Water Vapor Imagery

infrared image when surface temperatures and cloud top temperatures are relatively the same. Water Vapor Imagery Concentrations of water vapor in the atmosphere absorb essentially all 6.7 µm radiation coming from below. Thus, one of the infrared sensors carried aboard the GOES and the METEOSAT measures radiation at this wavelength. When the energy measurements from this type of sensor are composed into an image, the result, shown in figure 1-13, is called a water-vapor channel or WV image. Areas of high water-vapor content (high humidity) appear in the lighter gray shades while lower humidity areas appear darker. The main advantage of the water vapor channel is better definition of the moisture distribution in the upper atmosphere. If moisture is present in the upper levels, we associate this with upward vertical motion. Conversely, upper-level dryness is a good indication Figure 1-13.—GOES full disk (hemisphere) infrared water-vapor (WV) channel image (top) and full disk visual (VIS) image (bottom) at the same time. The WV image shows a better depiction of the extent of the system than the VIS image. 1-13