satellites and varies from relatively low resolution to
high resolution.
APT direct-readout imagery is normally
transmitted in the 136-MHz to 139-MHz band. The
data signals are transmitted from the satellite to earth
within seconds of being scanned by the satellite
sensors. This is sometimes called real-time imagery;
the image is available as the satellite scans the earth.
APT service is designed to be received by anyone with
a standard, relatively low-cost satellite receiver.
Signals from DMSP satellites also provide APT.
However, the signals are encrypted. Additional
information on APT direct-readout services may be
found in the NOAA KLM User’s Guide.
The IMOSS satellite module can receive, process,
display, grid, and enhance APT direct-readout service
from nearly all polar-orbiting environmental satellites.
It is not equipped to decrypt the imagery signal from
the DMSP satellites. The AN/SMQ-11 is capable of
copying both APT data as well as DMSP encrypted
signals.
A second type of direct-readout service available
from both the NOAA and DMSP satellites is the High-
Resolution Picture Transmission (HRPT) service.
This is data scanned at a rate of 360 lines per minute to
provide 1.1-kilometer resolution (fig. 1-22). High-
resolution imagery can be, and usually is, transmitted
from satellites as a continuous broadcast. HRPT
Figure 1-22.—HRPT imagery.
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