Estimating the High-Resolution Mean Sea-Surface Velocity Field by Combined Use of Altimeter and Drifter Data for Geoid Model Improvement

2003 ◽  
Vol 108 (1/2) ◽  
pp. 195-204 ◽  
Author(s):  
Shiro Imawaki ◽  
Hiroshi Uchida ◽  
Kaoru Ichikawa ◽  
Daisuke Ambe
Keyword(s):  
High Resolution ◽  
Velocity Field ◽  
Sea Surface ◽  
Surface Velocity ◽  
Geoid Model ◽  
Combined Use ◽  
Mean Sea Surface ◽  
Model Improvement

scholarly journals Adjusting altimetric sea surface height observations in coastal regions. Case study in the Greek Seas

2014 ◽  
Vol 4 (1) ◽  
Author(s):  
Ioannis Mintourakis
Keyword(s):  
Satellite Altimetry ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Altimetry Data ◽  
Geoid Model ◽  
Sea Surface Topography ◽  
Marine Gravity ◽  
Mean Sea Surface ◽  
Process Strategy ◽  
Satellite Altimetry Data

AbstractWhen processing satellite altimetry data for Mean Sea Surface (MSS) modelling in coastal environments many problems arise. The degradation of the accuracy of the Sea Surface Height (SSH) observations close to the coastline and the usually irregular pattern and variability of the sea surface topography are the two dominant factors which have to be addressed. In the present paper, we study the statistical behavior of the SSH observations in relation to the range from the coastline for many satellite altimetry missions and we make an effort to minimize the effects of the ocean variability. Based on the above concepts we present a process strategy for the homogenization of multi satellite altimetry data that takes advantage ofweighted SSH observations and applies high degree polynomials for the adjustment and their uniffcation at a common epoch. At each step we present the contribution of each concept to MSS modelling and then we develop a MSS, a marine geoid model and a grid of gravity Free Air Anomalies (FAA) for the area under study. Finally, we evaluate the accuracy of the resulting models by comparisons to state of the art global models and other available data such as GPS/leveling points, marine GPS SSH’s and marine gravity FAA’s, in order to investigate any progress achieved by the presented strategy

High‐resolution, high‐accuracy altimeter derived mean sea surface in the Norwegian Sea

1990 ◽  
Vol 14 (1) ◽  
pp. 57-76 ◽  
Author(s):  
Frédérique Blanc ◽  
Sabine Houry ◽  
Pierre Mazzega ◽  
Jean François Minster
Keyword(s):  
High Resolution ◽  
High Accuracy ◽  
Sea Surface ◽  
Norwegian Sea ◽  
Mean Sea Surface

scholarly journals Accurate Sea Surface heights from Sentinel-3A and Jason-3 retrackers by incorporating High-Resolution Marine Geoid and Hydrodynamic Models

2021 ◽  
Vol 11 (1) ◽  
pp. 58-74
Author(s):  
M. Mostafavi ◽  
N. Delpeche-Ellmann ◽  
A. Ellmann
Keyword(s):  
High Resolution ◽  
Baltic Sea ◽  
Hydrodynamic Model ◽  
Average Distance ◽  
Sea Surface ◽  
Hydrodynamic Models ◽  
Geoid Model ◽  
Sea Surface Heights ◽  
Ice Conditions ◽  
The Baltic

Abstract One of the major challenges of satellite altimetry (SA) is to produce accurate sea surface heights data up to the shoreline, especially in geomorphologically complex sea areas. New advanced re-tracking methods are expected to deliver better results. This study examines the achievable accuracy of Sentinel-3A (S3A) and Jason-3 (JA3) standard retrackers (Ocean and MLE4) with that of improved retrackers adapted for coastal and sea ice conditions (ALES+ SAR for S3A and ALES+ for JA3). The validation of SA data was performed by the integration of tide gauges, hydrodynamic model and high-resolution geoid model. The geoid being a key component that links the vertical reference datum of the SA with other utilized sources. The method is tested in the eastern section of Baltic Sea. The results indicate that on average reliable sea surface height (SSH) data can be obtained 2–3 km from the coastline for S3A (for both Ocean and ALES+SAR) whilst an average distance of 7–10 km for JA3 (MLE4 and ALES+) with a minimum distance of 3–4 km. In terms of accuracy, the RMSE (with respect to a corrected hydrodynamic model) of S3A ALES+ SAR and Ocean retrackers based SSH were 4–5 cm respectively, whereas with the JA3 ALES+ and MLE4 associated SSH RMSE of 6–7 cm can be achieved. The ALES+ and ALES+ SAR retrackers show SSH improvement within a range of 0.5–1 cm compared to the standard retrackers. This assessment showed that the adaptation of localized retrackers for the Baltic Sea (ALES+ and ALES+SAR) produced more valid observation closer to the coast than the standard retrackers and also improved the accuracy of SSH data.

High-resolution numerical modelling of the altimetry-derived gravity disturbances and disturbing gradients

2020 ◽  
Author(s):  
Róbert Čunderlík ◽  
Marek Macák ◽  
Michal Kollár ◽  
Karol Mikula
Keyword(s):  
High Resolution ◽  
Numerical Solution ◽  
Finite Volume ◽  
Sea Surface ◽  
Computational Domain ◽  
Disturbing Potential ◽  
Gravity Disturbances ◽  
Mean Sea Surface ◽  
Upper Boundary ◽  
Goce Satellite

<p>Recent high-resolution mean sea surface models obtained from satellite altimetry in a combination with the GRACE/GOCE-based global geopotential models provide valuable information for detailed modelling of the altimetry-derived gravity data. Our approach is based on a numerical solution of the altimetry-gravimetry boundary-value problem using the finite volume method (FVM). FVM discretizes the 3D computational domain between an ellipsoidal approximation of the Earth's surface and an upper boundary chosen at a mean altitude of the GOCE satellite orbits. A parallel implementation of the finite volume numerical scheme and large-scale parallel computations on clusters with distributed memory allow to get a high-resolution numerical solution in the whole 3D computational domain. Our numerical experiment presents the altimetry-derived gravity disturbances and disturbing gradients determined with the high-resolution 1 x 1 arc min at two altitude levels; on the reference ellipsoid and at the altitude of 10 km above the ellipsoid. As input data, the Dirichlet boundary conditions over oceans/seas are considered in the form of the disturbing potential. It is obtained from the geopotential evaluated on the DTU18 mean sea surface model from the GO_CONS_GCF_2_TIM_R5 geopotential model and then filtered using the nonlinear diffusion filtering. On the upper boundary, the FVM solution is fixed to the disturbing potential generated from the GO_CONS_GCF_2_DIR_R5 model while exploiting information from the GRACE and GOCE satellite missions.</p>

scholarly journals Temporal Multi-Looking of SAR Image Series for Glacier Velocity Determination and Speckle Reduction

2020 ◽  
Author(s):  
Silvan Leinss ◽  
Shiyi Li ◽  
Philipp Bernhard ◽  
Othmar Frey
Keyword(s):  
High Resolution ◽  
Velocity Field ◽  
Cross Correlation ◽  
Surface Velocity ◽  
Sar Image ◽  
Sar Images ◽  
Glacier Surface ◽  
Radar Images ◽  
Glacier Velocity ◽  
Offset Tracking

<p>The velocity of glaciers is commonly derived by offset tracking using pairwise cross correlation or feature matching of either optical or synthetic aperture radar (SAR) images.  SAR images, however, are inherently affected by noise-like radar speckle and require therefore much larger images patches for successful tracking compared to the patch size used with optical data. As a consequence, glacier velocity maps based on SAR offset tracking have a relatively low resolution compared to the nominal resolution of SAR sensors. Moreover, tracking may fail because small features on the glacier surface cannot be detected due to radar speckle. Although radar speckle can be reduced by applying spatial low-pass filters (e.g. 5x5 boxcar), the spatial smoothing reduces the image resolution roughly by an order of magnitude which strongly reduces the tracking precision. Furthermore, it blurs out small features on the glacier surface, and therefore tracking can also fail unless clear features like large crevasses are visible.</p><p>In order to create high resolution velocity maps from SAR images and to generate speckle-free radar images of glaciers, we present a new method that derives the glacier surface velocity field by correlating temporally averaged sub-stacks of a series of SAR images. The key feature of the method is to warp every pixel in each SAR image according to its temporally increasing offset with respect to a reference date. The offset is determined by the glacier velocity which is obtained by maximizing the cross-correlation between the averages of two sub-stacks. Currently, we need to assume that the surface velocity is constant during the acquisition period of the image series but this assumption can be relaxed to a certain extend.</p><p>As the method combines the information of multiple images, radar speckle are highly suppressed by temporal multi-looking, therefore the signal-to-noise ratio of the cross-correlation is significantly improved. We found that the method outperforms the pair-wise cross-correlation method for velocity estimation in terms of both the coverage and the resolution of the velocity field. At the same time, very high resolution radar images are obtained and reveal features that are otherwise hidden in radar speckle.</p><p>As the reference date, to which the sub-stacks are averaged, can be arbitrarily chosen a smooth flow animation of the glacier surface can be generated based on a limited number of SAR images. The presented method could build a basis for a new generation of tracking methods as the method is excellently suited to exploit the large number of emerging free and globally available high resolution SAR image time series.</p>

scholarly journals High-resolution mean sea surface computed with altimeter data of Ers-1 (geodetic mission) and topex-poseidon

1996 ◽  
Vol 125 (3) ◽  
pp. 696-704 ◽  
Author(s):  
A. Cazenave ◽  
P. Schaeffer ◽  
M. Berge ◽  
C. Brossier ◽  
K. Dominh ◽  
...  
Keyword(s):  
High Resolution ◽  
Sea Surface ◽  
Altimeter Data ◽  
Mean Sea Surface

scholarly journals The Unique Role of the Jason Geodetic Missions for high Resolution Gravity Field and Mean Sea Surface Modelling

2021 ◽  
Vol 13 (4) ◽  
pp. 646
Author(s):  
Ole Baltazar Andersen ◽  
Shengjun Zhang ◽  
David T. Sandwell ◽  
Gérald Dibarboure ◽  
Walter H. F. Smith ◽  
...  
Keyword(s):  
High Resolution ◽  
Gravity Field ◽  
Orbital Plane ◽  
Sea Surface ◽  
Gravity Models ◽  
Life Phase ◽  
Mean Sea Surface ◽  
Successful Launch ◽  
Gravity Recovery ◽  
First Time

The resolutions of current global altimetric gravity models and mean sea surface models are around 12 km wavelength resolving 6 km features, and for many years it has been difficult to improve the resolution further in a systematic way. For both Jason 1 and 2, a Geodetic Mission (GM) has been carried out as a part of the Extension-of-Life phase. The GM for Jason-1 lasted 406 days. The GM for Jason-2 was planned to provide ground-tracks with a systematic spacing of 4 km after 2 years and potentially 2 km after 4 years. Unfortunately, the satellite ceased operation in October 2019 after 2 years of Geodetic Mission but still provided a fantastic dataset for high resolution gravity recovery. We highlight the improvement to the gravity field which has been derived from the 2 years GM. When an Extension-of-Life phase is conducted, the satellite instruments will be old. Particularly Jason-2 suffered from several safe-holds and instrument outages during the GM. This leads to systematic gaps in the data-coverage and degrades the quality of the derived gravity field. For the first time, the Jason-2 GM was “rewound” to mitigate the effect of the outages, and we evaluate the effect of “mission rewind” on gravity. With the recent successful launch of Sentinel-6 Michael Freilich (S6-MF, formerly Jason CS), we investigate the possibility creating an altimetric dataset with 2 km track spacing as this would lead to fundamental increase in the spatial resolution of global altimetric gravity fields. We investigate the effect of bisecting the ground-tracks of existing GM to create a mesh with twice the resolution rather than starting all over with a new GM. The idea explores the unique opportunity to inject Jason-3 GM into the same orbital plane as used for Jason-2 GM but bisecting the existing Jason-2 tracks. This way, the already 2-years Jason-2 GM could be used to create a 2 km grid after only 2 years of Jason-3 GM, rather than starting all over with a new GM for Jason-3.

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