04/07/2025
CONFUSED OVER AIR TEMPERATURE MEASUREMENT?
With the very high temperatures upon us understanding what the various temperature measurements mean is important.
Tools are increasingly being developed to perform temperature measurement. Nevertheless, the temperature that we indicate in our forecasts only represents a measurement of a precise variable: that of the air near the ground in other words that felt by the population.
Today there are different variables of temperature measurements across the planet, divided into three main categories:
- The "Atmospheric" measurement: this is the temperature of the air above the earth's surface (near the ground, or at different altitudes).
- The "Soil" measurement: this is the temperature of the soil, either at surface level or at depth.
- The "Oceanic" measurement: this is the temperature of the seas and oceans, generally at the surface but also over the first few meters.
The temperature measurement of the surface of the ground is carried out for the most part by remote sensing (satellite sensor), via the radiation of the soil emitted towards space (even if certain terrestrial sensors make it possible to carry out in-situ measurements on the first meters below the surface). This is a measurement that varies significantly according to many parameters: such as the reflection of solar energy: a white surface will be more reflected and will accumulate less heat than a black surface), the state of humidity soil or the type of soil (vegetated, bare, urbanized, burned, snow-covered). The variations in surface temperature are therefore much greater than the variations in air temperature.
What are the Air Temperatures measurement standards?
To perform air temperature measurement in good conditions, and in a homogeneous way in all countries, the World Meteorological Organization (WMO) has listed a series of demanding standards, defined through its "Guide to instruments and methods". This guide specifically requires the installation of sensors according to these criteria:
- The sensors inside the weather shelter must be installed at a height determined by the Meteorological Service between 1.25 and 2m above the surface of the ground. The height should in no case be less than 1.25 m;
- The thermometer and its shelter must be installed in the most open environment possible because the obstacles around the shelter affect the measurement. Indeed, a shelter installed near a vertical obstacle (tree, building, etc.) runs the risk of being “protected” from solar radiation or night time radiative cooling of the air, thus running the risk of causing overheating or vice versa;
- The thermometer must be kept absolutely away from any heat source, reflective surface (buildings, concrete areas, car parks, etc.) and bodies of water (ponds, lakes, irrigated areas, etc.) which may affect the measurement according to the ambient wind conditions.
These are the ones used for example by IPMA in the daily weather forecasts
