NOAA KLM User's Guide

Section 5.1

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Introduction Page, NOAA KLM TOC, Acronyms
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5.1 TBUS Bulletin

The TBUS bulletin contains information on satellite equator crossing times and longitudes, orbit numbers, orbital period, longitudinal time, and longitudinal increments between successive orbits; also, satellite positions at two-minute intervals (for a reference orbit), transmission frequencies, and other information related to satellite tracking and performance. The orbital information is valid for the third day after the date on which the bulletin is prepared and transmitted.

The bulletins are prepared by NESDIS and transmitted through the National Weather Service Telecommunications Gateway (KWBC) to major meteorological centers and relay points around the world, which comprise the Global Telecommunications Service (GTS). The GTS primarily serves the international meteorological community. However, the TBUS bulletin receives further distribution via the Internet, electronic mail, high frequency radio broadcasts and commercial data services.

There are two forms of the TBUS bulletin. One form, identified as TBUS-1, is used to convey information about satellites that are descending in daylight (traveling north-to-south on the sunlit portion of the orbit). The second form, TBUS-2, provides data for satellites that are ascending in daylight (northbound on the sunlit portion of the orbit).

A schematic representation of the TBUS-1 and TBUS-2 bulletins is shown in Figure 5.1-1.

Figure showing schematic representation of TBUS-1/TBUS-2 information

Both bulletins consist of four parts. Part 1 is quite short. It identifies a reference orbit on a given day (three days after the date of the bulletin) and gives the equator crossing time and longitude for this reference orbit. This is followed by an orbital nodal period and a longitudinal increment--the separation between successive equator crossings, measured in degrees. The orbit number of the fourth and eighth orbits following the reference orbit are then listed along with the equator crossing times and longitude of these orbits.

By itself, Part 1 contains sufficient information to permit the user to calculate future equator crossing times and longitudes several days in advance with considerable accuracy. During periods of maximum solar activity, however, the accuracy extrapolated from Part 1 information diminishes if the extrapolations are carried much more than a week ahead.

Parts II and III of the bulletins are quite lengthy. Part II (Day) contains predicted subpoint and height data at two-minute intervals for the portion of the orbit that is sunlit north of the equator. Part III (Day) contains predicted subpoint and height data at two-minute intervals for the portion of the orbit in darkness north of the equator. Part III (night) contains predicted subpoint and height data at two-minute intervals for the portion of the orbit in darkness south of the equator. All times are referenced to the ascending node (northbound equator crossing) and are given as minutes after or before this time (refer to Figure 5.1-1).

Part IV is relatively short, and usually consists of four items: a code group, transmission frequencies of each operating direct readout sensor system, the on-board clock variations and remarks. The code group consists of orbital parameters used to generate parts I through III. It is intended for use by those station operators needing more precision in satellite tracking and having appropriate computer programs to ingest such data and produce both equator crossings and antenna pointing angles.

The remarks in Part IV are in plain language and advise of problems or changes in the mode of operating the satellite, including the AVHRR/3 channels selected for the APT transmissions. Direct readout transmission frequencies are discussed elsewhere; in summary, the APT service for NOAA KLM will utilize 137.50 or 137.62 MHz; the HRPT will transmit on 1698.0 or 1707.0 MHz (1702.5 MHz is available for standby); the DSB beacon will operate on 137.35 or 137.77 MHz.

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