A successful session of collecting thermal imagery in the field requires that the survey planning take into account how to best use the factors and techniques that we can control and integrate them with those that we cannot control. This chapter deals with the effects of phenomena that have a dominating influence on the quality of imagery gathered in the field. The effects of the atmosphere, diurnal cycle, and continually changing micrometeorological conditions are beyond our control but must always be included in the planning of a data-gathering effort. In the sections that follow we provide insight on how these continually changing gifts of nature affect thermal images and how to best manage their deleterious side effects on the imagery and at the same time use the advantageous side of these effects to help optimize the detect ability.