SSEC FAQ

Questions

  1. How are water vapor satellite images used?
  2. Where can I get printed Hubble Space Telescope pictures?
  3. How can I know when the Space Station is overhead?
  4. What do all those funny bunches of letters mean, in the advisories of the National Weather Service?
  5. What does "radiative transfer" mean?
  6. What does the GOES mean in GOES satellite pictures?
  7. What are weather satellites?
  8. What do the abbreviations and numbers in the captions of satellite images mean?
  9. What is GMT or UTC?
  10. Why do the satellite images have the distortion near the map lines?
  11. Why can't I get images and data via ftp anymore?
  12. What is the difference between IR 3.9 µm and IR 10.7 µm satellite images?
  13. How can I make my own weather animations or how can I get longer animations?
  14. What are MOS and MRF and what do they do?
  15. How do you interpret water vapor images? What do the different shades of darker and lighter regions mean?
  16. How can I save individual images that are in SSEC movies/animations?
  17. There are no 9:00 GMT GOES West images, visible or IR?
  18. How can I obtain an image/animation for a specific date/time, in a particular format or for a specific location?
  19. I am having problems viewing one of your animations?
  20. Where can I learn more about the AMRC icebergs?
  21. Can I use one of your images for ...? Is the content on this website copyrighted?
  22. Problems with the Lake Erie NOAA CoastWatch website
    (http://coastwatch.glerl.noaa.gov/modis/modis.cgi/modis?region=e&page=1)
  23. Do you have a satellite picture showing a particular place and time in which I can see people, buildings or cars?
  24. Why does the earth sometimes wobble in certain satellite movies / animations?


Answers

  1. How are water vapor satellite images used?
    Basically, water vapor images and loops/movies show how moist or dry the middle and upper atmosphere is. They also show the air circulation in the middle and upper atmosphere. For more information, refer to the following web page at the Verner E. Suomi Virtual Museum:
    http://ProfHorn.meteor.wisc.edu/wxwise/museum/a3/a3wv.html
  2. Where can I get printed Hubble Space Telescope pictures?
  3. How can I know when the Space Station is overhead?
  4. What do all those funny bunches of letters mean, in the advisories of the National Weather Service?
    These are terminology and phrases that are used frequently in forecast discussions and have been replaced with contractions. Refer to http://www.awc-kc.noaa.gov/info/domestic_contractions.html for more information.
  5. What does "radiative transfer" mean?
    The exchange of energy in the form of electromagnetic radiation, like light, between the earth's atmosphere, the surface of the earth, and space. Refer to http://cimss.ssec.wisc.edu/goes/comet_new/radiative_transfer.html for more information.
  6. What does the GOES mean in GOES satellite pictures?
    GOES is an acronym used for a series of U.S. weather satellites that stands for "Geostationary Operational Environmental Satellite."
    • Geostationary means that the satellite is always above the same location on the earth. The current GOES satellites, GOES-10 (West) and GOES-8 (East) are located above 135° west longitude, 0° latitude; and 75° west longitude, 0° latitude. Refer to http://www.ssec.wisc.edu/datacenter/real-time.html#satellite for more information.
    • Operational means that these satellites are used on a daily basis for a variety of applications, like weather forecasting. This is different from a research satellite that is used primarily for conducting research.
    • Environmental because the satellite measures a variety of environmental properties, including temperature, and moisture.
    • Satellite because, well, it's a satellite. Refer to "What are weather satellites" for more information.
  7. What are weather satellites?
  8. What do the abbreviations and numbers in the captions of satellite images mean?
    The caption on our satellite images, like
    6 MAR 02 - G-8 IMG - 10:15,
    usually contains the date
    "6 MAR 02"  =   March 6, 2002,
    an abbreviation for the weather satellite that recorded the image being viewed
    "G-8"  =   GOES-8 (additional acronyms),
    the satellite band (also called channel); i.e., visible, infrared, water vapor
    "IMG"  =   Visible light satellite image,
    (Additional information on interpreting satellite images in various channels)
    and the time, in GMT
    "10:15"  =   10:15 GMT .
  9. What is GMT or UTC?
    GMT stands for Greenwich Mean Time, now called UTC (Universal Coordinated Time), and is the local time at Greenwich-England, which is at 0° longitude. Weather observations, including satellite images, are recorded in GMT as a way of solving the problem of trying to use weather data from different time zones. For the U.S., here are the hours that must be subtracted from GMT time to convert to local time:
    PST (Pacific Standard Time):   8 hours
    MST (Mountain Standard Time):   7 hours
    CST (Central Standard Time):   6 hours
    EST (Eastern Standard Time):   5 hours
    (this information is for dates outside of Daylight Savings Time: during that time, subtract one hour less; i.e., subtract 7 hours to convert to PST during Daylight Savings Time). Additional references:
  10. Why do the satellite images have the distortion near the map lines?

    These are image compression artifacts. Many of the images we put online are in JPEG format, which uses what is called a "lossy" image compression method. What this means is that the JPEG format does not try to perfectly reproduce the original image, and image errors or artifacts can and do occur. In the case of our satellite images, these distortions near the map lines occur because the JPEG algorithm has problems with the sharp boundary between the gray-scale satellite image and the brightly colored map lines.

    We use this format because it makes the image file sizes smaller and therefore faster to download, especially over a modem connection.

    For many of our images, we also include the same image in GIF format, which uses what is called a "lossless" image compression method - the image is compressed so that it is perfectly reproduced. However, this means that the file size can be significantly larger and therefore longer to download.

  11. Why can't I get images and data via ftp anymore?

    Many of the images and data that were previously being served via ftp.ssec.wisc.edu are now only available through http. To view this data interactively just point your web browser to http://www.ssec.wisc.edu/data/

    To get it in an automated fashion you can use a tool such as wget or a free Java application called GetURL.

    One important thing to note - in many cases your ISP may be using web caching to speed up your page accesses. This is ordinarily 'invisible' to most users, but if you use automated tools you may get 'stale' data. To ensure you get the latest data:

    1. wget - use these option:

      wget --cache=no --header='Cache-Control: max-age=0, no-cache' ...url...
    2. GetURL (a Java application) has been modified to always get a non-cached copy. You can get it from: http://www.ssec.wisc.edu/~tomw/geturl
    3. If you are using some other application, be sure that it adds these two HTTP directives to every request:

      Cache-control: no-cache, max-age=0
      Pragma: no-cache
  12. What is the difference between IR 3.9 µm and IR 10.7 µm satellite images?
    These are two different wavelengths of infrared radiation. IR 3.9 µm images are useful for seeing fog at night, differentiating between different types of clouds, measuring the temperature of the surface of the sea, and many other uses.

    Some of the uses of IR 10.7 µm images include identifing severe weather as well as areas of heavy rainfall.

    See also:
    The CIMSS GOES Sounder and Imager Page
    Interpreting Satellite Images (Suomi Virtual Museum)
  13. How can I make my own weather animations or how can I get longer animations?
    You can create your own animations using one of the same tools that is used on the SSEC website: FlAniS or AniS.

    Regarding creating longer animations, we do not archive the images that go online, so we are generally unable to provide longer animations upon request. One possible solution to this is to periodically download the images you wish to animate over the time frame that you wish to view and to then use FlAniS or AniS to animate on your own machine. To download images that are being animated with either FlAniS or AniS, click on the "Stop" button, and then click on the "Show" button - this will display the image currently being displayed in a new window where you can save it (either via "File" --> "Save As" or right-clicking on the image and saving).

    If you are interested in purchasing customized data products, please contact the SSEC Data Center.
  14. What are MOS and MRF and what do they do?
    Model Output Statistics (MOS): The Hydrometeorological Center of the National Environmental Prediction Centers (formerly National Meteorological Center) produces a short range (6 to 60 hours) MOS (Model Output Statistics) guidance package generated from the NGM (Nested Grid Model) for over 300 individual stations in the continental United States. These alphanumeric messages are made available at approximately 0400 and 1600 UTC for the 0000 and 1200 UTC forecast cycles, respectively. Model Output Statistics are a set of statistical equations that use model output to forecast the probability of precipitation, high and low temperature, cloud cover, and precipitation amount for many cities across the USA. The statistical equations were specifically tailored for each location, taking into account factors such as each location's climate. To indicate snow and precipitation type forecasts, the message varies between the cold (September 16 through May 15) and warm (May 16 through September 15) seasons. Snow and precipitation type forecasts are never issued for certain Florida and California stations.

    For more information refer to the following webpages:
    http://www.ssec.wisc.edu/localweather/ located in MOS Guidance for Madison.
    http://www.ssec.wisc.edu/cgi-bin/lc?mos MOS on the SSEC web page.
    The MOS definition is from the NOAA web page http://www.crh.noaa.gov/dtx/?page=glossary/m.

    MRF - Medium-Range Forecast model: One of the operational forecast models run at NCEP. The MRF is one of the main models forecasters use for the medium range time period beyond 48 hours into the future. It is run twice daily (0000 UTC and 1200 UTC). The MRF model forecasts for the entire northern hemisphere, unlike the national models, which only forecast for North America. The resolution of the MRF model is about 150 km, which is far less than the national models. The MRF is primarily used for the medium range time period from 60 to 240 hours (10 days) into the future. The MRF, like the previous models, has its own set of Model Output Statistics (MOS) equations known as MRF MOS.

    For more information, refer to the following web pages:
    http://www.ssec.wisc.edu/localweather/ under MRF Forecast.
    http://www.ssec.wisc.edu/cgi-bin/lc?mrf MRF Forecast for Madison.
    The MRF definition is from the NOAA web page http://www.crh.noaa.gov/dtx/?page=glossary/m.
  15. How do you interpret water vapor images? What do the different shades of darker and lighter regions mean?
    Moist regions of the mid-troposphere are gray, and dark areas in the image represent dry regions. http://cimss.ssec.wisc.edu/wxwise/class/wvexample_mk.gif

    Refer to this page - http://profhorn.meteor.wisc.edu/wxwise/museum/a3/a3wv.html for more information.
  16. How can I save individual images that are in SSEC movies/animations?
    To download images that are being animated with AniS, click on the "Stop" button, and then click on the "Show" button - this will display the image currently being displayed in a new window where you can save it (either via "File" --> "Save As" or right-clicking on the image and saving). If the animation in question does not have a "Show" button, please let us know: SSEC Webmaster (make sure to send us the URL of the animation).
  17. There are no 9:00 GMT GOES West images, visible or IR?
    The GOES satellites enter what is called an eclipse season twice a year near the equinoxes. The eclipse season lasts about 2 months. During eclipse season, orbits of geostationary satellites enter Earth's shadow every day. Since most Weather Geostationary satellites are solar powered, and their battery is not able to last through out this period, imaging is suspended during the pass through the shadow. The length of this outage varies through out eclipse season.

    The latest eclipse schedules for data collected at SSEC can be found at:

    http://www.ssec.wisc.edu/datacenter/eclipse.html
  18. How can I obtain an image/animation for a specific date/time, in a particular format or for a specific location?
    Unless specifically noted, we do not archive the free image products that appear on our website nor do we provide specific images/animations other than what is on our website. However, the SSEC Data Center does archive "raw" data from all the geostationary satellites. They can also reproduce any non-project specific product that appears on the SSEC website, as well as custom data/imagery. If you are interested in purchasing a specific image or set of data that is no longer available on our website or any other imagery, you can contact the SSEC Data Center.
  19. I am having problems viewing one of your animations?
    1. First, determine if the animation you are viewing is using our AniS Java applet or our Flash Flanis tool. Usually, if you can't right click on the image then the animation is using a Java applet. If you can right click on the image and one of the options is something like "About Adobe Flash" then the animation is using Flash.
    2. Then, use one of the following pages to determine if you have the appropriate plugin installed and working properly:

      For Java animations

      For Flash animations

    Additional information on our Java animations

    If you have any questions or have reason to believe that the issues you are dealing with are due to a problem on our end rather than with your computer or browser, please contact us. However, please note that we do not and can not provide you with technical support to fix problems with your computer or web browser.

  20. Where can I learn more about the AMRC icebergs?
  21. Can I use one of your images for ...? Is the content on this website copyrighted?
    Please see our Disclaimer and Image Usage page
  22. Problems with the Lake Erie NOAA CoastWatch website
    (http://coastwatch.glerl.noaa.gov/modis/modis.cgi/modis?region=e&page=1)

    If you are having problems with the NOAA CoastWatch Lake Erie MODIS Imagery website (http://coastwatch.glerl.noaa.gov/modis/modis.cgi/modis?region=e&page=1) please be aware that SSEC is not responsible for that website and you will need to contact the NOAA CoastWatch webmaster for issues regarding their website.

    SSEC does have our own real-time MODIS imagery website that you might consider as an alternative: MODIS Today

  23. Do you have a satellite picture showing a particular place and time in which I can see people, buildings or cars?

    The majority of satellite imagery that SSEC focuses on, such as GOES, NOAA polar satellites, Aqua/Terra, etc., is geared towards viewing Earth's meteorology, oceanography and climate and does not have the spatial resolution to see things like people or cars. For example, the MODIS instrument on the Aqua and Terra satellites has a resolution of 250 meters which means that it can't resolve anything smaller than that. However, the WisconsinView organization which operates here at SSEC does work with high resolution satellite imagery that could be of use for observing smaller scale objects/places on the ground.

    Specifically, WisconsinView maintains a free online archive of civilian public domain color satellite imagery and aerial photos of Wisconsin with spatial resolutions ranging from 15cm (6-inch) to 250m (273yds). The higher resolution imagery is generally collected statewide by USDA contract aircraft during annual or semi-annual NAIP (National Agricultural Imagery Program) surveys conducted between June and August. Special collections over urban areas or during "leaf-off" early spring may be available at less frequent intervals. New imagery is posted shortly after it is received, usually 3-6 months after acquisition. We do not have access to any high resolution real- or near real-time imagery. The date-stamped 1-meter imagery of the archive has been found useful for settling property or permit disputes but is generally not collected frequently enough to aid in search and rescue applications for which there are occasional inquiries.

    For large natural disasters such as floods and tornadoes, the Landsat 30m imagery (available every 8-16 days) and MODIS 250m imagery (available daily) can be used to map damage extents or swaths for emergency management. This coarser resolution imagery is generally available within hours after it is collected, but ground observation is limited by potential cloud cover.

    For more information visit the WisconsinView website.
  24. Why does the earth sometimes wobble in certain satellite movies / animations?

    The reason for this is that some geostationary satellites have high inclination orbits, and the imagery is not rectified onto a common projection before being displayed.

    Some background:
    Normally geostationary satellites stay directly over one location on the earth directly over the equator. Over time the satellite drifts slightly, so orbit corrections (or maneuvers) are performed to keep it over the equator. As satellites run low on fuel, those orbital corrections are made less often or sometimes not at all. This causes the orbit to become more and more inclined with respect to the equatorial plane. Looking at the satellite from the surface of the earth (if you had a very powerful telescope) you would see the geostationary satellite actually following what looks like a figure eight path. As the inclination gets very large, the figure eight gets very large … some times a few degrees from the equator. From the satellite perspective, the satellite will view the earth at different angles along its figure eight path. The images then presented will look like the earth is wobbling, when in reality, it is the satellite viewing the earth from different angles.

    Note, this occurs on all geostationary satellites, but in some cases, (such as GOES-East and GOES-West) the inclination is so small, that there will be no perceptible wobble. In other cases, the satellite may have a high inclination orbit, but the image is rectified before being used. Or finally in some cases, like Meteosat over 0° E, and MTSAT, the inclination is small, and the images are rectified, so no wobble is seen there for both reasons.