where floe sizes are smaller, and a mixture of thicker FYI and second year ice is present. Figure 4: Waveform parameters of different ice types covering all winter seasons. (**a**) Pulse peakiness, (**b**) scaled mean power, (**c**) stack standard deviation and (**d**) mean HV backscatter intensities of altimeter footprint. Solid lines represent a kernel density estimate from measured histograms. Figure 7 shows the freeboard distributions of different ice types and winter seasons based on our selected samples. The solid lines represent kernel density estimates of the histograms. Samples with zero freeboard, 59% of FYI and 24% of MYI samples, as well as with negative freeboard, 3% of FYI and 6% of MYI samples, have been excluded from the analysis. The high percentage of zero freeboard samples is caused by samples that are relatively lead-like but have been retained in our analysis because of their low peak power. Negative freeboards are possible if an ice floe gets submerged by a heavy snow load, but are unlikely to be measured by the radar as scattering probably will occur before the ice-snow interface. Errors in retracking the correct surface elevation because of distorted waveforms are more likely especially for high negative values. Expectedly, MYI ice shows a higher freeboard compared to FYI but also has a significant portion in the range of FYI freeboard values. These are probably caused by the influence of off-nadir smooth areas below SAR resolution as demonstrated in Section 3.2 and could therefore not be avoided in the selection process. Further examples of freeboard underestimation for mixed ice types and apparent homogeneous areas in SAR images are shown in Section 4.2. We see that FYI freeboard rarely exceeds 40 cm for the selected samples. Freeboard estimates for FYI and MYI are stable between the three winter seasons and are therefore not significantly affected by the variations in waveform parameters. No significant difference is recognizable between the early winter measurements of 2016/17 compared to the other two winters. Slightly higher MYI freeboard for the winter season 2016/17 could be caused by samples of older sea ice compared to the other winters. In this section, we demonstrated that waveform parameters principally distinguish between FYI, MYI and large leads. FYI shows larger variations of these parameters for three winter seasons compared to MYI, but has more consistent HV backscatter. The principal difference in waveform parameters over different ice types forms the basis to study the waveform response to small-scale sea ice features such as ridges and MYI floes, which we now present in Section 4.2. Figure 5: Waveform parameters of FYI for the different winter seasons. (**a**) Pulse peakiness, (**b**) scaled mean power, (**c**) stack standard deviation and (**d**) mean HV backscatter intensities of altimeter footprint. Solid lines represent a kernel density estimate from measured histograms. Figure 6: Waveform parameters of MYI for the different winter seasons. (**a**) Pulse peakiness, (**b**) scaled mean power, (**c**) stack standard deviation and (**d**) mean HV backscatter intensities of altimeter footprint. Solid lines represent a kernel density estimate from measured histograms.