Hornbuckle Group Research Interests

Hornbuckle group research infrastructure.

Water supports both plant and animal communities and is an important source of moisture for the atmosphere. In our research, we use both remote sensing and in-situ instruments to monitor the cycling of water and energy among the soil, vegetation, and atmosphere in agricultural ecosystems. This research, best described as agronomic physics, spans many disciplines of study, including radio science, soil science, plant science, atmospheric science, and engineering.


The primary goal of our research is to use microwave remote sensing to determine the liquid water content of soil and vegetation. We use an instrument called a microwave radiometer to measure the amount of microwave radiation naturally emitted by the land surface. Three microwave radiometers are pictured at left. The amount of microwave radiation emitted by the ground is related to the water content of the soil and vegetation. A microwave radiometer can be thought of as camera that "sees" microwave radiation instead of visible light. Wet soils appear "dark" while dry soils appear "bright." Vegetation is semi-transparent. Vegetation absorbs some of the microwave radiation emitted by the soil but it also emits its own microwave radiation according to its water content.

Ultimately microwave and other remotely-sensed measurements will be used in conjunction with models to predict the distribution of water within the landscape and the moisture and energy exchange between the land surface and the atmosphere at a variety of scales, from field to watershed to region. Including better information on current land surface water content in numerical weather prediction models will drastically improve short- and long-term forecasting. Agriculture will also benefit since it is fundamentally limited by the availability of water resources.

smos satellite Since 2009, a new Earth-orbiting satellite has been carrying the most significant soil moisture microwave remote sensing instrument in human history into space. The European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission is recording images of the microwave radiation emitted by Earth's surface and thus enabling scientists to better understand the global water cycle. We are members of the SMOS Validation and Retrieval Team. Our task is to verify, using ground-based measurements, that the soil moisture observed by SMOS is correct. In January of 2015 NASA launched its own soil moisture remote sensing satellite, called the Soil Moisture Active Passive (SMAP) mission. We are also assisting with the validation of SMAP using instruments located in the South Fork Iowa River Watershed. smap satellite

There are two main types of activities in our research group. First, we undertake intensive field experiments (pictured at right) during which relevant variables such as emitted microwave radiation, soil and vegetation water content, other land surface biophysical properties, and local atmospheric conditions are carefully measured.

In the second type of activity, these measurements are integrated with models of microwave emission and models of heat and moisture transport among the soil, vegetation, and atmosphere.

field experiment

We plan to develop models of the microwave radiation emitted by the earth's surface. These models will be coupled with land surface process models in order to predict land-atmosphere water and energy cycling and to simulate changes in soil and vegetation properties pertinent to the emitted microwave radiation. For example, dry soil may crack and water will move through the soil much faster than expected resulting in the underestimation of soil water content with remote sensing techniques. Similarly, wilted vegetation will appear differently than fresh vegetation. Current emission models neglect these types of changes. In support of this main goal, we have interests in the following areas:

  • measurement of land surface microwave brightness

  • modeling of the land surface water and energy balance

  • modeling of scattering and emission in soil and vegetation

  • characterization of soil and vegetation physical properties

  • in-situ measurement of soil moisture

  • measurement of soil moisture with cosmic-ray neutron detectors

  • measurement of land surface temperature

  • millimeter-scale measurement of soil topography (roughness)

  • measurement of dew and evapotranspiration

  • validation of in-situ and remotely sensed measurements from the point-scale to the plot-scale and beyond
graduate student

Hornbuckle group research infrastructure.

Undergraduate research mentoring notes.

Brian Hornbuckle