Merged envisat and jason satellite altimeters using crossovers adjustment to determine sea level variability

It is considered that climate change has been increasing the global air temperature and rising sea level. Thus, the monitoring of sea level is necessary to mitigate the hazard risk. For estimating sea level change from various altimetric missions, attention must be taken to determine the bias of measurements between altimetric different missions. The aim of this study is to merge both of Jason series and Envisat satellite altimeters for estimating sea level variability around the Indonesian Seas. To create sea level time series, two adjustment methods are employed: tandem mission data and sea level anomaly differences at crossovers. The adjustment using tandem mission between Jason-1 and Jason-2 obtained a relative difference of 32.8 5.4 mm. The adjustment method at crossovers is applied for combining Envisat and Jason series which is already intercalibrated. The mean crossovers differences between Envisat and reference missions are less than 2.5 cm. By using merged datasets from all missions, it is discovered that the trend in the Indonesian seas for a period of 10 years is 11.9 mm years^-1. The map of sea level trends from all satellites data for that period is performed in 1° × 1° regular grids.