The next three satellites in the current GOES series, GOES-M thru O, with the first to be launched in summer of 2001, will have slightly changed Imager instruments, with a new band (band-6) at 13.3 um. The new band was introduced to help with winds from cloud motion. Unfortunately this band is not an additional band. Instead, it replaces the 12.0 um band (band-5) used to identify atmospheric dust, smoke, and ash.

In order to simulate the effect of the new band on usage of GOES for volcanic ash detection, selected bands of Moderate Resolution Imaging Spectroradiometer (MODIS) data were used. MODIS contains 36 bands, and six of those bands have central wavelengths that correspond nicely to the six (old and new) GOES bands.

To determine the effect of the band change on GOES-M, the new band was substituted into a volcanic ash product that is used operationally by the Washington (DC) Volcanic Ash Advisory Center (VAAC). That product consists of image differences generated by Principal Component Image (PCI) analysis of the three GOES IR bands (bands 2, 4, and 5). The band 2/4 difference in PCI-2 shows volcanic hot spots, and the band 4/5 difference in PCI-3 is the best for detection of the volcanic ash plume. Two test versions of the PCIs were generated, one using simulated GOES bands 2, 4, and 5; and the other using simulated GOES bands 2, 4, and 6. The much-simpler two-band split-window image difference was also simulated using the old and new bands.

Results show that the simple two-band difference technique is not suitable for ash detection with the new GOES-M band-6, when simulated using MODIS data. Rather a three-band difference shows the ash plume better, although not as well as that with the old set of GOES bands. The choice for the ash analyst is to either generate PCIs directly from the new set of GOES-M bands or utilize a similarly-configured three-band difference of GOES-M bands.