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Automatic Picture Transmission (APT) System

NSSDCA ID: 1967-114A-01

Mission Name: ESSA 6
Principal Investigator:


The ESSA 6 Automatic Picture Transmission (APT) subsystem was a camera and transmitter combination designed to transmit real-time, daylight, slow-scan television pictures of cloud cover to any properly equipped ground receiving station. The camera system consisted of two redundant APT cameras with 2.54-cm-diameter vidicons. Each camera had a 108-deg wide-angle F/1.8 objective lens with a focal length of 5.7 mm. The cameras were mounted 180 deg apart on the side of the spacecraft, with their optical axes perpendicular to the spin axis. The cameras were programmed to take four or eight APT pictures per orbit. The actual picture taking required 8 sec and the transmission 200 sec. Earth-cloud images retained on the photosensitive surface of the vidicon read out at four lines per second to produce an 800-line picture. Two 5-w transmitters (137.5 MHz) relayed the pictures to local APT stations within communication range. The faceplate of the vidicon had reticle marks that appeared on the picture format to aid in relating the picture to its geographical position on the earth's surface. At nominal satellite attitude and altitude (approximately 1450 km), a picture covered a 3100- by 3100-km square with a horizontal resolution of about 4 km at nadir. There was 30 percent overlap between pictures along the track to ensure complete coverage. The experiment was successful and operated nearly continuously until the camera system was deactivated on November 4, 1969. Identical experiments were flown on ESSA 2, 4, and 8. APR data were primarily intended for operational use within the local APT acquisition station. However, copies of pictures taken over the United States are maintained on file at NOAA-NESS, Suitland, Maryland.

Alternate Names

  • APT

Funding Agency

  • Unknown (United States)


  • Earth Science: Atmospheric Dynamics

Additional Information

Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Principal InvestigatorNOAA National Environmental Satellite, Data and Information Service
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