Reducing uncertainties in coastal sea level trend estimates requires a better understanding of altimeter measurements and local sea level dynamics. Using long-term sea level time series from the Nouméa tide gauge (New Caledonia) and in situ data collected as part of the GEOCEAN-NC campaign, this study presents a method inspired from Cal/Val studies to re-analyse about 20 years of altimetry observations and re-address the question of sea level evolution in the lagoon.