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tidal misfits in the northwestern Mediterranean Sea for M2 constituent: background chart represents the tidal amplitude in cm from FES 2004 model. The size of the red circles is proportional to the modulus of the complex difference between model and observation.
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Oceanographic applications using satellite altimeter data become very challenging when leaving the deep ocean for the coastal regions. Close to the coast, altimeter observations are often of lower quality for a number of reasons, including land contamination of the satellite footprints or inaccurate resolution of the corrections of the high frequen...
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... the Kerguelen Archipelago, X-TRACK altimeter products are de- aliased with global corrections FES2004 and Mog2D-G. In Figure 2 and Figure 3, altimeter-derived tidal constants are compared to the reference global tidal model FES2004. The overall root-mean-square (rms) error is 0.7cm on both M2 and K1 tidal constituents. ...
Citations
... The along-track SSH data have a spatial resolution of approximately 6-7 km, with the satellite ground track repeating every 10 days. [22], through the use of BRAT software [23] The 36 J-2 data in 2019 were processed. Also, the SSH for a region near Hawaiian island was extracted & and showed a trend of rising. ...
Over the past few years, the effects of global warming have become more pronounced, particularly with the melting of the polar ice caps. This has led to an increase in sea levels, which poses a threat of flooding to coastal cities and islands. Furthermore, monitoring and analyzing changes in water levels has proven effective in predicting natural disasters caused by rising sea levels. One vital factor in understanding the impact of global warming is sea surface height (SSH). Measuring SSH can provide valuable information about changes in ocean levels. This study used data from the Jason 2 altimetry radar satellite, which provided 36 cycle periods per year, to investigate water heights around the Hawaiian Islands in 2019. To accurately evaluate water height variations , a specific area near the Pacific Ocean close to the Hawaiian Islands was selected. By analyzing the collected satellite data, a chart of water heights was generated, which showed an overall increase in height over one year. This analysis provided evidence of changing ocean levels in the region, highlighting the urgency of addressing potential threats faced by coastal communities. The study also explored several factors that contribute to water height variations, such as sea surface temperature , precipitation, and sea surface pressure in the Google Earth engine cloud-based platform. Algorithms , including MLP and XGBOOST, were used to model water height within the specified range. The results showed that the XGBOOST algorithm was superior in accurately predicting water height, with an impressive R-squared value of 0.95. In comparison, the MLP algorithm achieved an R-squared value of 0.92. This study shows that advanced machine learning techniques are effective in understanding and modeling the complex changes in water height due to climate change. This information can help policymakers and local authorities make informed decisions and create strategies to protect coastal cities and islands from the growing threats of rising sea levels. Taking pro-active measures is crucial in reducing the risks posed by more frequent and severe natural disasters caused by global warming.
... Problems related to data processing procedures are explained in detail in Ref. [2]. Today, the most used data processing algorithms in the coastal area are ALES (Adaptive Leading Edge Subwaveform) and X-TRACK [24,25]. Altimetry retrackers compare the wave strength of return signals most often with previously known wave models, and in this way, reconstruct measurements of water surfaces [24]). ...
Radar satellite altimetry is one of the basic satellite measurement techniques intended primarily for solving global geodetic tasks by means of radar measurements from satellites toward the Earth. Satellite altimetry ensures the collection of high precision global data of uniform accuracy on sea level, which enables monitoring of the geophysical characteristics of the sea and larger water surfaces, that is, marine topography and circulation within liquid water bodies. During the last four decades, satellite altimetry has revolutionized geosciences, especially oceanography, geophysics,
and geodesy. This measurement method found its application in modeling the shape of the Earth and the Earth’s field of acceleration of gravity, modeling the relief of the seabed and vertical displacements of the Earth’s crust in coastal areas, and
monitoring climate phenomena and long-term climate changes. Satellite altimetry data is distributed in the form of original measurements and products ready for use in geosciences, most often calculated models, or calculation services. This chapter presents the fundamental principles of the radar altimetric measurement method, its historical development, achievements, and expected improvements in technology soon, as well as the scientific and professional results achieved so far in the development and application of technology.
... The along-track SSHA data have a spatial resolution of 6∼7 km, and the satellite ground track was repeated every 10 days. The CTOH provides access to its frequently updated altimetric databases, including TOPEX/Poseidon, Jason-1, Jason-2, GFO, and Envisat data using X-TRACK software [41,42], which contains a relatively larger number of valid data points than those generated by the standard geophysical data record (GDR) [43]. The SSHA estimates are observed more than 10 km from the coastline in AVISO, while those derived from X-TRACK are closer to land, at around 5 km [43]. ...
Inthis study, remote sensing measurements were utilized to examine the characteristics of storm surges and sea surface cooling in Chinese coastal waters caused by typhoons. Altimetric data from satellite altimeters were used to determine the magnitude, cross-shelf decaying scale, and propagating speed of storm surges from typhoons. The results were in agreement with estimates obtained from a theoretical model and tide gauge data, showing that the two storm surges propagated as continental shelf waves along the southeastern coast of China. The sea surface cooling, driven by Typhoons 1319Usagi and 1323Fitow, was analyzed using the remote sensing sea surface temperature product, named the global 1 km sea surface temperature (G1SST) dataset, revealing a considerable decrease in the temperature, with the largest decrease reaching 4.5 °C after the passage of 1319Usagi, in line with buoy estimates of 4.6 °C. It was found that 1323Fitow and 1324Danas jointly impacted the southeastern coast of China, resulting in a significant temperature drop of 4.0 °C. Our study shows that incorporating remotely sensed measurements into the study of oceanic responses to typhoons has significant benefits and complements the traditional tide gauge network and buoy data.
... There are eight (8) sites with collocated GNSS receivers, and these are: Cagayan de Oro, Cebu, Davao, El Nido, Guian, Manila, Legaspi, and San Fernando (highlighted with red triangles) in Figure 1. The 25 sites were decided based on agreement Among these TGs, six (6) of these have long term observations of 19 years and more. These are Cebu, Davao, Manila, Legaspi, Puerto Princesa and San Fernando. ...
... Referring all sea level to one datum facilitates the comparison of sea surface height (SSH) with TGSL. The SSH computed from altimeter data were given in 1 Hz and 20 Hz and retracked using ALES [3], MLE4 [4], [5], and X-TRACK [6]. [7] then convergences through the Nelder-Mead nonlinear optimization technique using least-square estimation [3]. ...
... The X-TRACK data processor [6] was developed to improve both the quantity and quality of altimeter data redefining the data editing strategy to minimize the loss of data during the correction phase and by using improved local modelling of tidal and short-period atmospheric forcing. The processor adopts therefore, new data screening strategy and filtering techniques allowing to recover data that would otherwise be flagged as bad [8]. ...
The Philippines being an archipelagic country has the fifth longest coastline in the world. Its shores are defined by varying geologic form and composition that defines how sea water could impact its configuration. Being in a tectonically active setting, the country is also affected by ground motion. Specifically, the vertical land motion (VLM) has a significant effect on the observed sea level along the coast. As it is surrounded by large bodies of water, ocean dynamics and climate pattern have also contributed to the variations of sea level. The changing climate altered the global atmospheric pattern that results in varying regional/local effects on the coastal sea level. These local factors are the reasons why sea level varies differently in different places with the global mean sea level (GMSL). This study investigated the coastal sea level trend in 25 out of 50 tide gauge (TG) sites. The observed TG sea level (TGSL) were computed and analyzed for trends. Similarly, sea level trends were also determined from retracked satellite altimeter (SA) products from different satellite missions. The influence of VLM, a non-climatic factor, on the sites were determined using Permanent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) and validated using data from GNSS (Global Navigation Satellite System) receivers collocated with the TG. The investigation of the occurrence of El Niño was undertaken to explain the computed sea level trend. Results showed that areas with long period of observations (19 years or more) exhibit an increasing sea level that varies from 1.38 to 13.13 mm/year. However, majority of the TGs that were installed in 2007 and 2008 recorded only 13 and 12 years of observation, respectively. A decreasing sea level trend were observed on said TGs except for those located in Palawan. Similar trends were also observed from sea surface height (SSH) from satellite altimeter. A 0.96 correlation was computed between TGSL and 20 Hz SSH. Investigation showed the strong influence of El Niño during this short period of observation that caused the sea level to fall. The effect of Pacific Decadal Oscillation (PDO) was not analyzed due to limited period of recorded data. The VLM contribution to the observed sea level was determined for 9 sites with collocated GNSS receivers. Most of these sites experienced land subsidence of around-3 to-7 mm/year. The PSInSAR and GNSS VLM rates have a correlation of 0.89. In Manila Bay where sea level rise is accelerating at 13.13 mm/year, one of the contributors is increasing river water loading. However, north of Manila, land subsidence showed 8-12 mm/year rate based on PSInSAR.
... Instead, coastal waveforms have been developed based on di erent methods (e.g., waveform shape, multiple waveforms to detect brightest target prior to retracking, retracking of sub-waveform etc.). These advanced coastal retrackers are expected to provide better and more accurate near-coast SSH (Passaro et al., 2014;Dinardo et al., 2014;Roblou et al., 2007). ...
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.
... The spatial and temporal sampling of satellite al-timetry is in general appropriate for measuring sea level variations over the open ocean, where the signals and corrections to be applied are well understood [2]. The usual validity checks for altimeter data editing have been designed for deep ocean regions [3]. ...
Satellite altimetry provides an important measurement source for coastal studies. The main aim of this study was to make an
effort to check the availability of valid altimeter data and to compare and validate altimeter data in the coastal region of India. The
study shows that by adopting specific coastal processing, it is possible to retrieve valid altimeter measurements in the coastal regions.
The combined use of improved coastal multi-altimeter data would allow us to efficiently observe the temporal and spatial
scales of coastal dynamics [16]. Thus, in the present study, two different altimetry missions were considered. The coastal sea-level
data was computed from two different altimeter missions the Jason-2 PISTACH coastal data and SARAL Altika data separately and for
sea level validation only the RED3 re-tracker and for SARAL 40 Hz high-frequency data was analysed and validated with In-situ tide
gauge and PSMSL data. The RED3 re-tracker from Jason-2 PISTACH coastal product with In-situ measurements show that the valid
altimeter data can be retrieved around 10 km close to the coast also. Also, the 41 point filtered data was able to reduce the noise in
the data set and be able to capture all the oceanographic signals in the raw RED3 re-tracker. The comparison of RED3 re-tracker and
filtered data show good matching with the In-situ data. This data helps us to obtain valid altimetry measurements more close to the
coast. Similarly, for the SARAL Altika, SSHA measurements show very promising results in the coastal regions of India. This SARAL
also enables us to reach as close as 3 km close to the coast because it is the first of its kind to provide sea level measurements in the
proximity of the coastal regions due to its narrow footprint size. The validation of altimeter data from multiple missions with tide
gauge data shows encouraging results. Along-track comparison shows that valid altimeter measurements were available close to the
coast. Improvement of both qualitative and quantitative measurements in the coastal zone was observed from the coastal altimetry
... The importance of coastal altimetry has been indeed recognized by the major space and other funding agencies, which have been supporting research and development (R&D) in the field. Thanks to this effort, progress has been achieved in the last years in the frame of projects such as ALTICORE (Lebedev et al., 2008), COASTALT (Cipollini et al., 2009), X-TRACK (Roblou et al., 2007), PISTACH (CLS Report, 2015), eSurge (Cipollini et al., 2012) and CryoSat+ for Ocean (CP4O, Cotton, 2015). These projects have aimed at improving range and geophysical corrections (the wet tropospheric path delay and ocean tide in particular) in the coastal zone for both conventional and SAR altimetry. ...
... The importance of coastal altimetry has been indeed recognized by the major space and other funding agencies, which have been supporting research and development (R&D) in the field. Thanks to this effort, progress has been achieved in the last years in the frame of projects such as ALTICORE (Lebedev et al., 2008), COASTALT (Cipollini et al., 2009), X-TRACK (Roblou et al., 2007), PISTACH (CLS Report, 2015), eSurge (Cipollini et al., 2012) and CryoSat+ for Ocean (CP4O, Cotton, 2015). These projects have aimed at improving range and geophysical corrections (the wet tropospheric path delay and ocean tide in particular) in the coastal zone for both conventional and SAR altimetry. ...
Just as CryoSat-2, Sentinel-3 embarks on board a radar altimeter (SRAL) with the novel Synthetic Aperture Radar (SAR) mode that enables higher resolution and more accurate altimeter-derived parameters in the coastal zone, thanks to the reduced along-track footprint. Exploiting the SAR data in the recent years, many researchers have already proven that the performance of SAR altimetry with specific coastal retrackers is superior to collocated Pseudo-Low Resolution Mode (PLRM) coastal altimetry algorithms but they also pointed out that residual errors due to land contamination are still present in the very proximity of the land (0-3 km).
The objective of this work is to further improve these results by exploiting extra information provided by SAR altimeters, namely the so-called Range Integrated Power (RIP), the new waveform built by a simple integration of the Doppler beams in the range direction. The RIP characterizes the backscattering state of the ground cell, towards which all the Doppler beams have been steered. These developments lead to a new retracker, here coined SAMOSA++, in which the RIP, as computed from the L1B-S data, is converted into a surface backscattering profile and directly integrated in the SAMOSA retracker as part of the model formulation itself. In this way, the modified SAMOSA model is automatically and autonomously able to cope with the different return waveform shapes from different surface types: either diffusive or specular. The mean square slope computed from the RIP is also estimated, representing a new output of the retracker.
The performance of this new retracker is here cross-compared against its previous version, SAMOSA+, and against the standard Sentinel-3 marine PDGS (Payload Data Ground Segment) SAR retracker (SAMOSA2) in both coastal zone and open ocean in order to ensure a seamless transition between these zones.
The new retracker SAMOSA++ is validated in the North East Atlantic region, where appropriate in situ validation data are available. The retrievals from the new retracker are cross-compared against the network of tide gauges and buoys in the German Bight and versus the output of the GCOAST Helmholtz-Zentrum Geesthacht (HZG) regional circulation and wave model. In addition, sea level estimates derived with different ocean tide and wet path delay geophysical correction models are compared. Results indicate that in this region the best geophysical correction models are the FES2014b tide model and the GPD+ wet tropospheric correction that incorporates data from the Sentinel-3 on-board radiometer.
Analyses show that both SAMOSA+ and SAMOSA++ ensure the continuity of the PDGS SAR Marine retracker in the open ocean, leading to clear improvements in the coastal zone, larger for SAMOSA++ than for SAMOSA+. In summary, the new SAMOSA++ retracker retrieves more accurate altimetric parameters in the coastal zone, with a better consistency with respect to regional ocean models and in situ data.
... Further, the tidal harmonic constants provided by the CTOH (Roblou et al., 2007(Roblou et al., , 2011 which derived from the TOPEX/Poseidon and Jason-1 sea surface height data are also used to check the model tidal performance in the open seas. Jason-1 is the successor of TOPEX/Poseidon and they shared the same orbit, and their ground paths (initial orbit) passing the model domain as well as the simulating errors are shown in Fig. 3. Figure 3 also reveals reasonable model performance, the MAE for the M 2 , S 2 , K 1 and O 1 tidal constituents are 2.1, 2.1, 2.1 and 5.8 cm in amplitudes and 6.6º, 20.6º, 6.1º and 6.1º in phases at 344 measured points, respectively. ...
Wave-current interaction and its effects on the hydrodynamic environment in the Beibu Gulf (BG) have been investigated via employing the Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) modeling system. The model could simulate reasonable hydrodynamics in the BG when validated by various observations. Vigorous tidal currents refract the waves efficiently and make the seas off the west coast of Hainan Island be the hot spot where currents modulate the significant wave height dramatically. During summer, wave-enhanced bottom stress could weaken the near-shore component of the gulf-scale cyclonic-circulation in the BG remarkably, inducing two major corresponding adjustments: Model results reveal that the deep-layer cold water from the southern BG makes critical contribution to maintaining the cold-water mass in the northern BG Basin. However, the weakened background circulation leads to less cold water transported from the southern gulf to the northern gulf, which finally triggers a 0.2°C warming in the cold-water mass area; In the top areas of the BG, the suppressed background circulation reduces the transport of the diluted water to the central gulf. Therefore, more freshwater could be trapped locally, which then triggers lower sea surface salinity (SSS) in the near-field and higher SSS in the far-field.
... This product is a combination of geophysical data record (GDR), corrections from CTOH database and 1Hz SLA with a spatial interval of about 6-7 km. Roblou, et al. (2007) produced a centimeter error level using the X-TRACK processor on both Mediterranean Sea and Karguelen Archipelago. Birol, et al. (2017) present the improvements of the 2016 X-TRACK relative to in-situ TG measurements in the Bay of Biscal in Western Africa. ...
Coupled with the occurrence of regional/local sea level rise on urbanized coastal cities is the possibility of land subsidence that contaminates the measurement by the tide gauge (TG) sensors. Another technology that could possibly check the in-situ data from tide gauge is satellite altimetry. The sea surface height (SSH) measured from satellite altimeter is compared with the observed tide gauge sea level (TGSL) to detect vertical land motion (VLM). This study used satellite altimeter retracked products near the TG Stations in Tagbilaran, Bohol; Dumaguete, Negros Oriental; and Mambajao, Camiguin located in the vicinity of the South East Bohol Trench and Fault (SEBTF).Based on the results, the TG site in Tagbilaran is undergoing land subsidence. The rate of VLM is around 5 mm/year from 2009 to 2017. The same trend was manifested in the GNSS observed data in the PHIVOLCS monitoring station in Tagbilaran and the geodetic levelling done in the area. After the October 15, 2013 earthquake in Bohol, downward trends of around 27 mm/year and 17 mm/year were observed from GNSS measurements and SSH-TGSL difference respectively. These different rates may be due to the distance between the two sensors. The comparison between SSH and TGSL in Dumaguete showed small difference with a VLM rate of 1.8 mm/year. The difference in SSH-TGSL in Mambajao is quite large with a downward rate of 9.4 mm/year. This result needs to be further investigated for TG or TGBM instability or monitored for a possibility of land uplift.
