Wide-Swath Ocean Topography using Formation Flying Under Squinted Geometries: The Harmony Mission Case

An Analytical Method for Dynamic Wave-Related Errors of Interferometric SAR Ocean Altimetry under Multiple Sea States

Remote Sensing ◽

10.3390/rs13050986 ◽

2021 ◽

Vol 13 (5) ◽

pp. 986

Author(s):

Yao Chen ◽

Mo Huang ◽

Yuanyuan Zhang ◽

Changyuan Wang ◽

Tao Duan

Keyword(s):

Electromagnetic Scattering ◽

Analytical Method ◽

Wave Spectrum ◽

High Accuracy ◽

Sea State ◽

Error Budget ◽

Ocean Topography ◽

Mean Square Errors ◽

Dynamic Wave ◽

Wide Swath

The spaceborne interferometric synthetic aperture radar (InSAR) is expected to measure the sea surface height (SSH) with high accuracy over a wide swath. Since centimeter-level accuracy is required to monitor the ocean sub-mesoscale dynamics, the high accuracy implies that the altimetric errors should be totally understood and strictly controlled. However, for the dynamic waves, they move randomly all the time, and this will lead to significant altimetric errors. This study proposes an analytical method for the dynamic wave-related errors of InSAR SSH measurement based on the wave spectrum and electromagnetic scattering model. Additionally, the mechanisms of the dynamic wave-related errors of InSAR altimetry are analyzed, and the detailed numerical model is derived. The proposed analytical method is validated with NASA’s Surface Water and Ocean Topography (SWOT) project error budget, and the Root-Mean-Square Errors (RMSEs) are in good agreement (0.2486 and 0.2470 cm on a 0.5 km2 grid, respectively). Instead of analysis for a typical project, the proposed method can be applied to different radar parameters under multiple sea states. The RMSEs of Ka-band under low sea state, moderate sea state, and high sea state are 0.2670, 1.3154, and 6.6361 cm, respectively. Moreover, the RMSEs of X-band and Ku-band are also simulated and presented. The experimental results demonstrate that the dynamic wave-related errors of InSAR altimetry are not sensitive to the frequencies but are sensitive to the sea states. The error compensation method is necessary for moderate and higher sea states for centimetric accuracy requirements. This can provide feasible suggestions on system design and error budget for the future interferometric wide-swath altimeter.

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Analysis on the Accuracy of Marine Gravity Inversion from the Wide-swath Altimeter Mission

10.5194/egusphere-egu2020-12239 ◽

2020 ◽

Author(s):

Mao Zhou ◽

Taoyong Jin ◽

Jiancheng Li ◽

Shengjun Zhang ◽

Minzhang Hu

Keyword(s):

Sea Surface Height ◽

Sea Surface ◽

Gravity Inversion ◽

Vertical Deflection ◽

The North ◽

Marine Gravity ◽

The Indian Ocean ◽

Ocean Topography ◽

East West ◽

Wide Swath

<p>Marine gravity is mainly inversed by the nadir satellite altimetry observations. However, the accuracy of the east-west component of vertical deflection is significantly lower than the north-south component. The wide-swath altimeter is one of the main altimetry missions in the future. Its two-dimensional design is expected to obtain high-precision and high-resolution sea surface height simultaneously, and to improve the accuracy of the marine gravity inversion. Taking the SWOT (Surface Water and Ocean Topography) wide-swath altimeter mission as an example, based on the parameters including the ground track and the width of swath, the static sea surface height observations of SWOT, as well as the nadir altimeter missions Jason-1/GM, Cryosat-2/LRM, and SARAL/GM were simulated. Then, the vertical deflections were calculated from above observations to analyze the ability of marine gravity inversion in the South China Sea and part of the Indian Ocean. Compared with EGM2008 model, the vertical deflections determined by one cycle of SWOT are better than the result determined by combining Jason-1/GM, Cryosat-2/LRM, and SARAL/GM. And the results determined by SWOT improve the accuracy of the east-west component of vertical deflection significantly. And then, several specific errors of SWOT satellite were simulated, and their influence on the determination of the vertical deflection was analyzed. It is noted that these errors have certain influence on the accuracy, but can be weakened by using a simple Gaussian filter. In addition, the influence of SWOT sea surface height resolution on the gravity field inversion was analyzed. As a result, under the premise of the designed accuracy and resolution of the SWOT mission, its observations can improve the quality of marine gravity inversion effectively.</p>

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

Ocean Science ◽

10.5194/os-17-1791-2021 ◽

2021 ◽

Vol 17 (6) ◽

pp. 1791-1813

Author(s):

Robert R. King ◽

Matthew J. Martin

Keyword(s):

Mean Squared Error ◽

Surface Current ◽

Surface Currents ◽

Correlated Errors ◽

North West ◽

Forecasting System ◽

Negative Impacts ◽

Ocean Topography ◽

The Impact ◽

Wide Swath

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.

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Using High-Resolution Altimetry to Observe Mesoscale Signals

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-12-00032.1 ◽

2012 ◽

Vol 29 (9) ◽

pp. 1409-1416 ◽

Cited By ~ 22

Author(s):

M.-I. Pujol ◽

G. Dibarboure ◽

P.-Y. Le Traon ◽

P. Klein

Keyword(s):

Simulation Experiment ◽

Signal Reconstruction ◽

Optimal Interpolation ◽

Mesoscale Variability ◽

Sea Level Anomaly ◽

Temporal Sampling ◽

Mesoscale Structures ◽

Ocean Topography ◽

Geostrophic Velocities ◽

Wide Swath

Abstract An Ocean System Simulation Experiment is used to quantify the observing capability of the Surface Water and Ocean Topography (SWOT) mission and its contribution to higher-quality reconstructed sea level anomaly (SLA) fields using optimal interpolation. The paper focuses on the potential of SWOT for mesoscale observation (wavelengths larger than 100 km and time periods larger than 10 days) and its ability to replace or complement altimetry for classical mesoscale applications. For mesoscale variability, the wide swath from SWOT provides an unprecedented sampling capability. SWOT alone would enable the regional surface signal reconstruction as precisely as a four-altimeter constellation would, in regions where temporal sampling is optimum. For some specifics latitudes, where swath sampling is degraded, SWOT capabilities are reduced and show performances equivalent to the historical two-altimeter constellation. In this case, merging SWOT with the two-altimeter constellation stabilizes the global sampling and fully compensates the swath time sampling limitations. Benefits of SWOT measurement are more important within the swath. It would allow a precise local reconstruction of mesoscale structures. Errors of surface signal reconstruction within the swath represent less than 1% (SLA) to 5% (geostrophic velocities reconstruction) of the signal variance in a pessimistic roll error reduction. The errors are slightly reduced by merging swath measurements with the conventional nadir measurements.

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Nonstationary Internal Tides Observed Using Dual-Satellite Altimetry

Journal of Physical Oceanography ◽

10.1175/jpo-d-15-0020.1 ◽

2015 ◽

Vol 45 (9) ◽

pp. 2239-2246 ◽

Cited By ~ 18

Author(s):

E. D. Zaron

Keyword(s):

Sampling Error ◽

Temporal Correlation ◽

Internal Tides ◽

Sea Surface ◽

Novel Approach ◽

Nonstationary Variance ◽

Time Lagged ◽

Nonstationary Tides ◽

Ocean Topography ◽

Wide Swath

AbstractDual-satellite crossover data from the Jason-2 and Cryosat-2 altimeter missions are used in a novel approach to quantify stationary and nonstationary tides from time-lagged mean square sea surface height (SSH) differences, computed for lags from 1 to 1440 h (60 days). The approach is made feasible by removing independent estimates of the stationary tide and mesoscale SSH variance, which greatly reduces the sampling error of the SSH statistics. For the semidiurnal tidal band, the stationary tidal variance is approximately 0.73 cm2, and the nonstationary variance is about 0.33 cm2, or 30% of the total. The temporal correlation of the nonstationary tide is examined by complex demodulation and found to be oscillatory with first 0 crossing at 400 h (17 days). Because a significant fraction of the time-variable mesoscale signal is resolved at time scales of roughly 150 h by the present constellation of satellite altimeters, the results suggest that it may be feasible to predict the nonstationary tide from modulations of the resolved mesoscale, thus enhancing the efficacy of tidal corrections for planned wide-swath altimeters such as the Surface Water and Ocean Topography (SWOT) mission.

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Facilitating Inversion of the Error Covariance Models for the Wide-Swath Altimeters

Remote Sensing ◽

10.3390/rs12111823 ◽

2020 ◽

Vol 12 (11) ◽

pp. 1823

Author(s):

Max Yaremchuk ◽

Joseph M. D’Addezio ◽

Gregg Jacobs

Keyword(s):

Covariance Matrix ◽

Cost Savings ◽

Strongly Correlated ◽

Error Covariance Matrix ◽

Error Covariance ◽

Covariance Models ◽

Ocean Topography ◽

Cent Error ◽

Along Track ◽

Wide Swath

Wide-swath satellite altimeter observations are contaminated by errors caused by the uncertainties in the geometry and orientation of the on-board interferometer. These errors are strongly correlated across the track, while also having similar error structures in the along-track direction. We describe a method for modifying the geometric component of the error covariance matrix which facilitates accuracy in the removal of the respective error modes from the signal and improves computational efficiency of the data assimilation schemes involving wide-swath altimeter observations. The method has been tested using the Surface Water and Ocean Topography simulator. We show substantial computer cost savings in the pseudo-inversion of the respective error covariance matrix. This efficiency improvement comes with a few per cent error in the approximation of the original covariance model simulating uncertainties in the geometry and orientation of the on-board interferometer.

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