Abstract
Coastal zones are highly dynamical systems affected by a variety of natural and anthropogenic forcing factors that include sea level rise, extreme events, local oceanic and atmospheric processes, ground subsidence, etc. However, so far, they remain poorly monitored on a global scale. To better understand changes affecting world coastal zones and to provide crucial information to decision-makers involved in adaptation to and mitigation of environmental risks, coastal observations of various types need to be collected and analyzed. In this white paper, we first discuss the main forcing agents acting on coastal regions (e.g., sea level, winds, waves and currents, river runoff, sediment supply and transport, vertical land motions, land use) and the induced coastal response (e.g., shoreline position, estuaries morphology, land topography at the land-sea interface and coastal bathymetry). We identify a number of space-based observational needs that have to be addressed in the near future to understand coastal zone evolution. Among these, improved monitoring of coastal sea level by satellite altimetry techniques is recognized as high priority. Classical altimeter data in the coastal zone are adversely affected by land contamination with degraded range and geophysical corrections. However, recent progress in coastal altimetry data processing and multisensor data synergy, offers new perspective to measure sea level change very close to the coast. This issue is discussed in much detail in this paper, including the development of a global coastal sea-level and sea state climate record with mission consistent coastal processing and products dedicated to coastal regimes. Finally, we present a new promising technology based on the use of Signals of Opportunity (SoOp), i.e., communication satellite transmissions that are reutilized as illumination sources in a bistatic radar configuration, for measuring coastal sea level. Since SoOp technology requires only receiver technology to be placed in orbit, small satellite platforms could be used, enabling a constellation to achieve high spatio-temporal resolutions of sea level in coastal zones.
Highlights
Today about 600 million people live very close to the sea at an altitude less than 10 m and this number is expected to double by 2060 (Nicholls, 2010)
Global Navigation Satellite System Reflectometry (GNSS-R) The origin of SoOp altimetry can be traced back to the PARIS (Passive Reflectometry and Interferometry System) concept proposed by Martín-Neira (1993), in which GNSS transmitters were proposed as the signal source
We have identified a number of parameters, which are require to be systematically monitored to improve knowledge on the forcing agents and the morphological changes of the shorelines in response to imposed forcing
Summary
Today about 600 million people (mostly concentrated in several of the world’s largest megacities) live very close to the sea at an altitude less than 10 m and this number is expected to double by 2060 (Nicholls, 2010). We briefly review the need for systematic monitoring of the world coastal zones, with an emphasis on space observations of both forcing agents (e.g., sea level, winds, waves and currents, river runoff, sediment supply and transport, vertical land motions, land use) and coastal responses (e.g., shoreline position, estuaries morphology, land topography at the land–sea interface and coastal bathymetry). Forcing agents acting on coastal zones include sea level change, extreme events, winds, waves and currents, vertical ground motions, sediment supply, river runoff, land use change and urbanization. Depending on the time-scale of processes acting in coastal zones (from extreme events to long-term sea level rise), different types of observations are required to monitor and understand the response of coastal zones to the forcing agents and associated shoreline changes. While this seems technically feasible, further research is needed to meet the users’ requirements in terms of temporal resolution, especially in near-shore areas
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