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Airport Automated Weather Observing System (AWOS)

Airport Automated Weather Observing System (AWOS)
​​An Automated Weather Observing System (AWOS) supports many operational user groups at an airport, including Air Traffic Controllers, Meteorological Observers and Maintenance personnel.
​​​​​​​​​​An Automated Weather Observing System (AWOS) supports many operational user groups at an airport, including Air Traffic Controllers, Meteorological Observers and Maintenance personnel. It shall provide accurate and reliable data to ensure airport safety and operational efficiency.

This webinar will cover the following topics and provide answers to the following questions:
  • What should you consider when purchasing an International Civil Aviation Organization (ICAO) regulated AWOS solution?
  • What do Air Traffic Controller, Meteorological Observer/Forecaster and Briefing office displays look like and what intelligence is behind them?
  • What kind of alerts are available to help airport personnel improve efficiency? 
  • How can you reduce airport operational costs and ensure/enhance airport safety during weather events?

Questions & Answers

Q: Can the Vaisala AWOS output messages in XML?
A: Yes, Extensible Markup Language is supported by Vaisala. Vaisala has its own XML schema which is available in electronic format under Non-disclosure agreement.

Q: Is it easy to switch between different units on the AWOS displays (for example mps to kt)?
A: Switching between units is easy. However, we want to remind you that in the design of AWOS "pages", different units are clearly visible (e.g.  mps or kts; hPa or mmHg or inHg).

Q: How many runways are supported by the Vaisala AWOS system? 
A: The number of runways can be unlimited within Vaisala’s AviMet® AWOS software. However, a practical restriction comes from METAR/SPECI reporting as stated by ICAO (Annex 3, 18th Edition) b) "...up to a maximum of four...". Please note that if there are many of runways in use, the coordination with the ATIS shall be taken into consideration. For example, the arrival and departure messages should be based on the local reports fed by the AWOS system (Annex 11, g).

Q: Is it possible to integrate the aviation lightning system and RWIS system into the Vaisala AviMet® software? 
A: They can be integrated through web feature integration. However, it is important to carefully design the local network infrastructure because these systems are hosted outside of the local network and accessible via Internet.

Q: How does the communication work between sensor stations along the runway and the AWOS system? 
A: Sensor data sent over modem line, fiberoptic, or serial communication methods are always converted into TCP/IP or UDP protocol before reaching the AWOS servers. The AWOS servers communicate with the AWOS client workstations over TCP/IP protocol via the Local Area Network.

Q: Can sensors from other manufacturers be connected to the Vaisala AWOS? 
A: If the sensor output message is explicit and clearly defined (containing all possible combinations in the message content), we can integrate the information into the Vaisala AWOS system. Proper testing and documentation need to take place in all external integration cases.

Q: How can we calculate the direction of wind by using three components of speed data measured by the WS425 wind sensor? 
A: As such the wind sensor has an array of three equally spaced ultrasonic transducers on a horizontal plane. Wind speed (WS) and wind direction (WD) are determined by measuring the time it takes the ultrasound to travel from each transducer to the other two. The wind sensor measures the transit time (in both directions) along the three paths established by the array of transducers. This transit time depends on wind speed along the ultrasonic path. For zero wind speed, both the forward and reverse transit times are the same. With wind along the sound path, the upwind direction transit time increases and the downwind transit time decreases. Unfortunately, this is sensor internal calculation and these details are not available for end user. Now the WMT700, that is successor for WS425, is able to provide wind speed data vectors with the Cartesian coordinates both as instant and average values. End user has access to these data with user defined data messages.

Q: Can you provide examples of different runway categories? 
A: We have to refer to ICAO Annex 6/ Part I/9th Edition July 2010 that provides exact definitions for the following runway categories: CAT I, CAT II, CAT IIIA, CAT IIIB, and CAT IIIC. For example, for a CAT II operation: "A precision instrument approach and landing with: a) a decision height lower than 60 m (200 ft), but not lower than 30 m (100 ft); and b) a runway visual range not less than 300 m." Please note the additional statement by ICAO: "Where decision height (DH) and runway visual range (RVR) fall into different categories of operation, the instrument approach and landing operation would be conducted in accordance with the requirements of the most demanding category..."

Q: How do you determine the cloud fraction using an automated system? 
A: We believe this question refers to the detection and reporting of cloud amounts (okta coverage). Vaisala AWOS software analyzes a certain time period (typically 30 minutes with a higher weighting on the latest 10 minute period within this 30-minute time period) of cloud sensor measurements from one or more ceilometers. We "cluster" the altitude and time measurements provided by the ceilometers to estimate the cloud amount (octa coverage). Also, Vertical Visibility is processed within this algorithm.

Q: How can we detect thunderstorms using an automated system? How can we integrate thunderstorm information in AWOS? 
A: Vaisala can provide different solutions for detecting thunderstorms. One of these solutions consists of the integration of a local, single-point lightning detection sensor (e.g. Vaisala’s TSS928 sensor) into the AWOS system that gives the user a graphical display of lightning detected within 56 km of the airport. A more powerful solution consists of the integration of Vaisala’s Airport Lightning Information System (ALIS) into the Vaisala AWOS system. ALIS provides a web-based, GIS map display of lightning detected within a 500 km radius of an airport using high accuracy lightning data detected by the Global Lightning Dataset (GLD360) network. Both TSS928 and ALIS solutions can be further used inside the AWOS system to automatically update the aerodrome present weather (w’w’) and recent weather (REw’w’) thunderstorm codes using Vaisala’s multi-sensor weather algorithm.

Q: I could see in your slide that the pressure measurement is outdoors. Where does the pressure sensor have to be installed; indoors or in the weather station outdoors? If the location of the pressure sensor is not that important, what is your recommendation? 
A: The pressure sensor(s) can be installed outdoors or indoors. In some cases, the pressure sensor is mounted inside the meteorological office, but then you have to consider the influence of draught (e.g. closing/opening of windows/doors). Most often the pressure sensor is installed outdoors with the other sensors. To accurately calculate the QNH and QFE pressure values, it is important to define the sensor height and the aerodrome reference altitude for the AWOS software. Vaisala’s AWOS system can consist of several barometers installed outdoors and indoors at an airport. The QNH values can be compared and raise an alarm if the difference is too big. Users can also manually insert the barometric pressure into the Vaisala AWOS to calculate critical pressure values, such as QNH, QFE, and QFF.

Pirkko Väkimies

​​Pirkko Väkimies
Airports Customer Solutions Architect

Pirkko joined Vaisala in 1998 as a member of the Aviation Weather System software development team. For the past 15 years, Pirkko has been a key person ensuring Vaisala’s Automated Weather Observing System (AWOS) software performs well in-house and on-site. In her demanding role as a system expert in AWOS system deliveries, Pirkko has completed numerous Vaisala projects and is well-respected for her runway visual range (RVR) expertise.
In Pirkko’s current role as an Airport Customer Solution Architect, she works with airport customers to find innovative and reliable solutions that best fulfill their needs. Pirkko’s interest in different cultures and language skills have been highly appreciated by Vaisala’s customers during the many training sessions she has given over the past 15 years.​


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