Poor
Good
Best
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BestFor a given area four versions of the image are available. The two buttons on the left of the page link to JPEG images highly compressed so some loss of quality is visible but downloading time is minimized. The two buttons on the right are links to GIF images. Use the right-most button if you have a fast connection. A map showing the complete satellite pass is given under the word "pass". Areas close to the centerline of the pass will have higher resolution. Also the sun altitude is shown on the pass map. The satellite direction is given in the map text: ascending passes were traveled from south to north. The NOAA AVHRR data used to make these images has 5 channels. For daylight passes 3 channels are used to make a color composite image. Channel 1 is visible and is colored red. Channel 2 is near infrared and is colored green. Channel 4 is thermal infrared and is colored blue after reversing the brightness to make the clouds bright instead of dark. Vegetation reflects highly in the near infrared so land areas often show as green. Cloud colors vary depending on their temperature. Low clouds are warmer and appear darker in the reversed channel 4, high clouds appear brighter, and since channel 4 is colored blue the low clouds will apear more yellow and the high clouds more white or blue/white. Cold water will show as brighter blue than warmer water on the color composites. Nighttime passes use only reversed channel 4 images so are black and white. Twilight images use a blend of the color composite and the black and white images.
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:
| Small images: | Poor |
Good |
Best |
| Large images: | Poor |
Good |
Best |
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.
Web page by:
Ray Sterner
http://fermi.jhuapl.edu/res