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

Interannual Variability of Water Level in Two Largest Lakes of Europe

Regional climate change affects the state of inland water bodies and their water balance, which is determined by a number of hydrometeorological and hydrogeological factors. An integral characteristic of changes in the water balance is the behavior of the level of lakes and reservoirs, which not only largely determines the physical and ecological state of water bodies, but also significantly affects the coastal infrastructure and socio-economic development of the region. This paper investigates the interannual variability of the level of the Ladoga and Onega lakes, the largest lakes in Europe located in the northwest of Russia, according to satellite altimetry data for 1993–2020. For this purpose, we used three specialized altimetry databases: DAHITI, G-REALM, and HYDROWEB. Water level data from these altimetry databases were compared with in-situ records at water level gauge stations. Information on air temperature (1945–2019) and precipitation (1966–2019) acquired at three meteostations located at Ladoga and Onega lakes was used to investigate interannual trends in the regional climate change. Finally, we discuss the potential impact of the lake level rise and regional climate warming on the infrastructure and operability of railways in this region

Integrated Use of Satellite Altimetry in the Investigation of the Meteorological, Hydrological, and Hydrodynamic Regime of the Caspian Sea

Oscillations in the Caspian Sea level represent the result of mutually related hydrometeorological processes, which proceed not only in the sea catchment area but also far beyond it. The change in the tendency of mean sea level variations that occurred in the mid 1970s, when a long-term level fall was replaced by a rapid and significant rise, represents an important indicator of the changes in the natural regime of the Caspian Sea. Therefore, sea level monitoring and long-term forecast of sea level changes represent an extremely important task. The aim of this publication is to show the results of the application of satellite altimetry methods to the investigation of seasonal and interannual variability of the sea level, wind speed and wave height in different parts of the Caspian Sea and Kara-Bogaz-Gol Bay, and the Volga River level. The work is based on the 1992 - 2006 TOPEX/Poseidon and Jason-1 datasets

Railway Transport Adaptation Strategies to Climate Change at High Latitudes: A Review of Experience from Canada, Sweden and China

Impact of climate change on railway transport manifests in a variety of consequences, such as rail buckling, rail flooding, expansion of swing bridges, overheating of electrical equipment and its damage, bridge scour, failure of earthworks, ground settlement, pavement deterioration, damage to sea walls, coastal erosion of tracks and earthworks, and an increased number of railway accidents in general. Such impacts can cause considerable disruption of railway operations and lead to substantial financial expenses for repair of the railway infrastructure. Therefore, it is crucial to include adaptation strategies already in the design phase of the railway construction to ensure stability and integrity of the railway operations. This paper provides a literature review of adaptation considerations in Canada, China and Sweden and discusses climate change challenges that these countries face in their railway systems. In conclusion, the authors provide recommendations for adaptation approaches based on the reviewed international experience which can be useful for policymakers and managers of railway companies

The Turkmen Lake Altyn Asyr and Water Resources in Turkmenistan

XII, 123 p. 100 illus., 97 illus. in color.onlin

Ice cover and sea level of the Aral Sea from satellite altimetry and radiometry (1992-2006)

International audienceWe discuss recent seasonal and interannual variations of ice cover and lake surface level in the Aral Sea from satellite data for 1992-2006. First, we provide an overview of the evolution of the Aral Sea's environmental conditions, hydrological and ice regime, existing observations and current state of the scientific research. Desiccation of the Aral Sea led to disappearance of the infrastructure in the coastal zone, including meteorological and sea level gauge stations. The current lack of reliable in-situ measurements and time series for sea level and ice cover parameters since mid-1980s can be partly overcome with radar altimeter and microwave satellite observations that provide reliable, frequent, regular and weather-independent data. In our study, we use radar altimeter data from TOPEX/Poseidon, Jason-1, ENVISAT and GFO satellites, as well as the Special Sensor Microwave/Imager (SSM/I) radiometer. An ice discrimination method, based on the synergy of active and passive data from the four altimetric missions and SSM/I, is proposed and applied to the entire satellite dataset to define the specific dates of ice events for 1992-2006. We then analyse the evolution of the sea level in the Large and Small Aral sea and Sarykamysh lake. For this purpose, we compare time series from several sources (Hydroweb, USDA Reservoir Database, Integrated Satellite Altimetry Data Base and others), perform an intercomparison of the available observations and discuss the reasons for potential differences. Using the data from the four altimetric retrackers for ENVISAT we also estimate how the presence of ice could affect the altimeter range measures. We estimate the associated uncertainties and provide recommendations for adjusting sea level time series for altimeters where only ocean retracker (T/P, Jason-1, GFO) is present

Patterns of seasonal and interannual changes of surface chlorophyll concentration in the Black Sea revealed from the remote sensed data.

Several years of CZCS-measured surface pigment’s ecosystems (e.g., Shushkina et al., 1995; Vinogradov et concentrations in the Black Sea are analyzed to appraise al., 1995; 1996a,b; Nihoul et al., 1998). The analysis of the seasonal and year-to-year fluctuations of phytoplank- the images of the ocean color collected with the help of ton biomass and understand the causes of these fluctua- remote sensing seems to be one of the most productive tions in terms of the Black Sea’s general dynamics. The methods of estimation the general patterns of temporal pattern of seasonal variations is typical for subtropical and spatial variations of plant pigment concentration in rather than temperate regions. The range of the absolute surface layer of sea water. value of plant pigment surface concentration measured The chlorophyll concentrations measured by remote by remote sensing does not differ greatly from the values sensing methods are known to be the subject of serious measured by direct methods. The pattern of year-to-year discrepancies as compared with in situ measurements variations seems to correlate with cyclic oscillations of (e.g., Chavez, 1995; Martin and Perry, 1994; Mitchell, winter air temperature. In western shallow regions it is 1992; Nihoul et al., 1998). However, these observations also correlated with the Danube discharge intensity. are rather regular and numerous; thus they are worth at- More intensive winter–spring blooms and a slightly lower tention for the analysis of the variations of the Black level of pigment concentration during warm season are Sea’s ecosystem. typical for years of with a mild winter. The causes of The Coastal Zone Color Scanner (CZCS) was develthese regularities seem to be the peculiarities of hydrolog- oped by NASA. It was launched on the Nimbus-7 satelical and meteorological regimes of the Black Sea. The in- lite in October 1978. During its 7.5 year lifetime (Octotensity of winter–spring bloom of phytoplankton appears ber 1978–June 1986), the CZCS acquired nearly 68,000 to depend on hydrological mechanism (i.e., the intensity images, each covering up to 2 million square kilometers of water mixing during winter period due to thermic con- of ocean surface. The Nimbus Project Office in collabovection and wind mixing) rather than the illumination in- ration with the National Aeronautics and Space Administensity

Remote sensing of ice conditions in the Southeastern Baltic Sea and in the Curonian Lagoon and validation of SAR-Based ice thickness products

Here we analyze ice conditions in the Southeastern Baltic (SEB) Sea and in the Curonian Lagoon (CL) using spaceborne synthetic aperture radar (SAR) data combined with in-situ measurements from coastal stations during four winter seasons between 2009–2013. As shown, the ice conditions in the SEB and in the CL are strongly varying from year to year and do not always correlate with each other. In the SEB, ice cover may form only within 5–15 km band along the coast or spread up to 100 km offshore covering almost the entire region. The mean ice season duration here is 45 days. The CL is almost fully ice-covered every year apart of its northern part subjected to sea water inflow and active shipping. The ice regime is also more stable here, however, it also possesses multiple periods of partial melting and re-freezing. In this study we also perform a validation of three SAR-based ice thickness products (Envisat ASAR 0.5-km and 1-km, and RADARSAT-2 0.5-km) produced by the Finnish Meteorological Institute versus in-situ measurements in the CL. As shown, all satellite products perform rather well for the periods of gradual ice thickness growth. When the ice thickness grows rapidly, all products underestimate the observed values by 10–20 cm (20–50%). The best results were obtained for the RADARSAT-2 ice thickness product with the highest R2 value (0.68) and the root mean square error around 8 cm. The results of the study clearly show that multi-mission SAR data are very useful for spatial and temporal analysis of the ice regime in coastal waters and semi-enclosed shallow water bodies where the number of field observations is insufficient or lacking