To get the clearest image possible, satellite sensors are typically created to be most sensitive to photons with a wavelength in an “atmospheric window”, where atmospheric transmissivity is at its highest      This way, more photons reach the satellite sensor, translating into a stronger electrical signal from which to create an image However, sensors can also make use of the fact that a certain molecule (such as water vapor, ozone or carbon dioxide) creates a lower atmospheric transmissivity      By making a satellite sensor that receives photons from these non-window regions, images are created that show variations in the molecular composition of the atmosphere           Example:  Water vapor imagery is created by looking near the 6.7 micron wavelength, where atmospheric water vapor absorbs many of the outgoing photons

Note the obvious differences between this false color (blue-tinted) visible and a thermal infrared image, taken from the GMS-5 geostationary satellite at the same time      The visible image has a “terminator” or shadow line at the top left of the image.  This is created because the angle of the sun does not fully illuminate the entire globe from the GMS-5 satellite’s perspective at this time of day      Australia is easily seen in the visible image, but invisible in the IR.  This is because at this time of year and this time of day (late morning) there is not a large difference in the temperature of the land mass compared with the ocean      The visible image shows more stratus and stratocumulus clouds while the infrared shows more (and denser) cirrus clouds.  This is typical and will be discussed in future training

Note the obvious differences between thermal IR (usually just called IR) and water vapor IR (usually just called water vapor) images from the same satellite at the same time      It is easy to tell from thermal IR the cloud top temperature; water vapor is more ambiguous      The presence of the polar front jet is easy to see in water vapor imagery, even without the presence of a comma cloud or baroclinic leaf

     The microwave image is cruder, yet can distinguish which parts of the cirrus shield around the tropical cyclone have regions of active convection (cirrus clouds do not show up on microwave imagery)