scholarly journals On the resolutions of ocean altimetry maps

2019 ◽  
Author(s):  
Maxime Ballarotta ◽  
Clément Ubelmann ◽  
Marie-Isabelle Pujol ◽  
Guillaume Taburet ◽  
Florent Fournier ◽  
...  
Keyword(s):  
Sea Level ◽  
Spatial Resolution ◽  
Tide Gauge ◽  
Optimal Interpolation ◽  
Climate Forecasting ◽  
Ocean Altimetry ◽  
The Mean ◽  
Marine Environment Monitoring ◽  
Monitoring Service ◽  
Along Track

Abstract. The DUACS system produces sea level global and regional maps that serve oceanographic applications, climate forecasting centers, geophysics and biology communities. These maps are constructed from optimal interpolation of altimeter observations and are provided on a global 1/4° × 1/4° (longitude × latitude) and daily grid resolution framework (1/8° × 1/8° longitude × latitude grid for the regional products) through the Copernicus Marine Environment Monitoring Service (CMEMS). Yet, the dynamical content of these maps is not ensured to have a full 1/4° spatial and 1-day resolution, due to the filtering properties of the optimal interpolation. In the present study, we estimate the effective spatial and temporal resolutions of the newly reprocessed delayed-time DUACS maps (aka, DUACS-DT2018). Our approach is based on the spectral coherence between maps and independent datasets (along-track and tide gauge observations), which represents the correlation between two sea level signals as a function of wavelength. We found that the spatial resolution of the DUACS-DT2018 global maps based on sampling by three altimeters simultaneously ranges from ~ 100 km-wavelength at high latitude to ~ 800 km-wavelength in the Equatorial band and the mean temporal resolution is ~ 28 days period. The mean effective spatial resolution at mid-latitude is estimated to ~ 200 km. The mean effective spatial resolution is ~ 120 km for the regional Mediterranean Sea product and ~ 140 km for the regional Black Sea product. An inter-comparison with former DUACS reprocessing systems (aka, DUACS-DT2010 and DUACS-DT2014) highlights the progress of the system over the past 8 years, in particular a gain of resolution in highly turbulent regions. The same diagnostic applied to maps constructed with two altimeters and maps with three altimeters confirms a modest increase of resolving capabilities and accuracies in the DUACS maps with the number of missions.

scholarly journals On the resolutions of ocean altimetry maps

Ocean Science ◽  
2019 ◽  
Vol 15 (4) ◽  
pp. 1091-1109 ◽  
Author(s):  
Maxime Ballarotta ◽  
Clément Ubelmann ◽  
Marie-Isabelle Pujol ◽  
Guillaume Taburet ◽  
Florent Fournier ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Interpolation Method ◽  
Tide Gauge ◽  
Optimal Interpolation ◽  
Signal Ratio ◽  
Spectral Content ◽  
Climate Forecasting ◽  
Ocean Altimetry ◽  
The Mean ◽  
Marine Environment Monitoring

Abstract. The Data Unification and Altimeter Combination System (DUACS) produces sea level global and regional maps that serve oceanographic applications, climate forecasting centers, and geophysics and biology communities. These maps are generated using an optimal interpolation method applied to altimeter observations. They are provided on a global 1∕4∘ × 1∕4∘ (longitude × latitude) and daily grid resolution framework (1∕8∘ × 1∕8∘ longitude × latitude grid for the regional products) through the Copernicus Marine Environment Monitoring Service (CMEMS). Yet, the dynamical content of these maps does not have full 1∕4∘ spatial and 1 d temporal resolutions due to the filtering properties of the optimal interpolation. In the present study, we estimate the effective spatial and temporal resolutions of the newly reprocessed delayed-time DUACS maps (a.k.a. DUACS-DT2018). Our approach is based on the ratio between the spectral content of the mapping error and the spectral content of independent true signals (along-track and tide gauge observations), also known as the noise-to-signal ratio. We found that the spatial resolution of the DUACS-DT2018 global maps based on sampling by three altimeters simultaneously ranges from ∼100 km wavelength at high latitude to ∼800 km wavelength in the equatorial band and the mean temporal resolution is ∼34 d. The mean effective spatial resolution at midlatitude is estimated to be ∼200 km. The mean effective spatial resolution is ∼130 km for the regional Mediterranean Sea and for the regional Black Sea products. An intercomparison with previous DUACS reprocessing systems (a.k.a., DUACS-DT2010 and DUACS-DT2014) highlights the progress of the system over the past 8 years, in particular a gain of resolution in highly turbulent regions. The same diagnostic applied to maps constructed with two altimeters and maps with three altimeters confirms a modest increase in resolving capabilities and accuracies in the DUACS maps with the number of missions.

scholarly journals Dynamic Mapping of Along-Track Ocean Altimetry: Performance from Real Observations

2020 ◽  
Vol 37 (9) ◽  
pp. 1593-1601 ◽  
Author(s):  
Maxime Ballarotta ◽  
Clément Ubelmann ◽  
Marine Rogé ◽  
Florent Fournier ◽  
Yannice Faugère ◽  
...  
Keyword(s):  
Optimal Interpolation ◽  
Resolution Limit ◽  
Simulation Experiments ◽  
Qualitative And Quantitative ◽  
Dynamic Mapping ◽  
System Experiment ◽  
Ocean Altimetry ◽  
Marine Environment Monitoring ◽  
Monitoring Service ◽  
Along Track

AbstractThe dynamic optimal interpolation (DOI) method merges altimetric sea surface height (SSH) data into maps that are continuous in time and space. Unlike the traditional linear optimal interpolation (LOI) method, DOI has the advantage of considering a nonlinear temporal propagation of the SSH field. DOI has been successfully applied to along-track pseudo-observations in observing system simulation experiments (OSSEs), demonstrating a reduction in interpolation error in highly turbulent regions compared to LOI mapping. In the present study, we further extend the validation of the DOI method by an observing system experiment (OSE). We applied and validated the DOI approach with real nadir-altimetric observations in four regional configurations. Overall, the qualitative and quantitative assessments of these realistic SSH maps confirm the higher level of performance of the DOI approach in turbulent regions. It is more of a challenge to outperform the conventional LOI mapping in coastal and low-energy regions. Validations against LOI maps distributed by the Copernicus Marine Environment Monitoring Service indicate a 10%–15% increase in average performance and an improved resolution limit toward shorter wavelengths. The DOI method also shows improved mesoscale mapping of intense jets and fronts and reveals new eddies with smoother trajectories.

scholarly journals DUACS DT2018: 25 years of reprocessed sea level altimetry products

Ocean Science ◽  
2019 ◽  
Vol 15 (5) ◽  
pp. 1207-1224 ◽  
Author(s):  
Guillaume Taburet ◽  
Antonio Sanchez-Roman ◽  
Maxime Ballarotta ◽  
Marie-Isabelle Pujol ◽  
Jean-François Legeais ◽  
...  
Keyword(s):  
Sea Level ◽  
Coastal Areas ◽  
Optimal Interpolation ◽  
Altimeter Data ◽  
Dynamic Topography ◽  
Combination System ◽  
Map Generation ◽  
Marine Environment Monitoring ◽  
Monitoring Service ◽  
Along Track

Abstract. For more than 20 years, the multi-satellite Data Unification and Altimeter Combination System (DUACS) has been providing near-real-time (NRT) and delayed-time (DT) altimetry products. DUACS datasets range from along-track measurements to multi-mission sea level anomaly (SLA) and absolute dynamic topography (ADT) maps. The DUACS DT2018 ensemble of products is the most recent and major release. For this, 25 years of altimeter data have been reprocessed and are available through the Copernicus Marine Environment Monitoring Service (CMEMS) and the Copernicus Climate Change Service (C3S). Several changes were implemented in DT2018 processing in order to improve the product quality. New altimetry standards and geophysical corrections were used, data selection was refined and optimal interpolation (OI) parameters were reviewed for global and regional map generation. This paper describes the extensive assessment of DT2018 reprocessing. The error budget associated with DT2018 products at global and regional scales was defined and improvements on the previous version were quantified (DT2014; Pujol et al., 2016). DT2018 mesoscale errors were estimated using independent and in situ measurements. They have been reduced by nearly 3 % to 4 % for global and regional products compared to DT2014. This reduction is even greater in coastal areas (up to 10 %) where it is directly linked to the geophysical corrections applied to DT2018 processing. The conclusions are very similar concerning geostrophic currents, for which error was globally reduced by around 5 % and as much as 10 % in coastal areas.

scholarly journals DUACS DT-2018: 25 years of reprocessed sea level altimeter products

2019 ◽  
Author(s):  
Guillaume Taburet ◽  
Antonio Sanchez-Roman ◽  
Maxime Ballarotta ◽  
Marie-Isabelle Pujol ◽  
Jean-François Legeais ◽  
...  
Keyword(s):  
Sea Level ◽  
Coastal Areas ◽  
Optimal Interpolation ◽  
Dynamic Topography ◽  
Map Generation ◽  
Marine Environment Monitoring ◽  
Monitoring Service ◽  
Along Track ◽  
Delayed Time

Abstract. For more than twenty years, the multi-satellite DUACS system has been providing Near Real Time (NRT) and Delayed Time (DT) altimetric products. These data are ranging from along-track to multi-mission maps of Sea Level Anomaly (SLA) and Absolute Dynamic Topography (ADT). A reprocessing of 25 years of data, namely: DUACS DT2018, has been carried out and is available through the Copernicus Marine Environment Monitoring Service (CMEMS) and Copernicus Climate Change Service (C3S) since April 2018. Several changes have been implemented in the DT2018 processing in order to improve the quality of the products. New altimeter standards and geophysical corrections has been used, refined data selection has been implemented and Optimal Interpolation (OI) parameters have been reviewed for global and regional map generation. Through this paper, an extensive assessment has been carried out. The error budget associated to the DT2018 products at global and regional scales has been refined and the improvements compared with the previous version quantified (DT2014; Pujol et al., 2016). The DT2018 errors at mesoscales are reduced by nearly 3 to 4 % for global and regional products compared to the DT2014. This reduction is much more important in coastal areas (reduction is up to 10 %) where it is directly linked to the altimeter geophysical corrections used in the DT2018 processing. Conclusions are very similar concerning geostrophic currents, where error is reduced by 5 % and up to 10 % in coastal areas.

scholarly journals A comparison of methods to estimate vertical land motion trends from GNSS and altimetry at tide gauge stations

Ocean Science ◽  
2018 ◽  
Vol 14 (2) ◽  
pp. 187-204 ◽  
Author(s):  
Marcel Kleinherenbrink ◽  
Riccardo Riva ◽  
Thomas Frederikse
Keyword(s):  
Time Series ◽  
Sea Level ◽  
Tide Gauge ◽  
Satellite System ◽  
Vertical Land Motion ◽  
Correlation Threshold ◽  
The Mean ◽  
Highly Correlated ◽  
Global Navigation Satellite ◽  
Along Track

Abstract. Tide gauge (TG) records are affected by vertical land motion (VLM), causing them to observe relative instead of geocentric sea level. VLM can be estimated from global navigation satellite system (GNSS) time series, but only a few TGs are equipped with a GNSS receiver. Hence, (multiple) neighboring GNSS stations can be used to estimate VLM at the TG. This study compares eight approaches to estimate VLM trends at 570 TG stations using GNSS by taking into account all GNSS trends with an uncertainty smaller than 1 mm yr−1 within 50 km. The range between the methods is comparable with the formal uncertainties of the GNSS trends. Taking the median of the surrounding GNSS trends shows the best agreement with differenced altimetry–tide gauge (ALT–TG) trends. An attempt is also made to improve VLM trends from ALT–TG time series. Only using highly correlated along-track altimetry and TG time series reduces the SD of ALT–TG time series by up to 10 %. As a result, there are spatially coherent changes in the trends, but the reduction in the root mean square (RMS) of differences between ALT–TG and GNSS trends is insignificant. However, setting correlation thresholds also acts like a filter to remove problematic TG time series. This results in sets of ALT–TG VLM trends at 344–663 TG locations, depending on the correlation threshold. Compared to other studies, we decrease the RMS of differences between GNSS and ALT–TG trends (from 1.47 to 1.22 mm yr−1), while we increase the number of locations (from 109 to 155), Depending on the methods the mean of differences between ALT–TG and GNSS trends vary between 0.1 and 0.2 mm yr−1. We reduce the mean of the differences by taking into account the effect of elastic deformation due to present-day mass redistribution. At varying ALT–TG correlation thresholds, we provide new sets of trends for 759 to 939 different TG stations. If both GNSS and ALT–TG trend estimates are available, we recommend using the GNSS trend estimates because residual ocean signals might correlate over long distances. However, if large discrepancies ( > 3 mm yr−1) between the two methods are present, local VLM differences between the TG and the GNSS station are likely the culprit and therefore it is better to take the ALT–TG trend estimate. GNSS estimates for which only a single GNSS station and no ALT–TG estimate are available might still require some inspection before they are used in sea level studies.

scholarly journals A newly reconciled data set for identifying sea level rise and variability in Dublin Bay

2021 ◽  
Author(s):  
Amin Shoari Nejad ◽  
Andrew C. Parnell ◽  
Alice Greene ◽  
Peter Thorne ◽  
Brian P. Kelleher ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Tide Gauge ◽  
High Water ◽  
Data Set ◽  
Quality Checks ◽  
Bayesian Linear Regression ◽  
The Mean ◽  
Water Values ◽  
Water Level Measurements

Abstract. We provide an updated sea level dataset for Dublin for the period 1938 to 2016 at yearly resolution. Using a newly collated sea level record for Dublin Port, as well as two nearby tide gauges at Arklow and Howth Harbour, we perform data quality checks and calibration of the Dublin Port record by adjusting the biased high water level measurements that affect the overall calculation of mean sea level (MSL). To correct these MSL values, we use a novel Bayesian linear regression that includes the Mean Low Water values as a predictor in the model. We validate the re-created MSL dataset and show its consistency with other nearby tide gauge datasets. Using our new corrected dataset, we estimate a rate of 1.08 mm/yr sea level rise at Dublin Port between 1953–2016 (95 % CI from 0.62 to 1.55 mm/yr), and a rate of 6.48 mm/yr between 1997–2016 (95 % CI 4.22 to 8.80 mm/yr). Overall sea level rise is in line with expected trends but large multidecadal varaibility has led to higher rates of rise in recent years.

Sea level variations in the coastal region from altimetry – Using optimal interpolation in the Baltic Sea for 3-day mean sea level from altimetry, tide gauge and model data

2021 ◽  
Author(s):  
Ida Margrethe Ringgaard ◽  
Jacob L. Høyer ◽  
Kristine S. Madsen ◽  
Adili Abulaitijiang ◽  
Ole B. Andersen
Keyword(s):  
Baltic Sea ◽  
Sea Level ◽  
Temporal Resolution ◽  
Satellite Altimetry ◽  
Tide Gauge ◽  
Coastal Region ◽  
Optimal Interpolation ◽  
The Baltic Sea ◽  
Spatial Coverage ◽  
The Baltic

<p>The rise and fall of the sea surface in the coastal region is observed closely by two different sources: tide gauges measure the relative sea level anomaly at the coast at high temporal resolution (minutes or hours) and satellite altimeters measure the absolute sea surface height of the open ocean along tracks multiple times a day. However, these daily tracks are scattered across the Baltic Sea with each track being repeated at a lower temporal resolution (days). Due to the inverse relationship between spatial and temporal coverage of the satellite altimetry data, gridded satellite altimetry products often prioritize spatial coverage over temporal resolution, thus filtering out the high sea level variability. In other words, the satellite data, and especially averaged products, often miss the daily sea level variability, such as storm surges, which is most important for all societies in the coastal region. To compensate for the sparse spatial coverage from satellite altimetry, we here present an experimental product developed as part of the ESA project Baltic+SEAL:  on a 3-day scale, the DMI Optimal Interpolation (DMI-OI) method is combined with error statistics from a storm surge model as well as 3-day averages from both tide gauge observations and satellite altimetry tracks to generate a gridded sea level anomaly product for the Baltic Sea for year 2017. The product captures the overall temporal evolution of the sea level changes well for most areas with an average RMSE wrt. tide gauge observations of 17.2 cm and a maximum of 34.2 cm. Thus, the 3-day mean gridded product shows potential as an alternative to monthly altimetry products, although further work is needed.</p>

scholarly journals Recent Sea Level Change in the Black Sea from Satellite Altimetry and Tide Gauge Observations

2020 ◽  
Vol 9 (3) ◽  
pp. 185 ◽  
Author(s):  
Nevin Avşar ◽  
Şenol Kutoğlu
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Black Sea ◽  
Satellite Altimetry ◽  
Tide Gauge ◽  
The Black Sea ◽  
Sea Level Changes ◽  
Early 19Th Century ◽  
Mean Sea Level ◽  
The Mean

Global mean sea level has been rising at an increasing rate, especially since the early 19th century in response to ocean thermal expansion and ice sheet melting. The possible consequences of sea level rise pose a significant threat to coastal cities, inhabitants, infrastructure, wetlands, ecosystems, and beaches. Sea level changes are not geographically uniform. This study focuses on present-day sea level changes in the Black Sea using satellite altimetry and tide gauge data. The multi-mission gridded satellite altimetry data from January 1993 to May 2017 indicated a mean rate of sea level rise of 2.5 ± 0.5 mm/year over the entire Black Sea. However, when considering the dominant cycles of the Black Sea level time series, an apparent (significant) variation was seen until 2014, and the rise in the mean sea level has been estimated at about 3.2 ± 0.6 mm/year. Coastal sea level, which was assessed using the available data from 12 tide gauge stations, has generally risen (except for the Bourgas Station). For instance, from the western coast to the southern coast of the Black Sea, in Constantza, Sevastopol, Tuapse, Batumi, Trabzon, Amasra, Sile, and Igneada, the relative rise was 3.02, 1.56, 2.92, 3.52, 2.33, 3.43, 5.03, and 6.94 mm/year, respectively, for varying periods over 1922–2014. The highest and lowest rises in the mean level of the Black Sea were in Poti (7.01 mm/year) and in Varna (1.53 mm/year), respectively. Measurements from six Global Navigation Satellite System (GNSS) stations, which are very close to the tide gauges, also suggest that there were significant vertical land movements at some tide gauge locations. This study confirmed that according to the obtained average annual phase value of sea level observations, seasonal sea level variations in the Black Sea reach their maximum annual amplitude in May–June.

scholarly journals Celebrating 80 years of the Permanent Service for Mean Sea Level (PSMSL)

2015 ◽  
Vol 365 ◽  
pp. 1-5
Author(s):  
L. Rickards ◽  
A. Matthwes ◽  
K. Gordon ◽  
M. Tamisea ◽  
S. Jevrejeva ◽  
...  
Keyword(s):  
Sea Level ◽  
Tide Gauge ◽  
Tide Gauge Records ◽  
International Union ◽  
Mean Sea Level ◽  
Level Change ◽  
The Mean ◽  
Set Up ◽  
The 19Th Century

Abstract. The PSMSL was established as a “Permanent Service” of the International Council for Science in 1958, but in practice was a continuation of the Mean Sea Level Committee which had been set up at the Lisbon International Union of Geodesy and Geophysics (IUGG) conference in 1933. Now in its 80th year, the PSMSL continues to be the internationally recognised databank for long-term sea level change information from tide gauge records. The PSMSL dataset consists of over 2100 mean sea level records from across the globe, the longest of which date back to the start of the 19th century. Where possible, all data in a series are provided to a common benchmark-controlled datum, thus providing a record suitable for use in time series analysis. The PSMSL dataset is freely available for all to use, and is accessible through the PSMSL website (www.psmsl.org).

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