Evaluation of Sentinel-3A SAR Altimetry Observations over the Taiwan coastal region

Pulse-limited radar altimeters have been proven to be an excellent data source in oceanography for monitoring sea surface heights and inland water surface elevations since the 1990s. However, the measurements of conventional altimetry missions in coastal areas present the principal problems related to the inherent limitations of this technique such as wider footprint resulting in contaminated waveforms and relatively unreliable media and geophysical corrections. The European Space Agency (ESA) and the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) joint mission Sentinel-3A, launched in February 2016, is the first altimetry mission to provide 100% global coverage of ocean observations in Synthetic Aperture Radar (SAR) mode. The Sentinel-3A carries a dual-frequency (Ku- and C-band) Synthetic Aperture Radar Altimeter (SRAL) with a new on-board tracking system (open-loop tracking mode) to employ SAR altimetry technologies providing finer along-track spatial resolution up to ~300 m. Compared with the similar mission Cryosat-2, Sentinel-3A has a better ability to observe the global monitoring of ocean dynamics with a shorter repeat cycle of 27 days and less affected by topography in contaminated waveforms from coastal regions due to open-loop tracking mode with a good prior surface elevation estimate on-board. In this study, the SAR altimetry observations of Sentinel-3A over the Taiwan coastal region were reprocessed by a proposed retracking strategy to obtain more accurately retrieved sea level observations. The main objective of this study is to evaluate the performance of Sentinel-3A in coastal observation by using a near-by tide gauge measurements or other altimetry mission like SARAL/Altika and Jason-3.

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Sentinel-3 radar altimetry for river monitoring – a catchment-scale evaluation of satellite water surface elevation from Sentinel-3A and Sentinel-3B

10.5194/hess-2020-165 ◽

2020 ◽

Cited By ~ 2

Author(s):

Cecile M. M. Kittel ◽

Liguang Jiang ◽

Christian Tøttrup ◽

Peter Bauer-Gottwein

Keyword(s):

Synthetic Aperture Radar ◽

Water Surface ◽

Open Loop ◽

Surface Elevation ◽

Synthetic Aperture ◽

Catchment Scale ◽

Radar Altimetry ◽

Water Surface Elevation ◽

Tracking Mode ◽

Aperture Radar

Abstract. Sentinel-3 is the first satellite altimeter to operate in Synthetic Aperture Radar (SAR) mode and in open-loop tracking mode nearly globally. Both features are expected to improve the ability of the altimeters to observe inland water bodies. In this study we evaluate the possibility to extract river water surface elevation (WSE) at catchment level from Sentinel-3A and Sentinel-3B radar altimetry, using Level-1b and Level-2 data from two public platforms. The objectives of the study are to evaluate the density of valuable observations and establish a WSE monitoring network. Additionally, we demonstrate the potential application of Sentinel-3 for monitoring river interactions with wetlands and floodplains. In the Zambezi basin, 175 virtual stations (VS) contain useful WSE information in both datasets, far exceeding the number of VS available in standard databases. The RMSD is between 2.7 cm and 31.2 cm at six in-situ stations and the VS reflect the observed WSE climatology throughout the basin. Additional VS are available in both the Copernicus Open Access Hub and GPOD (Grid Processing on Demand), highlighting the value of considering multiple processing options. In particular, we show that the processing options available on GPOD strongly affect the number of useful VS; in particular, extending the size of the receiving window, considerably improved data at 13 Sentinel-3 VS. The number of VS delivering usable data increased after the Open-Loop Tracking Command (OLTC) on-board Sentinel-3A was updated. However, the open-loop tracking mode poses two new challenges: correct on-board elevation information is crucial, and steep changes in the receiving window position can have detrimental effects on the WSE observations. Finally, we extract Sentinel-3 observations over key wetlands in the Zambezi basin. We show that clear seasonal patterns are captured in the Sentinel-3 WSE, reflecting flooding events in the floodplains. These results highlight the potential of using Sentinel-3 as a SWOT (Surface Water and Ocean Topography) surrogate while awaiting the mission launch. The results show the benefit of the high-resolution Synthetic Aperture Radar (SAR) altimeter, as well as the benefits and disadvantages of the open-loop tracking mode.

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Assessment of DUACS Sentinel-3A Altimetry Data in the Coastal Band of the European Seas: Comparison with Tide Gauge Measurements

Remote Sensing ◽

10.3390/rs12233970 ◽

2020 ◽

Vol 12 (23) ◽

pp. 3970

Author(s):

Antonio Sánchez-Román ◽

Ananda Pascual ◽

Marie-Isabelle Pujol ◽

Guillaume Taburet ◽

Marta Marcos ◽

...

Keyword(s):

Synthetic Aperture Radar ◽

Tide Gauge ◽

Synthetic Aperture ◽

Altimetry Data ◽

Radar Altimeter ◽

Long Wave ◽

Tide Gauge Measurements ◽

European Seas ◽

Aperture Radar

The quality of the Data Unification and Altimeter Combination System (DUACS) Sentinel-3A altimeter data in the coastal area of the European seas is investigated through a comparison with in situ tide gauge measurements. The comparison was also conducted using altimetry data from Jason-3 for inter-comparison purposes. We found that Sentinel-3A improved the root mean square differences (RMSD) by 13% with respect to the Jason-3 mission. In addition, the variance in the differences between the two datasets was reduced by 25%. To explain the improved capture of Sea Level Anomaly by Sentinel-3A in the coastal band, the impact of the measurement noise on the synthetic aperture radar altimeter, the distance to the coast, and Long Wave Error correction applied on altimetry data were checked. The results confirmed that the synthetic aperture radar altimeter instrument onboard the Sentinel-3A mission better solves the signal in the coastal band. Moreover, the Long Wave Error processing contributes to reduce the errors in altimetry, enhancing the consistency between the altimeter and in situ datasets.

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The Use of Sentinel-1 Synthetic Aperture Radar (SAR) Images and Open-Source Software for Cultural Heritage: An Example from Paphos Area in Cyprus for Mapping Landscape Changes after a 5.6 Magnitude Earthquake

Remote Sensing ◽

10.3390/rs11151766 ◽

2019 ◽

Vol 11 (15) ◽

pp. 1766 ◽

Cited By ~ 8

Author(s):

Marios Tzouvaras ◽

Dimitris Kouhartsiouk ◽

Athos Agapiou ◽

Chris Danezis ◽

Diofantos G. Hadjimitsis

Keyword(s):

Cultural Heritage ◽

Synthetic Aperture Radar ◽

Open Source ◽

European Space Agency ◽

Synthetic Aperture ◽

Active Sensors ◽

Heritage Sites ◽

Space Agency ◽

World Heritage List ◽

Aperture Radar

Active satellite remote sensors have emerged in the last years in the field of archaeology, providing new tools for monitoring extensive cultural heritage landscapes and areas. These active sensors, namely synthetic aperture radar (SAR) satellites, provide systematic datasets for mapping land movements triggered from earthquakes, landslides, and so on. Copernicus, the European program for monitoring the environment, provides continuous radar datasets through the Sentinel-1 mission with an almost worldwide coverage. This paper aims to demonstrate how the use of open-access and freely distributed datasets such as those under the Copernicus umbrella, along with the exploitation of open-source radar processing software, namely the sentinel applications platform (SNAP) and SNAPHU tools, provided respectively by the European Space Agency (ESA) and the University of Stanford, can be used to extract an SAR interferogram in the wider area of Paphos, located in the western part of Cyprus. The city includes various heritage sites and monuments, some of them already included in the UNESCO World Heritage list. The interferogram was prepared to study the effects of an earthquake to the buildings and sites of the area. The earthquake of a 5.6 magnitude on the Richter scale was triggered on 15 April 2015 and was strongly felt throughout the whole island. The interferogram results were based on Differential Synthetic Aperture Radar Interferometry (D-InSAR) methodology, finding a maximum uplift of 74 mm and a maximum subsidence of 31 mm. The overall process and methodology are presented in this paper.

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Korteweg-deVriès limitations for the interpretation of SAR images in the Strait of Gibraltar: impact of different stratifications on ISW surface signature.

10.5194/egusphere-egu2020-21497 ◽

2020 ◽

Author(s):

Morgane Dessert ◽

Xavier Carton ◽

Jean-Marc Le Caillec ◽

Christophe Messager ◽

Lucie Bordois ◽

...

Keyword(s):

Synthetic Aperture Radar ◽

Internal Waves ◽

Solitary Waves ◽

Density Profile ◽

Ocean Dynamics ◽

Synthetic Aperture ◽

Internal Solitary Waves ◽

Sar Images ◽

Surface Signature ◽

Aperture Radar

Internal Solitary Waves (ISW) are particularly large amplitude internal waves which may propagate in the ocean over tens of kilometres while preserving their shape via a balance between non-linearity and non-hydrostatics effects. These waves may have wide impacts on the ocean dynamics (mixing or inducing vertical currents) and on human activities (fisheries, underwater acoustic or offshore activities).ISW can be detected on satellite scenes. For instance, they may induce surface currents and thus enhance or damp the capillary waves at the sea surface which signed on the Synthetic Aperture Radar (SAR) scenes. On SAR images, ISW appear as successions of bright and dark bands over a grey background. From these images, the amplitude of the ISW and the depth of the pycnocline may be inferred using the Korteweg-DeVries (KdV) theoretical framework. Several SAR images interpretation methods have been developed based on curve fitting or Peak-to-Peak methods (Zheng et al., 2001) or parametric autoregressive techniques (Le Caillec, 2006). The KdV theory relies on the weakly nonlinear approximation and a Two-Layers Ocean Model (TLOM).In Gibraltar Strait, the tidal dynamic leads to strong periodic currents. The exchanges between the Mediterranean sea and the Atlantic ocean occurred according a two layer scheme that maintains large density gradient located at the interface between Atlantic and Mediterranean Waters.&#160; At some tidal outflow, an internal hydraulic jump is formed above Camarinal sill, when the tidal ouflow slackens, it is released and leads to the formation of eastward propagating internal solitary waves. The site is thus considered as an ISW &#8220;hot-spot&#8221;. Part of the energy carried by these waves propagates eastward into the Alborean Sea, although the stratification may differ from the TLOM.If the stratification differs from TLOM, a given surface signature of ISW could match to several configurations of the pycnocline geometry and ISW amplitude, depending on the associated stratification.In order to assess the impact of the stratification on the surface signature of the ISW, we implemented an idealized 2DV (one vertical and one longitudinal directions) configuration with the Coastal and Regional Ocean modelling COmmunity model (CROCO) using its non-Boussinesq (pseudo compressible) capability. The bathymetry and the density profile are inspired from oceanic observations. The tidal forcing is simplified to a pure monochromatic M2 tide.First, simulations are initialized with a two-layer density profile and different pycnocline depths. Then, we added continuous stratification in each of the two (surface/bottom) layers. We tested also several tidal regimes in order to represent the various strengths between the neap and spring tide. SAR images interpretation techniques are then tested in each configurations. Pycnocline depths and ISW amplitudes computed from SAR methods are then compared with the ones initially simulated by the CROCO model.&#160;Le Caillec, J.-M., 2006. Study of the SAR signature of internal waves by nonlinear parametric autoregressive models. IEEE Trans. Geosci. Remote Sens. 44, 148&#8211;158. https://doi.org/10.1109/TGRS.2005.859954Zheng, Q., Yuan, Y., Klemas, V., Yan, X.-H., 2001. Theoretical expression for an ocean internal soliton synthetic aperture radar image and determination of the soliton characteristic half width. J. Geophys. Res. Oceans 106, 31415&#8211;31423. https://doi.org/10.1029/2000JC000726

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Open-loop adaptive filtering for speckle reduction in synthetic aperture radar images

Conference Record of the Thirty-Fourth Asilomar Conference on Signals, Systems and Computers (Cat. No.00CH37154) ◽

10.1109/acssc.2000.910948 ◽

2002 ◽

Cited By ~ 1

Author(s):

J.A. Rohwer ◽

N. Magotra ◽

S.D. Stearns

Keyword(s):

Synthetic Aperture Radar ◽

Adaptive Filtering ◽

Open Loop ◽

Synthetic Aperture ◽

Speckle Reduction ◽

Radar Images ◽

Aperture Radar

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Brief communication: Hurricane Dorian: automated near-real-time mapping of the “unprecedented” flooding in the Bahamas using synthetic aperture radar

Natural Hazards and Earth System Science ◽

10.5194/nhess-20-1463-2020 ◽

2020 ◽

Vol 20 (5) ◽

pp. 1463-1468

Author(s):

Diego Cerrai ◽

Qing Yang ◽

Xinyi Shen ◽

Marika Koukoula ◽

Emmanouil N. Anagnostou

Keyword(s):

Synthetic Aperture Radar ◽

Real Time ◽

European Space Agency ◽

Synthetic Aperture ◽

Management Service ◽

Sar Images ◽

The Bahamas ◽

Space Agency ◽

Continental Area ◽

Aperture Radar

Abstract. In this communication, we present application of the automated near-real-time (NRT) system called RAdar-Produced Inundation Diary (RAPID) to European Space Agency Sentinel-1 synthetic aperture radar (SAR) images to produce flooding maps for Hurricane Dorian in the northern Bahamas. RAPID maps, released 2 d after the event, show that coastal flooding in the Bahamas reached areas located more than 10 km inland, covering more than 3000 km2 of continental area. RAPID flood estimates from subsequent SAR images show the recession of the flood across the islands and present high agreement scores when compared to Copernicus Emergency Management Service (Copernicus EMS) estimates.

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Evaluation of the Performances of Radar and Lidar Altimetry Missions for Water Level Retrievals in Mountainous Environment: The Case of the Swiss Lakes

Remote Sensing ◽

10.3390/rs13112196 ◽

2021 ◽

Vol 13 (11) ◽

pp. 2196

Author(s):

Frédéric Frappart ◽

Fabien Blarel ◽

Ibrahim Fayad ◽

Muriel Bergé-Nguyen ◽

Jean-François Crétaux ◽

...

Keyword(s):

Synthetic Aperture Radar ◽

Water Level ◽

Open Loop ◽

Water Levels ◽

Synthetic Aperture ◽

Low Resolution ◽

Radar Altimetry ◽

Constant Bias ◽

Aperture Radar

Radar altimetry is now commonly used to provide long-term monitoring of inland water levels in complement to or for replacing disappearing in situ networks of gauge stations. Recent improvements in tracking and acquisition modes improved the quality the water retrievals. The newly implemented Open Loop mode is likely to increase the number of monitored water bodies owing to the use of an a priori elevation, especially in hilly and mountainous areas. The novelty of this study is to provide a comprehensive evaluation of the performances of the past and current radar altimetry missions according to their acquisition (Low Resolution Mode or Synthetic Aperture Radar) and tracking (close or open loop) modes, and acquisition frequency (Ku or Ka) in a mountainous area where tracking losses of the signal are likely to occur, as well as of the recently launched ICESat-2 and GEDI lidar missions. To do so, we evaluate the quality of water level retrievals from most radar altimetry missions launched after 1995 over eight lakes in Switzerland, using the recently developed ALtimetry Time Series software, to compare the performances of the new tracking and acquisition modes and also the impact of the frequency used. The combination of the Open Loop tracking mode with the Synthetic Aperture Radar acquisition mode on SENTINEL-3A and B missions outperforms the classical Low Resolution Mode of the other missions with a lake observability greater than 95%, an almost constant bias of (−0.17 ± 0.04) m, a RMSE generally lower than 0.07 m and a R most of the times higher than 0.85 when compared to in situ gauge records. To increase the number of lakes that can be monitored and the temporal sampling of the water level retrievals, data acquired by lidar altimetry missions were also considered. Very accurate results were also obtained with ICESat-2 data with RMSE lower than 0.06 and R higher than 0.95 when compared to in situ water levels. An almost constant bias (0.42 ± 0.03) m was also observed. More contrasted results were obtained using GEDI. As these data were available on a shorter time period, more analyses are necessary to determine their potential for retrieving water levels.

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Quantification of oil lost from tanker vessel using space borne radar datasets - Case study of Haldia port oil spill, July 2018.

International Oil Spill Conference Proceedings ◽

10.7901/2169-3358-2021.1.686884 ◽

2021 ◽

Vol 2021 (1) ◽

Author(s):

S.J Prasad ◽

T.M. Balakrishnan Nair

Keyword(s):

Synthetic Aperture Radar ◽

Oil Spill ◽

European Space Agency ◽

Fuel Oil ◽

Synthetic Aperture ◽

Synthetic Aperture Radar Data ◽

Space Agency ◽

Sar Data ◽

Spilled Oil ◽

Aperture Radar

Abstract 686884 Determining the spilled volume of the marine oil pollutant is an essential requisite for the oil spill modellers and the responders. Generally, the mass of the spilled pollutant is computed from the total quantity and the remaining quantity of the storage tank of the distressed vessel. A method to estimate the quantity of the spilled oil pollutant using the space -borne synthetic aperture radar dataset is elaborated here. The synthetic aperture radar data, its ability to penetrate cloud cover, irrespective of weather conditions, has been widely used to detect the signature of spilt oil. SAR data available from European Space Agency and Canadian Space Agency were used to detect the oil spills as they are proved to be appropriate for oil spill detection. Minor oil spill occured off Haldia Port, off Kolkata from SSL tanker vessel on 14 July 2018. The geographical location of the distressed vessel is 88.775 ′E, 21.441 ′N. The zone of the vessel distress was monitored for oil slicks. The acquisition plan of the Radar satellite Sentinel -1A was obtained from European Space Agency. As per that, the pass of the Sentinel -1A was available on 15 July 2018 and 17 July 2018 for the region of study. The Synthetic Aperture Radar (SAR) datasets were obtained from Sentinel -1A as per their availability. Those datasets were processed using Sentinel Application Platform (SNAP) tool box. The SAR data is subjected to terrain correction, which automatically reprojects the radar scene. The next stage is performing radiometric calibration, which converts the amplitude into intensity values. The radar reflectance values are converted to Sigma0 intensity values in Sentinel tool box. This Sigma0 values were wrote in netcdf format for identifying the oil slicks. The pixels of lesser intensity values are identified and are interpreted for oil slicks. The zone of the oil slicks in the radar scene are considered as irregular polygons. The area of those polygons were computed. Later the volume of the spilled oil is computed using the thickness of the spilled oil pollutant. Finally the mass of the pollutant is computed. It was collectively estimated from the SAR datasets, that, 33 Tons of Fuel oil was lost from SSL vessel that sank off Haldia Port. This paper elaborates in detail about the method of processing SAR dataset and estimating the quantity of oil lost from the vessel using SAR datasets.

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Flood Mapping in the Coastal Region of Bangladesh Using Sentinel-1 SAR Images: A Case Study of Super Cyclone Amphan

Journal of the Civil Engineering Forum ◽

10.22146/jcef.64497 ◽

2021 ◽

Vol 7 (3) ◽

pp. 267

Author(s):

Pollen Chakma ◽

Aysha Akter

Keyword(s):

Synthetic Aperture Radar ◽

Coastal Region ◽

Flood Damage ◽

Synthetic Aperture ◽

Flood Mapping ◽

Sar Images ◽

Radar Images ◽

Super Cyclone ◽

Aperture Radar

Floods are triggered by water overflow into drylands from several sources, including rivers, lakes, oceans, or heavy rainfall. Near real-time (NRT) flood mapping plays an important role in taking strategic measures to reduce flood damage after a flood event. There are many satellite imagery based remote sensing techniques that are widely used to generate flood maps. Synthetic aperture radar (SAR) images have proven to be more effective in flood mapping due to its high spatial resolution and cloud penetration capacity. This case study is focused on the super cyclone, commonly known as Amphan, stemming from the west Bengal-Bangladesh coast across the Sundarbans on 20 May 2020, with a wind speed between 155 -165 gusting up to 185 . The flooding extent is determined by analyzing the pre and post-event synthetic aperture radar images, using the change detection and thresholding (CDAT) method. The results showed an inundated landmass of 2146 on 22 May 2020, excluding Sundarban. However, the area became 1425 about a week after the event, precisely on 28 May 2020 . This persistency generated a more severe and intense flood, due to the broken embankments. Furthermore, 13 out of 19 coastal districts were affected by the flooding, while 8 were highly inundated, including Bagerhat, Pirojpur, Satkhira, Khulna, Barisal, Jhalokati, Patuakhali and Barguna. These findings were subsequently compared with an inundation map created with a validation survey immediately after the event and also with the disposed location using a machine learning-based image classification technique. Consequently, the comparison showed a close similarity between the inundation scenario and the flood reports from the secondary sources. This circumstance envisages the significant role of CDAT application in providing relevant information for an effective decision support system.

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