Global Surface Water Extent Dataset V4.0 (2000-2023/8-day/250 m)

The GSWED product has the good capabilities to monitor a variety of surface water changes both in spatial patterns and long-term temporal trends (such as the abrupt change (floods), seasonal change, and long-term change trend with increasing/decreasing fluctuations).GSWED V2.0：（1）The coordinate system of GSWED V2.0 is: WGS-84.（2）The meaning of the attribute value updated into (preliminary extracted surface water 1 and temporal interpolated surface water 2 were merged into 1): 1 Water, 3 Ice and Snow, 4 Land, 5 Mountain Shadows, 6 Clouds.（3）The naming rule of the data file in GSWED V2.0 is (because there is no data partitioning problem in GSWED V2.0): "Left longitude_right longitude_low latitude_up latitude_grid latitude and longitude grid order (from 0, left to right, bottom to top sorting) _grid longitude size_ grid latitude size (7-5 ​​represents 7.5 degrees) _start year-end year", where positive latitude and longitude indicate north latitude and east longitude, and negative latitude and longitude indicate south latitude and west longitude.Example: -18_54_16_26_grid0_6_5_2000-2020, this data is the 0th grid between 18°W and 54 °E, between 16°N and 26 °N, whose longitude size is 6 degrees and latitude size is 5 degrees.（4）The organization of GSWED V2.0: GSWED V2.0 is in the GSWED2000-2020 folder (807 files in total), which is organized into five folders according to the continents: GSWED_Africa2000-2020, GSWED_America2000-2020, GSWED_Asia2000-2020, GSWED_Europe2000-2020, GSWED_Oceania2000-2020.

The folders respectively have 125, 273, 241, 83, and 85 data files, and each data file has 955 layers, representing the surface water of the corresponding date (from 2000 to 2020 with 8-day temporal resolution). For the specific date information of each layer, see BandDate2000-2020.xlsx.（5）The total data volume of GSWED V2.0: 73.5 GB.（6）There is geographic offset in June 26, 2010 (band474), so our water results also have a corresponding geographic offset in June 26, 2010 (band474).

There is a corresponding geographic offset in July 4, 2010 (band475) and in July 12, 2010 (band476) due to temporal interpolation.（7）The algorithm update: Due to some missing data in the original data MOD09Q1, most of these pixels are distributed in the middle of large lakes, but some pixels are also distributed in land areas. GSWED V 1.0 classifies it directly as water, which cause some misclassification errors. The updated algorithm in GSWED V2.0 performs time interpolation on these missing pixels in the land area, optimizing the results of the spatiotemporal distribution of water, while the large lake area retains the GSWED V1.0 processing method.For the water results, we performed spatiotemporal filtering to remove fine water patches.

We calaulated the annual water frequency and spatial connectivity of water pixels. The meta value is land. The water pixels with water frequency less than 5/46 and spatial connectivity less than 5 pixels are assigned as land.GSWED V3.0：We produced data for 2021 and 2022 based on GSWED V2.0, others are all same as V2.0.(1) Organization of GSWED V3.0 dataset: GSWED V3.0 is stored in GSWED2021 and GSWED2022 folders, with a total of 807 data files under each folder.

Each folder is divided into five folders by continent (2021 for example, and the same for 2022): GSWED_Africa2021, GSWED_America2021, GSWED_Asia2021, GSWED_Europe2021, and GSWED_Oceania2021. Each folder has 125, 273, 241, 83, 85 data files. Each data file has 46 layers representing surface water bodies on corresponding dates (with a temporal resolution of 8 days).

See BandDate2021.xlsx and BandDate2022.xlsx for specific date information for each layer.(2) Data volume of GSWED V3.0: 8.2 GB.GSWED V4.0：We produced data for 2023 based on GSWED V2.0, others are all same as V2.0.(1) Organization of GSWED V4.0 dataset: GSWED V4.0 is stored in GSWED2023 folder, with a total of 807 data files under each folder. Each folder is divided into five folders by continent: GSWED_Africa2023, GSWED_America2023, GSWED_Asia2023, GSWED_Europe2023, and GSWED_Oceania2023.

Each folder has 125, 273, 241, 83, 85 data files. Each data file has 46 layers representing surface water bodies on corresponding dates (with a temporal resolution of 8 days). See BandDate2023.xlsx for specific date information for each layer.(2) Data volume of GSWED V4.0: 3.34 GB.