Include Only One Variable per GeoTIFF File

Recommendation Details: The GeoTIFF format was initially developed during the early 1990’s with the objective being to leverage a mature platform independent file format (TIFF) by adding metadata required for describing and using geographic image data (OGC, 2019).

The term "Band" is associated with the GeoTIFF format.  As defined in the OGC GeoTIFF Standard version 1.1 (OGC, 2019), Band represents a "range of wavelengths of electromagnetic radiation that produce a single response by a sensing device."

With the easiness to use and strong support from both commercial and open source software (ESO, 2019), the GeoTIFF format has been widely used in the Earth science community (and more) to store data beyond what the GeoTIFF format was originally designed for.  Some data producers tend to pack multiple different variables as different bands in a GeoTIFF file, even though these different variables do not necessarily represent "response" from measurements with "range of wavelengths".  One such example is the "ABoVE: AirSWOT Ka-band Radar over Surface Waters of Alaska and Canada, 2017" dataset archived at the ORNL DAAC.  Each of these GeoTIFF files contains 6 bands, representing 6 different variables (elevation, incidence_angle, magnitude, interferometric correlation, height_sensitivity, and error_bar). 

We Discourage Packing Multiple Different Variables in a Multi-Band GeoTIFF File:  At this moment, there is no commonly-agreed-upon approach to tag GeoTIFF files at the band-level to associate metadata (e.g. variable name and units) to each individual band.  Even though there are libraries (like GDAL) that support adding custom-defined metadata tags to individual bands of GeoTIFF files, many tools and applications still lack the capability to add or use such custom-defined metadata tags at the band-level.  Such GeoTIFF files become less self-descriptive and thus decreasing their interoperability.  Different data variables must be in the same data type (e.g. Int16 and Float32) once being physically stacked as multiple bands in a GeoTIFF file.

Some Advice Regarding Storing Complex Data in GeoTIFF Files:  Rather than storing complex data (e.g., multiple data variables and multi-dimensional data) in GeoTIFF files, please consider using formats like HDF5 and/or netCDF, which have established community standards/conventions to embed variable- and file-level metadata inside the files to make such files self-descriptive and interoperable, and the data from such files can be used to generate single-variable GeoTIFF files.

If the GeoTIFF format is really preferred, then please include only one variable per GeoTIFF file, and consider an approach, such as GDAL's Virtual Dataset (VRT) format, to "virtually" aggregate multiple single-variable GeoTIFF files together into a metadata-rich data file/asset without having to change their native data types.

References:

ESO, ESO Recommended Standard, GeoTIFF File Format, September 2019. https://earthdata.nasa.gov/esdis/eso/standards-and-references/geotiff

OGC, OGC GeoTIFF Standard, OGC Document 19-008r4, September 14, 2019. http://docs.opengeospatial.org/is/19-008r4/19-008r4.html