Day 62: Identifying Low Clouds with Satellite
Above is a visible satellite image from 2045 UTC (2:45 PM CST) today (3 March). A visible satellite image is the equivalent of a photo – it is what a human would “see” if he or she were located where the satellite was located. One issue with visible satellite imagery is that it is hard to distinguish between “high” clouds and “low” clouds. Also, any snow on the ground will show up as white in the satellite “photo” making it hard to identify what might be clouds and what might be snow in places where there is a lot of snow on the ground (i.e. Iowa!). Take the image above, there are several areas where the predominant cloud type is actually low clouds and fog. Can you identify where they are? Can you distinguish between what is snow cover and what might be clouds?
To help aid meteorologists distinguish between areas of low clouds and high clouds, researchers developed ways of using satellites to “see” clouds in ways that humans can’t. This is done in a variety of ways by “looking” at the various different forms of radiation that are emitted from the earth. Without going into a whole lot of details, objects at different temperatures emit radiation at different wavelengths. This means that if a satellite “looks” at these different wavelengths, it can determine the temperature of the cloud. From this, meteorologists can determine if a cloud is low (typically warmer) or high (typically colder). By combining different wavelengths, meteorologists can get an even better idea of where the clouds are located. Also, using combination techniques it is possible to differentiate between snow cover and clouds.
The image above uses a combination of radiation wavelengths to help forecasters determine if a cloud is a low cloud or a high cloud. Low clouds tend to be bright white and smooth where as higher clouds tend to be “bumpy” and have variations in color. Based on that, can you identify several areas of low clouds? The image below has three such areas highlighted. Also, notice anything different about Iowa?
Thanks for mentioning IA. Iowa is currently experiencing gradual but significant thawing and melting, so the satellite image will hopefully look much different next week at this time… if we aren’t under water by then