Multiscale soil moisture measurements on the Southern US Great Plains: How small is too small?

Abstract:

Until recently, soil moisture measurements at the scale of tens of hectares has been difficult to obtain, except by aggregating point-scale data from invasive sensors. The cosmic-ray soil moisture probe provides a near surface (tens of cm integration depth) measurement over a large radial area, approximately covering 40 ha. Two cosmic ray probes from the Cosmic-ray Soil Moisture Observing System (COSMOS), operating since 2010 at heavily instrumented sites in Oklahoma, offer a special opportunity to examine soil moisture across different scales. One probe was installed at the ARM Southern Great Plains site near Lamont, OK, and the other at the SMAP in situ Test Bed near Stillwater, OK. Point samples taken within and adjacent to the footprint of the probes show a remarkable variability at each site, whereas the timeseries for the two probes are remarkably consistent, both in terms of dynamics and absolute values, despite the 80 km separation between the probes. The results highlight the value of large area measurements in eliminating point scale variability.