From AMS Glossary
- The distance upstream of a measurement site, receptor site, or region of meteorological interest, that is relatively uniform.
If a measurement site is located in the middle of a farm field with homogeneous land use, and if there are no changes to the land use and no obstructions such as trees or buildings immediately upstream of the site, then the site is said to have "large fetch". Large fetch is usually considered good if the measurements are to be representative of the atmosphere over the farm field. Similarly, measurements over a homogeneous forest could also have large fetch if there are no clearcuts or changes in the tree characteristics upstream of the measurement site.