Altimetry for the future: Building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Altimetry for the future: building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

An improved Satellite Altimetry Data Processing along the Coastal Areas: Validation over the Algerian Coast

In coastal systems, shorter spatial and temporal scales make ocean dynamics particularly complex, so the coastal domain represents a challenging target for processing of satellite altimetry data. The main objective of this paper is to improve the altimetric measurement in coastal areas by analyzing the atmospheric corrections which must be applied to obtain a precise surface height.The processing of Saral/AltiKa Geophysical Data Records with in-house developed algorithms, includes: 1) re-tracking which is important for the last 7 km next to the coast; 2) a more accurate wet troposphere correction (decontaminated correction) and better modelling of atmospheric effects. A better determination of the sea surface height over the Algerian coast can be retrieved. The obtained surface was validated with the in-situ tide gauge data, and found in good agreement.Dans les systèmes côtiers, des échelles spatiales et temporelles plus courtes rendent la dynamique des océans particulièrement complexe, de sorte que le domaine côtier représente une cible difficile pour le traitement des données altimétriques satellitaires. L'objectif principal de cet article est d'améliorer la mesure altimétrique en zone côtière en analysant les corrections atmosphériques qui doivent être appliquées pour obtenir une hauteur de surface précise.Le traitement des données géophysiques du satellite Saral/AltiKa avec notre propre algorithme comprend : 1) le retraçage qui est important pour les 7 derniers kilomètres à partir de la côte ; 2) une correction plus précise de la troposphère humide (correction décontaminée) et une meilleure modélisation des effets atmosphériques. Une meilleure détermination de la hauteur de la surface de la mer sur la côte algérienne peut être récupérée.La surface obtenue a été validée avec les données marégraphiques in-situ et le résultat est satisfaisant

Analyse spatio-temporelle de l’évolution de la surface de la mer Méditerranée

Cet article résume les résultats de l'étude de la variabilité spatio-temporelle du niveau moyen de la mer Méditerranée ainsi que sa  représentation par les modes fondamentaux permettant une réduction des données. L’analyse de la série temporelle d’anomalies moyennes de hauteur de la mer (ou sea level anomalies-SLA), issues des mesures recueillies par les différentes missions d’altimétrie satellitaire sur la période de janvier 1993 à décembre 2015, montre une différenciation évidente Est-Ouest. Le bassin oriental a  augmenté de façon très nette. Par contre, au niveau de l'Italie (mer Ionienne), le niveau a baissé. Afin de décrire les modes fondamentaux de variabilité, une décomposition du set des données en fonctions orthogonales empiriques (EOF) a été effectuée. Les fonctions calculées, tronquées à 20, permettent une réduction de l'espace des données tout en expliquant prés de 80% de la variance des données analysées. Les cartes reconstruites à partir des EOFs estimés sont en concordance avec les données sources.   English title: Spatio-temporal analysis of the evolution of the Mediterranean Sea surface This paper focuses on the analysis of the spatio-temporal variability of Mediterranean sea level and its representation by fundamental modes allowing a reduction of the data. The analysis of the temporal series of sea level anomalies (SLA), derived from the measurements from various satellite altimetry missions over the period from January 1993 to December 2015 shows a differentiation obvious East-West. The Eastern basin has increased sharply. On the other hand, the sea level has decreased at the level of Italy (Ionian Sea). In order to describe the fundamental modes of Mediterranean sea level variability, a decomposition of the set of data into Empirical Orthogonal Functions (EOF) was performed. The computed functions, truncated at 20, allow a  reduction of the space of the data while explaining nearly 80% of the variance of the analyzed data. The maps reconstructed from the estimated EOFs are in agreement with the original data