Pacific Northwest National Laboratory (PNNL) has recently developed a hybrid infrared technique for standoff chemical detection. Active infrared detection typically involves a sender and receiver telescope separated by (100’s) of meters and is quite sensitive, but is extremely cumbersome to align and is extremely sensitive to misalignment as the two telescopes must not only be parallel, but coaxial. Passive infrared sensing offers facile alignment (simply point the input optics), but relies on a happenstance temperature difference ΔT between the chemical plume and its background. Oftentimes the ΔT found in the field is only 1 or 2 K, and the passive method is thus not very sensitive in many cases. The “semi-active” technique creates a large temperature difference ΔT by placing an extended blackbody source at some distance away from the receiver telescope. The blackbody is designed to fill the telescope’s FOV at a typical distance of 100 m, and provides a typical temperature difference ΔT on the order of 80 to 100 K. Design considerations and experimental results in a direct comparison of passive, active, and semi-active measurements will be discussed.