AMOSSG/4-SN No. 15

26/8/03

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FOURTH MEETING

Montreal, 15 to 18 September 2003

Agenda Item	6:	Capability of automatic observing equipment to meet aeronautical requirements

AUTOMATIC WEATHER STATION NETWORKS

(Presented by Bryan Boase)

SUMMARY
This study note raises the issue of employing networks of automatic weather station observing systems strategically located within and outside of the "aerodrome vicinity" to support the provision of forecast products and aviation operations applicable to that aerodrome.

1.	INTRODUCTION

1.1	This paper recognizes the value and role of automatic weather stations and associated sensors in either supplementing or replacing human weather observations. Of concern however, is the replacement of the human weather observer either entirely or partially, by single "stand alone" automatic weather station and associated sensors.

1.2	It is contended that total replacement of the human weather observer can only be achieved by a network (more than one) of automatic weather stations and or associated sensors strategically located to support activities applicable to that location.

1.3	The situation is exacerbated in large regions where there is only sparse observational data on which to base forecast and operational aviation weather related decisions. The reliance upon this limited observational data for critical forecast and operational decisions is not a satisfactory situation.

2.	DISCUSSION

2.1	Replacement and or, supplementation of human weather observations

2.1.1	Properly maintained and calibrated, today's automatic weather sensors are of a high quality and in terms of measuring elements such as; wind speed and direction, temperatures, QNH and rainfall, out-perform the human weather observer. It is noted, that at AMOSSG/3 it was agreed that visibility was the only one of the critical elements that could be observed using fully automatic observing equipment.

2.1.2	Although recognizing significant advances in technology, it was also noted at AMOSSG/3 that there is still some discussion over the capability of automatic systems to assess the current meteorological conditions as comprehensively as a human weather observer. In particular elements such as cloud and present weather be their occurrence within or outside of the aerodrome vicinity.

2.1.3	Debatably the situation is exacerbated when the human observer is replaced by only one set of cloud and visibility sensors at the aerodrome. The human has the ability to see all sectors whereas sensors are somewhat limited. For example, the ceilometer only measures cloud directly above.

2.2	Impact on forecast quality and real-time aviation operations

2.2.1	The provision of observations that are not fully representative of a given aerodrome can or may have, a detrimental affect on aviation operations into that location.

2.2.2	The resultant impact can be a safety and or, economical issue. For example, a very conservative forecast can have direct economical impacts in terms of the optimum payload not being carried for a particular flight. Conversely, when a forecast does not identify the onset of adverse weather conditions and aircraft safety is compromised.

2.2.3	A similar potential exists for aircraft arriving at a given location where the parameters reported in the aerodrome weather report, are not completely representative of the overall current conditions.

2.3	Networks of automatic weather stations and sensors at specific aerodromes and within or outside of the aerodrome vicinity

2.3.1	Critical aerodrome forecast decisions can and are made on observational data acquired some considerable distance outside of the defined aerodrome vicinity.

2.3.2	The human weather observer may identify the onset of adverse weather conditions at considerable distances from their observing point. For example, thunder and lightning from distant Cb may be observed. This very observation may well be of significant value if the location is not covered by weather radar and or lightning sensors.

2.3.3	There are strong arguments emerging that suggest the strategic installation of automatic weather stations and sensors in a network around an aerodrome, would be of great value and particularly, for "nowcasting" forecast activities.

2.3.4	The strategic location of instrumentation in such network installations may well be 100 kilometres or more from the aerodrome. This would be highly dependant on the climatology of the location and predominant weather patterns impacting on it.

3.	ACTION BY THE GROUP

3.1	The group is invited to:

a)	consider the merit in firstly recognizing the value of a network of automatic weather stations and sensors as opposed to a stand alone unit;

b)	consider whether changes to Annex 3 are required in order to reflect the positive impact on forecast quality and real-time observations from a network of automatic weather stations at, in the vicinity or outside of the aerodrome vicinity; and

c)	consider the need for guidance material on the installation of networks of automatic weather stations at, in and or outside of the aerodrome vicinity.

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