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Advancements in the Usage of Envisat Individual Echoes (IEs)
Stefano Vignudelli1, Ron Abileah2, Andrea Scozzari3
1Consiglio Nazionale delle Ricerche (CNR-IBF) Italy; 2Jomegak; 3Consiglio Nazionale delle Ricerche (CNR-ISTI) Italy
The Envisat radar altimeter had a PRF of around 1800 Hz, which was intended to provide the maximum number of independent observations per second. The conventional processing and analysis of sea surface returns uses incoherent sums for noise averaging. Standard Envisat altimeter data are averaged at a rate of 20 Hz. However, a provision was made in Envisat for an 'Individual Echoes' (IE) recording mode that collects 1-second bursts of 1984 x 128 range bins of individual complex echo returns every 3 minutes. This acquisition mode was designed to support experiments beyond the conventional methods. A large collection of IE data packets has been provided by the European Space Agency and is now catalogued on disk. The available IE data cover almost all sorts of water targets, including open ocean, coastal zone and inland water. The analysis was primarily conceived for inland water study, but it’s clear that the development of tools for the inland water context also supports the observation of the coastal zone. Matlab routines were developed for processing IE data in order to investigate ways of exploiting the complex data. In this work, we explain the current implemented capabilities, show evidence of observed features from selected case-studies in coastal zone, rivers and estuaries, discussing the impact of those aspects, such as the variability of the surface roughness, which are peculiar to the coastal zone.
Comparison with the Coastal Sea Surface Height Retrieved from Along-Track Jason-2 Continuous Waveforms and the HF Ocean Radar Data in the Tsushima Strait
Xi Feng Wang1, Kaoru Ichikawa2
1ESST, Kyushu University, Japan; 2RIAM, Kyushu University, Japan
A new algorithm is proposed to retrieve sea surface height (SSH) from Jason-2 waveforms contaminated near coastal areas. Unlike the other algorithms such as ALES that detect contamination in each single waveform independently, continuous waveforms along a track are used at once to detect contamination referring consistency with adjacent points. In this study, Jason-2 waveforms near Tsushima Island, Japan are processed and found closer SSH retrieval to the coast than the other algorithms. The obtained SSH is compared with surface velocity observed by the HF ocean radar data in which tidal and wind-driven current components have been removed separately. Spatial smoothing is found necessary for better comparison, which emphasises importance of closer SSH retrieval in coastal areas, especially in narrow channels where the number of altimeter data tends to be insufficient.