Suitability and Limitations of ENVISAT ASAR for Monitoring Small Reservoirs in a Semiarid Area

Liebe, Jens; Giesen, Nick van de; Andreini, M.; Steenhuis, Tammo S.; Walter, M. Todd

doi:10.1109/tgrs.2008.2004805

Cited by 34 publications

(28 citation statements)

References 16 publications

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“…The alignment of the waves with respect to the direction of the incident radar wave is also important here. The effect is greatest when the incident signal is orthogonal to the alignment of the wave (or parallel to the wind direction), and may not occur at all when the radar signal and the wave direction are parallel (Liebe et al, 2009).Finally, the strength of the radar signal returned to the sensor is reduced by an increasing incidence angle (Monsiváis et al, 2006). Whilst simple geometry allows us to calculate the theoretical degree of this effect, its precise value is the combination of various target characteristics averaged over a pixel-space, and is therefore not readily known for a given time.…”

Section: Theoretical Basismentioning

confidence: 99%

Use of ENVISAT ASAR Global Monitoring Mode to complement optical data in the mapping of rapid broad-scale flooding in Pakistan

O’Grady

Leblanc

Gillieson

2011

Hydrol. Earth Syst. Sci.

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Abstract. Envisat ASAR Global Monitoring Mode (GM) data are used to produce maps of the extent of the flooding in Pakistan which are made available to the rapid response effort within 24 h of acquisition. The high temporal frequency and independence of the data from cloud-free skies makes GM data a viable tool for mapping flood waters during those periods where optical satellite data are unavailable, which may be crucial to rapid response disaster planning, where thousands of lives are affected. Image differencing techniques are used, with pre-flood baseline image backscatter values being deducted from target values to eliminate regions with a permanent flood-like radar response due to volume scattering and attenuation, and to highlight the low response caused by specular reflection by open flood water. The effect of local incidence angle on the received signal is mitigated by ensuring that the deducted image is acquired from the same orbit track as the target image. Poor separability of the water class with land in areas beyond the river channels is tackled using a region-growing algorithm which seeks threshold-conformance from seed pixels at the center of the river channels. The resultant mapped extents are tested against MODIS SWIR data where available, with encouraging results.

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Section: Theoretical Basismentioning

confidence: 99%

Use of ENVISAT ASAR Global Monitoring Mode to complement optical data in the mapping of rapid broad-scale flooding in Pakistan

O’Grady

Leblanc

Gillieson

2011

Hydrol. Earth Syst. Sci.

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“…Compared to previous studies the use of nine sensors for the monitoring of wetlands or open water bodies is unique. Santoro et al (2015), Westra et al (2010), and Liebe et al (2009) for example used only data of Envisat ASAR. But a combination of two to three different sensors is not exceeded, regardless of whether SAR data alone or combined with optical data were utilized (e.g., Bwangoy et al, 2010;Munyaneza et al, 2009;Li and Chen, 2005).…”

Section: Introductionmentioning

confidence: 99%

Long-Term Monitoring of Water Dynamics in the Sahel Region Using the Multi-Sar-System

Bertram

Wendleder

Schmitt

et al. 2016

Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci.

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ABSTRACT:Fresh water is a scarce resource in the West-African Sahel region, seasonally influenced by droughts and floods. Particularly in terms of climate change, the importance of wetlands increases for flora, fauna, human population, agriculture, livestock and fishery. Hence, access to open water is a key factor. Long-term monitoring of water dynamics is of great importance, especially with regard to the spatio-temporal extend of wetlands and drylands. It can predict future trends and facilitate the development of adequate management strategies. Lake Tabalak, a Ramsar wetland of international importance, is one of the most significant ponds in Niger and a refuge for waterbirds. Nevertheless, human population growth increased the pressure on this ecosystem, which is now degrading for all uses. The main objective of the study is a long-term monitoring of the Lake Tabalak's water dynamics to delineate permanent and seasonal water bodies, using weather-and daytime-independent multi-sensor and multi-temporal Synthetic Aperture Radar (SAR) data available for the study area. Data of the following sensors from 1993 until 2016 are used: Sentinel-1A, TerraSAR-X, ALOS PALSAR-1/2, Envisat ASAR, RADARSAT-1/2, and ERS-1/2. All SAR data are processed with the Multi-SAR-System, unifying the different characteristics of all above mentioned sensors in terms of geometric, radiometric and polarimetric resolution to a consistent format. The polarimetric representation in Kennaugh elements allows fusing single-polarized data acquired by older sensors with multi-polarized data acquired by current sensors. The TANH-normalization guarantees a consistent and therefore comparable description in a closed data range in terms of radiometry. The geometric aspect is solved by projecting all images to an earth-fixed coordinate system correcting the brightness by the help of the incidence angle. The elevation model used in the geocoding step is the novel global model produced by the TanDEM-X satellite mission. The advantage of the Multi-SAR-System is that it comprises ortho-rectification, radiometric enhancement, normalization and Kennaugh decomposition, independent from sensors, modes, polarizations or acquisition date of SAR data. In addition, optical satellite data can be included as well, to fill gaps where SAR data are missing due to the special normalization scheme. This kind of pre-processing is exclusively implemented at the Earth Observation Center of the German Aerospace Center in Oberpfaffenhofen, Germany. Therefore, the dynamic change of the open water of the Lake Tabalak could be classified over dry and rainy seasons and years, using different SAR data. The study provides a unique database and contributes to a better understanding of wetland systems in the Sahel region influenced by human pressure and climate change.

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“…A strong limitation of optical imagery is its dependence on cloud-and smoke-free day acquisitions, which makes its application for operational monitoring very limited. For the detection and the creation of a base map, optical imagery is, however, very suitable [14].…”

Section: Introductionmentioning

confidence: 99%

“…The application of SAR imagery for small reservoir monitoring has recently been studied based on Envisat ASARimages [4,14]. Smooth open water acts as a specular reflector, reflecting most of the radar signal away from the sensor.…”

Section: Introductionmentioning

confidence: 99%

Remotely Sensed Monitoring of Small Reservoir Dynamics: A Bayesian Approach

et al. 2014

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Multipurpose small reservoirs are important for livelihoods in rural semi-arid regions. To manage and plan these reservoirs and to assess their hydrological impact at a river basin scale, it is important to monitor their water storage dynamics. This paper introduces a Bayesian approach for monitoring small reservoirs with radar satellite images. The newly developed growing Bayesian classifier has a high degree of automation, can readily be extended with auxiliary information and reduces the confusion error to the land-water boundary pixels. A case study has been performed in the Upper East Region of Ghana, based on Radarsat-2 data from November 2012 until April 2013. Results show that the growing Bayesian classifier can deal with the spatial and temporal variability in synthetic aperture radar (SAR) backscatter intensities from small reservoirs. Due to its ability to incorporate auxiliary information, the algorithm is able to delineate open water from SAR imagery with a low land-water contrast in the case of wind-induced Bragg scattering or limited vegetation on the land surrounding a small reservoir.

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Suitability and Limitations of ENVISAT ASAR for Monitoring Small Reservoirs in a Semiarid Area

Cited by 34 publications

References 16 publications

Use of ENVISAT ASAR Global Monitoring Mode to complement optical data in the mapping of rapid broad-scale flooding in Pakistan

Use of ENVISAT ASAR Global Monitoring Mode to complement optical data in the mapping of rapid broad-scale flooding in Pakistan

Long-Term Monitoring of Water Dynamics in the Sahel Region Using the Multi-Sar-System

Remotely Sensed Monitoring of Small Reservoir Dynamics: A Bayesian Approach

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