Atmospheric Characterisation, is not just about Characteristics of Atmosphere, rain, hot-dry wind, bombastic ice, sleet, inside a high-pressure burst onto a certain, random point in the desert.
In fact, it seems to me, to be some sort of way or means of measuring celestial bodies in the heavens around us, relatively, which we don’t know about, but are seeking to find.
It like most stuff outside our solar system even, is denoted, or the Folks who do this kind of “measuring”, divining, detection, do so by “near area” READING. That is to say, we find a body in space, by looking at bodies around it, and studying how they act, and based on what we know already (assuming about how things in the universes we do ‘know’), we infer that there’s something else nearby, which affects it. Therefore, something else must be around. There is more to the picture than what meets the ‘eye’, as it were. At least, as I understand it, this is what is.