Compendium of Lecture Notes on Meteorological Instruments for Training Class III and Class IV Meteorological Personnel [1/1-2] 9263106223

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WORLD METEOROLOGICAL ORGANIZATION

COMPENDIUM OF LECTURE NOTES ON

METEOROLOGICAL INSTRUMENTS FOR

TRAINING CLASS Ill AND CLASS IV METEOROLOGICAL PERSONNEL Prepared by Dr. D.A. Simidchiev

VOLUME I PART 1 -

Meteorological instruments

PART 2 -

Meteorological instrument maintenance workshops, calibration laboratories and routines

WMO- No.-622 Secretariat of the World Meteorological Organization- Geneva- Switzerland

1986

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© 1986, World Meteorological Organization ISBN 92-63-10622-3

NOTE The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the World Meteorological Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

C 0 N T E NT S

PART 1

METEOROLOGICAL INSTRUMENTS Page

FOREWORD

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INTRODUCTION

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CHAPTER 1 - MEASUREMENT OF METEOROLOGICAL VARIABLES

1.1

Specific features of meteorological measurements

4

1.2

Direct and indirect meteorological measurements

4

1.3

General - block diagram of a meteorological instrument

5

1.4

Dynamic behaviour of measuring instruments first-order measuring instruments second-order measuring instruments general features of meteorological instruments ............ .

8

General requirements for siting and exposure of meteorological instruments the meteorological shelter

11

CHAPTER 2 - MEASUREMENT OF ATMOSPHERIC PRESSURE

2.1

Nature of atmospheric pressure

2.2

Principles underlying the operation of atmospheric-pressure measuring instruments .•....•..................................

14

2.2.1

Mercury barometers

15

2.2.2

Aneroid barometers analogue and digital read-out the barograph ..................................................... .

23

Hypsometers temperature

30

2.2.3

units of measurement

Fortin and contracted-scale types

14

measurement of pressure through boiling

2.2.4

Altimeters

2.3

Exposure of atmospheric-pressure measuring instruments

32

2.4

Testing and calibration of atmospheric-pressure measuring instruments .................................................. .

33

altitude-through-pressure measurements

31

CHAPTER 3 - MEASUREMENT OF AIR TEMPERATURE

3.1

Nature and units of measurement of air temperature temperature scales used in meteorology conversion

35

Principles underlying the operation of air-temperature measuring instruments ..• , ............••......... , , , , ......... .

37

3.2.1

Mercury-in-glass thermometers

37

3.2.2

Spirit-in-glass thermometers

40

3.2

VI

CONTENTS

3.2.3

The bimetallic thermometer

3.2.4

Electrical resistance thermometers

3.2.5

Thermocouple temperature sensor

3.3

station thermograph •••••••••••••••••••

3.4

Settling time of thermometers

3.5

Calibration and testing of temperature-measuring instruments

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CHAPTER 4 - MEASUREMENT OF ATMOSPHERIC HUMIDITY

4.1

Nature and units of measurement of absolute humidity, relative humidity and dew point other humidity parameters ..••....•.

66

4.2

General principles of hygrometers

67

4.2.1

Humidity-measuring instruments based on change of dimension of hygroscopic substances the hair hygrometer •...............

68

4.2.2

The organic membrane hygrometer

72

4.2.3

The electrical-resistance hygrometer

72

4.2.4

The psychrometer

72

4.2.5

Remote-reading and recording psychrometers

77

4.2.6

The dewcel

78

CHAPTER 5 - MEASUREMENT OF SURFACE-WIND DIRECTION AND SPEED 5.1

Wind direction and wind speed measurement

specific features

units of

82

5.2

Principles of wind-measuring instruments

85

5.2.1

Sensing the wind direction the wind vane mechanical, electrical potentiometric, selsyn signal converters •.....•....

85

5.2.2

The pressure-plate anemometer

89

5.2.3

propeller. Signal converters The rotation sensor: cup-wheel for rotation sensors electrical contact breaker lightchopper direct-current generator alternating-current generator ................ , ............................ , ...... .

91

5.2.4

The Pitot tube/Krell's micromanometer arrangement

99

5.2.5

Thermoanemometers

102

5.2.6

Anemometers measuring run-of-wind

104

5.2.7

Anemographs the pressure-tube type and the electrical ring-potentiometer type ... , .................................. . 105

CHAPTER 6 - MEASUREMENT OF PRECIPITATION

6,1

General liquid and solid precipitation units of measurement •.•.................... , ...................... , ... , 110

VII

CONTENTS

6.2

Principles of the point measurement of precipitation

110

6.2.1

Non-recording precipitation gauges daily raingauges of the unshielded and shielded types totalizers accessories

110

6.2.2

Recording precipitation gauges syphon (float) type tipping-bucket weighing-balance type .................. . 113

6.2.3

The rate-of-rainfall recorder (Jardi)

120

6.2.4

Snow-measuring instruments

122

6.2.5

Dew-measuring instruments

124

6.2.6

Radar precipitation-measurement principle

125

6,3

Exposure requirements concerning precipitation pointmeasurement instruments ....................................... 130

6.4

Routine care of precipitation-measuring instruments

130

6,5

Factors affecting the accuracy of point-precipitation measurements

130

6.5.1

Wind-error conversion factor

131

6.5.2

Wetting loss

6.5.3

Evaporation loss

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CHAPTER 7 - MEASUREMENT OF EVAPORATION 7.1

General

units of measurement

7.2

Principles of evaporation-measuring instruments

7.2.1

The evaporation pan: Class-A pan the elephant pan (20 m2 tank) Piche

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7.2.2

Atmometers

7.2.3

Evaporation-recording instruments

141

7.2.4

Evapotranspirometers

142

7.3

General requirements for the evaporation-measuring instruments' exposure •........................................• 144

7.4

Routine care of evaporation-measuring instruments

7.5

Comparability of measurement results obtained through different evaporation-measuring instruments .••••••......•..... 145

144

CHAPTER 8 - SUNSHINE-DURATION MEASUREMENT

8.1

General

146

8.2

Principles of sunshine-duration measurement

146

8.2.1

The Campbell-Stokes sunshine-duration recorder

146

8.2.2

The Jordan and Marvin sunshine-duration recorders

150

8.3

Siting and exposure requirements for sunshine-duration measuring instruments factors affecting the sunshine records of the Campbell-Stokes instrument .................... . 151

CONTENTS

VIII

8,4

CHAPTER 9

Routine care of the Campbell-Stokes sunshine recorder measurement of burn trace on the cards ••.........•.......• 155 - SOLAR-RADIATION MEASURING INSTRUMENTS

9.1

General

9.2

Solar-radiation measuring instruments

9.2.1

Direct solar-radiation measuring instruments

9.2.2

Total (global) solar-radiation measuring instruments

9.2.3

Measurement of diffuse solar radiation

176

9,3

Siting and exposure of solar-radiation measuring instruments

177

9.4

Routine care, checking and testing of solar-radiation measuring instruments •.••....... , .........•. , .....•.•........ 177

units of measurement

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••••.•......•.••. 160 •..••.•.• 169

CHAPTER 10 - CLOUD-BASE HEIGHT MEASUREMENT

10.1

General

180

10.2

Principles of cloud-base height measuring instruments

10.2.1

The pilot-balloon ceiling measurement

10.2.2

The cloud searchlight- alidade

10.2.3

The modulated light-beam ceilograph

185

10,2.4

Principle of lidar cloud-base height measurement

188

10.2.5

Brief evaluation of common ceilometer technology

190

10.3

Siting of cloud-ceiling measuring instruments

191

10.4

Routine care of cloud-ceiling measuring instruments

191

units of measurement

•...•••• 181

•......•........••••.... 181

.•.•.••.....•................. 181

CHAPTER 11 - VISIBILITY MEASUREMENTS

11.1

General parameters

definition of visibility

units of measurement

192

11.1.1

Photometric terms and units

193

11.1.2

Attenuation of light in the atmosphere

193

11.1. 3

Threshold of contrast

11.1. 4

Koschmieder's law

11.1. 5

Visibility at night

11.2

Principles of visibility-measuring instruments

11.2.1

Lohle's relative telephotometer

11.2.2

The Collier-Taylor transmissometer

200

11.2.3

The scopograph transmissometer

201

11.2.4

The Brewer-Beutel scatter-meter

204

11.3

Sources of error in visibility measurements

205

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IX

CONTENTS Page 11.4

Routine care of visibility-measuring instruments

............. 206

CHAPTER 12 - UPPER-WIND MEASUREMENTS 12.1

General

units of measurements

12.2

Meteorological balloons

207

12.3

Gases for inflation of meteorological balloons

209

12.4

Hydrogen generators for aerological purposes

210

12.4.1

The ferrosilicon and caustic-soda high-pressure hydrogen generator .•...•...........................................•.. 211

12.4.2

The caustic-soda and aluminium hydrogen generator

212

12.4.3

The Stuart hydrogen electrolytic generator

213

12.5

Theory of upper-wind measurement

214

12.5.1

Graphical method for the evaluation of the pilot-balloon observation ("pibal") ••.•.................................... 215

12.5.2

Buoyancy of a meteorological balloon

217

12.5.3

Vertical velocity of a meteorological balloon

217

12.5.4

Change in the ascent velocity of the balloon with height

218

12.5.5

The pilot-balloon theodolite

221

207

CHAPTER 13 - RADIOSOUNDING OF THE UPPER ATMOSPHERE 13.1

General

13.2

Principle of the radiosounding system

13.3

Principle of the radiosounding ascent evaluation

223

units of measurement

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CHAPTER 14 - COUNTING OF LIGHTNING FLASHES 227

14.1

Nature of lightning

purpose of flash-counting

14.2

The Sullivan-Wells lightning-flash counter

229

14.3

The transistorized lightning-flash counter

231

14.4

Installation and siting of lightning-flash counters

232

14.5

Routine maintenance of lightning-flash counters

232

CHAPTER 15 - AUTOMATION OF THE MEASUREMENT OF METEOROLOGICAL VARIABLES objectives

233

15.1

Technical and economic aspects of automation

15.2

Classification of automatic weather stations

234

15.3

Basic block diagram of an automatic weather station

235

15.4

Sensors used with automatic weather stations

238

15.5

Maintenance of automatic weather stations

238

15.6

Reliability of automatic equipment

241

CONTENTS

X

PART 2

INTRODUCTION

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METEOROLOGICAL INSTRUMENT MAINTENANCE WORKSHOPS, CALIBRATION LABORATORIES AND ROUTINES

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CHAPTER 16 - METEOROLOGICAL INSTRUMENT MAINTENANCE WORKSHOP ACTIVITIES

16.1

Installation and maintenance of station facilities and equipment

249

16.2

Installation and maintenance of meteorological instruments

249

16.3

Repair of existing and design of new meteorological instruments and equipment o • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

250

General approach to the assessment of the instrument maintenance and repair workload •••.••..••......••.••.•..••••

251

16.5

Layout of workshop and storage space

253

16.6

Lighting - heating - ventilation - acoustic insulation -

16.4

safety considerations

••..•.••••..••••..••.••••••••..•••..•..

256

16.7

Layout of machines, tools and equipment - general

258

16.8

Workshop personnel -general - qualifications

261

16o9

The fine mechanics maintenance workshop (FMMW)

262

16.9.1

The FMMW furniture

263

16.9.2

The FMMW tools and equipment

16.10

Electrical and electronics maintenance workshop (EEMW)

271

16.10.1

Furniture layout of the average EEMW

272

16.10.2

EEMW equipment

274

16.10.3

EEMW personnel - qualifications

277

16.11

The mechanical maintenance workshop

277

16.11.1

Layout of furniture and machine-tools in the lathe-turning, milling and shaping sub-unit •••.•••••..•.•.•...••..•....••••

278

Layout of furniture and equipment in the sheet-iron workshop ••.•.••.••..•.........•.................•.......•.••

281

16.11.3

Forging, gas- and arc-welding workshop

287

16.11.4

Electroplating workshop

16 .11. 5

The carpenter's workshop

16.12

The mobile workshop

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CHAPTER 17 - METEOROLOGICAL INSTRUMENT CALIBRATION LABORATORIES AND ROUTINES

17.1

Calibration laboratories - general

299

XI

CONTENTS

17.2

Layout of the calibration laboratories (general) interaction with other branches dealing with meteorological observations and instruments ••••••••••••••••••.••••.••••••.•

300

17.3

Working conditions and safety considerations

300

17.4

Personnel - qualifications

301

17.5

Periodic and non-periodic activities

302

17.6

Atmospheric-pressure laboratory

303

17.601

Calibration and testing equipment

303

17.6.2

Standard instruments and routines

312

17.6.3

Mercury-purification and barometer-filling station

317

17.7

Temperature/humidity laboratory

325

17.7 .1

333

17.7 .2

Summary of the desirable features of thermostats and test chambers ·················••o••••···························· Standard instruments

17.7. 3

Routines

334

17.7 .4

Calibration of thermographs

17.7. 5

Psychrometer testing

17.7 .6

Calibration of hair hygrometers and hygrographs

1708

Anemometry laboratory

17,8.1

Calibration equipment

17.8,2

Standard instruments

17.8,3

Calibration routines

17.9

Solar-radiation laboratory

17.9.1

Standard instruments

17 9,2

Meteorological and performance control over solar-radiation measuring instruments -routine activities ••••••••••••••.••

349

17.10

Failure statistics of meteorological instruments

359

REFERENCES

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NOTE CONCERNING FIGURES ACKNOWLEDGEMENTS

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