Automated Weather Observation System - AWOS

FOREWORD

Traditionally, surface weather observations have been recorded and transmitted by contract observers as well as qualified employees from Environment Canada (EC), NavCanada (NC), (formerly part of Transport Canada), Community Aerodrome Radio Stations (CARS) and Department of National Defence (DND). In 1987 EC announced the Strategic Plan. It was a 20 year plan designed to take the Meteorological Service of Camada's (MSC) weather programs into the 21st century. A major initiative of the Strategic Plan was the automation of the surface weather observing network.

EC has been making use of automated surface weather observation systems since 1969, with the installation of the MARS I (Meteorological Automatic Reporting System) generation of autostations. MARS II followed in 1975, MAPS I (Modular Acquisition Processing System) in 1979 and MAPS II in 1983. In general, these autostations observe and transmit only the basic weather parameters of pressure, temperature, humidity, and wind speed and direction, although a few have the capability to report cloud, visibility, and precipitation accumulation. They were used mainly in remote data sparse areas to supplement the existing network.

In 1988 the first of a new generation of autostation was installed in a test mode at the Winnipeg airport. Very much in the development stage, READAC (Remote Environmental Atmospheric Data Acquisition Concept) was a collection of independently operating sensors, the information from which was integrated by a processor into a weather observation each minute. It came with the capability to report the additional parameters of cloud height and amount, visibility, and occurrence of some weather phenomena. Also, its pressure sensor was approved by TC for use in providing altimeter settings to aircraft. READAC also provided the capability for issuing special weather observations ('SPECIALS') when certain criteria were met. Thus, the automation of weather observations for the aviation community was now a possibility, and READAC was the first autostation with the potential to replace the human observer.

Between 1990 and 1995, Phases I and II of the READAC project saw the installation of 60 sites. In addition, DND installed 28 sites for a total of 88 READAC's across the country. As the systems moved beyond the developmental stages and came into stand-alone usage, the idea of "Concept" no longer seemed appropriate, and these autostations became known simply as AWOS (Automated Weather Observation System). In 1996, Nav Canada specified the requirements for automated aviation observations from approximately 50 sites, not including the DND AWOS network. Also, several software components of the AWOS are being upgraded in an effort to improve the product to the end-user. This guide discusses the state of the AWOS assuming these upgrades are in place.

This manual is intended to provide guidance information to all users of AWOS data. Because it contains new or updated information it supersedes the First Edition of 1997. This manual is divided into Chapters, Sections and Sub-Sections. Chapters are groupings of information pertaining to the same subject areas. Sections provide a smaller grouping, and Subsections and headings in the text help the user find more specific information. A number of tables and figures incorporated within a Chapter are concise presentations of information needed within the Chapter. Those presented in Appendices provide additional detailed information.

Interpretation of Terms - 'Output', 'Code', 'Message' and 'Report'

• 'Output' refers to the product generated by an automated system or sensor. Examples include AWOS Output (fixed and free format), Cloud Output, POSS Output, etc. The output may or may not become part of a transmitted message.
• 'Code' refers to the way in which a product is presented to an end user. Examples include METAR code, SM code, etc.
• 'Message' or 'Report' (as a noun) each refer to the product that is actually transmitted to the end user. Examples include RA Message, METAR Report, Synoptic Report, SA Message, etc.

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