Comparison and validation of two Antarctic SSH products (Deliverable D1.3)

Sea Level Anomalies (SLA) are a key parameter of the Earth Climate System. Aside from the societal impact of sea-level rise, measuring SLA allows for the observation of the upper ocean circulation on a large scale (International Altimetry Team, 2021). To do so, we rely on altimetry. With a satellite sending an electromagnetic wave and recording the echo sent back by the surface, also called waveform, most of the ocean SLA field has been monitored over the last 30 years (Cazenave et al., 2014). However, SLA at high latitudes have remained unknown for a long time. This is due to the presence of sea ice, which acts as a physical barrier for altimetry. Recently, two European groups have developed new satellite-based Sea Level Anomaly (SLA) products, offering unprecedented SLA estimates in the seasonally ice-covered Southern Ocean over the past 20 years. These products have the ability to strongly enhance our understanding of the region's circulation and variability, but have not yet been validated. This deliverable presents the first systematic comparison and evaluation of these products against each other and against independent in situ observations. When compared against each other, both products show consistent SLA estimates with a local mean squared error of 1-2 cm and a correlation above 0.7 in ice-covered regions. The overall error compared to in situ observations is 3-6 cm, reflecting typical uncertainty for these satellite-based products.