Wide-swath Altimetry Research Articles

Improving High-Frequency Marine Gravity Anomaly Recovery: The Efficacy of SWOT Wide-Swath Altimetry

Improving High-Frequency Marine Gravity Anomaly Recovery: The Efficacy of SWOT Wide-Swath Altimetry

The Effect of Spatially Correlated Errors on Sea Surface Height Retrieval from SWOT Altimetry

The upcoming technology of wide-swath altimetry from space will enable monitoring the ocean surface at 4–5 times better spatial resolution and 2–3 times better accuracy than traditional nadir altimeters. This development will provide a chance to directly observe submesoscale sea surface height (SSH) variations that have a typical magnitude of a few centimeters. Taking full advantage of this opportunity requires correct treatment of the correlated SSH errors caused by uncertainties in environmental conditions beneath the satellite and in the geometry and orientation of the on-board interferometer. These observation errors are highly correlated both along and across the surface swath scanned by the satellite, and this presents a significant challenge for accurate processing. In particular, the SWOT precision matrix has off-diagonal elements that are too numerous to allow standard approaches to remain tractable. In this study, we explore the utility of a block-diagonal approximation to the SWOT precision matrix in order to reconstruct SSH variability in the region east of Greenland. An extensive set of 2dVar assimilation experiments demonstrates that the sparse approximation proposed for the precision matrix provides accurate SSH retrievals when the background-to-observation error ratio ν does not exceed 3 and significant wave height is below 2.5 m. We also quantify the range of ν and significant wave heights over which the retrieval accuracy of the exact spatially correlated SWOT error model will outperform the uncorrelated model. In particular, the estimated range is found to be substantially wider (ν<10 with significant wave heights below 8–10 m), indicating the potential benefits of further improving the accuracy of approximations for the SWOT precision matrix.

Calibration of the Instrumental Errors on Marine Gravity Recovery from SWOT Altimeter

The wide-swath altimetry mission, Surface Water and Ocean Topography (SWOT), makes it possible to further break through the accuracy and resolution of marine gravity field recovery. However, as its main payload, the Ka-band radar interferometer (KaRIN) is easy to be affected by the spacecraft attitude, mechanical deformations and dual antenna signal reception status, which generates instrumental errors including roll errors, phase errors, baseline dilation errors, timing errors, and KaRIN noise. Together with ocean temporal variations, the instrumental errors have large effects on the SWOT Sea Surface Height (SSH) observations and hence the marine gravity field recovery. Here, taking the sea area around Japan as an example, we investigated the calibrations of instrumental errors and ocean temporal variations on the recovery of the marine gravity field. The SSH observations of SWOT are first simulated by Mean Sea Surface (MSS), Absolute Dynamic Topography (ADT), Mean Dynamic Topography (MDT) and instrumental errors. Next, the influence of instrumental errors on determining vertical deflection within single-cycle data was analyzed. Then, three calibration methods (KaRIN/KaRIN cross-calibration, Representative KaRIN/KaRIN cross-calibration, and KaRIN/Nadir cross-calibration) are used to reduce the instrumental errors; the experimental results show KaRIN/KaRIN cross-calibration is the optimal one. Last, for the multi-cycle observations containing ocean temporal variations, crossover calibration is done in single cycle and then followed by collinear adjustment in multi-cycles. This approach is verified by considering 18 simulated cycles that cover almost 1 year. Our result indicates an improvement in the accuracy of marine gravity anomaly by about 45% compared to that of one cycle. The calibration strategy of instrumental errors and ocean temporal variations can be used for high-precision marine gravity field recovery with abundant SWOT observations in the near future.

Overlapping-calibration of wide-swath altimeter baseline errors using two satellites formation flying design

The sea surface height (SSH) measured by future wide-swath altimetry satellites contains observation error due to baseline measurement, which is called SSH_Error_Baseline. It is a huge challenge for satellite engineering to maintain such high accuracies of the baseline roll and length in orbit to ensure that the SSH_Error_Baseline can be maintained below 1 cm. Therefore, how to effectively reduce the SSH_Error_Baseline is extremely important. In order to solve the existing problem, an innovative overlapping-calibration method is proposed based on two-satellite formation flight design with overlapping swath. In this study, the differences of SSH data observed by these two satellites in the overlapping area is so small that it can be ignored, and the SSH_Error_Baseline dominates the difference. Then, the baseline parameters of the two satellites can be well estimated by adopting an optimal inverse method. A total of 9 groups of observing system simulation experiments (OSSEs) have been carried out, and they respectively indicate different pessimistic theoretical scenarios of baseline measurement systems. According to the results, this design can effectively reduce the SSH_Error_Baseline in most scenarios. Regarding the advantage of this method, it can be applied to all along-track observation data without requiring the application of additional auxiliary data (i.e. model data, SSH derived from nadir altimetry). Therefore, when two wide-swath altimetry satellites are simultaneously designed, the formation flight scheme proposed in this paper is recommended, especially when the measurements of the baseline cannot meet the expected accuracies.

Satellite Altimetry: Achievements and Future Trends by a Scientometrics Analysis

Scientometric reviews, facilitated by computational and visual analytical approaches, allow researchers to gain a thorough understanding of research trends and areas of concentration from a large number of publications. With the fast development of satellite altimetry, which has been effectively applied to a wide range of research topics, it is timely to summarize the scientific achievements of the previous 50 years and identify future trends in this field. A comprehensive overview of satellite altimetry was presented using a total of 8541 publications from the Web of Science Core Collection covering the years from 1970 to 2021. We begin by presenting the fundamental statistical results of the publications, such as the annual number of papers, study categories, countries/regions, afflictions, journals, authors, and keywords, in order to provide a comprehensive picture of satellite altimetry research. We discuss the co-occurrence of the authors in order to reveal the global collaboration network of satellite altimetry research. Finally, we utilised co-citation networks to detect the development trend and associated crucial publications for various specific topics. The findings show that satellite altimetry research has been changed immensely during the last half-century. The United States, France, China, England, and Germany made the most significant contributions in the field of satellite altimetry. The analysis reveals a clear link between technology advancements and the trend in satellite altimetry research. As a result, wide swath altimetry, GNSS-reflectometry, laser altimetry, terrestrial hydrology, and deep learning are among the most frontier study subjects. The findings of this work could guide a thorough understanding of satellite altimetry’s overall development and research front.

Assessing the performance of the Tiangong-2 wide-swath imaging altimeter observations for water level monitoring over complex and shallow lakes

As a significant hydrological parameter, the water level of complex and shallow river-lake wetland has important implications for a number of hydrological, biological, physical and chemical processes. Current in-situ and satellite-based methods both have disadvantages in capturing water levels over smaller surface water bodies with spatial heterogeneity or complexity. Interferometric imaging radar altimeter (InIRA) is a latest generation of Ku-band radar altimeter onboard Tiangong-2 (TG-2), the Chinese space laboratory, launched in 2016. Similar to the design idea of NASA’s SWOT, it is expected to improve this situation through wide-swath altimetry. However, the capacity of the TG-2 InIRA to measure water levels within small surface water bodies remains unexamined. To explore these performances, particularly their potential impact on hydrology research, an assessment and comparison between in-situ and TG-2 derived measurements was performed over the largest river-lake wetland in China. The results showed that the TG-2 InIRA, with a broad range of coverage, was able to effectively capture most of the surface water at its elevation. For the focused shallow depressions, a relatively good correlation was observed between the in-situ and InIRA-derived water surface elevations (WSEs), with an R2 of 0.97, RMSE of 0.29 m, and absolute difference ranging from 3 to 55 cm. The accuracy of InIRA-derived WSEs was highly controlled by the depression sizes, and the absolute biases broadly increased in a power law fashion as the size of the depression decreased. In addition, surface water profiles along the Ganjiang and Xiushui River channels indicated that the TG-2 InIRA could also measure river WSEs, with absolute differences below 0.43 m. Although differences were observed, the results of the river gradient distribution were consistent with the practical situation and showed overall slopes of 18.72 cm/km and 12.43 cm/km for the Xiushui and Ganjiang Rivers, respectively. Such results demonstrated that TG-2 InIRA measurements can satisfactorily capture spatial patterns of the surface water gradient, which is useful for accurately estimating river discharge. This study will not only bridge the gap between in-situ measurements and forthcoming SWOT products but also contribute to water resource management and hydrologic service assessments over data-sparse regions of river-lake systems within the study area.

Sparse Approximation of the Precision Matrices for the Wide-Swath Altimeters

The upcoming technology of wide-swath altimetry from space will deliver a large volume of data on the ocean surface at unprecedentedly high spatial resolution. These data are contaminated by errors caused by the uncertainties in the geometry and orientation of the on-board interferometer and environmental conditions, such as sea surface roughness and atmospheric state. Being highly correlated along and across the swath, these errors present a certain challenge for accurate processing in operational data assimilation centers. In particular, the error covariance matrix R of the Surface Water and Ocean Topography (SWOT) mission may contain trillions of elements for a transoceanic swath segment at kilometer resolution, and this makes its handling a computationally prohibitive task. Analysis presented here shows, however, that the SWOT precision matrix R−1 and its symmetric square root can be efficiently approximated by a sparse block-diagonal matrix within an accuracy of a few per cent. A series of observational system experiments with simulated data shows that such approximation comes at the expense of a relatively minor reduction in the assimilation accuracy, and, therefore, could be useful in operational systems targeted at the retrieval of submesoscale variability of the ocean surface.

Contribution of a constellation of two wide-swath altimetry missions to global ocean analysis and forecasting

Abstract. Swath altimetry is likely to revolutionize our ability to monitor and forecast ocean dynamics. To meet the requirements of the EU Copernicus Marine Service, a constellation of two wide-swath altimeters is envisioned for the long-term (post-2030) evolution of the Copernicus Sentinel 3 topography mission. A series of observing system simulation experiments (OSSEs) is carried out to quantify the expected performances. The OSSEs use a state-of-the-art high-resolution (1/12∘) global ocean data assimilation system similar to the one used operationally by the Copernicus Marine Service. Flying a constellation of two wide-swath altimeters will provide a major improvement of our capabilities to monitor and forecast the oceans. Compared to the present situation with three nadir altimeters flying simultaneously, the sea surface height (SSH) analysis and 7 d forecast error are globally reduced by about 50 % in the OSSEs. With two wide-swath altimeters, the quality of SSH 7 d forecasts is equivalent to the quality of SSH analysis errors from three nadir altimeters. Our understanding of ocean currents is also greatly improved (30 % improvements at the surface and 50 % at 300 m depth). The resolution capabilities will be drastically improved and will be closer to 100 km wavelength compared to about 250 km today. Flying a constellation of two wide-swath altimeters thus looks to be a very promising solution for the long-term evolution of the Sentinel 3 constellation and the Copernicus Marine Service.

Site selection for the validation of wide-swath interferometric altimeter in the South China Sea

ABSTRACT Altimetry is widely used in the research of oceanic phenomena. Particularly, wide-swath interferometric altimetry (WIA) can be used to measure sea surface height (SSH) with sufficiently high resolution. Although it has provided that the steric height can be used to validate the SSH by the theoretical and the observation data, validating sea-level variability in the two dimensions of WIA remains a difficult task. Site selection and influencing factor analysis are important in the validation process. In this paper, we analyze the validation process at three sites (Panyu site, DJxxxx site, and Wanshan site) in the South China Sea and discuss the effects of different sites on the validation of SSH variability. On this basis, we analyze the influencing factors, which include significant wave heights, wind, and currents, at three sites. Based on the results, we discuss how site selection for the validation process of WIA can be improved. At DJxxxx site, greater water depth and more equipment layout schemes have emerged with better performance in wavenumber. At the same time, the performance under the tidal, wave, wind and current is different for the other two sites. However, further analysis is necessary for the site selection.

Assimilating realistically simulated wide-swath altimeter observations in a high-resolution shelf-seas forecasting system

Abstract. The impact of assimilating simulated wide-swath altimetry observations from the upcoming Surface Water and Ocean Topography (SWOT) mission is assessed using observing system simulation experiments (OSSEs). These experiments use the Met Office 1.5 km resolution North West European Shelf analysis and forecasting system. In an effort to understand the importance of future work to account for correlated errors in the data assimilation scheme, we simulate SWOT observations with and without realistic correlated errors. These are assimilated in OSSEs along with simulated observations of the standard observing network, also with realistic errors added. It was found that while the assimilation of SWOT observations without correlated errors reduced the RMSE (root mean squared error) in sea surface height (SSH) and surface current speeds by up to 20 %, the inclusion of correlated errors in the observations degraded both the SSH and surface currents, introduced an erroneous increase in the mean surface currents and degraded the subsurface temperature and salinity. While restricting the SWOT data to the inner half of the swath and applying observation averaging with a 5 km radius negated most of the negative impacts, it also severely limited the positive impacts. To realise the full benefits in the prediction of the ocean mesoscale offered by wide-swath altimetry missions, it is crucial that methods to ameliorate the effects of correlated errors in the processing of the SWOT observations and account for the correlated errors in the assimilation are implemented.

Monitoring intertidal topography using the future SWOT (Surface Water and Ocean Topography) mission

Intertidal flats are very dynamic environments pressured by anthropogenic activities and climate change. There is an increasing need for updated intertidal topography maps for scientific and coastal management purposes. The future wide-swath altimetry mission SWOT (Surface Water and Ocean Topography) will provide valuable data for intertidal topography monitoring. SWOT will use interferometry to measure heights over water surfaces only, which will prevent the use of this method over intertidal areas. Since SWOT is expected to provide highly accurate 2D sea level measurements in coastal areas, it will be very beneficial for the waterline method. The waterline method is one of the most commonly used spaceborne methods for mapping intertidal topography. This method uses a combination between a series of satellite images acquired at different tidal stages (radar or optical) and sea level information (tide gauge records, models output, or satellite measurements). The aim of this study is to investigate the performance of SWOT in generating intertidal Digital Elevation Models (DEMs) using the waterline method (with a brief investigation regarding the interferometric capabilities of SWOT over intertidal areas). To this end, tests were made by generating intertidal DEMs from SWOT-type observables for two intertidal bays situated on the French coast: the Arcachon Bay and the Bay of Veys. SWOT-type observables were simulated using the SWOT large scale simulator developed by the French space agency (CNES - Centre National d’Etudes Spatiales). By comparing SWOT-derived DEMs to the validation DEMs (generated by the waterline method using Sentinel-1 and -2 images), SWOT showed a great potential for monitoring intertidal topographies. Mean Absolute Errors (MAE) and Root Mean Squared Errors (RMSE) reached respectively 5.2 cm and 8.4 cm for the Arcachon Bay and 10.2 cm and 17.3 cm for the Bay of Veys. However, the accuracy of SWOT is dependent on SWOT's orbit. An unfavorable sampling due to tidal aliasing decreases the accuracy of the DEMs. Thus, the period during which the series of satellite images are acquired (the acquisition period) shall be chosen carefully in order to generate accurate SWOT DEMs. SWOT will be able to generate relatively accurate DEMs with period of acquisitions of 3 months. With acquisition periods that provide adequate sampling of the tidal range, SWOT will be able to detect topographic changes between consecutive DEMs. The present work was supported by the CNES in the framework of the future mission SWOT.

Discharge Estimation via Assimilation of Multisatellite-Based Discharge Products: Case Study Over the Amazon Basin

River flows are an essential component of the water cycle and are directly accessible for human consumption and activities. River water flux (i.e., river discharge) not only can be measured locally at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> gauges but also can be estimated at larger scales with the river routing models. However, the number of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> gauges is declining worldwide while emerging river-related products from satellites are becoming more available. Especially, discharge products based on satellite altimetry water elevations are emerging. These altimetry missions provide different spatial and temporal coverages and may not provide the same amount of information. In this study, discharge products from two satellite altimetry missions (ENVISAT and JASON-2) were assimilated into the large-scale hydrologic model Intéractions Sol-Biosphére-Atmosphére-CNRM’s Total Runoff and Integrating Pathways (ISBA-CTRIP) using an ensemble Kalman filter, to correct the simulated discharge. This work investigates whether it is better to assimilate products with a dense spatial coverage but a lower temporal sampling (ENVISAT) or the opposite (JASON-2). Three experiments have been performed: the first two assimilated each product separately, and the last one assimilated the combined product. The open-loop normalized root-mean-square error evaluated against <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> discharge (RMSEn) is 69%. RMSEn is decreased for all experiments. Specifically, it is slightly lower when assimilating ENVISAT-based discharge product (51%) than JASON-2 product (53%) as the ENVISAT-based product spatial coverage is denser. The best results are obtained when both products are assimilated (RMSEn=49%). These results are very encouraging and could be improved when the future Surface Water and Ocean Topography (SWOT) wide swath altimetry mission discharge product will be available.

Effects of Interferometric Radar Altimeter Errors on Marine Gravity Field Inversion.

The traditional altimetry satellite, which is based on pulse-limited radar altimeter, only measures ocean surface heights along tracks; hence, leads to poorer accuracy in the east component of the vertical deflections compared to the north component, which in turn limits the final accuracy of the marine gravity field inversion. Wide-swath altimetry using radar interferometry can measure ocean surface heights in two dimensions and, thus, can be used to compute vertical deflections in an arbitrary direction with the same accuracy. This paper aims to investigate the impact of Interferometric Radar Altimeter (InRA) errors on gravity field inversion. The error propagation between gravity anomalies and InRA measurements is analyzed, and formulas of their relationship are given. By giving a group of possible InRA parameters, numerical simulations are conducted to analyze the accuracy of gravity anomaly inversion. The results show that the accuracy of the gravity anomalies is mainly influenced by the phase errors of InRA; and the errors of gravity anomalies have a linear approximation relationship with the phase errors. The results also show that the east component of the vertical deflections has almost the same accuracy as the north component.

The demand analysis of oceanic T-S-V 3D reconstruction on wide-swath SSH data features based on ROMS and 4DVAR

Summary Future wide-swath altimetry missions will provide high-resolution information about ocean surface elevation, and facilitate the characterization of meso- and sub-mesoscale ocean activities. In this study, the demand analysis of three-dimensional (3D) oceanic state reconstruction on wide-swath SSH data features was evaluated using a data assimilation strategy. Three groups of experiments were performed to determine if the wide-swath altimetry observations would improve the three-dimensional (3D) field estimates of ocean temperature-salinity-velocity (T-S-V), and to evaluate how the spatial and temporal resolution and accuracy of the wide-swath altimetry observations affected the ocean state estimation. The Regional Ocean Modeling System and the four-dimensional variational data assimilation method were used in the experiments, with numerical simulation for the Taiwan region at a resolution of 1/10° as the example. The sensitivity of the 3D ocean state construction to the wide-swath altimetry measurements was also investigated. The results showed that the wide-swath sea surface height (SSH) measurements would have an overall positive impact on the 3D T-S-V field and that the positive effect would increase as the resolution and accuracy of the observations increased, but the net benefits would gradually decrease. Among the three examined features of the wide-swath altimetry observations, the temporal resolution had the most influence on the 3D ocean state analysis.

Some Expectations for Submesoscale Sea Surface Height Variance Spectra

AbstractIn anticipation of the Surface Water and Ocean Topography (SWOT) wide-swath altimetry mission, this study reviews expectations for sea surface height (SSH) variance spectra at wavelengths of 10–100 km. Kinetic energy spectra from in situ observations and numerical simulations indicate that SSH variance spectra associated with balanced flow drop off steeply with wavenumber, with at least the negative fourth power of the wavenumber. Such a steep drop-off implies that even drastic reductions in altimetry noise yield only a modest improvement in the resolution of balanced flow. This general expectation is made concrete by extrapolating SSH variance spectra from existing altimetry to submesoscales, the results of which suggest that in the extratropics (poleward of 20° latitude) SWOT will improve the resolution from currently about 100 km to a median of 51 or 74 km, depending on whether or not submesoscale balanced flows are energetic. Internal waves, in contrast to balanced flow, give rise to SSH variance spectra that drop off relatively gently with wavenumber, so SSH variance should become strongly dominated by internal waves in the submesoscale range. In situ observations of the internal-wave field suggest that the internal-wave signal accessible by SWOT will be largely dominated by internal tides. The internal-wave continuum is estimated to have a spectral level close to but somewhat lower than SWOT’s expected noise level.

Observing storm surges in China's coastal areas by integrating multi-source satellite altimeters

Storm surge is one of the most dangerous and destructive natural disasters in the world, which is a serious threat to the survival and development of human beings in coastal areas. Therefore, in order to mitigate damage and loss, it is necessary to enhance our capabilities of observing, understanding and forecasting storm surges. In this study, we used 25-year (1993–2017) of multi-source satellite altimeters and coastal tide-gauge data to monitor storm surges in China's coastal regions. We then found that satellite altimetry can be used as a useful complementary dataset to study storm surges. During the above study period, the multi-source satellite altimeters captured 32 storm surge events, accounting for nearly 26% of storm surge events were identified from tide gauges in this study area. Although coastal surge heights identified by tide gauges is significantly higher than those recorded by satellite altimeters at most tide gauges, coastal surge heights captured by satellite altimeters can reflect the transient spatial and temporal dynamic surge process. Simultaneously, this study also shows that the altimetry mission to capture storm surges is of an opportunistic nature, and the presence of multiple satellite tracks in a region greatly enhances the probability of capturing signals of extreme events. Though satellite altimeters have been proven to be a complementary means of observing storm surges, effective strategies will be required for regular monitoring of storm surges in the future. In addition, storm surge is also affected by global climate change and rising sea levels. Therefore, we can use wide-swath altimetry or joint multi-mission gridded altimeter products and reanalysis dataset to monitor storm surges in the future.

Contribution of future wide-swath altimetry missions to ocean analysis and forecasting

Abstract. The impact of forthcoming wide-swath altimetry missions on the ocean analysis and forecasting system was investigated by means of OSSEs (observing system simulation experiments). These experiments were performed with a regional data assimilation system, implemented in the Iberian–Biscay–Ireland (IBI) region, at 1∕12∘ resolution using simulated observations derived from a fully eddy-resolving free simulation at 1∕36∘ resolution over the same region. The objective of the experiments was to assess the ability of different satellite constellations to constrain the ocean analyses and forecasts, considering both along-track altimeters and future wide-swath missions; consequently, the capability of the data assimilation techniques used in the Mercator Ocean operational system to effectively combine the different kinds of measurements was also investigated. These assessments were carried out as part of a European Space Agency (ESA) study on the potential role of wide-swath altimetry in future versions of the European Union Copernicus programme. The impact of future wide-swath altimetry data is evident for investigating the reliability of sea level values in OSSEs. The most significant results were obtained when looking at the sensitivity of the system to wide-swath instrumental error: considering a constellation of three nadir and two “accurate” (small instrumental error) wide-swath altimeters, the error in ocean analysis was reduced by up to 50 % compared to conventional altimeters. Investigating the impact of the repetitivity of the future measurements, the results showed that two wide-swath missions had a major impact on sea-level forecasting – increasing the accuracy over the entire time window of the 5-day forecasts – compared with a single wide-swath instrument. A spectral analysis underlined that the contributions of wide-swath altimetry data observed in ocean analyses and forecast statistics were mainly due to the more accurate resolution, compared with along-track data, of ocean variability at spatial scales smaller than 100 km. Considering the ocean currents, the results confirmed that the information provided by wide-swath measurements at the surface is propagated down the water column and has a considerable impact (30 %) on ocean currents (up to a depth of 300 m), compared with the present constellation of altimeters. The ocean analysis and forecasting systems used here are those currently used by the Copernicus Marine Environment and Monitoring Service (CMEMS) to provide operational services and ocean reanalysis. The results obtained in the OSSEs considering along-track altimeters were consistent with those derived from real data (observing system experiments, OSEs). OSSEs can also be used to assess the potential of new observing systems, and in this study the results showed that future constellations of altimeters will have a major impact on constraining the CMEMS ocean analysis and forecasting systems and their applications.

Hurricane Isaac storm surges off Florida observed by Jason-1 and Jason-2 satellite altimeters

Storm surges can cause damage to properties and loss of life in coastal communities. Thus it is important to enhance our capabilities of observing, understanding and forecasting storm surges for mitigating damage and loss. Previous studies have shown that cross-shelf altimetric sea surface height profiles can be used to determine storm surge features. In this study we combine satellite altimetry with tide-gauge data to study storm surge features off Florida in the Gulf of Mexico during Hurricane Isaac 2012. Satellite observations show a storm surge of about 0.8 m near Cedar Key and Apalachicola decreasing westward and southward in the early morning of August 28, 2012 (UTC), consistent with tide-gauge measurements. Our analysis of satellite data reveals that the storm surge propagates northward from Naples to Cedar Key with a phase speed of 14–16m/s and a cross-shelf decay scale of 190–220km, in approximate agreement with the estimates from tide-gauge data. In contrast, an analysis of tide-gauge data reveals that the storm surge propagates westward from Apalachicola to Pensacola with a phase speed of 6–7m/s and a cross-shelf decay scale of about 85km. It is further shown that the post-storm sea level variations at these stations are associated with first-mode continental shelf waves. The present study shows that along-shelf altimetric sea surface height profiles can be useful to observe and understand storm surge features as cross-shelf ones demonstrated previously, of importance to improvement of storm surge forecasting. It suggests that a constellation of altimeter missions especially with wide-swath altimetry could be suited to monitor storm surges.

Inland Water Height Estimation Without Ground Control Points for Near-Nadir InSAR Data

Surface Water and Ocean Topography (SWOT) is a future wide-swath radar altimetry mission. The main instrument is the Ka-band radar interferometer (KaRIn). It provides interferometric radar images that will be processed to obtain water elevation estimates worldwide. Due to the specific geometric and radiometric characteristics of KaRIn/SWOT, the phase-to-height conversion is one of the most critical processing steps. We propose methods to estimate water heights without using classical approaches based on spatial phase unwrapping and control points. Results obtained on the simulated SWOT data are shown.

Engaging the Applications Community of the future Surface Water and Ocean Topography (SWOT) Mission

Abstract. NASA and the French space agency, CNES, with contributions from the Canadian Space Agency (CSA) and United Kingdom Space Agency (UKSA) are developing new wide swath altimetry technology that will cover most of the world’s ocean and surface freshwater bodies. The proposed Surface Water and Ocean Topography (SWOT) mission will have the capability to make observations of surface water (lakes, rivers, wetland) heights and measurements of ocean surface topography with unprecedented spatial coverage, temporal sampling, and spatial resolution compared to existing technologies. These data will be useful for monitoring the hydrologic cycle, flooding, and characterizing human impacts on a changing environment. The applied science community is a key element in the success of the SWOT mission, demonstrating the high value of the science and data products in addressing societal issues and needs. The SWOT applications framework includes a working group made up of applications specialists, SWOT science team members, academics and SWOT Project members to promote applications research and engage a broad community of potential SWOT data users. A defined plan and a guide describing a program to engage early adopters in using proxies for SWOT data, including sophisticated ocean and hydrology simulators, an airborne analogue for SWOT (AirSWOT), and existing satellite datasets, are cornerstones for the program. A user survey is in development and the first user workshop was held in 2015, with annual workshops planned. The anticipated science and engineering advances that SWOT will provide can be transformed into valuable services to decision makers and civic organizations focused on addressing global disaster risk reduction initiatives and potential science-based mitigation activities for water resources challenges of the future. With the surface water measurements anticipated from SWOT, a broad range of applications can inform inland and coastal managers and marine operators of terrestrial and oceanic phenomena relevant to their work.