The NOAA AVHRR data used to make these images has 5 channels. For daylight passes channel 2, near infrared, is used. Channel 4, thermal infrared, is used when it is too dark for channel 2. Channel 4 images show cold clouds as dark and warm water as bright.
Not all passes that include the area of interest are useful. Pass quality is rated as Poor, Good, and Best. The worst passes are weeded out entirely. To be included a pass must cover at least 50% of the area of interest and have a central resolution no worse than 2.8 km. Such passes are rated Poor. Good passes must have a minimum coverage of at least 70% and no worse than 2 km central resolution. The Best passes must cover at least 80% and have a central resolution of 1.5 km or better. Two image sizes are included. The image size and quality is indicated by the button size and color:
The images are geographically registered. Fine tuning of this registration is called image navigation and is done automatically for these images. Sometimes for various reasons the images are not registered so well. Close inspection may show some misregistration between the plotted coastlines and the real coastlines in the image. The coordinates labeled on the sides of the image correspond to the plotted coastlines so allowances must be made for any errors in registration.
For storm track plots and higher quality images see the JHU/APL Hurricane Track Map web site.
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