S-1 Reference Water Mask - Revision history

Admin at 12:17, 10 March 2021

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Admin: /* Note */

2021-03-10T11:43:08Z

‎Note

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-The '''Sentinel-1 Reference Water Mask''' identifies the pixels classified as open and calm water, both permanent and seasonal, using Sentinel-1 SAR backscatter intensity using the ensemble flood mapping algorithm described in section 0. <br>
+The '''Sentinel-1 Reference Water Mask''' identifies the pixels classified as open and calm water, both permanent and seasonal, using Sentinel-1 SAR backscatter intensity using an ensemble flood mapping algorithm. <br>
 Whereas the permanent water extent mapping uses as input the median backscatter of all Sentinel-1 data from a time period of two years, the seasonal reference water mapping uses as input the median backscatter of all Sentinel-1 data from a given month over a two-year period. As a result, twelve masks are available, one per month, which includes information on the permanent and seasonal reference water extent. This parameter database is updated once a year. <br>
 For example, the NRT system running in 2021 will rely on Sentinel-1 reference Water Mask extracted from the Sentinel-1 pre-processed data cube from 2019 and 2020. The algorithm relies also on offline-generated Sentinel-1 SAR parameters and auxiliary thematic datasets such as Exclusion Mask, DEM and HAND index. The Sentinel-1 Reference Water Mask values are described below.

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-====Further details====
+====<u>Further details</u>====
 In order to identify the flood extent, the Sentinel-1 observed water extent derived by the proposed ensemble approach has to be masked by a reference water layer, which represents the extent of open water bodies under normal conditions. In the literature reference masks of the permanent water extent are often used for this purpose (Wieland and Martinis, 2019<sup>[1]</sup>). <br>
 A truly permanent water area would mean that there was observed water coverage in every single observation of the considered time period; i.e. the ''Water Occurrence'' (WO), which is the ratio between the number of water detections during a certain time period and the number of valid observations of the same period, would be 100 %. <br>

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-====Note====
+====Further details====
 In order to identify the flood extent, the Sentinel-1 observed water extent derived by the proposed ensemble approach has to be masked by a reference water layer, which represents the extent of open water bodies under normal conditions. In the literature reference masks of the permanent water extent are often used for this purpose (Wieland and Martinis, 2019<sup>[1]</sup>). <br>
 A truly permanent water area would mean that there was observed water coverage in every single observation of the considered time period; i.e. the ''Water Occurrence'' (WO), which is the ratio between the number of water detections during a certain time period and the number of valid observations of the same period, would be 100 %. <br>

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 For example, the NRT system running in 2021 will rely on Sentinel-1 reference Water Mask extracted from the Sentinel-1 pre-processed data cube from 2019 and 2020. The algorithm relies also on offline-generated Sentinel-1 SAR parameters and auxiliary thematic datasets such as Exclusion Mask, DEM and HAND index. The Sentinel-1 Reference Water Mask values are described below.
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+[[File:figure4.jpg|border]]
 ====Note====

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 The seasonal reference masks will be provided on a monthly basis by applying the ensemble approach on the median backscatter derived from monthly data stacks over a time period of also two years. If, for example, the currently analysed Sentinel-1 scene is acquired in the January 2021 it will be compared by the seasonal reference water mask computed from data acquired in January of the previous years 2019 and 2020. <br>
-The application of the ensemble approach on the median backscatter instead of computing the Water Occurrence based on each single observation has the advantage that the processing efficiency can be strongly increased. The reference water masks will be updated once a year in an offline environment in order to compare the Sentinel-1 observed water extent with the reference water extent of the two previous years. This helps to provide up-to-date reference water masks. The reference period of two years is chosen as compromise in order to base the computation on a sufficient number of Sentinel-1 data and to remove long-term hydrologic changes which would be integrated in the reference waters masks if longer time periods would be considered.
+The application of the ensemble approach on the median backscatter instead of computing the ''Water Occurrence'' based on each single observation has the advantage that the processing efficiency can be strongly increased. The reference water masks will be updated once a year in an offline environment in order to compare the Sentinel-1 observed water extent with the reference water extent of the two previous years. This helps to provide up-to-date reference water masks. The reference period of two years is chosen as compromise in order to base the computation on a sufficient number of Sentinel-1 data and to remove long-term hydrologic changes which would be integrated in the reference waters masks if longer time periods would be considered.
 ====<u>References</u>====