In-season nitrogen management for corn is a challenge because the crop is growing rapidly and active sensors, as well as imagery, have difficulty penetrating very deep into the canopy. Remote sensing technologies strive to evaluate plant chlorophyll status (greenness) as an indication of current nitrogen availability in soil and accumulated biomass as an indication of crop vigor. Several new active sensors were evaluated relative to commercially available active sensors for their ability to assess plant chlorophyll status and biomass. The goal is to develop vegetation indices that have greater sensitivity to plant N status.