A method includes measuring a first frequency response of an electrode at a first frequency across a range of environmental conditions, measuring a second frequency response of the electrode at a second frequency across the range of environmental conditions, and comparing the first and second frequency responses measured to define a data set representing an effect of the environmental conditions. An occupant detection system includes an electrode and a detector circuit. The detector circuit is configured to measure an actual frequency response of the electrode and compare the actual frequency response to the data set to determine the effect of the current environmental condition.