Free gases in scattering media and different techniques for such studies are discussed in the present paper. Connections between two techniques that constitute a major research area at our laboratory are presented. One of the techniques concerns measurements of free gas in scattering media, such as human tissue and food products, on a small scale, while the other one is a technique for trace-gas measurements in the lower atmosphere. We show that the basic ideas are very similar and that, by applying the knowledge obtained on one scale to the other, little differences exist. This study motivates us to perform a measurement linking the two techniques.