Noumea: A new multi-mission Cal/Val site for past and future altimetry missions?

Abstract. To better understand sea level evolution in coastal areas, one needs to link and combine global observations from altimetry satellites with the scattered but long-term tide gauges measurements. In New-Caledonia, the Noumea lagoon is an example of this challenge as altimetry, coastal tide gauge and vertical land movements from Global Navigation Satellite Systems (GNSS) do not provide consistent information. The GEOCEAN-NC 2019 field campaign tries to address this question with the deployments of in situ instruments in the lagoon, with a particular interest for the crossing point of three different altimetry tracks (Jason/Sentinel-3a). Thanks to GNSS buoy and pressure gauge observations, we propose a method to virtually transfer the Noumea tide gauge offshore, to obtain a long-term sea surface height (SSH) time series at the altimetry crossover point. We also reprocess the 20 Hz along-track data from Jason and Sentinel-3a Geophysical Data Records (GDR) with the best correction parameters in the area. These two SSH time series (i.e. in situ and altimetry) allow us to compute the altimeter biases time series over the entire Jason and Sentinel-3a period. With our 3 weeks field campaign, we reanalyse about 20 years of altimetry observations and find inter-mission biases consistent with historical calibration sites, thus further increasing our knowledge of the local sea level rise in this region. This offers many opportunities to develop Cal/Val activities in the lagoon, which is also the subject of several experiments for the scientific calibration phase of the future large-swath altimetry mission SWOT.