Handout (459.6 kB)
Among the ABI bands, the 3.9 ìm band is of primary interest because its greater sensitivity to warm temperatures and the desire to capture very hot scene temperatures for detection and characterization of hot spots (e.g., forest and range fires). Thus this shortwave infrared (IR) band has a specified instrument maximum scene temperature of 400 K, much greater than the specified temperatures for the other ABI bands. Due to the finer field-of-view size of the ABI (compared to the current GOES imager), this hotter saturation temperature is needed. However, of the IR bands, this band suffers the most from increasing noise (in temperature units) at low scene temperatures, as a result of the basic physics of the Plank equation for shorter wavelengths. Of course this same shortwave band is also used for cloud characterization on the cold temperature end. Temperature noise in this band is much greater at low temperatures than that for the other ABI bands and can be an undesirable feature of the increased instrument maximum scene temperature. In particular, this band seems to require a 15-bit scale to meet ABI specifications, but that would still result in a quantization noise per count step of 2.1 K @200 K. Thus, it appears that a higher-resolution scale, or a 16-bit scale in this case, is more desirable, resulting in a quantization noise per count step of 1 K @200 K.