Koehn has research interests in the areas of hydrogeophysics, computational methods in geophysics and groundwater hydrology. His research primarily focuses on characterizing groundwater systems through the application of near-surface geophysics, and using the analytic element method to devise solutions for groundwater, geotechnical and agricultural engineering problems. Koehn has a strong interest in developing novel numerical and geophysical techniques to bridge the gap between geophysics and hydrology to improve groundwater model parameterization.