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Snow Storm of 1997

AVHRR Imagery

The Advanced Very High Resolution Radiometer (AVHRR) is a sensor that is mounted on the NOAA series of meteorological satellites. There are currently two such satellites in polar orbit which takes them around the Earth approximately every 102 minutes, NOAA-12 and NOAA-14. This orbital period allows for 14.1 orbits per day with the satellites orbiting on opposite sides of the Earth.

There are several data sets that are available from the NOAA AVHRR sensor:

  • HRPT - High Resolution Direct Readout AVHRR
  • LAC - Recorded HRPT AVHRR
  • GAC - Reduced Resolution Recorded AVHRR

TOVS - TIROS Operational Vertical Sounder, which includes:

  • MSU - Microwave Sounding Unit
  • SSU - Stratospheric Sounding Unit
  • HIRS/2 - High Resolution Infrared Radiation Sounder/2

For more information about each of these, the reader is referred to the NOAA website located at: http://perigee.ncdc.noaa.gov/docs/intro.htm

The Center for Advanced Land Management Information Technologies (CALMIT), located here at UNL, receives the HRPT product and maintains a month-long image archive it which is available for download. The CALMIT website is located at http://calmit.unl.edu/; just follow the directions on how to reach the archives.

The five bands that are available on the website are listed below:

Channel 1 2 3 4 5
Wavelength .58 - .68 .73 - 1.10 3.55 - 3.93 10.3 - 11.3 11.5 - 12.5
Description Reflected Visible Reflected Near-infrared Emitted Thermal Emitted Thermal Emitted Thermal

Although designed for meteorological purposes, the AVHRR sensor has been used to assess landcover and landuse all over the Earth. A representation of this can be seen below:

This Image is from the NOAA-14 Satellite and was acquired on October 17, 1997. The colors that you see are the result of two of the bands being represented by the colors of red, green and blue. In this image Band 2 (the reflected near-infrared) is being represented by red, while Band 1 is being represented by the colors of green and blue. In this representation, the presence of vegetation is represented by tones of red. The darker-toned red feature near the top of the image is the South Dakota Black Hills. The similar feature toward the left of the image is the Colorado Front Range. The state of Nebraska is located in the center of the image. The other reddish-toned features are probably either agricultural crops, or natural vegetation.

This is a particularly useful representation to observe the extent of the snowcover that resulted from the October snowstorm as you can see in the figure below.

As you can see the snow coverage is a particularly narrow band, extending from Colorado in an east, northeast direction. The depth of the snow varied considerably as the figure below illustrates.

Although the preceeding two figures do not cover exactly the same area, they combination of the two provide a good indication of the extent and depth of the snow cover that can be observed form satellite imagery.

Although the bands of information shown in the AVHRR images show a lot of detail, such a representation cannot be obtained from the GOES satellites.