Meteorological Measurements and Instrumentation

Giles Harrison is Professor of Atmospheric Physics at the Department of Meteorology at the University of Reading, UK. His research focuses on one of the oldest experimental topics in meteorology, atmospheric electricity and the development of new surface and balloon-carried instruments for environmental measurements.

"“Thorough” is an apt description for the content of this book. A specialist book on Meteorological Measurements is long overdue, and this book is welcome. If a book was destined for sensor system designers it would need to be a thick volume, but for meteorologists needing to have a less detailed description of instruments it is ideal....all scientists/engineers need to be conversant with sensor systems, albeit at a high level (ie. to know how a system works, not necessarily to design it!). So, this book is “pitched” at just the right level." Weather, Royal Meteorological Society, April 2015

• Series Foreword xiPreface xiiiAcknowledgements xvDisclaimer xvii1 Introduction 11.1 The instrumental age 21.2 Measurements and the climate record 21.3 Clouds and rainfall 31.4 Standardisation of air temperature measurements 41.5 Upper air measurements 51.5.1 Manned balloon ascents 61.5.2 Self-reporting upper air instruments 71.6 Scope and structure 82 Principles of Measurement and Instrumentation 92.1 Instruments and measurement systems 92.1.1 Instrument response characterisation 102.1.2 Measurement quality 122.2 Instrument response time 142.2.1 Response to a step-change 142.2.2 Response to an oscillation 152.3 Deriving the standard error 182.3.1 Sample mean 182.3.2 Standard error 202.3.3 Quoting results 202.4 Calculations combining uncertainties 212.4.1 Sums and differences 212.4.2 Products and quotients 222.4.3 Uncertainties from functions 232.5 Calibration experiments 233 Electronics and Analogue Signal Processing 273.1 Voltage measurements 283.2 Signal conditioning 283.2.1 Operational amplifiers 293.2.2 Operational amplifier fundamentals 303.2.3 Signal amplification 313.2.4 Buffer amplifiers 333.2.5 Inverting amplifier 333.2.6 Line driving 353.2.7 Power supplies 363.3 Voltage signals 383.3.1 Electrometers 383.3.2 Microvolt amplifier 403.4 Current measurement 413.4.1 Current to voltage conversion 423.4.2 Photocurrent amplifier 433.4.3 Logarithmic measurements 443.4.4 Calibration currents 453.5 Resistance measurement 463.5.1 Thermistor resistance measurement 463.5.2 Resistance bridge methods 473.6 Oscillatory signals 503.6.1 Oscillators 503.6.2 Phase-locked loops 533.6.3 Frequency to voltage conversion 543.7 Physical implementation 544 Data Acquisition Systems and Initial Data Analysis 574.1 Data acquisition 574.1.1 Count data 594.1.2 Frequency data 604.1.3 Interval data 604.1.4 Voltage data 614.1.5 Sampling 634.1.6 Time synchronisation 664.2 Custom data logging systems 664.2.1 Data acquisition cards 674.2.2 Microcontroller systems 674.2.3 Automatic Weather Stations 684.3 Management of data files 694.3.1 Data logger programming 694.3.2 Data transfer 704.3.3 Data file considerations 714.4 Preliminary data examination 724.4.1 In situ calibration 724.4.2 Time series 734.4.3 Irregular and intermittent time series 754.4.4 Further data analysis 755 Temperature 775.1 The Celsius temperature scale 775.2 Liquid in glass thermometry 785.2.1 Fixed interval temperature scales 785.2.2 Liquid-in-glass thermometers 795.3 Electrical temperature sensors 805.3.1 Thermocouple 815.3.2 Semiconductor 815.3.3 Thermistor 825.3.4 Metal resistance thermometry 835.4 Resistance thermometry considerations 865.4.1 Thermistor measurement 875.4.2 Platinum resistance measurement 895.5 Thermometer exposure 905.5.1 Radiation error of air temperature sensors 905.5.2 Thermometer radiation screens 915.5.3 Radiation errors on screen temperatures 935.5.4 Lag times in screen temperatures 955.5.5 Screen condition 985.5.6 Modern developments in screens 995.6 Surface and below-surface temperature measurements 995.6.1 Surface temperatures 995.6.2 Soil temperatures 1005.6.3 Ground heat flux density 1006 Humidity 1036.1 Water vapour as a gas 1036.2 Physical measures of humidity 1056.2.1 Absolute humidity 1066.2.2 Specific humidity 1066.2.3 Relative humidity 1076.2.4 Dew point and wet bulb temperature 1076.3 Hygrometers and their operating principles 1096.3.1 Mechanical 1096.3.2 Chemical 1116.3.3 Electronic 1116.3.4 Spectroscopic 1126.3.5 Radio refractive index 1136.3.6 Dew point meter 1146.3.7 Psychrometer 1146.4 Practical psychrometers 1166.4.1 Effect of temperature uncertainties 1186.4.2 Ventilation effects 1186.4.3 Freezing of the wet bulb 1206.5 Hygrometer calibration using salt solutions 1216.6 Comparison of hygrometry techniques 1227 Atmospheric Pressure 1237.1 Introduction 1237.2 Barometers 1237.2.1 Liquid barometers 1247.2.2 Mercury barometers 1257.2.3 Hypsometer 1277.2.4 Aneroid barometers 1277.2.5 Precision aneroid barometers 1287.2.6 Flexible diaphragm sensors 1297.2.7 Vibrating cylinder barometer 1297.3 Corrections to barometers 1297.3.1 Sea level correction 1307.3.2 Wind speed corrections 1318 Wind Speed and Direction 1338.1 Introduction 1338.2 Types of anemometer 1338.2.1 Pressure plate anemometers 1338.2.2 Pressure tube anemometer 1348.2.3 Cup anemometers 1348.2.4 Propeller anemometer 1368.2.5 Hot sensor anemometer 1378.2.6 Sonic anemometer 1398.3 Wind direction 1418.3.1 Wind vanes 1428.3.2 Horizontal wind components 1448.3.3 Multi-component research anemometers 1468.4 Anemometer exposure 1468.4.1 Anemometer deficiencies 1468.5 Wind speed from kite tether tension 1489 Radiation 1519.1 Introduction 1519.2 Solar geometry 1549.2.1 Orbital variations 1549.2.2 Diurnal variation 1559.2.3 Solar time corrections 1559.2.4 Day length calculation 1569.2.5 Irradiance calculation 1579.3 Shortwave radiation instruments 1589.3.1 Thermopile pyranometer 1589.3.2 Pyranometer theory 1599.3.3 Silicon pyranometers 1629.4 Pyrheliometers 1629.5 Diffuse solar radiation measurement 1649.5.1 Occulting disk method 1649.5.2 Shade ring method 1659.5.3 Reflected shortwave radiation 1689.5.4 Fluctuations in measured radiation 1699.6 Reference solar radiation instruments 1719.6.1 Cavity radiometer 1729.6.2 Secondary pyrheliometers 1729.7 Longwave instruments 1739.7.1 Pyrradiometer theory 1739.7.2 Pyrradiometer calibration 1749.7.3 Pyrgeometer measurements 1759.7.4 Commercial pyrradiometers 1759.7.5 Radiation thermometry 1779.8 Sunshine duration 1789.8.1 Campbell–Stokes sunshine recorder 1809.8.2 Electronic sensors 18110 Clouds, Precipitation and Atmospheric Electricity 18310.1 Introduction 18310.2 Visual range 18310.2.1 Point visibility meters 18410.2.2 Transmissometers 18510.2.3 Present weather sensors 18510.3 Cloud base measurements 18610.4 Rain gauges 18710.4.1 Tilting siphon 18810.4.2 Tipping bucket 18810.4.3 Disdrometers 19110.5 Atmospheric electricity 19110.5.1 Potential Gradient instrumentation 19110.5.2 Variability in the Potential Gradient 19210.5.3 Lightning detection 19311 Upper Air Instruments 19511.1 Radiosondes 19511.1.1 Sounding balloons 19611.2 Radiosonde technology 19711.2.1 Pressure sensor 19911.2.2 Temperature and humidity sensors 20011.2.3 Wind measurements from position information 20111.2.4 Data telemetry 20211.2.5 Radio transmitter 20311.3 Uncertainties in radiosonde measurements 20411.3.1 Response time 20411.3.2 Radiation errors 20411.3.3 Wet-bulbing 20611.3.4 Location error 20711.3.5 Telemetry errors 20811.4 Specialist radiosondes 20911.4.1 Cloud electrification 20911.4.2 Ozone 20911.4.3 Radioactivity and cosmic rays 21011.4.4 Radiation 21011.4.5 Turbulence 21111.4.6 Supercooled liquid water 21111.4.7 Atmospheric aerosol 21211.5 Aircraft measurements 21211.5.1 Air temperature 21211.5.2 Wind 21211.5.3 Pressure 21311.5.4 Altitude 21311.6 Small robotic aircraft 21312 Further Methods for Environmental Data Analysis 21512.1 Physical models 21512.1.1 Surface energy balance 21512.1.2 Turbulent quantities and eddy covariance 21712.1.3 Soil temperature model 21812.1.4 Vertical wind profile 22012.2 Solar radiation models 22212.2.1 Langley’s solar radiation method 22212.2.2 Surface solar radiation: Holland’s model 22412.3 Statistical models 22512.3.1 Histograms and distributions 22612.3.2 Statistical tests 22612.3.3 Wind gusts 22912.4 Ensemble averaging 22912.4.1 Solar radiation variation 23012.4.2 Pressure tides 23112.4.3 Carnegie curve 23112.5 Spectral methods 23312.5.1 Power spectra 23312.5.2 Micrometeorological power spectra 23512.6 Conclusion 237Appendix A Writing a Brief Instrumentation Paper 239A.1 Scope of an instrument paper 239A.2 Structure of an instrument paper 239A.2.1 Paper title 239A.2.2 Abstract 240A.2.3 Keywords 240A.2.4 Motivation 240A.2.5 Description 240A.2.6 Comparison 241A.2.7 Figures 241A.2.8 Summary 242A.2.9 Acknowledgements 242A.3 Submission and revisions 242Appendix B Anemometer Coordinate Rotations 243References 247Index 253