1. Visibility Chain at Regional Airports in the Netherlands Wiel Wauben R&D Information and Observation Technology

2. TECO 2012 | Visibility Chain 2 Introduction KNMI automated the aeronautical observations at regional civil airports, the so-called AUTO METAR system. During the evaluation many questions related to visibility arose. It was realized that documentation was scattered between departments and incomplete; not always verified against current practices or ICAO requirements and recommendations; background of deviations were sometimes unclear (requirements old system or by local agreement?).  review of visibility chain against WMO 2008, 2010, ICAO 2005, 2006, 2010 and KNMI handbooks, reports and (manufacturer’s) system documentation, work instructions and configurations.

3. TECO 2012 | Visibility Chain 3 Visibility Chain Public KNMI internal document (http://www.knmi.nl/bibliotheek/knmipubIR/IR2012-02.pdfhttp://www.knmi.nl/bibliotheek/knmipubIR/IR2012-02.pdf Contents 11. Server and client network systems 12. System monitoring and data validation 13. Continuous remote verification 14. Derivation of VIS and RVR 15. Averaging of VIS and RVR 16. Selection and backup of VIS and RVR 17. Available VIS and RVR variables 18. Meteorological reports 19. Technical infrastructure 20. Data flow 21. Conclusions and recommendations 1. Introduction 2. Sources of meteorological information for users 3. Definitions of visibility 4. Causes of visibility reductions 5. Visibility requirements 6. Sensors for the measurement of MOR 7. Calibration of MOR measurements 8. Maintenance and effect of contamination 9. Sensor locations 10. SIAM sensor interface and MUF cascade

4. TECO 2012 | Visibility Chain 4 Visibility requirements WMO (2008) specifies the range of RVR as 10 to 1500 m, whereas ICAO (2010) recommends a RVR range from 50 to 2000 m. The requirements for background luminance are not clearly stated. Range given in examples and ICAO (2006) only mentions that an uncertainty of ±10 % is considered acceptable.

5. TECO 2012 | Visibility Chain 5 Calibration of MOR measurements Reference restricted to MOR < 1500 m and without precipitation!? Furthermore the linearity of the sensor over the MOR range is not verified. Background luminance checked via calibrator of manufacturer. Traceability is currently under review. Transmitter ↑ SB receiver ↑ FD12P ↑ LB receiver → A field reference setup of TMM and FS is used the transfer the calibration of the TMM to the FS by means of a so-called scatter plate.

6. TECO 2012 | Visibility Chain 6 linearity FS

7. TECO 2012 | Visibility Chain 7 Maintenance and effect of contamination Flying insects in the measurement volume of the FS sensor can give significant reductions of the MOR. The solution...? see poster P1(28)! Describes the maintenance and monitoring of lens contamination level and the effect of contamination of the MOR measurements.

8. TECO 2012 | Visibility Chain 8 Selection and backupof VIS and RVR No backup of VIS/RVR at touchdown by FS at other end of RWY in local MET report (arrival). Backup of background luminance is allowed. Usage of video camera’s to determine whether VFR conditions apply in case of sensor failure, but quality images too poor.

9. TECO 2012 | Visibility Chain 9 Data flow

10. TECO 2012 | Visibility Chain 10 Conclusions The review of the visibility chain was appreciated by internal and external users. During the review some errors in the chain could be pointed out. Some of these were directly solved, but others require consensus between parties involved and/or further investigations. The recommendations (37) are managed in a spreadsheet. Persons have been assigned, but items have not yet been prioritised and sometimes their impact is unclear. Meanwhile new items have been added to the list. The maintenance of the document is still under discussion. Inclusion in Dutch handbook on observations versus coupling to documentation of the underlying systems, regulations and agreements.

11. TECO 2012 | Visibility Chain 11 A useful contribution Track changes in WMO / ICAO documentation e.g. used in proposals for the amendment of Annex 3 and including rationale!