## 1 Introduction  
The climate of the Arctic Ocean is influenced by the presence of sea-ice--the frozen ocean surface that sits between and dominates atmosphere and ocean interactions. The past 20 years have seen reductions in the summer sea ice extent of approximately 10% per decade [1, 2], further revealing the open ocean surface of the Beaufort and Siberian Seas. Ocean surface gravity waves generated by the wind are a key feature of the atmosphere-ocean interface over the global ocean controlling atmosphere-ocean exchanges of momentum and heat [3]. Ocean gravity waves interact with the sea ice that floats upon the ocean surface throughout the Marginal Ice Zone (MIZ): a region potentially 100 s of km wide [4] typified by increasing ice floe diameters and decreasing wave heights further into the sea ice pack and defined by sea ice concentrations of between 15% and 80%. The interactions are complex due to the multiple physical processes at play: sea ice floe mechanical breakup [5], gravity wave attenuation due to the damping caused by movement of sea ice floes [4, 6], the spectral non-linearity of wave attenuation [7] and the differing wave attenuation of newly formed grease and pancake ice compared to consolidated pack ice [8]. Models exist that endeavour to replicate these physical processes [9] giving the spectral wave climate across the polar oceans and through the sea ice pack. For the inclusion of sea ice floes within a wave model, the presence of sea ice stores and dissipates mechanical energy, typically represented as a viscoelastic medium [10]. Ref. [11] asses the performance of a variety of wave model parameterisations against observations in the north west Atlantic in the presence of sea ice and ocean currents showing the importance of wave scattering by sea ice floes in the MIZ. The validation of such models is challenging due to the limited availability of wave data within pack ice, and the rapidly changing wind and thus wind driven wave state. Ref. [12] contrast differing satellite sea ice concentration data, showing how the difference between them alters hindcasts by the WaveWatch 3 wave model for 2018 in the Chukchi Sea. They show that despite model uncertainty for the complex physics in wave ice interaction, the concentration and extent of sea is a leading order influence in the modelling of wave height propagation through the sea ice pack. Whilst there has been a global increase in ocean wave heights [13], the trend in the Arctic Ocean is inconclusive [9]. The larger expanse of summer Arctic open ocean allows for increased available wave fetch though wind swells (wind driven ocean surface waves) when encountering the sea ice edge cause the break up of sea-ice floes and the damping of the gravity wave spectrum. Forecasts and measurements of surface waves are critically important for operations at sea and understanding the interaction between surface waves and coastlines is of pressing concern: global sea level rise has lead to increased coastal erosion [14], and positive trends in global wind speed have driven trends in the most extreme wave heights [15]. Earth observation satellites have been in orbit for nearly five decades [16] carrying downward facing radar altimeters to study the height of the ocean surface. The shape of the radar impulse response can be analysed to asses the roughness of the ocean surface and thus the height of ocean swell waves. Successive satellites have carried altimeters and their data have been incorporated into continuous coherent global data sets on ocean dynamics and waves [17; 18]. Additionally over this period there have been continuous advances in the accuracy of the radar instruments, the satellite tracking and the theoretical interpretation of the raw retrieved data. However the form of the radar instruments has not altered greatly: a normal incidence, pulse-limited altimeter with a circular 1 m diameter antenna. CryoSat-2 (CS2) was launched on 8 April 2010 [19] into a highly inclined 92\({}^{\circ}\) retrograde orbit giving coverage up to 88\({}^{\circ}\)N/S.