Water surface elevation in coastal and inland waters using satellite radar altimetry

Changes in water surface elevation are traditionally measured in situ by single instruments at a fixed point, yielding a measurement relative to the land where the instrument is installed. Values are generally taken with frequent sampling (order of minutes or less). Such an instrument is called a tide gauge in the ocean environment and more generically a water gauge in lakes and reservoirs. In rivers, the instrument is usually called a stream gauge, because the water surface elevation is then used to derive discharges. Several types of installations are currently in use in hydrometric practice (Vuglinskiy et al., 2009; WMO, 2010), depending on the kind of water target. Many databases around the world collect and make available water surface elevations. Concerning extreme events, there is a clear requirement for high-frequency (ie, sampling at subhour intervals) information. The GESLA-2 (Global Extreme Sea Level Analysis version 2) database is an updated data set of high-frequency water surface elevations obtained from tide gauges operated by many agencies around the world (Woodworth et al., 2016). Fig. 4.1 shows the geographical distribution of the 1355 stations presently available in GESLA-2.