The Long-Series Surface Freeze-Thaw Dataset of China - Decision Tree Algorithm (1987-2009) was extracted by decision tree classification using passive microwave remote sensing SSM/I brightness temperature data.

The dataset uses the EASE-Grid projection ( equal product cut cylindrical projection with ±30° standard latitude) with a spatial resolution of 25.067525km to provide a day-by-day classification of the surface freezing and thawing state of the main part of mainland China.The dataset is stored by year and consists of 23 folders in total, from 1987 to 2009.Each folder contains the day-by-day surface freeze-thaw classification results for the year as ASCII files with the naming convention:SSMI-frozenYYYY.txt, where YYYY stands for year and stands for Julian day (001~365/366).The txt file of the freeze-thaw classification results can be opened directly by the text program, as well as by the ArcView + Spatial Analyst extension or the Asciigrid command of Arcinfo.

The original data used to extract the surface freeze-thaw was derived from daily passive microwave data processed by the US National Snow and Ice Data Center (NSIDC) since 1987, using the EASE-Grid (Equivalent Area Expandable Earth Grid) as the standard format.

The attributes of long series surface freeze-thaw dataset of China - Decision tree algorithm (1987-2009) consist of the spatial and temporal resolution, projection information, and data format of this dataset.

Temporal and spatial resolution: the temporal resolution is day-by-day, the spatial resolution is 25.067525km, the longitude range is 60° to 140°E and the latitude is 15° to 55°N.

Projection information: global equiprobable cylindrical EASE-Grid projection. Detailed information on the EASE-Grid projection can be found in the description of this projection in the Data Preparation.

Data format: The dataset consists of 23 folders from 1987 to 2009, each folder contains the day-by-day surface freeze-thaw classification results for that year, stored as txt files by day. The file naming rules: e.g. SMI-frozen1994001.txt represents the surface freeze-thaw classification results for day 1 of 1994. The ASCII file of this dataset is composed of a header file and the main content. The header file consists of six lines of descriptive information including rows, columns, coordinates of the lower left point of the x-axis, coordinates of the lower left point of the y-axis, raster size, and no data area marker values; the main content is a two-dimensional array based on the number of rows and columns, arranged in column order, with integer values from 1 to 4, with 1 representing freezing, 2 representing thawing, 3 representing desert, and 4 representing precipitation. Because all the ASCII files in this dataset describe the space for the whole of China, the header files for these files are unchanged and are extracted below (where xllcenter, yllcenter and cellsize are in m):

ncols 308

nrows 166

xllcorner 5778060

yllcorner 1880060

cellsize 25067.525

nodata_value 0

All ASCII files in this dataset can be opened directly with a text program (e.g. Notepad). Apart from the header file, the main content is a numerical representation of the state of freezing and thawing of ground: 1 for freezing, 2 for melting, 3 for desert and 4 for precipitation. To display this graphically, we recommend using ArcView + 3D or the Spatial Analyst extension to read it, which generates a grid format file during the reading process. Reading method:

[1] Add the 3D or Spatial Analyst extension to the ArcView software and create a new View;

[2] Activate the View, click on the File menu, select the Import Data Source option, the Import Data Source selection box will pop up, select ASCII Raster in the Select import file type: box, a dialog box to select the source ASCII file will pop up automatically, click on Find Click on Find any ASCII file in the dataset, and then press OK;

[3] In the Output Grid dialog box type in the name of the Grid file (it is recommended to use a meaningful file name so that you can view it yourself later) and click on the path where this Grid file is stored, press Ok again and then press Yes (to select integer data) and Yes (to bring the generated grid file into the current view). The resulting file can be edited for properties according to the Grid file standard. This completes the process of displaying the ASCII file into a Grid file.

[4] For batch processing, you can use ARCINFO's ASCIIGRID command, write it as an AML file, and then use the Run command to complete it in the Grid module:

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Usage: ASCIIGRID {INT | FLOAT}