Detecting Surface Features in Water Vapor Channel Imagery (Part 2)

December 18th, 2006 |

GOES-11/GOES-12/GOES-13 water vapor images

Another example of detection of surface features on “water vapor channel” imagery was apparent on 18 December 2006. In this particular case, the “surface” was the high terrain of the Absaroka Range, Wind River Range, and Big Horn Mountains in Wyoming (all of which reach altitudes in excess of 13,000 feet / 4000 m), making it easier to sense radiation from the ground using the 6.5µm/6.7µm water vapor channel. Since this channel is essentially an InfraRed (IR) channel, the cold temperature signature of the snow-covered mountain features (morning temperatures were as cold as -30 F / -34 C at Old Faithful in Yellowstone Park, where 22 inches / 56 cm of snow were on the ground) was very obvious against the warmer background temperature of the surrounding bare ground at lower elevations. Very little water vapor was present within the atmospheric column, so the water vapor channel weighting function (calculated using the Riverton, Wyoming rawinsonde profile) for both GOES-11 and GOES-12 peaked at an altitude just below 500 hPa (very near the altitude of the aforementioned mountain features).

A Java animation of GOES-11, GOES-12 and GOES-13 water vapor imagery shows that the mountain features become more apparent as a drier pocket of air passed over the region. Due to the higher spatial resolution (4km) of the spectrally-wider 6.5µm water vapor channel on both GOES-12 and GOES-13, the mountain features are resolved with greater clarity compared to the 8km resolution 6.7µm channel on GOES-11. In addition, since the mid-tropospheric winds across that region were fairly light (and generally parallel to the orientation of the terrain), there were no “mountain wave” signatures to the lee of these mountain ranges.