Automated Weather Observation System - AWOS

CHAPTER 2:
TELECOMMUNICATIONS OF AWOS DATA

2.3.1 Limitations of the Communications Controller

2.4.1 Fixed Format
2.4.2 Free Format
2.4.3 Sensor Configuration

2.5.1 RA's from MSC/DND stations
2.5.2 RA's from Flight Service Stations

2.6.1 CODECON II
2.6.2 MixMaster
2.6.3 BUFR to METAR
2.6.4 Distribution of Messages

2.1 AWOS COMMUNICATIONS - OVERVIEW

2.2 TRANSFER OF SENSOR DATA

The individual sensor PIs send their information to the shelf controller (SC), which assembles the data into fixed and free format messages. The data are later transmitted under the bulletin header 'RA'. If special criteria have been crossed, the sensor PI will notify the SC, which will designate the message as 'SP', otherwise it will designate the message as 'SA'.

2.3 AWOS COMMUNICATIONS CONTROLLER

The communications controller (CC) polls the SC for the message once per minute and if a SP is detected on the hour, the message is re-labeled RS. The CC buffers the minutely data, and this is made available at all 4 ports. In order to get the message out to the long-line communications networks through the communications port (MAIN 1), various regional processes take over. Refer to the AWOS block diagram (Fig 1-1) for a visualization of these processes.

2.3.1 LIMITATIONS OF THE AWOS COMMUNICATIONS CONTROLLER

• Excessive specials

AWOS reports specials according to MANOBS criteria. The AWOS is much more vigilant than an observer because the automated system reports all Specials as they occur, while the observer may combine Specials under certain weather situations*. Filtering of Specials has been designed into some of the AWOS PIs, however users of the data should be aware that under some weather conditions excessive specials may occur.

*For example, an observer may report visibility as '1V' with 'VSBY VRBL 1/2-11/2' in Remarks for an hour or more. During this time a co-located AWOS may issue a dozen or more specials oscillating around one mile.

2.4 AWOS OUTPUT FROM THE COMMUNICATIONS CONTROLLER

There are five different types of output from the Communications Controller:

• Fixed format;
• Free format;
• Raw data;
• Diagnostic data, and;
• Station configuration data.

The fixed and free format data groups, as well as the station configuration data are combined to form the RA message and are generally available to users.

2.4.1 FIXED FORMAT

This includes data representing meteorological parameters for use in the METAR format.

Example:

YIO RS 060500 AUTO E-X1SCT11SCT14OVC25OVC/2.3V/S-/M/-6.7/

-7.9/18511G19/005//

To decode the fixed format data, refer to Appendix A-1.

2.4.2 FREE FORMAT

This includes supplementary data required for climatological, hydrological and other purposes, and for the production of the SM report.

Example:

2231010/12V60/10111/-67-65/18010G01917022/ /833-5/

To decode the free format data, refer to Appendix A-2.

2.4.3 STATION CONFIGURATION

This includes codes which indicate the sensors that are available at that particular site.

Example:

CL03/VC04/RC05/PB06/TC07/WC08/RE09/RD10

To decode the Station Configuration data refer to Appendix A-3.

2.5 TELECOMMUNICATIONS - TRANSFER OF RA TO NCCS

The RA is not an official code for aviation weather observations. The official code (METAR AUTO) is generated by software at CMC in Dorval. The AWOS transfers the RA message to the MSC Dorval National Communications Processor (NCP) for code conversion. From there the processed data is sent to the National Computer Communications System (NCCS) for distribution.

AWOS can be configured to either dial out for both regular hourly reports and specials, or to dial out for specials only and be polled for hourly reports. The first generation AWOS is polled on the hour for the hourly report and every 15 minutes for specials.

The AWOS transfers the RA message from the communications controller to the MSC Dorval network via either the Regional Telecom/Wide Area Network (WAN) or the Transport Canada/AFTN (Aeronautical Fixed Telecommunications Network) gateway.

2.5.1 RA'S FROM MSC/DND STATIONS

Regardless of whether AWOS is polled or dials out itself, the RA message goes from the Regional Telecom (also known as the RCP* or Regional Communications Processor), over the WAN (Wide Area Network) to the NCP (CMC Dorval National Communications Processor).

(*DND uses satellite communications to collect RA's from the northern DND AWOS locations.)

2.5.2 RA'S FROM FLIGHT SERVICE STATIONS (FSS)

RA data reaches the NCP from FSS sites via the ADIS (Automated Data Interchange System) gateway.

2.6 NCP SOFTWARE

2.6.1 CODECON II

Once the NCP receives the AWOS RA, CODECON II decodes the RA message into the Synoptic (SM) message and a code form known as "Binary Universal Form for Representation of meteorological data" or BUFR format.

2.6.2 MIXMASTER

The BUFR message leaves CODECON II and enters software known as MixMaster which manages data from man-machine mix programs. MixMaster decides whether or not to release the message according to the observer's schedule; If there is an observer at the site, no message is released, If no observer is present, the message is released.

2.6.3 BUFR TO METAR

The message then enters the translation software known as BUFR to METAR which processes the observation into its "official format" for aviation purposes i.e. METAR AUTO.

2.6.4 DISTRIBUTION OF MESSAGES

SM and METAR messages are then sent to the CMC Tandem which transmits them out to the regions via METSIS, as well as going to Flight Service Stations and other users via the ANIKOM satellite communications links (AMIS), and to the rest of the world over the Global Telecommunications System (GTS) via the AFTN and the NWS links. It is important to note that the RA message is only sent via METSIS, and is thus generally available only to MSC and some FSS stations.

The Green Lane^TM,
Environment Canada's World Wide Web Site.