About Coral Reef Watch HDF data files

Coral Reef Watch's raw data files are produced in HDF (Hierarchical Data Format) for public distribution. HDF is a commonly used data format and is a multi-objective file format for sharing scientific data in a distributed environment. HDF files are self-describing, containing comprehensive information (metadata) about the data and data location within the file. Many commonly used computer languages and software packages can read and process HDF files. The Coral Reef Watch HDF data files are produced in such a way that they are also compliant with NOAA CoastWatch's HDF Metadata Specification. As a result, Coral Reef Watch's HDF data can be viewed and analyzed in CoastWatch's Software Library and Utilities.

Please note that there is an array called surface_flag in each Coral Reef Watch HDF data file. This array contains pixel classification flags for the data array(s) in the HDF data file. The surface_flag array is an 8-bit binary array in the same size as the data array(s) in a Coral Reef Watch HDF data file. Each of our data arrays usually contains four types of pixels: water (data), land, missing data, and ice. In all of our data arrays (i.e., SST, SST anomaly, HotSpots, and Degree Heating Weeks), land, missing data, and ice pixels are all flagged -7777. As a result, the surface_flag array is added to each Coral Reef Watch HDF data file to distinguish different types of non-data pixels. The following table shows the pixel types and their corresponding flag values in a surface_flag array:

Flag Value      Pixel Type
     water (containing data values)
missing data

One of the built-in overlay groups in the CoastWatch Data Analysis Tool (CDAT), a part of the CoastWatch software tools, is designed to use this surface_flag array to classify and color different types of pixels in data visualization of Coral Reef Watch HDF data. Click for more information about the CoastWatch software tools.

We request proper credit and citation to NOAA Coral Reef Watch
and CoastWatch when using the data and software.

Acknowledgements: We thank Peter Hollemans (the creator and developer of the CoastWatch Software Library and Utilities) of Terrenus Earth Sciences and Ken Casey of NOAA NODC for their suggestions, comments, and assistance in developing our HDF metadata specification.