SATELLITE INTERPRETATION DISCUSSION

Two significant changes have been made to the Imager on GOES-12 (launched on 23 July 2001). Data from GOES-12 are available for the 5-week NOAA Science Test period (23 September through 27 October 2001).

A web page with a schedule of the tests executed each day of the Science Tests is available at: http://www.cira.colostate.edu/ramm/goesm/test_schedules.htm

Results of the Science Tests are available at:
http://www.cira.colostate.edu/ramm/goesm/test_results.htm

Changes to the Imager instrument on GOES-12 (and successive GOES) compared to previous GOES-8 through 11

Table 1 explains the differences between bands utilized by the two versions of the GOES Imager. Both versions have five bands. The current Imagers (on GOES-8 through 11) contain bands 1 through 5 and the GOES-12 Imager contains bands 1 through 4 and 6. Note as well the change in the spatial (line) resolution of the band-3 image.

Table 1: Basic information on the GOES Imager bands

GOES Imager Band	Wavelength Range (µm)	Spatial Resolution (km) at Nadir (East-west x north-south)	Meteorological Objective
1	0.55 to 0.75	0.6 x 1	Cloud cover and surface features during the day
2	3.8 to 4.0	2.3 x 4	Cloud phase (day and night)
3	6.5 to 7.0	2.3 x 8 (GOES-8 through 11) 2.3 x 4 (starting GOES-12)	Upper-level water vapor
4	10.2 to 11.2	2.3 x 4	Surface or cloud top temperature
5	11.5 to 12.5	2.3 x 4 (GOES-8 through 11)	Surface or cloud top temperature and low-level water vapor
6	12.9 to 13.7	2.3 x 8 (starting GOES-12)	Cloud detection

Changes to the GOES-12 Imager compared to previous GOES (8 through 11) include:

New band-6 image at 13.3 µm at 8 km spatial (line) resolution at nadir. This replaces band-5 image at 12.0 µm.

Water vapor (band-3) image now available at an increased 4 km spatial (line) resolution, compared to the 8 km (line) resolution on current GOES. The spectral response of the water vapor band was also shifted slightly and broadened.

Examples of both of these new features are shown and explained below.

New band-6 at 13.3 µm:

Figure 1 contains examples of each of the five bands available on the GOES-12 Imager. The band-5 image on current Imagers looks very similar to band-4 image, with only slight differences in radiance or temperature for most of the scene. Larger differences between the images generally occur for portions of the image that view thin cirrus or clouds edges.

The new band-6 image has a smaller transmittance of surface radiation and more emission of radiation from the lower levels of the atmosphere, making it easier to detect cloud features in the band-6 image when utilized along with the band-4 image. In addition, notice the reduced line resolution (8 km) of the band-6 image compared to the line resolution (4 km) of the other infrared bands.

Figure 1: Examples of GOES-12 bands 1 through 4 and 6 with color enhancements applied to the infrared bands.

Water vapor (band-3) image now available at 4 km spatial (line) resolution:

To show the effect of the increased spatial (line) resolution for the water vapor (band-3) image, a water vapor image was processed to simulate the lower spatial resolution available on previous GOES Imagers. Figure 2 contains two reproductions of the upper-left portion of the water vapor image from Figure 1. That image is shown both at full resolution (4 km, on top) and at reduced resolution (8 km, on bottom). The blockier look of the bottom image is accentuated by the 2 km display, replicating each pixel in the image by a factor of 2.

Figure 2: Upper left portion of the water vapor (band-3) image from Figure 1. That image is shown both at full resolution (4 km, on top) and at reduced resolution (8 km, on bottom) to show the effect of increased resolution.
The cloudy portions of both images are color enhanced.