Water Level Fluctuations in the Congo Basin Derived from ENVISAT Satellite Altimetry

Becker, Mélanie; Silva, Joécila Santos da; Calmant, Stéphane; Robinet, V.; Linguet, Laurent; Seyler, Frédérique

doi:10.3390/rs6109340

Cited by 67 publications

(41 citation statements)

References 30 publications

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“…The aggregated pixel at upper level is set as 1 if any pixel in the s by s pixel block is 1; otherwise the pixel value is set as 0. The spatial resolution of the image at level k (mk) is given in Equation (1).…”

Section: Image Pyramid Constructionmentioning

confidence: 99%

“…Resource managers require efficient means of routinely monitoring river flows over large regions to help anticipating changes in the frequency of extreme events, and to both document and project long-term alterations to the rivers flow regime (e.g., [1][2][3]). Remote sensing is an efficient and inexpensive approach for the detection and monitoring of water bodies over large areas, relative to ground based survey methods.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Natural-Rule-Based-Connection (NRBC) Method for River Network Extraction from High-Resolution Imagery

Zeng

Bird²,

Luce

et al. 2015

Remote Sensing

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This study proposed a natural-rule-based-connection (NRBC) method to connect river segments after water body detection from remotely sensed imagery. A complete river network is important for many hydrological applications. While water body detection methods using remote sensing are well-developed, less attention has been paid to connect discontinuous river segments and form a complete river network. This study designed an automated NRBC method to extract a complete river network by connecting river segments at polygon level. With the assistance of an image pyramid, neighbouring river segments are connected based on four criteria: gap width (Tg), river direction consistency (Tθ), river width consistency (Tw), and minimum river segment length (Tl). The sensitivity of these four criteria were tested, analyzed, and proper criteria values were suggested using image scenes from two diverse river cases. The comparison of NRBC and the alternative morphological method demonstrated NRBC's advantage of natural rule based selective connection. We refined a river centerline extraction method and show how it outperformed three other existing centerline extraction methods on the test sites. The extracted river polygons and centerlines have a multitude of end uses including rapidly mapping flood extents, monitoring surface water supply, and the provision of validation data for OPEN ACCESSRemote Sens. 2015, 7 14056 simulation models required for water quantity, quality and aquatic biota assessments. The code for the NRBC is available on GitHub.

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Section: Image Pyramid Constructionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Natural-Rule-Based-Connection (NRBC) Method for River Network Extraction from High-Resolution Imagery

Zeng

Bird²,

Luce

et al. 2015

Remote Sensing

View full text Add to dashboard Cite

show abstract

“…A combination of MODIS data of river velocity and Envisat water levels was used by Tarpanelli et al (2015) to estimate discharge in the Po River. Becker et al (2014) used Envisat altimetry data to obtain a comprehensive dataset of water levels over the Congo Basin, a poorly gauged river system. The dense sampling pattern of ICESat was used by O'Loughlin et al (2013) to derive water-level slopes along the Congo River.…”

Section: Combining Satellite Altimetry With River Modelsmentioning

confidence: 99%

Application of CryoSat-2 altimetry data for river analysis and modelling

Schneider

Godiksen

Villadsen

et al. 2017

Hydrol. Earth Syst. Sci.

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Abstract. Availability of in situ river monitoring data, especially of data shared across boundaries, is decreasing, despite growing challenges for water resource management across the entire globe. This is especially valid for the case study of this work, the Brahmaputra Basin in South Asia. Commonly, satellite altimeters are used in various ways to provide information about such river basins. Most missions provide virtual station time series of water levels at locations where their repeat orbits cross rivers. CryoSat-2 is equipped with a new type of altimeter, providing estimates of the actual ground location seen in the reflected signal. It also uses a drifting orbit, challenging conventional ways of processing altimetry data to river water levels and their incorporation in hydrologic-hydrodynamic models. However, CryoSat-2 altimetry data provides an unprecedentedly high spatial resolution. This paper suggests a procedure to (i) filter CryoSat-2 observations over rivers to extract water-level profiles along the river, and (ii) use this information in combination with a hydrologic-hydrodynamic model to fit the simulated water levels with an accuracy that cannot be reached using information from globally available digital elevation models (DEMs) such as from the Shuttle Radar Topography Mission (SRTM) only. The filtering was done based on dynamic river masks extracted from Landsat imagery, providing spatial and temporal resolutions high enough to map the braided river channels and their dynamic morphology. This allowed extraction of river water levels over previously unmonitored narrow stretches of the river. In the Assam Valley section of the Brahmaputra River, CryoSat-2 data and Envisat virtual station data were combined to calibrate cross sections in a 1-D hydrodynamic model of the river. The hydrologichydrodynamic model setup and calibration are almost exclusively based on openly available remote sensing data and other global data sources, ensuring transferability of the developed methods. They provide an opportunity to achieve forecasts of both discharge and water levels in a poorly gauged river system.

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“…Over ocean, wet troposphere delay is calculated by means of water vapors observed by microwave radiometers onboard altimeter satellites, but these are unable to work over land [24,25]. Considering this limitation, most previous studies corrected altimeter data by using wet troposphere delay derived from global climate models (e.g., [26]); however, the accuracy of these models is unknown or varies across regions on lands. Therefore, further assessing the accuracy of the correction derived from global climate models is needed.…”

Section: Introductionmentioning

confidence: 99%

Monitoring Vertical Land Motions in Southwestern Taiwan with Retracked Topex/Poseidon and Jason-2 Satellite Altimetry

et al. 2015

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This study successfully uses satellite altimetry, including Topex/Poseidon and Jason-2, retrieved by novel retrackers to monitor vertical land motions in Southwestern Taiwan. Satellite altimetry was originally designed to measure open oceans, so waveform retracking should be applied to overcome the complex waveforms reflected from lands. Modified threshold and improved subwaveform threshold retrackers were used in the study to improve the accuracy of altimetric land surface heights (LSHs) in Southwestern Taiwan. Results indicate that the vertical motion rates derived from both retrackers coincide with those calculated by 1843 precise leveling points, with a correlation coefficient of 0.96 and mean differences of 0.43 and 0.52 cm/yr (standard deviations: 0.61 and 0.69 cm/yr). In addition, wet troposphere delay by precise point positioning with the use of Global Navigation Satellite System data was employed to evaluate the impact of the delay on the estimates of vertical motion rates compared with that traditionally derived from the European Center for Medium-Range Weather Forecasts model when the microwave radiometer is non-functional over lands. The accuracies of retracked altimetric land motion rates corrected by wet troposphere delays derived from both models show no remarkable differences in the Tuku and Yuanchang areas because the accuracy of retracked altimetric LSHs is significantly worse than that of wet troposphere delays.

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Water Level Fluctuations in the Congo Basin Derived from ENVISAT Satellite Altimetry

Cited by 67 publications

References 30 publications

A Natural-Rule-Based-Connection (NRBC) Method for River Network Extraction from High-Resolution Imagery

A Natural-Rule-Based-Connection (NRBC) Method for River Network Extraction from High-Resolution Imagery

Application of CryoSat-2 altimetry data for river analysis and modelling

Monitoring Vertical Land Motions in Southwestern Taiwan with Retracked Topex/Poseidon and Jason-2 Satellite Altimetry

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