Validating Sea-Level Altimetry Data against Tide Gauge for Coastal Risk Analysis in Mozambique

Abstract

Satellite altimetry data provide a solution to the lack of in situ tide gauge data, which are essential for comprehending various marine processes worldwide. In the present study, we seek to validate ALES-retrieved sea-level data against tide gauge observations from four ground stations on the coast of Mozambique. The approach consisted of extracting data from selected tracks of the Jason-1, Jason-2 and Jason-3 missions, and processing it to (i) remove outliers, (ii) collocate alongside tide gauge data, (iii) remove the tidal component and detrend, and (iv) perform a set of statistical analyses. Good agreement was found between the altimetry and tide gauge data in three of the four stations (Maputo, r = 0.59; Inhambane, r = 0.87; and Pemba, r = 0.75), with the exception of Beira. The annual and semi-annual cycles in the two datasets revealed that the altimetry signal is smaller in amplitude and ahead (with a few exceptions) of tide gauge by a varying number of days in each location. Both the annual and semi-annual cycles are far more comparable in Pemba, where the amplitude in particular has the same order of magnitude, followed by the Maputo station. The study concluded that the selected altimetry data for Pemba and Maputo stations are valid and can be used for coastal risk analysis and other applications. No altimetry data could be validated for Inhambane and Beira stations due to lack of consistent and sufficiently long tide gauge records. This difficulty urges the need for improved maintenance practices of ground stations located near human settlements that rely on sound information of the sea level and its variability to protect lives, infrastructure and livelihoods.