Enhancing GOES Channel-2 IR (3.9 um) Imagery

GOES shortwave infrared data are unique in that most of the energy sensed at that wavelength (3.9 um) is emitted from the earth's surface and clouds. During the daytime, however, some of that energy is composed of solar radiation reflected from the earth's surface and clouds, with the amount reflected depending on the albedo at 3.9 um. Three images (one un-enhanced and two with different enhancements) are presented to show steps to enhance imagery in this portion of the spectrum.
Inverted IR (ch.-2, 3.9 um)

This un-enhanced GOES channel-2 (3.9 um) image is available in 8-bit (0-255) display counts. This is the starting point for the two enhancements that follow. The 8-bit count values have been converted into temperatures which are written above the gray bar on the bottom of all images. The temperature scale is bi-linear with a 0.5 degree C per count resolution for temperatures warmer than -31 degrees C [242 K], and 1 degree C per count resolution for temperatures below that value. This temperature scale is the standard Look Up Table (LUT) applied to all GOES infrared channels except those for the water vapor channel available for AWIPS distribution. See: http://www.cira.colostate.edu/RAMM/cal-val/wvgini.htm

The original channel-2 image can be enhanced by inverting its gray shades. Some users of this shortwave infrared channel prefer this view since the added solar component often makes reflective cloud tops look dark in a non-inverted display. An inverted enhancement returns the thickest (and generally more reflective) cloud tops to brighter shades and the thinner (less reflective) cloud tops to darker shades.

Another way to enhance the channel-2 image is by the use of a fixed color enhancement table. In this image the inverted gray shades in the previous image are colored from white to black, and then to blue. The different shades of blue help the viewer distinguish variations in cloud reflectivity. Generally, the more reflective clouds have warmer effective temperatures due to the added reflected component, and the less reflective clouds have cooler effective temperatures due to a lack of that reflected component of radiation. This enhancement helps distinguish water (more reflective) clouds, which are colored very light gray, from ice (less reflective) clouds, which are colored black or turquoise.