NOAA-15 Channel 3A Data Transmission

Effective 9 March 1999, NOAA-15 will begin transmitting AVHRR Channel 3A
data.  3A transmissions will not be continuous, but will be shared with
Channel 3B data transmissions each day.

Channel 3A will be toggled on during daylight passes only, as the
spacecraft crosses the terminator into daylight. Additionally, 3A data
will will be toggled on only when the spacecraft subpoint is North of 40
degrees N. There will be no low latitude Northern Hemisphere or any
Southern Hemisphere Channel 3A data transmissions.  As the spacecraft
crosses the terminator into darkness, Channel 3A will be toggled off,
Channel 3B toggled on.

Channel 3A data is expected to continue through 20 April 1999 only.

The 3A transmission schedule may be interrupted in the event of a
volcanic eruption North of 40N where Channel 3B will be required for
hazards support.

For users of 3.55-3.93 um band data, note that NOAA-12 continues to
transmit Channel 3 data in the HRPT transmission service, and has
approximately the same Equator crossing time as NOAA-15.

NOAA-15 APT users should see no change, except possibly near the
terminator at the time of the 3A/3B switch.  APT day transmission uses
channel 2 and 4, while night transmission uses channel 3 and 4 when 3B
will be toggled on (normal IR channel).

The 2 March start date is subject to change to accomodate the Spacecraft
Operations Control Center schedule.

Posted to the NOAASIS 18 February 1999, 1700 UTC (with revised dates)