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Fieldwork: Measuring temperatures with an infrared thermometer

measuring temperatures - clouds

Introduction

Infrared thermometers provide an easy way of measuring the temperature of a range of things, which can give insights into (a) how solar energy (the driving force behind weather and climate) is absorbed and (b) clouds.

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Length of time

One hour plus.

 

Suitable locations

School grounds, field trips.

 

Equipment needed

Infrared thermometer

An infrared thermometer (pictured to the right). Typically £10-15 online. It should have a range down to minus 50C.

 

Objectives

  1. To measure the temperature of some objects outdoors.
  2. To understand the importance of solar radiation.
  3. To calculate the height of clouds.

 

Key skills

  • observing techniques
  • recording measurements
  • simple calculations.

 

Suggested delivery

An Infrared (IR) thermometer measures the temperature of any object in front of it, no matter how near or far – it could be the grass at your feet or a cloud 10km high. But the object has to fill the field of view of the thermometer, which is usually about a tenth of the distance. So an object 1m big will fill the field of view of the IR thermometer when it is 10m away or closer.

What is the temperature of things around us on a sunny day?

Different colours – Ask the students to compare the temperature of similar dark and light coloured objects; for example, grass, soil, sand, concrete and tarmac, or dark and light cars in a car park. (They should find that dark colours are warmer than light colours because dark colours absorb more of the sun’s energy than light colours do).

Sunny and shady – If the sun is shining, measure the temperature of the ground (tarmac, soil, grass) in sunlight and nearby in shade.

Wet and dry – Put some water on part of a tarmac or concrete surface and leave it for a minute or so. Does the wet patch have the same temperature as the dry patch next to it? If not, why not? (The wet part may be cooled due to evaporation of water from it).

What temperature are clouds?

NB: It is likely that temperatures of clouds will be negative (below freezing) so make sure students recognise the difference between positive and negative temperatures shown on the thermometer.

First, point the thermometers at something in the shade (e.g. grass) to get a very rough estimate for the air temperature at ground level. Next, point the thermometer at any cloud and measure its temperature. Are the clouds warmer or colder than the ground? So, does temperature rise or fall with height? (Temperature falls with height. The sun warms the ground. The ground warms the air in contact with it. The warmer air rises, and, because air pressure is lower as we go up, the rising air expands, and the expansion causes it to cool).

What are high clouds made of? The highest clouds, called cirrus, are made of tiny ice crystals which gives them their wispy appearance. Lower clouds (such as fluffy cumulus) are made of small water droplets. Clouds in between are a mixture of ice crystals and water droplets.

You can calculate the height of the base of the clouds by assuming that the temperature falls by 6°C for every km of height. So if the temperature near the ground is 10°C, and the cloud temperature is -20°C, giving a difference of 30°C, then the cloud base is about 30/6 = 5km high.

 

Potential risks to consider

IR thermometers are equipped with a laser pointer on the front; cover this with mastic so that no laser light is emitted. Take care not to wander into roads, ditches, obstacles etc. when wandering around with thermometers, especially when pointing them upwards to measure clouds.

 

Possible follow up activities

More detail about this investigation, some extension activities, and learning outcomes can be found at the Royal Meteorological Society’s Experiments with an Infrared Thermometer page.

 

Useful links

Identify different types of clouds, and the height they are at, using this cloud chart by the Royal Meteorological Society.

Other fieldwork ideas from the Royal Meteorological Society can be found here.

 

This collection of Fieldwork activities were created by Paula Richardson and the Fieldwork and Outdoor Learning Special Interest Group (FOLSIG) for the National Festival of Fieldwork, the GA invites everyone to take part during the summer term.

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