J. Braun and Louis Grasso
Figure 1: GOES-11 fog product for 8 UTC 2 March 2010.
Identification of liquid water cloud layers that have temperatures below freezing is important for aviation safety. Brightness temperature differencing two channels may be used to identify liquid water cloud layers. Figure 1 (above)shows the channel difference between 3.9 and 10.7 µm from GOES-11 prior to sunrise. A liquid water cloud layer (white) is evident over Nebraska, western Kansas, and western Oklahoma. 
Figure 2: GOES-11 (10.7-12.0) µm channel difference for 17 UTC 2 March 2010.
Nine hours later, the channel difference between 10.7 and 12.0 µm from GOES-11 (Figure 2 – above) indicates the same cloud liquid water cloud layer over central Nebraska and northern Kansas(red). MODIS imagery also captured the same cloud layer at 830 UTC at 3.9 µm (Figure 3 – below). Brightness temperature differences of MODIS imagery between 8.53-11.02 µm (Figure 4 – below) and 8.53-12.03 µm (Figure 5 – below) are unable to reveal the cloud layer. This is due to the lack of contrast between the liquid water cloud and the surrounding ground.
Figure 3: Modis 3.9 µm at 830 UTC 2 March 2010.
Figure 4: Modis 8.53 – 11.02 µm for 830 UTC 2 March 2010.
Figure 5: Modis 8.53 – 12.3 µm for 830 UTC 2 March 2010.
However, brightness temperature differences of MODIS imagery between 11.02 – 12.03 µm does reveal the liquid water cloud layer (Figure 6 – below). These examples highlight the benefit of channel differencing to identify liquid water cloud layers. When this information is combined with the GOES-11 skin temperature (Figure 7 – below), one can see that the liquid water cloud layer, shown in the above figures, has a cloud top temperature below freezing. This may be valuable information to those concerned with icing potential of aircraft.
Figure 6: Modis 11.02 – 12.3 µm for 830 UTC 2 March 2010.
Figure 7: GOES-11 skin temperature at 17 UTC 2 March 2010.