Filling in the soil moisture mapping gaps

Tuesday, October 17, 2017

Soil moisture influences many decisions by landowners and property managers. Determining the moisture level of precise locations is a daunting task, due, in part, to the many factors that can cause fluctuations.

“Soil moisture conditions at two places just 30 feet apart can be almost completely uncorrelated,” said Tyson Ochsner, associate professor in Oklahoma State University’s Department of Plant and Soil Sciences. “Differences in soil texture, vegetation types, weather conditions and many other factors cause soil moisture conditions to vary tremendously.”

To help alleviate some of the unknowns and missing information about soil moisture, Ochsner and a team of researchers are working to develop a more complete monitoring system across the state. The National Science Foundation, Established Program to Stimulate Competitive Research, project is designed to create statewide high-resolution soil moisture maps to improve drought monitoring, wildfire forecasting and hydrologic modeling.

Until this project, measurements from the Oklahoma Mesonet provided soil moisture information, but only for approximately 120 monitoring stations across the state. However, Ochsner’s research team was able to enhance soil moisture estimates to provide statewide coverage by incorporating information from digital soil maps and radar-based precipitation data from the National Weather Service.

“The soil moisture sensors at each Mesonet site measure soil moisture at a single point in space,” Ochsner said. “On a state level, although we have more than 100 monitoring sites, that is still far too sparse to make reliable soil moisture maps from those measurements alone.”

To fill in the gaps, the team used a special mobile instrument called a cosmic-ray neutron rover.

“The rover detects soil moisture within about 650 feet of the instrument and up to 2 feet deep in the soil, and it can continuously measure from a moving vehicle,” said Geano Dong, Ph.D. student working under Ochsner. “The data from the rover will help us determine the primary factors causing spatial variability in soil moisture around and between the Oklahoma Mesonet point measurement locations. We will incorporate that understanding into models that will allow us to make high resolution soil moisture maps for the whole state.”

In collaboration with the OSU High Performance Computing Center, Ochner’s team created a unique high resolution mapping system for Oklahoma.

“This system takes daily soil moisture observations from the Oklahoma Mesonet and radar precipitation estimates from the National Weather Service and combines those data with detailed soil maps to reveal previously undetectable meso-scale patterns in soil moisture,” Ochsner said.

Users are able to view soil moisture data through an interactive website via soilmoisture.okstate.edu.

OSU researcher, Phil Alderman, will utilize soil moisture data obtained by this project on another EPSCoR grant to develop a forage-forecasting framework for grazing management decisions. This will provide a forecast of the amount of forage production to expect for the upcoming season given current soil moisture and rainfall projections.