What is the APT/WEFAX to LRPT/LRIT transition?

During the next ten years, there will be a transition of the present low-resolution satellite services called APT and WEFAX to Low Rate Picture Transmission (LRPT) and Low Rate Information Transmission (LRIT), respectively. The transition will have a direct and potentially large impact on existing and planned ground receiving equipment belonging to WMO Members. The following is a description of the activities undertaken by the Secretary-General to inform and assist Members during the transition.

In February 1998, the Secretary-General informed WMO Members of an initiative within the Secretariat, which has three phases. First, Members will be notified of the status of the conversion on a regular and as required basis. Secondly, and in order to assess the extent of required changes, Members will be advised of the information held by the WMO Secretariat with regard to receiving equipment in their country. The present level of information is not complete enough to advise them adequately of necessary software and/or hardware changes to enable reception of the new digital services and thus, they will receive a request for additional information. Based on this new information and through Secretariat interactions with the satellite operators (both at meetings of the Coordination Group for Meteorological Satellites, CGMS, and bilaterally) and manufacturers, they will be advised of necessary actions they must undertake to enable reception. Finally, Members will receive a new (to be developed) Technical Document describing how to exploit the new digital services. The updating of information will occur during the first half of 1998 and subsequent notification of necessary actions will occur when available. The new Technical Document should be available prior to the commencement of the new digital service. Extensive use of the WMO Satellite Activities Home Page on Internet will be used to facilitate notification.

Tables were distributed in the February 1998 letter showing the status for LRIT and LRPT conversion for satellites in polar and geostationary orbit. The tables were reviewed at the Twenty-fifth session (June 1997) of the Coordination Group for Meteorological Satellites (CGMS). At CGMS-XXV, the satellite operators discussed the dates when the new digital services would commence for their satellite systems and the duration of a transition period when both analogue and digital services would be available.

An analysis of the table for LRIT conversion indicates that in WMO Regions I (Africa) and VI (Europe) there will be a three-year overlap starting in December 2000. WMO Regions II (Asia) and V (Southwest Pacific) will have a three-year overlap starting in March 2000. WMO Regions III and IV (South, Central and North America including the Caribbean) have not yet identified a transition date. The Indian Ocean area (RA-II) appears to have no overlap starting in 2002. An analysis of the table for LRPT conversion shows that the morning (AM) satellite will start LRPT in 2002 while the afternoon (PM) satellite will start LRPT in 2009. Since there will be no transition period for the AM orbit or PM orbit separately, but rather a seven year period when both APT (PM) and LRPT (AM) will be available, it will be necessary to maintain a dual capability (APT and LRPT) during the period 2002-2009 if it is deemed necessary to have information from AM and PM satellites. It can also be seen that the inclusive transition period for all Regions will cover the period from 2000 until 2009 or more.

The Commission for Basic Systems Working Group on Satellites has previously developed "SAT-13, A Description of a Standard Small Satellite Groundstation for Use by WMO Members, 1995 (WMO/TD No. 660) (198Kb - WordPerfect 6.1)". The Third Session of the Working Group on Satellites was held 27 April through 1 May 1998 in Geneva, Switzerland. At the meeting, a description of the attributes of LRIT/LRPT and their implementation was prepared. The description was entitled "Application and Presentation Layer Specifications for the LRIT/LRPT/HRIT/HRPT data formats. Once finalized, the new specifications will be distributed to all concerned as well as being made available on the WMO Home Page.