The global marine gravity anomaly model is predominantly recovered from along-track radar altimeter data. Despite significant advances in gravity anomaly recovery, the improvement of the gravity anomaly model remains constrained by the absence of cross-track geoid gradients and the reduction in radar altimeter data, especially in coastal and high-latitude regions. ICESat-2 laser altimetry, with a three-pair laser beam configuration, a small footprint, and a near-polar orbit, facilitates the determination of cross-track geoid gradients and provides valid observations in certain regions. We present an ICESat-2 altimeter data processing strategy that includes the determination of cross-track geoid gradients and the combination of along-track and cross-track geoid gradients. Utilizing these methods, we developed a new global marine gravity model, SDUST2022GRA, from radar and laser altimeter data. Different weight determination methods were applied to each type of altimeter datum. The precision and spatial resolution of SDUST2022GRA were assessed against published altimeter-derived global gravity anomaly models (DTU17, V32.1, NSOAS22) and shipborne gravity measurements. SDUST2022GRA achieved a global precision of 4.43 mGal, representing an improvement of approximately 0.22 mGal over existing altimeter-derived models. In local coastal and high-latitude regions, SDUST2022GRA showed an enhancement of 0.16–0.24 mGal compared to the other models. The spatial resolution of SDUST2022GRA is approximately 20 km in certain regions, which is slightly superior to the other models. The percentage contribution of ICESat-2 to the improvement of the gravity anomaly model is 4.3 % in low- to mid-latitude regions by comparing SDUST2022GRA with ICESat-2 to SDUST2021GRA without ICESat-2, and this is increasing in coastal regions. These assessments suggest that SDUST2022GRA is a reliable global marine gravity anomaly model. The SDUST2022GRA data are freely available at https://doi.org/10.5281/zenodo.8337387 (Li et al., 2023).

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

An algorithm is proposed for determining water level in inland water bodies and coastal zones of seas and oceans. The algorithm was tested for the water area of the Gorki Reservoir, for which radioaltimeter databases show considerable data losses. A model was constructed, describing the shape of a mean impulse reflected from a statistically heterogeneous piecewise-constant underlying surface (topographic model). The model was used to substantiate criteria for data choice for the Gorki Reservoir and to construct a regional algorithm for estimating water level using data from Jason-1 satellite and based on the analysis of the shape of telemetric impulses (retracking). Water level was calculated with the use of an algorithm of regional adaptive retracking Sensor Geophysical Data Record databases for the Gorki and Rybinsk reservoirs. Algorithm application has been shown to considerably increase the amount of actual data and significantly improve the accuracy of water level evaluation. The general principles of retracking of a complex domain (a coastal zone, an inland water body, etc.) are discussed. The principles are based on the calculation of signal with allowance made for the roughness of the reflecting surface and they can be applied to different geographic regions.

Standard altimetry data processing developed for open ocean conditions can be inapplicable for the case of inland waters, especially for narrow, elongated waterbodies and rivers, where the distance between shores is less than 10 km (while the eliminated area within the gain of the radar antenna for Jason-1,2 is about 50 km). These conditions are typical, for example, of the majority of reservoirs of the Volga River cascade (with one exception: the Rybinskoe Reservoir). Under these conditions only a few telemetric impulses fit the validity criteria, which causes a severe loss of data. Besides, errors in the water level retrieved from the altimetric measurements are enormous, as was demonstrated on the basis of comparison of in situ measurements at hydro-gauging stations for the water level of the Gorky Reservoir of the Volga River and all that is available along track 10 Hz TOPEX/Poseidon altimetry data and 20 Hz Jason altimetry data over the reservoir area. The problem of minimization of the errors can be resolved by retracking. For justification of the optimal retracking algorithm, the average impulse response of the statistically inhomogeneous surface was calculated theoretically, based on the works of Brown ( 1977) Brown, G. 1977. The average impulse response of a rough surface and its applications. Antennas and Propagation, IEEE Transactions, 25: 67–74. [Google Scholar] and Barrick and Lipa ( 1985) Barrick, D. and Lipa, B. 1985. Analysis and interpretation of altimeter sea echo. Advances in Geophysics, 27: 61–100. [Google Scholar] for the model of the terrain in the vicinity of the Gorky Reservoir. The model represents the main typical features of the waveform examples (e.g. high peaks or irregular complex shape), and the modelled waveforms are in good agreement with the Jason-1,2 waveforms for the same area. It was shown that for the Gorky Reservoir significant wave height (SWH) did not exceed 0.5 m (corresponding to the width of the leading edge less than 1 telemetric gate). Under these conditions the retracking algorithm based on the detection of the beginning of the leading edge of telemetric impulses is preferable for a correct assessment of variations in the water level in the Gorky Reservoir. A comparison of the data with in situ measurements at the hydro-gauging stations for the water level of the Gorky Reservoir shows that retracking dramatically increases the number of data involved in monitoring and significantly improves the accuracy of the measurement of the water level. The retracked data of water level have also been validated by comparing them with Jason-2 and Jason-1 after carrying out measurements for the Gorky Reservoir. The general principles of retracking algorithms for complex areas (land, coastal zone, inland waters, etc.), based on calculations of the waveform and taking into account statistical inhomogeneity of the reflecting surface adjusted to a certain geographic region, are discussed.