ection 4
What is direct readout?
D i rect readout is the capability to acquire information directly from environmental
(also called meteorological or weather) satellites.
Data can be acquired from U.S. satellites developed by NASA and operated by NOAA,
as well as from other nations’ satellites.
How do I get direct readout?
By setting up a personal computer-based ground (Earth) station to receive satellite sig-
nals. See a station configuration in the Ground Station Set-up chapter on page 119.
The electronic satellite signals received by the ground station are displayed as images
on the computer screen.
Imagery can be obtained from both geostationary and polar-orbiting satellites. The
low-resolution images (obtainable with the relatively inexpensive ground station equip-
ment) from U.S. satellites are:
- Weather Facsimile or WEFAX images, transmitted by GOES satellites. WEFAX trans-
missions are not real-time: the images are first transmitted to NOAA for initial pro-
cessing and then relayed back to the satellite for transmission to ground stations.
The slight delay enables the inclusion of latitude and longitude gridding, geopolitical
boundaries, weather forecast maps, temperature summaries, cloud analyses,
polar-orbiter imagery, etc. WEFAX has a resolution* of 8 kilometers for visible
images and 4 kilometers for infrared images. WEFAX images are broadcast on a
fixed schedule, 24 hours a day.
- Automatic Picture Transmission or APT is available from polar-orbiting satellites. APT
is real-time transmission, providing both visible and infrared imagery. The image
obtained during a normal 14 minute reception period covers a swath appro x i m a t e l y
1700 miles long. For example, a ground station in Baltimore will acquire an
Eastern U.S. image bordered by Cuba (S), Quebec (N), Minnesota (W), and the
Atlantic Ocean (E) from a typical satellite pass.
*Resolutionindicates the area represented by
each picture element--pixel--in an image. The
lower the number, the higher the resolution or
detail. For example, the two maps in figure 50
represent images on a computer screen, each
one with an equal number of pixels. However
each pixel in the map on top might represent
100 miles, each pixel in the world map at bot-
tom might have to represent 500 miles. So, the
lower number (the fewer meters, acres, miles,
etc.) represented by a single pixel, the higher
the resolution.
figure 50.
DI R E C T RE A D O U T F R O M
EN V I R O N M E N TA L SAT E L L I T E S
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