Satellite altimeters require correction for tropospheric delay to precisely measure sea surface heights (SSHs). Wide-swath altimeters (WSAs), operating near nadir, experience a slowdown in microwave signals and slight path bending due to changes in the atmospheric refractive index. The continued fraction-based global navigation satellite system (GNSS) mapping function, originally designed for low-elevation-angle GNSS observations, inadequately addresses the challenges faced by WSAs at very high-elevation angles. In addition, it necessitates time-and-location-specific calculations based on numerical weather models (NWMs), limiting its effectiveness in offline applications. This letter introduces a novel atmospheric delay mapping function specifically developed for WSAs with incident angles below 10°. Utilizing the European Centre for Medium-Range Weather Forecasts (ECMWF)’s stratified atmospheric pressure data and the ray-tracing method, this function improves accuracy by supplementing a first-order trigonometric function with remainders. This approach markedly reduces model errors from the millimeter-to-centimeter scale down to the sub-millimeter-to-millimeter scale. This new mapping function, dependent on elevation angle, allows for direct projection in the slant-range direction once the zenith delay is determined, thereby significantly simplifying its application.

Wet tropospheric delay (WPD) is a critical error source of altimeters. The current radiometers have been able to obtain ideal along-track correction values. However, the small-scale spatial variability of the water vapor is a huge challenge for correcting the wide-swath altimeter. Even though the total residual error can meet the error budget by a two-beam radiometer, the correction effect at the edge of the swath is still difficult to control. This paper proposes a WPD correction method based on mixing nadir radiometer and gridded data product by spatial correlation function. The corrected residual root mean square error (RMSE) and cross-track distribution characteristics of different methods are compared through the simulation data. The results show that the total RMSE of the mixed method is similar to the two-beam method but has better cross-track stability.

This paper uses the level-2 Ocean data (OCN) of Sentinel-1 Interferometric Wide swath (IW) model to retrieve the sea surface radial current velocity. The level-2 OCN data of IW mode includes two modules: radial surface velocity (RVL) and ocean wind field (OWI). The RVL module provides parameters such as radial Doppler frequency shift, which can be used to retrieve the sea surface current velocity. The OWI module provides wind field retrieved from the SAR image and is used as the input of the empirical model CDOP to remove the Doppler frequency shift caused by the sea surface wind-wave field. The retrieval results are verified by using HYCOM data, and the bias was less than 0.1m/s and the root mean square error was about 0.2m/s in 4 test areas, which showed good agreement and utility of Sentinel-1 Ocean data in retrieving ocean current data.

The Interferometric Imaging Radar Altimeter (InIRA) carried on the Tiangong-2 Space Laboratory can observe three-dimensional sea surface topography over a swath tens of kilometers wide. The InIRA represents a test mission that will provide valuable experience for the design and data processing technology of future wide-swath altimeters. In addition to the tropospheric delay, ionospheric delay, and sea state bias that affect traditional altimeters, InIRA was also affected by the cross-track error derived from roll error, baseline length error, and interference phase error, which had to be properly corrected. In this paper, range error correction based on correction models and cross-track error correction based on the reference topography data method were applied to a 15-day InIRA dataset and evaluated using the Jason-2, Jason-3, Saral/AltiKa, and Sentinel-3A. The results showed that the standard deviation between corrected InIRA and the combined dataset was 7.96 cm after eliminating the influence of tides and dynamic atmospheric correction, which was comparable to nadir altimeter measurement accuracy.

Wet troposphere path delay (WPD) is a crucial error source for wide-swath altimeters with high-resolution observations. This study generated a simulated wide-swath through the nadir microwave radiometer (MWR) track and evaluated four wide-swath wet tropospheric correction (WTC) methods based on multisource data from 2017 with strict spacetime windows. The Numerical Weather Model (NWM) method can provide a basic correction for the wide-swath altimeter. The MWR method, based on the extension of nadir 1-beam MWR, could not provide a reliable correction. The residual error increased rapidly after deviating from the nadir profile. The overall root-mean-square error (RMSE) of the combination method was approximately 0.58 cm and had high uniformity within the swath. Even at the far end of the swath, the correction was better than that on the NWM and MWR methods. The objective analysis (OA) method using linear spatiotemporal objective analysis had the best result among the four correction methods. The overall RMSE was only 0.49 cm, which was 34% lower than the NWM method. High consistency was maintained at each cross-track position of the swath. The last two wide-swath WTC methods provided in this study had high performance. For the wide-swath altimeter, the combination method is a scheme worthy of consideration, as it can provide WTC results conveniently, quickly, and accurately. Although the operation of the OA method is complex and depends on multisource observation data, it promises to be a high-quality scheme for the wide-swath altimeter WTC when a more accurate WTC value is required.

The wide-swath altimeter uses interferometric synthetic aperture radar technology to obtain a wide-swath detection capability. Referable to the slow undulation of the ocean surface, flat-earth phase is dominant in the interferometric, and the interferometric phase after flat-earth phase removal can reflect the ocean surface elevation change. The nadir altimeter carried by the platform can perform consistent measurements with the wide-swath altimeter, so it is an ideal source of flat-earth phase calculations. Baseline roll error and baseline length error are important sources of error in wide-swath altimeter measurements. The spatial distribution of the interferometric in the cross-track direction can be used to estimate the baseline error. The simulation results show that the correlation coefficients between the estimated value and simulated value of the baseline roll error and the baseline length error both can reach 0.99, indicating that the baseline error can be well controlled.

Ionosphere is part of the upper atmosphere of the Earth, research of ionosphere model is meaningful to reduce ionosphere delay on microwave signals. In this paper, the Back Propagation (BP) model was designed with data of Jason-2 altimeter from 2008 to 2018. The inputs of the model are year, day of the year, hour of the day, latitude and longitude, and the output is the double-frequency correction of the ionosphere. The best model is obtained by repeated training. The selected best model is validated with four cycles of Jason-3. The results show that the mean differences between the model and target of four cycles are between -0.2 and 0.06cm, the standard deviations are less than 1cm, the differences of 95% are located between ± 2cm, the correlation coefficients are all above 0.7. The result indicates that BP model is efficient for the correction of ionosphere delay and with a high accuracy.