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Visual Imagery
Water Vapor Imagery

Aerographers Mate, Module 03-Environmental Satellites and Weather Radar
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same  as  visible  light  (longer  wavelength  infrared energy is absorbed). Satellites normally carry sensors that measure energy levels in several specific bands of infrared  wavelengths,  and  the  radiation  measured  is directly related to the temperature of the different radiating  surfaces. Since all surfaces radiate some amount of thermal (heat) energy, a major advantage of infrared satellite imagery is that it is available even when the earth is dark. Energy levels are measured much  the  same  way  that  visual-range  energy  is measured. The individual measurements from each pixel, when composed into an image of the earth, form an  infrared image. Most infrared satellite imagery is measured at wavelengths of 10.2 µm to 12.8 µm (far infrared). Some satellites are able to augment visual and far infrared  imagery  by  also  measuring  near  infrared (NIR) wavelengths (.74 µm to 2.0 µm). NIR imagery generally   shows   better   land/water   contrast   and simplifies low-level feature identification, such as shorelines,  snow/ice,  and  vegetation. The  satellite  receiver  and  processor  control  how the composed image will look. Normally, the energy measurements for infrared image pixels are assigned g-ray shades with low-energy readings appearing white and high-energy readings appearing black. The lighter the gray shade, the colder the object seen. With IR images, space surrounding the earth is white, and warm land or water masses are dark gray or black. Infrared  imagery  is  an  excellent  tool  for oceanographic analysis, such as evaluating sea surface temperatures  and  determining  ocean  front  and  eddy locations.  It  is  also  very  helpful  for  identifying  high clouds and upper-level wind flow, but less reliable for identifying low-level features. Look at figure 1-12. Notice how lower level clouds, very distinct in the visual image, are more difficult to determine in the Figure 1-12.—GOES visual image on left compared to GOES infrared (IR) image on right. Space and cold cloud tops appear white and warm water and land areas appear dark gray to black in an IR image. 1-12







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