Characteristics of the AVHRR Sensor
- Average Orbital Height: 830 km (515 Miles)
- Spatial Resolution:
- Global Area Coverage (GAC): 4.4 kilometers
- Local Area Coverage (LAC): 1.1 kilometers (Available over the U.S. and in some parts of the world)
- Swath Width: 2800 kilometeres
- Coverage: 2 times per day per satellite
- Records Data in 5 Wavelength Intervals
(bands)
- Visible Green and Red (0.58 to 0.68 microns)
- Near Infrared (0.72 to 1.10 microns)
- Mid Infrared (3.53 to 3.93 microns)
- Thermal Infrared (10.3 to 11.3 microns)
- Thermal Infrared (11.5 to 12.5 microns)
- Bands 1 and 2 record reflected energy
- Band 3 records reflected energy during
the day and emitted energy at night.
- Bands 4 and 5 records emitted thermal (heat)
energy
AVHRR Sensor Calibration
Before the data can be used in a quantitative manner, it needs to be calibrated.
The calibration algorithm is based on information contained
in the
Polar Orbitor User's Guide. Briefly, the visible and near infrared
data (channels 1 and 2) are converted from raw counts to
percent albedo using a linear relationship determined prior
to launch. The thermal infrared data (channels 3, 4, and 5)
are converted from raw counts to radiances with a linear
relationship that is based on the raw count value associated
with cold space (roughly 3 degrees Kelvin) and the raw count
value associated with the temperature of an onboard target
(approximately 300 degrees Kelvin). A slight nonlinearity
in channels 4 and 5 is corrected using a quadratic function
of radiance. Lastly, the infrared radiances are converted
to temperature using the inverse Planck function.
Geographic Rectification and Registration
As the satellite passes over the earth, it scans the surface beneath
it at an angle of +/- 63 degrees. As a result, the spatial resolution
varies from 1.1 km directly beneath the satellite, to 5.5 km at the
edge of the swath. This causes geometric distortions to occur. The
image on the left shows an example of the unrectified data. In
our processing, we use an automated routine that utilizes satellite
tracking information to determine where the satellite was when it
acquired the data. Once the position of the satellite is known, the
data can be registered to and earth location. This registered data,
can then be rectified to any map projection. The image on the
right is the rectified version of the image shown on the left.
This page maintained by Dave Schneider (djschnei@mtu.edu)
