AMOSSG/5-SN No. 7

4/3/05

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FIFTH MEETING

Montreal, 11 to 14 April 2005

Agenda Item	5:	Aerodrome observation requirements
5.2:	Capability of automatic observing equipment to meet aeronautical requirements and the use of automated equipment during operational hours

WMO ACTIVITIES RELATED TO ATTAINABLE ACCURACY FOR SOME METEOROLOGICAL OBSERVATIONS

(Presented by S. Benarafa)

SUMMARY
The purpose of this paper is to provide information on WMO activities related to the review of currently attainable accuracy of measurement or observation for the various meteorological elements found in Part II, Attachment A to Annex 3/Technical Regulations, Volume II, [C.3.1].

1.	INTRODUCTION

1.1	During the Fourth Meeting of the Aerodrome Meteorological Observing Systems Study Group (AMOSSG) held in 2003, the WMO representative at the meeting, presented a working paper highlighting progress being made by WMO in updating the "attainable accuracy of measurements or observations" contained in Part II, Attachment A to Annex 3/Technical Regulations Volume II [C.3.1] (WMO No 49), Operationally Desirable and Currently Attainable Accuracy of Measurement or Observation.

1.2	The meeting was informed among others that initial discussions have led to a set of proposed levels of accuracy that could be obtained although their final approval was still awaited from the relevant WMO constituent bodies.

1.3	This paper presents the results of the review of "attainable accuracy of measurements or observations" by The CBS Expert Team on Requirements for Data from Automatic Weather Stations (ET-AWS) and the CIMO Expert Team on Surface Technology and Measurement Techniques (ET-ST&MT) made in 2004.

2.	DISCUSSION

2.1	The CBS ET on AWS meeting held in Geneva, 28 June -2 July 2004 updated the Operational Uncertainty Requirements and Instrument Performance with the assistance from experts of other WMO technical commissions.

2.2	The CIMO ET on ST&MT meeting held in Geneva, 13-16 October 2004 also reviewed the new proposal for the Operational Uncertainty Requirements and Instrument Performance which were subsequently reviewed by the Presidents of WMO technical commissions.

2.3	The results of all these reviews are attached as Table I to this paper. Amendments (values printed in bold) to the Sixth edition of the Guide to Instruments and Methods of Observation, WMO-No.8, Part I, Ch.1, ANNEX 1.B are also contained in Table I. It will be noted that the term "accuracy" is replaced by "uncertainty" in order to be in accordance with ISO standards on uncertainty of measurements.

2.4	The review as attached will be published in the Seventh Edition of the CIMO Guide to Instruments and Methods of Observation as "Table on Operational Uncertainties and Instrument Performances".

3.	ACTION BY THE GROUP

3.1	To consider whether any changes should be made to Attachment A of Annex 3 as a part of draft Amendment 74.

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