Coastal Altimetry: A Promising Technology for the Coastal Oceanography Community

Abstract

Satellite altimetry has been one of the most important implements for physical oceanographers. The conventional altimeter is best performed over open ocean surface, yet there are many attempts to exploit the potential of altimetry in coastal zone in the last decade. To achieve a high performance for coastal altimetry is a multi-fold effort: the more sophisticated instrument concepts, the smarter onboard trackers, the more expert data editing criteria, the more specific retracking algorithms, the more advanced error correction methods, etc. In this chapter, each of the above aspects is described in detail, and some representative works in the altimetry community are reviewed. Particularly, the coastal altimetry offshore Hong Kong is addressed as a case study to demonstrate the potential of the new technology. In the conclusive session, some prospects for the coastal oceanography community are presented.

Recent Change in Sea Level Along the Coast of New Zealand Using Tide Gauge and XTRACK Coastal Altimetry Data

“…In satellite altimeter, in principle, the travel and return time of the radar signal sent from the satellite sensor is measured in areas covered with water such as ocean, sea, lake, river, and dam, and the instant sea level is determined. The satellite altimeter, which was first used in 1969, was started to be used to determine the concepts such as ocean circulation and ocean tides, unlike TOPEX/POSEIDON's satellite altimeter equipment, which was put into use in 1993, and emerged as the second method in determining absolute position as a touchstone with its high accuracy [10,16].…”

“…The satellite altimeter was originally developed for the oceans and thus it poses some problems to use it in coastal areas [10]. In order to use it in coastal areas, it is required to solve complex waveforms, apply optimized altimeter corrections for open oceans (Regional tides, atmospheric smoothing, etc.…”

Sea-level variability and change along the Norwegian coast between 2003 and 2018 from satellite altimetry, tide gauges and hydrography

“…Satellite altimetry has made these, and other achievements, possible because it has provided continuous sea-level observations over large parts of the ocean, in areas where sea-level measurements were previously only occasional.While invaluable over the open ocean, satellite altimetry measurements have historically been flagged as unreliable within 20-50 km from the coast (e.g., Benveniste et al, 2020). Indeed, the accuracy of radar altimetry, which is 2-3 cm over the open ocean (e.g., Volkov and Pujol, 2012), deteriorates in coastal regions because of technical issues (e.g., Xu et al, 2019).Notably, land contaminates the returned echoes of radar altimeters, and the complex topography of continental shelves, together with the irregular shape of most coastlines, makes geophysical corrections in coastal areas less accurate than in the open ocean. To increase the accuracy of radar altimetry in coastal regions, Passaro et al (2014) have developed the Adaptive Leading Edge Subwaveform (ALES) retracking algorithm.…”

“…While invaluable over the open ocean, satellite altimetry measurements have historically been flagged as unreliable within 20-50 km from the coast (e.g., Benveniste et al, 2020). Indeed, the accuracy of radar altimetry, which is 2-3 cm over the open ocean (e.g., Volkov and Pujol, 2012), deteriorates in coastal regions because of technical issues (e.g., Xu et al, 2019).…”