ISO 18386:2025
(Main)Soil quality — Screening method for soil temperature — Measurement by infrared (IR) thermometer
Soil quality — Screening method for soil temperature — Measurement by infrared (IR) thermometer
This document specifies a method for quick measurement of soil temperature using an infrared (IR) thermometer. The method is applicable to a variety of technical fields, including geology, geotechnics, biology and agricultural sciences, as well as climate change studies and metrological investigation. Note The method designated in this document is recognized as a quick measurement in ISO 4974 and meets the definition of screening method as designated in ISO 12404:2021, 3.2.
Qualité du sol — Méthode de criblage pour la température du sol — Mesure par thermomètre infrarouge (IR)
General Information
Standards Content (Sample)
International
Standard
ISO 18386
First edition
Soil quality — Screening method for
2025-06
soil temperature — Measurement
by infrared (IR) thermometer
Qualité du sol — Méthode de criblage pour la température du sol
— Mesure par thermomètre infrarouge (IR)
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle and application . . 1
4.1 Fundamentals .1
4.2 IR detection principle .2
4.3 Typical original application of IR thermometers .2
4.4 Diversion of IR thermometers to soil temperature measurement .2
5 Apparatus . 3
6 Procedure . 3
6.1 General .3
6.2 Drilling a hole.3
6.3 IR detection .3
6.3.1 General .3
6.3.2 Close-to-a-spot measurement . . .4
6.3.3 Remote measurement .4
7 Quality assurance and quality control . 4
8 Test report . 4
Bibliography . 5
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
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This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3, Chemical
and physical characterization.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
Soil temperature gives useful information in the engineering and industrial fields, especially geology,
geotechnics, biology and agriculture. In recent years, climate change issues have been discussed globally,
including greenhouse gas emissions from soil. Microbial decomposition of organic matter contributes to
greenhouse gas emissions from soils, with the activity of the microbes and hence the rate or flux of these
emissions dependent on soil temperature. Hence the temperature of the soil can be an indirect indicator
of its risk of greenhouse gas emissions. Soil temperature directly affects the growth of plants. Optimum
temperatures or temperature ranges exist for plant germination, growth and ultimately yield.
The guidance document for measurement of soil temperature (ISO 4974) describes two approaches,
depending on the purpose of the investigation and the accuracy required. Conventional measurement is
applied where greater accuracy is needed, whereas quick measurements can be made (e.g. using an infrared
(IR) thermometer) where accuracy is not as critical, thus allowing to improve measurement efficiency (e.g.
measurement time per spot) in exchange for accuracy.
This document describes the principle of quick measurement for soil temperature applying infrared (IR)
detection, which is briefly introduced (without the measurement procedure descriptions) in ISO 4974 as one
of the soil temperature measurement methods. ISO 4974 contains general discussions about temperature
and its measurement principles, including what soil temperature is, why it is measured, by what kinds of
principles it can be measured and how measurement methods should be appropriately selected depending
on given soil temperature measurement purposes. This document describes the details of a specific soil
temperature measurement procedure using an IR thermometer and explains the measurement principle.
This method is positioned as one of the screening methods which have been developed under the concept
designated in ISO 12404, which is a general guidance document of screening methods.
v
International Standard ISO 18386:2025(en)
Soil quality — Screening method for soil temperature —
Measurement by infrared (IR) thermometer
1 Scope
This document specifies a method for quick measurement of soil temperature using an infrared (IR)
thermometer.
The method is applicable to a variety of technical fields, including geology, geotechnics, biology and
agricultural sciences, as well as climate change studies and metrological investigation.
NOTE The method designated in this document is recognized as a quick measurement in ISO 4974 and meets the
definition of screening method as designated in ISO 12404:2021, 3.2.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
soil temperature
temperature measured at a targeted spot in the soil or at the soil surface
Note 1 to entry: The temperature at a spot in the ground shallower than 300 mm is affected by the atmospheric
temperature. When measuring temperatures at such depths, one should be aware of this effect.
4 Principle and application
4.1 Fundamentals
Temperature cannot be measured directly. It can only be estimated by its influence on some properties of
matter that responds to variation in the intensity of heat in an object’s body. Liquid forms of matter such as
mercury have been used historically, but ethanol and kerosene are more commonly used today. Changes in
the volumes of these liquids with temperature are used as practical means to measure temperature. Alcohol
thermometers contain these organic liquids in a glass tube marked with a calibrated scale, which relates the
change in the volume of the solvent to changes in temperature.
When estimating the temperature of a target object using an alcohol thermometer, the liquid that responds to
the object is brought into close contact with the object. The measurement is made after thermal equilibriums
have been reached between the target object and alcohol responding to the object’s heat, as well as between
alcohol and its volume responding to the heat of alcohol itself. However, it takes time for both object and
alcohol and for both alcohol and its volume to reach the respective equilibriums.
Target objects for temperature measurement emit heat-generated signals (a typical one being IR radiation),
the intensities of which are directly proportional to the temperature within a certain range. The IR intensity
can be observed directly without matter such as alcohol that is used in liquid-in-glass thermometers to
indicate, as its volume changes, the target object temperature. An IR thermometer requires no thermal
equilibrium conditions which are to be achieved by methods using matter responsive to the object’s heat.
Thus, an IR thermometer permits to observe the IR intensity quickly and provides a remote measurement
of the target object temperature without contacts with the object. However, the accuracy is not necessarily
as high as achieved by direct temperature measurement using contact thermometers (such as alcohol
thermometers), due to the attenuation of the IR wave while propagating from the object to the sensor. In
order to overcome this complication of IR wave attenuation, great advances have been made (e.g. using a
lens to collect more IR waves from the object and focusing them on the sensor).
4.2 IR detection principle
Regarding the original application of IR thermometers and its diversion to soil temperature measurement,
the principle and procedure developed for measuring human body fever can be simply applied to soil
temperature measurement without any modification or alternation. The principle of the measurement by
IR thermometer is totally different to that of conventional soil temperature measurement methods (such as
liquid-in-glass thermometers) and offers advantages over conventional methods.
IR thermometers are used as a practical option for quick measurement of temperature. IR thermometers
are devices w
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