Using the Ice, Cloud, and land Elevation Satellite 2 (ICESat-2) global high-resolution elevation measurements, it is possible to distinguish individual surface ocean waves. With the vast majority of ocean surveying missions using radar satellites, ICESat-2 observations are an important addition to ocean surveys. ICESat-2 can also provide additional observations not possible with radar. In this paper, we consolidate the ICESat-2 ocean observations by comparing the significant wave height (SWH) with coincident CryoSat-2 radar observations during the CRYO2ICE campaign from August 2020 to August 2021. We use 136 orbit segments, constrained to the Pacific and Atlantic oceans as well as the Bering Sea, to compare observations to show the level of agreement between these systems. Three models based on ICESat-2 are used in the comparison: the standard ocean data output (ATL12), a method of modeling the individual surface waves using the geolocated photons and, functioning as a baseline, an approach using the standard deviation of the ocean surface. We find the following correlations between the SWHs from the models and the SWHs from CryoSat-2: 0.97 for ATL12, 0.95 for the observed waves model, and 0.97 for the standard deviation model. In the same comparison, we find mean differences relative to the observed SWHs for each model, as well as errors, which increase as the SWH increases. The SWH observed from ICESat-2 is found to agree with observations from CryoSat-2, with limitations due to changes in the sea state between the satellite observations. Observing the individual surface waves from ICESat-2 can therefore provide additional observed properties of the sea state that can be used alongside other global observations.

<p>Using global high-resolution elevation measurements from the Ice, Cloud, and land Elevation Satellite 2 (ICESat-2), it is possible to distinguish individual surface ocean waves. As the majority of ocean surveying missions are radar satellites, ICESat-2 observations are an important addition to ocean surveys and can provide additional observations not possible with radar. By utilizing the coincident orbits between CryoSat-2 and ICESat-2 during the CRYO2ICE campaign, the observations from ICESat-2 are compared along long stretches of the ground tracks, rather than at the usual crossover points. Therefore, from August 2020 to August 2021, 136 orbit segments from ICESat-2 in the Pacific and Atlantic oceans are used in the comparison. To allow for comparison of ICESat-2 during the coincident orbits, CryoSat-2 is validated against in-situ stations as well as satellite altimetry measurements. Using the validated CryoSat-2 observations, the significant wave height (SWH) is determined from the individual photon heights observed by ICESat-2, by three different methods. First, by using the standard ocean data output (ATL12), the SWH determined from this can be further validated. Then, the two methods derived in this study contain a model of deriving the SWH directly from the observed surface waves, as well as a model using the same method as ATL12, to act as a baseline for the wave-based model. The validation of this wave-based model for extended stretches with CryoSat-2 would allow for the further use of this model for studies. The carried out comparisons result in correlations between ICESat-2 and CryoSat-2 of 0.97 for ATL12 and 0.95 for the wave-based model, with a small mean deviation between the altimeters. The observations from ICESat-2 experience a larger variance than other altimeter crossover-comparison studies, however being constrained by a larger time-lag (<3h) between the coincident orbits for ICESat-2 and CryoSat-2 this is expected. From the study, ICESat-2 is found to agree with observations from CryoSat-2, and utilizing the possibility of distinguishing the surface waves, would therefore provide beneficial for ocean observations.</p>