NOAA KLM User's Guide
No significant changes are proposed in the method of mission data handling and acquisition from that developed for previous satellites in the TIROS-N/ATN series, but a sixth data format will be added for AMSU data handling. These six basic data formats are generated onboard the satellite, each associated with one or more of the acquisition modes (stored or real-time, very high frequency (VHF) or S-band transmission). These formats are as follows:
Under routine mission-orbit operations, the TIP output contains low-rate instrument data multiplexed with satellite housekeeping data. It contains all environmental instrument information except that from the AVHRR and the AMSU. It is available in real-time and as stored data.
Low rate instrument data are included every minor frame. Real-time TIP data are normally available through the VHF beacon link. See Section 4 for more information.
For early orbit support and maintenance operations, the TIP has three other operating modes: boost, dwell and satellite computer memory dump.
HRPT comprises full-resolution data from the AVHRR multiplexed with TIP and AMSU data. HRPT is dedicated to real-time transmissions and is available to local users in split-phase format via either of two S-band communications links with the option of transmission from a third with left circular polarization rather than right circular polarization, which the other two provide. An HRPT major frame comprises three minor frames. One minor frame will contain TIP data, one will contain AMSU data and one will contain backfill data. See Section 4 for more information.
The LAC data are essentially the stored version of HRPT, played back at either two or four times the real-time rate, and are made available for centralized processing. They are not intended for local users. LAC data storage is scheduled via the stored command table to provide up to 10 minutes of coverage per tape transport. See Section 4 for more information.
GAC data contains TIP, AMSU and reduced resolution AVHRR data. The overall data rate is one-tenth of the LAC data rate, allowing over 100 minutes of data to be stored on one tape transport. Record-to-playback ratio is either 20:1 or 40:1. The GAC stream is for stored data only and is used to develop global data sets for centralized processing and analysis. It is not intended for local users. The reduced resolution of this format allows 100% recovery of the data even under worst-case blind-orbit conditions. See Section 4 for more information.
APT data are specifically tailored for low-cost VHF local-user ground stations. Again, it is derived from AVHRR video data but at medium resolution. Any two of the five AVHRR channels provided to the MIRP can be selected and processed as "Video A" and "Video B."
One APT line, consisting of one line of Video A and one line of Video B, is output every third AVHRR scan. Ancillary AVHRR data appear at one edge of each line and their 64-second repetition period defines the APT frame length. The resulting line rate is two per second.
APT data are transmitted continuously over a dedicated VHF link as an analog signal consisting of an amplitude-modulated 2400 Hz subcarrier frequency modulating the RF carrier. Table 1.2.5-1 gives the APT line characteristics.
|Frequency Band||136 to 139 MHz band|
|Carrier Frequencies||137.50 to 137.62 MHz|
|Out-of-band Emissions||-60 dB at ±170 KHz and greater from carrier frequency|
|Transmitted Bandwidth||-3 dB at ±25 KHz from carrier frequency|
|Modulated Rate and Type||±17 kHz FM with a 2.4-kHz subcarrier|
AMSU data is available as part of a low-rate data format. This format contains both standard TIP data and AMSU sensor data. The primary use of this 16 kbps format will be for global recording and playback to CDA stations. It is anticipated that AMSU data will normally be extracted from HRPT, LAC and GAC data. See Section 4 for more information.
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