Many of us have to look twice to even notice that these two words are different!
But different they certainly are:
- Metrology is the science of measurement. Metrology comes from two Greek words (metron and logos) and literally means “the study of measurements”.
- Meteorology is the science of the atmosphere. This word also comes from two Greek words (meteor and logy) and literally means “the study of things high in the air”.
A modern dictionary definition of meteorology is:
· The branch of science concerned with the processes and phenomena of the atmosphere, especially as a means of forecasting the weather.
What, then is weather?
Weather is the ‘state of the atmosphere’ or ‘the atmospheric conditions’ at a particular place and time. A dictionary definition, as a noun, says it’s ‘the state of the atmosphere at a particular place and time as regards heat, cloudiness, dryness, sunshine, wind, rain, etc.’
We label the weather with all sorts of words. It can be good, bad, nice, awful, beautiful, terrible, and many other words that describe how we experience our local atmospheric conditions. But if we are to make a science of meteorology, we need to be able to measure some of these descriptors. Consequently we have developed technologies to measure things like temperature, wind conditions, moisture content, cloud conditions, etc.
A typical brief weather report from the Australian Bureau of Meteorology (‘The Bureau’ 😊) could look like this:
0.0mm rain since 9am.
While we all understand what such a brief report means, it is worth taking a little time to analyse how this has been achieved.
- Firstly, this information has to accommodate variations across the time range and across quite large areas (the weather even in Sydney varies quite a bit)
- There is a whole science around how, when and where to measure current temperature and wind speed.
- Forecasted maximum temperature is calculated via a model defined by Australian Standards.
- Even the descriptor “sunny”, while not a number, is still a defined observation – a measurement without a number if you like.
So, weather is effectively a group of measurements.
And one definition of measurement is the quantification of attributes of an object or event that can be used to compare with other objects or events.
As we are becoming more and more aware, weather is a global phenomenon. The weather in our neighbour’s paddock influences our paddock, so we would like to get our neighbours ‘group of measurements’ so we can understand how the weather moves around and affects different places.
It’s a good thing a measurement can be used to compare with other object or events. But how do we know that we can compare our measurements with our neighbour’s?
We wouldn’t want to be like the Swedish king Gustavus Adolphus in the 17th century, who ordered a ship with more fire power than any other on the sea. What he got tipped over and sank 1300 m into its maiden voyage! As it turns out the shipbuilders on one side of the ship were using a ruler calibrated in Swedish feet (consisting of 12 Swedish inches), while those on the other side were using a ruler calibrated in Amsterdam feet, consisting of 11 Amsterdam inches. The use of different units of length on the two sides of the vessel caused the ship to be heavier on the port side.
This is, of course, not the whole story of why the ship sank, but it certainly contributed!
These days we want to be confident that when our neighbour tells us that the temperature is 24 °C, that is the same as what we mean by 24 °C!
That’s why we depend so much on metrology.
What, then is metrology?
In the words Richard Brown, Head of Metrology from UK’s National Physical Laboratory:
“If philosophy is ‘thinking about thinking’, then metrology is ‘measuring measurement’.”
“Measurement is the process of experimentally obtaining one or more values that can reasonably be attributed to a quantity or property. Measurement is fundamental to almost all human activity and so it is important that the accuracy of any measurement is fit for its intended purpose.
Metrology is the science of measurement and its application. Metrology is not just about the routine making of measurements, it’s about the infrastructure that ensures that we have confidence in the accuracy of the measurement. It establishes a common understanding of units and measurement processes, crucial to human activity.
Metrology covers the accuracy, precision and repeatability of a measurement. It involves traceability or comparison with a “standard” or between different measuring systems. Metrology includes all theoretical and practical aspects of measurement, whatever the measurement uncertainty or the field of application.”
Texcel has always placed much emphasis on what we call “data integrity” – see our blog from December 2021. Our fixation on the accuracy, precision and repeatability of all our measurements continues into our weather measurements.
To recap, some key concepts in metrology are:
Measurement traceability is the unbroken chain of comparisons between a given measurement device and national or international standards. It gives you confidence that all measurements are stable, comparable and correct within their associated measurement uncertainty.
Calibration is the comparison of measurement values delivered by test equipment or a test sample with those of standard equipment or a standard sample of known accuracy. It can be used to determine how accurate a measurement instrument is. Measurement uncertainty necessarily increases along the sequence of calibrations.
Measurement uncertainty is the doubt that exists about the result of any measurement. Explained another way, it is the range of values within which the true value of a measurement lies. All measurements are subject to uncertainty and a measurement result is complete only when it is accompanied by a statement of the associated uncertainty.
These concepts can get complicated, but they are the reason we can be confident that when our neighbour gives us measurements, they mean the same as our measurements.
UK’s National Physical Laboratory is the UK’s National Measurement Institute (NMI), and as such is a key part of the international measurement system.
Australia too has a National Measurement Institute (NMI), which performs a key role in Australian Science and Industry. One of its key roles is:
- To develop and maintain national measurement standards that are recognised internationally
Texcel’s instruments are calibrated annually, and all calibrations are traceable to Australia’s NMI.
To summarise, what has metrology got to do with meteorology:
- In the words of Weather Observer’s Handbook:
Metrology is the science of instruments and their behaviour. Meteorology is the science of the atmosphere and its phenomena. The two are intimately related by far more than having all but two letters in common, for meteorology depends upon instrumentation to provide quantitative measurements of the state of the atmosphere at any time or over a period of time.