General Information of AWOS
An
Automated Weather Observing System (AWOS) is a comprehensive set of
meteorological instruments (or sensors) along the runway and a set of computers
inside the airport premises. The sensor
locations in runway area
are selected as
defined in ICAO
Airport design manuals. The sensors
are measuring automatically
certain weather parameters and this
information is sent
to Central Data
Unit (CDU) computer for further processing. The AWOS software
running in CDU and Workstation computers is the latest Vaisala Avimet software
revision (6.1) which automatically generates reports,
displays and archives the data.
AWOS layout in Tribhuvan
International Airport
The Kathmandu
AWOS is built
of sensors along
the runway, computers inside the
Airport buildings and
communication networks between
them.
The
sensor networks are
•
AWOS meteorological sensors in the primary landing direction of the runway
•
AWOS wind station in the other end of the runway Computers are connected
together via Local Area Network (LAN) and distributed in multiple locations
inside Airport buildings.
Sensors around the
Runway and Airport area
Central Data Unit
(CDU)
The Central
Data Unit (CDU)
is the main
computer of the Avimet system. It
collects data from
the sensors and
performs meteorological
calculations, generates reports,
and carries out
continuous diagnostics of the
incoming data and the entire system itself.
The CDU also stores the measured and calculated data as well as the
transmitted reports. The CDU software is divided into numerous services. These
services are background processes, which start automatically when the operating
system is started. A service receives
data either from sensors or other services. The service processes the data and
forwards it to other services or end-user applications. There can also be input from the user
interface.
The
Input/Output system controls the data flow to and from the runway sensors. It
also monitors the
operation of automatic
weather stations, data transmitters,
and the sensors
themselves. Most importantly,
this service validates incoming message correctness. Additionally, it takes care of AFTN data
transmission, as well as controls the data output to the interfaces.
The meteorological calculation
services validate the
incoming measurement data, and
derive additional variables
such as QNH
and RVR. The diagnostic services,
on the other hand, validate data and control alarm processing. Alarms can be
triggered by the meteorological calculation services, Input/Output system, and
by diagnostic services.
The message
generator services are
responsible for timing
and generating of the meteorological reports, while the data storage
services store the transmitted
reports on the
hard disk of
the CDU. The data storage services store also the
measured and calculated data and system alarms.
Each
workstation includes a similar set of applications. The
AWOS software applications can be launched
from the application
toolbar of the user
interface. The software
applications available for
each user depend on the user
account type in
use. This guarantees that only the relevant applications are visible for
each user group which, in turn, cuts back the operation time and improves
system safety.
For
example, in case of a workstation failure, the workstation roles can be
interchanged simply by logging in as a different user.
The
workstations operate independently from the CDUs. This means that the workstations and
applications installed on them can be freely started and stopped with no
adverse effect on the system operation.
Data interfaces
from sensors to CDU
All the optical sensors, Pressure sensors and field stations are intelligent, i.e. provided with microprocessors for data acquisition, averaging and communication interfacing. Optical sensors are independently making the measurement and providing the data derivatives. Data collectors and field stations are collecting data from various sensors via analogue or digital interfaces. Wind, Temperature, Humidity and Rain sensors are equipped with analog or simple digital signal interfaces. The data is collected with Vaisala data collector, MAWSfield stations. Primary interface between optical sensors and MAWS stations to CDU (server computer) is through the Fiber-Optical (F/O) network. Field stations are also equipped with radio modems for backup data transfer in case of malfunction in F/O network. The sensors and data loggers are sending data messages automatically with pre-defined intervals. The data is first averaged and reports and alarms are generated automatically. The communication between CDU and other computers is via LAN. Local Area Network is a vital part of the system operation.
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