Detection of permanent open water surfaces in central Siberia with ENVISAT ASAR wide swath data with special emphasis on the estimation of methane fluxes from tundra wetlands

Bartsch, Annett; Pathe, Carsten; Wagner, Wolfgang; Scipal, Klaus

doi:10.2166/nh.2008.041

Cited by 38 publications

(36 citation statements)

References 9 publications

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“…Although these four approaches were designed according to different requirements, their performances were satisfactory over the studied areas (17 out of 20 water masks reaching an overall accuracy larger than 90%). Other studies using SAR data for water monitoring locally and regionally under different environments can be listed, such as [10][11][12]. Mapping water bodies at global scale using SAR data was limited due to the lack of global observations, and the fact that SAR data are not easy to access freely.…”

Section: Introductionmentioning

confidence: 99%

Surface Water Monitoring within Cambodia and the Vietnamese Mekong Delta over a Year, with Sentinel-1 SAR Observations

Pham-Duc

Prigent

Aires

2017

Water

115

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This study presents a methodology to detect and monitor surface water with Sentinel-1 Synthetic Aperture Radar (SAR) data within Cambodia and the Vietnamese Mekong Delta. It is based on a neural network classification trained on Landsat-8 optical data. Sensitivity tests are carried out to optimize the performance of the classification and assess the retrieval accuracy. Predicted SAR surface water maps are compared to reference Landsat-8 surface water maps, showing a true positive water detection of ∼90% at 30 m spatial resolution. Predicted SAR surface water maps are also compared to floodability maps derived from high spatial resolution topography data. Results show high consistency between the two independent maps with 98% of SAR-derived surface water located in areas with a high probability of inundation. Finally, all available Sentinel-1 SAR observations over the Mekong Delta in 2015 are processed and the derived surface water maps are compared to corresponding MODIS/Terra-derived surface water maps at 500 m spatial resolution. Temporal correlation between these two products is very high (99%) with very close water surface extents during the dry season when cloud contamination is low. This study highlights the applicability of the Sentinel-1 SAR data for surface water monitoring, especially in a tropical region where cloud cover can be very high during the rainy seasons.

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Section: Introductionmentioning

confidence: 99%

Surface Water Monitoring within Cambodia and the Vietnamese Mekong Delta over a Year, with Sentinel-1 SAR Observations

Pham-Duc

Prigent

Aires

2017

Water

115

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“…For soil moisture retrieval the signal is impacted if the area covered by open water surface within the footprint is large [38]. A surface water fraction flag, derived from the Global Lakes and Wetlands Database [55], exists but it does not take wetland dynamics, temporary inundation and small lakes into account [54]. An improved flag of this kind could be derived from ASAR data [13,56].…”

Section: Discussionmentioning

confidence: 99%

“…The persistence of lake ice on large lakes well into the summer and the associated water body classification issues have already been pointed out by [47]. To identify any water surface effects, the water areas identified by the classification were replaced by the value −20 dB, which is a typical C-band backscatter value for smooth water surfaces in the used dataset [47,54]. This builds the reference dataset.…”

Section: Methodsmentioning

confidence: 99%

Assessing Seasonal Backscatter Variations with Respect to Uncertainties in Soil Moisture Retrieval in Siberian Tundra Regions

et al. 2014

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Knowledge of surface hydrology is essential for many applications, including studies that aim to understand permafrost response to changing climate and the associated feedback mechanisms. Advanced remote sensing techniques make it possible to retrieve a range of land-surface variables, including radar retrieved soil moisture (SSM). It has been pointed out before that soil moisture retrieval from satellite data can be challenging at high latitudes, which correspond to remote areas where ground data are scarce and the applicability of satellite data of this type is essential. This study investigates backscatter variability other than associated with changing soil moisture in order to examine the possible impact on soil moisture retrieval. It focuses on issues specific to SSM retrieval in the Arctic, Remote Sens. 2014, 6 8719 notably variations related to tundra lakes. ENVISAT Advanced Synthetic Aperture Radar (ASAR) Wide Swath (WS, 120 m) data are used to understand and quantify impacts on Metop (AAdvanced Scatterometer (ASCAT, 25 km) soil moisture retrieval during the snow free period. Sites of interest are chosen according to ASAR WS availability, high or low agreement between output from the land surface model ORCHIDEE and ASCAT derived SSM. Backscatter variations are analyzed with respect to the ASCAT footprint area. It can be shown that the low model agreement is related to water fraction in most cases. No difference could be detected between periods with floating ice (in snow off situation) and ice free periods at the chosen sites. The mean footprint backscatter is however impacted by partial short term surface roughness change. The water fraction correlates with backscatter deviations (relative to a smooth water surface reference image) within the ASCAT footprint areas (R = 0.91−0.97). Backscatter deviations of up to 5 dB can occur in areas with less than 50% water fraction and an assumed soil moisture related range (sensitivity) of 7 dB in the ASCAT data. The sensitivity is also positively correlated with water fraction in regions with low land-surface model agreement (R = 0.68). A precise quantification of the impact on soil moisture retrieval would, however, need to consider actual soil moisture changes and sensor differences. The study demonstrates that the usage of higher spatial resolution data than currently available for SSM is required in lowland permafrost environments.

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“…Wetland complexes agree in most parts with the classification of this study (compare Figure 14: "forested shrubs-and moss-dominated mires" agree with "areas with high degree of saturation", "sphagnum dominated bogs with pools and open stand trees" agree with regions with a mixture of "water bodies" and "areas with high degree of saturation".) Bartsch et al [10] suggested the use of metrics such as water bodies density for tundra wetland complex retrieval. A combined use of those two classes may lead to the delineation of classes as used in [35].…”

Section: Assessment and Discussionmentioning

confidence: 99%

“…The ENVISAT ASAR instrument operating in Wide Swath mode provides C-band backscatter data with a spatial resolution of 150 m. Thus, small tundra ponds and wetland patches can be captured, which are smaller than the resolution of coarse to medium resolution satellite data (about 25 km to 500 m). Open water bodies can be mapped efficiently and accurately using ENVISAT ASAR WS data as described in [10]. In continuation of that study, the approach has shown high applicability to derive the inundation dynamics of the boreal and tundra environments [11].…”

Section: Introductionmentioning

confidence: 95%

Capability of C-Band SAR for Operational Wetland Monitoring at High Latitudes

et al. 2012

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Wetlands store large amounts of carbon, and depending on their status and type, they release specific amounts of methane gas to the atmosphere. The connection between wetland type and methane emission has been investigated in various studies and utilized in climate change monitoring and modelling. For improved estimation of methane emissions, land surface models require information such as the wetland fraction and its dynamics over large areas. Existing datasets of wetland dynamics present the total amount of wetland (fraction) for each model grid cell, but do not discriminate the different wetland types like permanent lakes, periodically inundated areas or peatlands. Wetland types differently influence methane fluxes and thus their contribution to the total wetland fraction should be quantified. Especially wetlands of permafrost regions are expected to have a strong impact on future climate due to soil thawing. In this study ENIVSAT ASAR Wide Swath data was tested for operational monitoring of the distribution of areas with a long-term S W near 1 (hS W ) in northern Russia (S W = degree of saturation with water, 1 = saturated), which is a specific characteristic of peatlands. 2924Annual long-term monitoring of change in boreal and tundra environments is possible with the presented approach. Sentinel-1, the successor of ENVISAT ASAR, will provide data that may allow continuous monitoring of these wetland dynamics in the future complementing global observations of wetland fraction.

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Detection of permanent open water surfaces in central Siberia with ENVISAT ASAR wide swath data with special emphasis on the estimation of methane fluxes from tundra wetlands

Cited by 38 publications

References 9 publications

Surface Water Monitoring within Cambodia and the Vietnamese Mekong Delta over a Year, with Sentinel-1 SAR Observations

Surface Water Monitoring within Cambodia and the Vietnamese Mekong Delta over a Year, with Sentinel-1 SAR Observations

Assessing Seasonal Backscatter Variations with Respect to Uncertainties in Soil Moisture Retrieval in Siberian Tundra Regions

Capability of C-Band SAR for Operational Wetland Monitoring at High Latitudes

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