Observations of coherent emissions from soils

Observations of the microwave emissions at 1.413 GHz (L band) and 2.65 GHz (S band) from a silt loam soil exhibited an oscillatory behavior in time as the soil was being irrigated. The oscillations are attributed to interference between reflections from the air-soil interface and the wet soil-dry soil interface as the latter moved down in the soil. The magnitude of the first oscillation at L band was 56 K, and at S band it was 40 K, with oscillation damping out after about three cycles to the brightness temperature expected for the wet soil. The emission was modeled using a coherent model, and the results show qualitative and quantitative agreement with the observations.