  The 12-micrometer channel on GOES-11 has been replaced by the 13.3-micrometer
channel on the latest geosynchronous satellite, GOES-12. There has been concern
that this 13.3-micrometer channel will not be as accurate in detecting volcanic
ash. Volcanic ash is highlighted using a special volcanic ash algorithm, an
arithmetic combination of the brightness temperatures as measured by three
channels, yielding a unitless brightness count whose values comprise an IR
image. Degradation in cloud detection, especially low clouds, was also
expected. IR data from GOES-11 and GOES-12 for two Mexican volcanoes, Colima
and Popocatepetl, was analyzed. The data indicates that, in general, the
GOES-11 volcanic ash algorithm with the 12-micrometer band provides much better
data for various types of clouds. It emphasizes the importance of the
12-micrometer band and provides scope for future research in this area.
