ALES: A multi-mission adaptive subwaveform retracker for coastal and open ocean altimetry

Passaro, Marcello; Cipollini, Paolo; Vignudelli, Stefano; Quartly, Graham D.; Snaith, Helen

doi:10.1016/j.rse.2014.02.008

Cited by 205 publications

(194 citation statements)

References 25 publications

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“…The factors that impact on the waveforms are not only the presence of land in the altimetric footprints, but also the occurrence of 'bright targets' in the footprint such as patches of very calm water in sheltered areas (Gómez-Enri et al 2010). A summary of the various strategies proposed in recent years for coastal retracking is in Passaro et al (2014); these strategies include the use of a modified functional form (as in Halimi et al 2013), the pre-classification of waveforms and the retracking of 'sub-waveforms', i.e. a portion of the waveform unaffected (or less affected) by coastal artefacts (as in Yang et al 2012).…”

Section: Strategies For Improving the Coastal Altimetry Datamentioning

confidence: 99%

“…A solution recently proposed to improve the retrieval of sea level, SWH and wind in the coastal zone is the Adaptive Leading-Edge Subwaveform (ALES) algorithm (Passaro et al 2014). ALES is a two-pass retracking algorithm, based on the Brown model, where the secondpass sub-waveform window is selected based on the first-pass estimates of SWH, in a way that minimizes the performance degradation w.r.t.…”

Section: Strategies For Improving the Coastal Altimetry Datamentioning

confidence: 99%

“…an ideal, uncorrupted full-waveform case. This algorithm has been validated for sea level and SWH and used for different altimeters in number of case studies (Passaro et al 2014(Passaro et al , 2015aGómez-Enri et al 2016). Figure 5 shows an overpass of Jason-2 tangent to the coast of Elba Island in the Mediterranean Sea, where standard retracking algorithms yield unrealistic metre-level variations of the sea level while the adoption of ALES visually improves the height profile.…”

Section: Strategies For Improving the Coastal Altimetry Datamentioning

confidence: 99%

“…The line plots show the 20-Hz uncorrected SSH (i.e. orbital altitude of the satellite minus retracked range) measured during the overpass of that ground track during orbital cycle 252 (at 13:40 on 7 May 2015) using three different retrackers: the standard Brown 4-parameter available in the sensor geophysical data records ('SGDR', in blue), the 3-parameter maximum likelihood estimator also in the SGDR ('SGDR MLE3', in green), and the ALES retracker (Passaro et al 2014). The ALES estimates are much less affected by the proximity to the Elba Island coast within 42.65 and 42.8°N Surv Geophys (2017) 38:33-57 43 the coastal zone, the radiometer-based measurements degrade rapidly when land enters the radiometer footprint, which has a 10-50 km diameter depending on the particular channel.…”

Section: Strategies For Improving the Coastal Altimetry Datamentioning

confidence: 99%

“…Here we use along-track altimetry data from Jason-1 and Jason-2 as reprocessed by the coastally adapted ALES retracker (Passaro et al 2014) described in Sect. 3.1 and covering the period 2002-2015.…”

Section: A Case Study Around the Coast Of The Ukmentioning

confidence: 99%

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Monitoring Sea Level in the Coastal Zone with Satellite Altimetry and Tide Gauges

et al. 2016

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We examine the issue of sustained measurements of sea level in the coastal zone, first by summarizing the long-term observations from tide gauges, then showing how those are now complemented by improved satellite altimetry products in the coastal ocean. We present some of the progresses in coastal altimetry, both from dedicated reprocessing of the radar waveforms and from the development of improved corrections for the atmospheric effects. This trend towards better altimetric data at the coast comes also from technological innovations such as Ka-band altimetry and SAR altimetry, and we discuss the advantages deriving from the AltiKa Ka-band altimeter and the SIRAL altimeter on CryoSat-2 that can be operated in SAR mode. A case study along the UK coast demonstrates the good agreement between coastal altimetry and tide gauge observations, with root mean square differences as low as 4 cm at many stations, allowing the characterization of the annual cycle of sea level along the UK coasts. Finally, we examine the evolution of the sea level trend from the open to the coastal ocean along the western coast of Africa, comparing standard and coastally improved products. Different products give different sea level trend profiles, so the recommendation is that additional efforts are needed to study sea level trends in the coastal zone from past and present satellite altimeters. Further improvements are expected from more refined processing and screening of data, but in particular from the constant improvements in the geophysical corrections.

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Section: Strategies For Improving the Coastal Altimetry Datamentioning

confidence: 99%

Section: Strategies For Improving the Coastal Altimetry Datamentioning

confidence: 99%

Section: Strategies For Improving the Coastal Altimetry Datamentioning

confidence: 99%

Section: Strategies For Improving the Coastal Altimetry Datamentioning

confidence: 99%

Section: A Case Study Around the Coast Of The Ukmentioning

confidence: 99%

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Monitoring Sea Level in the Coastal Zone with Satellite Altimetry and Tide Gauges

et al. 2016

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Satellite Altimetry: Principles and Applications in Earth Sciences

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Blumstein

Cazenave

et al. 2017

Wiley Encyclopedia of Electrical and Electronics Engineering

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Satellite altimetry is a radar technique measuring the topography of the Earth surface. It was initially designed for the measuring of the topography of the sea surface with reference to an ellipsoid and for the determination of the marine geoid. It also provided valuable information on the ocean circulation. With the improvement of the orbit accuracy from the meter to the centimeter level, satellite altimetry has become a key measurement to estimate sea level variations from regional to global scales. Satellite altimetry is mostly used over the ocean to measure the surface geostrophic currents, eddy structures, wave heights, and the propagation of oceanic Kelvin and Rossby waves. Altimetry has also demonstrated a strong potential for ice and hydrology studies and is now commonly used for the monitoring of the Arctic and Antarctic ice sheets topography and of terrestrial surface water levels.

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Annual sea level variability of the coastal ocean: The Baltic Sea‐North Sea transition zone

2015

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The annual cycle is a major contribution to the nontidal variability in sea level. Its characteristics can vary substantially even at a regional scale, particularly in an area of high variability such as the coastal ocean. This study uses previously validated coastal altimetry solutions (from ALES data set) and the reference ESA Sea Level Climate Change Initiative data set to improve the understanding of the annual cycle during the Envisat years (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) in the North Sea-Baltic Sea transition area. This area of study is chosen because of the complex coastal morphology and the availability of in situ measurements. To our knowledge, this is the first time that the improvements brought by coastal satellite altimetry to the description of the annual variability of the sea level have been evaluated and discussed. The findings are interpreted with the help of a local climatology and wind stress from a reanalysis model. The coastal amplitude of the annual cycle estimated from ALES altimetry data is in better agreement with estimations derived from in situ data than the one from the reference data set. Wind stress is found to be the main driver of annual cycle variability throughout the domain, while different steric contributions are responsible for the differences within and among the subbasins. We conclude that the ALES coastal altimetry product is a reliable data set to study the annual cycle of the sea level at a regional scale, and the strategy described in this research can be applied to other areas of the coastal ocean where the coverage from the tide gauges is not sufficient.

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ALES: A multi-mission adaptive subwaveform retracker for coastal and open ocean altimetry

Cited by 205 publications

References 25 publications

Monitoring Sea Level in the Coastal Zone with Satellite Altimetry and Tide Gauges

Monitoring Sea Level in the Coastal Zone with Satellite Altimetry and Tide Gauges

Satellite Altimetry: Principles and Applications in Earth Sciences

Annual sea level variability of the coastal ocean: The Baltic Sea‐North Sea transition zone

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