Meteorological Measurements and Instrumentation

"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

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.

Series Foreword xi Preface xiii Acknowledgements xv Disclaimer xvii 1 Introduction 1 1.1 The instrumental age 2 1.2 Measurements and the climate record 2 1.3 Clouds and rainfall 3 1.4 Standardisation of air temperature measurements 4 1.5 Upper air measurements 5 1.5.1 Manned balloon ascents 6 1.5.2 Self-reporting upper air instruments 7 1.6 Scope and structure 8 2 Principles of Measurement and Instrumentation 9 2.1 Instruments and measurement systems 9 2.1.1 Instrument response characterisation 10 2.1.2 Measurement quality 12 2.2 Instrument response time 14 2.2.1 Response to a step-change 14 2.2.2 Response to an oscillation 15 2.3 Deriving the standard error 18 2.3.1 Sample mean 18 2.3.2 Standard error 20 2.3.3 Quoting results 20 2.4 Calculations combining uncertainties 21 2.4.1 Sums and differences 21 2.4.2 Products and quotients 22 2.4.3 Uncertainties from functions 23 2.5 Calibration experiments 23 3 Electronics and Analogue Signal Processing 27 3.1 Voltage measurements 28 3.2 Signal conditioning 28 3.2.1 Operational amplifiers 29 3.2.2 Operational amplifier fundamentals 30 3.2.3 Signal amplification 31 3.2.4 Buffer amplifiers 33 3.2.5 Inverting amplifier 33 3.2.6 Line driving 35 3.2.7 Power supplies 36 3.3 Voltage signals 38 3.3.1 Electrometers 38 3.3.2 Microvolt amplifier 40 3.4 Current measurement 41 3.4.1 Current to voltage conversion 42 3.4.2 Photocurrent amplifier 43 3.4.3 Logarithmic measurements 44 3.4.4 Calibration currents 45 3.5 Resistance measurement 46 3.5.1 Thermistor resistance measurement 46 3.5.2 Resistance bridge methods 47 3.6 Oscillatory signals 50 3.6.1 Oscillators 50 3.6.2 Phase-locked loops 53 3.6.3 Frequency to voltage conversion 54 3.7 Physical implementation 54 4 Data Acquisition Systems and Initial Data Analysis 57 4.1 Data acquisition 57 4.1.1 Count data 59 4.1.2 Frequency data 60 4.1.3 Interval data 60 4.1.4 Voltage data 61 4.1.5 Sampling 63 4.1.6 Time synchronisation 66 4.2 Custom data logging systems 66 4.2.1 Data acquisition cards 67 4.2.2 Microcontroller systems 67 4.2.3 Automatic Weather Stations 68 4.3 Management of data files 69 4.3.1 Data logger programming 69 4.3.2 Data transfer 70 4.3.3 Data file considerations 71 4.4 Preliminary data examination 72 4.4.1 In situ calibration 72 4.4.2 Time series 73 4.4.3 Irregular and intermittent time series 75 4.4.4 Further data analysis 75 5 Temperature 77 5.1 The Celsius temperature scale 77 5.2 Liquid in glass thermometry 78 5.2.1 Fixed interval temperature scales 78 5.2.2 Liquid-in-glass thermometers 79 5.3 Electrical temperature sensors 80 5.3.1 Thermocouple 81 5.3.2 Semiconductor 81 5.3.3 Thermistor 82 5.3.4 Metal resistance thermometry 83 5.4 Resistance thermometry considerations 86 5.4.1 Thermistor measurement 87 5.4.2 Platinum resistance measurement 89 5.5 Thermometer exposure 90 5.5.1 Radiation error of air temperature sensors 90 5.5.2 Thermometer radiation screens 91 5.5.3 Radiation errors on screen temperatures 93 5.5.4 Lag times in screen temperatures 95 5.5.5 Screen condition 98 5.5.6 Modern developments in screens 99 5.6 Surface and below-surface temperature measurements 99 5.6.1 Surface temperatures 99 5.6.2 Soil temperatures 100 5.6.3 Ground heat flux density 100 6 Humidity 103 6.1 Water vapour as a gas 103 6.2 Physical measures of humidity 105 6.2.1 Absolute humidity 106 6.2.2 Specific humidity 106 6.2.3 Relative humidity 107 6.2.4 Dew point and wet bulb temperature 107 6.3 Hygrometers and their operating principles 109 6.3.1 Mechanical 109 6.3.2 Chemical 111 6.3.3 Electronic 111 6.3.4 Spectroscopic 112 6.3.5 Radio refractive index 113 6.3.6 Dew point meter 114 6.3.7 Psychrometer 114 6.4 Practical psychrometers 116 6.4.1 Effect of temperature uncertainties 118 6.4.2 Ventilation effects 118 6.4.3 Freez