The 1999 Southern Great Plains Experiment (SGP'99) took place during the
second and third weeks in July 1999. The goals of this effort are to: understand how to effectively interpret and utilize the less than optimal sources of
satellite microwave data that are available now or will be in the near future
explore new approaches that may enhance the ability to measure soil moisture from
The gravimetric soil moisture sampling was taken during the period at several sites. For the most part, sampling was performed on sites approximately a quarter section (0.8 X 08km ) in size.
A standardized tool was used to extract a sample of the 0-5cm soil layer. This sample was then split in half to provide a 0-2.5cm and 2.5-5cm sample at the point.
More information is here here.