site also contains transmission schedules and
transmitting frequencies for various United States and
What is the purpose of a satellite atmospheric
What is the main advantage of geostationary
Which GOES satellite provides imagery over all
of South America?
What type of satellite is the NOAA 14?
What are the main advantages of polar-orbiting
What is the average swath width of a polar-
Which organization is responsible for providing
near real-time DMSP environmental imagery to
Q14. Which geostationary satellite will provide
imagery for Spain and Portugal?
LEARNING OBJECTIVES: Recognize the
particular advantages of imagery from
geostationary satellites and polar-orbiting
Define spatial resolution,
radiometer, electromagnetic wave, and albedo.
Define the terms visual, infrared, near
infrared, and water vapor as they relate to
satellite imagery. Recognize the advantages of
visual, infrared, and water vapor imagery.
The pictures or images available from
environmental satellites vary, depending on the type of
satellite and the type of sensor in use. Geostationary
satellites continuously "look" at the same geographical
area of the earth. However, the image area is centered
on the satellite subpoint on the equator. At the
subpoint, clouds are seen from directly overhead.
Further away from the subpoint, clouds seen in the
image are viewed from an angle, and feature distortion
occurs. Cloud cover is often overestimated toward
image edges because the sensor is actually viewing the
clouds from the side. Near the horizon, the image is
considered unusable due to distortion.
Polar-orbiting satellites are in much lower orbits
than geostationary satellites; therefore, the satellite
can only see a limited portion of the earth as the
satellite sensors scan from horizon to horizon.
Because of the acute view angle near the horizon, the
satellite image near the horizon is usually of little value
and is usually not processed or displayed by receiver
Satellite sensors designed to produce pictures or
images of earth, its oceans, and its atmosphere are very
different from the cameras used to take a photograph.
They are more like a video camera, only much more
specialized. These scanning sensors are called
radiometers, and instead of film, an electronic circuit
sensitive only to a small range of electromagnetic
wavelengths measures the amount of energy that is
received. Satellites may can-y several different image
sensors, each of which is sensitive to only a small band
of energy at a specific wavelength. The radiometer
used by the TIROS-N and POES series satellites is
known as the Advanced Very High Resolution
Radiometer (AVHRR) and contains many types of
Satellite sensors scan across the surface of the
earth in consecutive scan lines along a path normal to
the direction of travel of the satellite. As the sensor
moves through a scan line, it very rapidly measures
energy levels for only a very small portion of the earth
at a time. Each individual energy measurement will
compose a single picture element or pixel of the overall
satellite image. The sensor then assigns an intensity
level from 0 to 256 for each pixel. The size of the area
(field-of-view) scanned by the sensor determines the
spatial resolution of the overall image. Thus, the
smaller the area scanned for each pixel, the higher the
spatial resolution. Some sensors may scan an area as
small as 0.5 km across (high resolution), while others
scan areas as large as 16 km (low resolution). When
composed into an image, smaller pixels allow the
image to be much clearer and show greater detail.
Clouds and land boundaries appear better defined. If
objects are smaller than the sensor resolution, the
sensor averages the brightness or temperature of the
object with the background. Normally, the sensors
aboard satellites are able to provide better resolution
for visual imagery than for infrared imagery. DMSP
satellites have very high-resolution capabilities in both
visual and infrared.