Detection of wetland dynamics with ENVISAT ASAR in support of methane modelling at high latitudes

Bartsch, A.; Trofaier, A.M.; Hayman, G.; Sabel, D.; Schlaffer, S.; Clark, D.; Blyth, E.. 2011 Detection of wetland dynamics with ENVISAT ASAR in support of methane modelling at high latitudes. Biogeosciences Discussions, 8 (4). 8241-8268. 10.5194/bgd-8-8241-2011

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Spatial information on inundation dynamics is expected to improve greenhouse gas estimates in climate models. Satellite data can provide land cover information from local to global scale. The detection capability for dynamics is however limited. Cloud cover and daylight independent methods are required for frequent updates. Suitable are therefore sensors which make use of microwaves. The purpose of the present study is to assess such data for determination of wetland dynamics from the viewpoint of use in climate models of the boreal and tundra environments. The focus is on synthetic aperture radar (SAR) operating in C-band due to, among microwave systems, comparably good spatial resolution and data availability. Continuity is also expected for such systems. Simple classification algorithms can be applied to detect open water in an automatised way allowing the processing of time series. Such approaches are robust when the water surface is smooth. C-band data from ENVISAT ASAR (Advanced SAR) operating in wide swath mode (150 m resolution) have been investigated for implementation of an automated detection procedure of open water fraction. More than 4000 samples (single acquisitions tiled into 0.5 degree grid cells) have been analysed for July/August 2007 and 2008. Modification of input parameters results in differences below 1 % open water fraction. The actual challenge is the frequent occurrence of waves due to wind and precipitation. This reduces the separability of the water class from other land cover. The possible update intervals for surface water extent are therefore decreased considerably. Statistical measures of the backscatter distribution can be applied in order to retrieve the for classification suitable data. The Pearson correlation between each sample dataset and a location specific representation of the bimodal distribution has been used for assessment. On average only 40 % of acquisitions allow a separation of the open water class. Satellite data are available every 2–3 days over the Western Siberian study region. With respect to the irregular acquisition intervals and varying length of unsuitable weather periods a minimum update interval of 10 days is suggested for the Northern Eurasian test case. Although SAR data availability is currently constraint future satellite missions which aim for operational services such as Sentinel-1 with its C-band SAR instrument may provide the basis for inundation monitoring in support of climate modelling.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.5194/bgd-8-8241-2011
Programmes: CEH Topics & Objectives 2009 onwards > Biogeochemistry
CEH Sections: Reynard
ISSN: 1810-6277
Additional Information. Not used in RCUK Gateway to Research.: Open Access article - click on the Official URL link for full text
NORA Subject Terms: Agriculture and Soil Science
Ecology and Environment
Date made live: 27 Sep 2011 08:45

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