With the early TIROS, visible imagery showed clouds as bright white and ground as dark, a direct relationship between scene energy and image grey scale. When the first longwave infrared (IR) imagery was received and visible lookup tables were used to display the data, high energy areas (ground and ocean) were white and low energy areas (cirrus and thunderstorm tops) were dark. This was opposite from the convention analysts were accustomed to using. As a result, it was decided to invert the IR display table so that low infrared energy was displayed as white and high infrared energy as dark. This has served us well for many years, but now, since the 3.9 um channel senses both reflected and emitted radiation during the daytime, a choice must be made as to how that channel should be displayed. (Perhaps, in time, it will be presented as a derived image product, in combination with one or more other channels.)
In this tutorial the 3.9 um imagery is presented in terms of energy vs. grey scale (as with the VIS imagery), cold clouds, ice, ice clouds and snow appear dark; while warm surfaces, water clouds and sun glint appear light-to-bright (sun glint at 3.9 um is much more intense than at visible wavelengths). Land surfaces, being both hot and reflective, can appear very bright. Alternatively, the 3.9 um information may be presented as any one of the other wavelengths/channels. Whatever choice is made, the user must analyze the information in terms of energy and cloud/surface type to minimize confusion. See a winter storm example for comparing the presentation of the different imager channels.