Proposed are two passive ranging approaches using a single camera, based on intensity and contrast measurements. According to the Beer-Lambert law and known atmosphere extinction coefficient and initial range, the range to a moving object is estimated. Using these approaches in a real infrared surveillance sequence, better results are obtained than with methods which use image size measurements. The relative error of 3.2% for contrast and 2.3% for intensity features are obtained. Results indicate that range estimation is possible to a fidelity required for object tracking.