ＩＳＳＮ１３４６－７８４０

港湾空港技術研究所
資料
TECHNICAL NOTEOFTHE PORT AND AIRPORT RESEARCH INSTITUTE

No.1412

December 2023

Quick measurement of soil temperature by means of IR thermometer

杉山 友理，渡部 要一，森川国立研究開発法人

嘉之海上・港湾・航空技術研究所

National Institute of Maritime,
Port and Aviation Technology, Japan

CONTENTS
Synopsis ···························································································································

2

1. Introduction ··················································································································

4

2. Soil temperature measurement method ·············································································

4

3. Measurement results in the field ······················································································

8

3.1

Results of continuous measurements ···········································································

8

3.2

Results of narrow view angle type IR thermometer ·························································

9

3.2.1

Results at Site 1·································································································

9

3.2.2

Results at Site 2································································································

11

3.3

Comparison between the narrow and wide view angle types ··············································

13

3.4

Measurement results in the soil containers ····································································

13

3.5

Summary of measurement results ···············································································

13

4. Conclusions ················································································································

14

Acknowledgement ············································································································ 14
References ······················································································································ 14-1-Quick measurement of soil temperature by means of IR thermometerYuri SUGIYAMA*
Yoichi WATABE**
Yoshiyuki MORIKAWA***

Synopsis
In waterfront soil mechanics for tidal flat, the subsurface soil temperature distribution at depths
where suction develops above groundwater is one of the most important parameters in describing thesoil dynamics. In addition, the subsurface temperature is important for managing curing temperatureof cement treated soil in cold regions. These require the measurement of subsurface temperature overa wide area, so an efficient measurement method is required. In recent years, new methods such as
microbial solidification have also been studied, and it is possible that temperature control in the soil
will become more important. Various types of thermometers are available today, and many of which
can be used to measure soil temperatures. In this study, a method that can avoid the problems ofdamage to the sensor and shorten the standing-by time required for thermal equilibrium wasdeveloped and investigated its applicability to a quick soil temperature measurement. Specifically,
instead of conventional contact thermometers, infrared (IR) thermometer which is a noncontact
thermometer recently developed was attempted to measure soil temperature quickly. A casing pipewith a spacer made of polyvinyl chloride was penetrated from the ground surface to a target depth.
After removing the spacer, the IR thermometer was set into the casing pipe, and then, soil temperature
was measured quickly in about 5 seconds. A stable measurement was successively conducted. It was
confirmed that measured temperature using IR thermometer is sufficiently accurate based on acomparison with the temperature measured by self-recording thermistor thermometer. Bothmeasuring methods using the narrow view angle type IR thermometer setting at the top of the casing
pipe with a longer distance from the target depth and the wide view angle type IR thermometer setting
inside of the casing pipe with a shorter distance from the target depth can measure soil temperature
with sufficient accuracy. Because the linearity between the actual temperature and the displayed
temperature possibly tends to be lost particularly in a low temperature range, it is necessary to pay
attention to the measurable temperature range of the IR thermometer by calibration. As it was
confirmed in this study, because IR thermometer can efficiently/quickly and reliably measure soil
temperature, this new thermometer is applicable to construction management requiring temperature
control, e.g., placement of cement treated soils in winter season in cold region.
Key Words: Soil temperature, thermometer, infrared* Senior researcher, Soil Mechanics and Geo-environment Group, Geotechnical Engineering Department** Visiting Senior Researcher (Professor, Faculty of Engineering, Hokkaido University)*** Director of Geotechnical Engineering Department
3-1-1, Nagase, Yokosuka, Kanagawa 239-0826, JapanPort and Airport Research Institute
Phone : +81-46-844-5053
Fax : +81-46-844-4577
E-mail : sugiyama-yu@p.mpat.go.jp-2-赤外線温度計を用いた地中温度計測
杉山

友理*・渡部

要一**・森川

要

嘉之***

旨

干潟を対象とした水辺の土質力学において，地下水位より上にサクションが発生する深度における地中温度分布は，土質力学において最も重要なパラメータの一つである．また，寒冷地におけるセメント処理土の養生温度管理においても，地中温度の把握は重要である．この場合，広域の地中温度を計測する必要があり，効率的な測定方法が求められる．また，近年では微生物固化などの新しい手法について研究が進められており，地盤中の温度管理がより重要になる可能性が高い．現在，様々なタイプの温度計が販売されており，その多くが地中温度測定に利用可能である．本研究では，センサーの破損の問題を回避し，熱平衡に達するまでの時間を短縮できる方法を開発し，迅速な地中温度測定への適用性について検討した．具体的には，従来の接触型温度計の代わりに，近年開発された非接触型温度計である赤外線（IR）温度計を用いた地中温度の迅速測定方法について検討した．
ポリ塩化ビニルでできたスペーサー付きのケーシングパイプを地表から目標深さまで貫入し，スペーサーを取り外した後，ケーシングパイプに IR 温度計をセットして地中温度を約 5 秒で素早く測定したところ，安定して温度測定をすることができた．自記録式サーミスタ温度計による測定温度との比較から，高い精度で IR 温度計による測定が可能であることを確認した．測定対象深度からの距離が長く，ケーシングパイプ上部に設置する狭視野タイプの IR 温度計と，測定対象深度からの距離が短く，ケーシングパイプ内部に設置する広視野タイプの IR 温度計のいずれの測定方法でも十分な精度で地中温度を測定することができた．しかし，特に低温域においては，実測温度と表示温度との直線性が損なわれることがあるため， IR 温度計の測定可能温度範囲に注意し，必要に応じてキャリブレーションを実施する必要がある．本研究で確認されたように，IR 温度計は効率的・迅速かつ高精度に地中温度を計測できるため，寒冷地における冬季のセメント処理土の打設など，温度管理が必要な施工管理にも適用できるといえる．

キーワード：地中温度，温度計，赤外線* 地盤研究領域土質研究グループ 主任研究官** 客員研究官（北海道大学 大学院 工学研究院 教授）*** 地盤研究領域長〒239-0826 神奈川県横須賀市長瀬3—1—1 国立研究開発法人海上・港湾・航空技術研究所港湾空港技術研究所
電話: 046-844-5053
Fax : 046-844-4577
E-mail : sugiyama-yu@p.mpat.go.jp-3-

1. Introduction

which are easier to handle and require a shorter standing-by timethan mercury-in-glass thermometers, are now widely used. In

In waterfront soil mechanics for tidalflat, the subsurface soil

many cases of these electrical measurement thermometers, thetemperature distribution at depths where suction develops above

sensor itself is protected by a thin metal sheath, which is easily

groundwater is one of the most important parameters indamaged. In addition, because the length of the sensor is as longdescribing the soil dynamics. In addition, the subsurface

as 200 mm (mostly 100 to 150 mm), it is necessary to excavatetemperature is important for managing curing temperature of

the ground to an appropriate depth to measure a temperature at

cement treated soil in cold regions. Temperature control (heatinga target depth deeper than the length of the sensor.

system) is required in placement of cement treated soils in

Considering the background mentioned above, in this study,

winter season in cold region because cement treated soil doesa method that can avoid the problems of damage to the sensor

not harden under very cold temperature. These require theand shorten the standing-by time required for thermal

measurement of subsurface temperature over a wide area, so an

equilibrium was developed and investigated its applicability toefficient measurement method is required.

a quick soil temperature measurement. Specifically, instead ofSoil temperature from ground surface to about 500 mm depth

conventional contact thermometers, infrared (IR) thermometeris an important parameter for evaluating the activity

which is a noncontact thermometer recently developed wasenvironment of microbes that contribute to the decomposition

attempted to measure soil temperature quickly in about 5of organic matters in the soil1)

seconds after the start of measurement using a hole pre-drilled. In recent years, new methods

to a target depth.

such as microbial solidification have also been studied, and it ispossible that temperature control in the soil will become more

2. Soil temperature measurement method

important.
Various types of thermometers are available today2),3),4), andmany of which can be used to measure soil temperatures5). In

The procedure of the quick temperature measurement

the previous days, mercury-in-glass thermometers had been

attempted in this study is shown in Figure 1. The casing pipe

mainly used to measure soil temperatures. Although theused to hold the predrilled hole was a polyvinyl chloride pipe

measurement accuracy of the mercury-in-glass thermometer is(VP30) with an inner diameter of 31 mm and an outer diametervery high, the glass tube is easily damaged, and it takes aof 38 mm, with a length of 900 mm. A polyvinyl chloridestanding-by time for thermal equilibrium after the start ofcylindrical spacer (polyvinyl chloride round rod with an outermeasurement.

withdiameter of 30 mm) having a polyvinyl chloride conical tip withthermistor thermometers and thermocouple thermometers,

an angle of 60° (or tip angle of 30° in a case of stiff soil) was

Therefore,

electricalmeasurement

Figure 1. Procedure for quick soil temperature measurement using an IR thermometer-4-

Figure 2. Distance between IR thermometerand target soil surface
Left: Narrow view angle type
Right: Wide view angle typeFigure 3. Depths of self-recording thermistor thermometers and measurement of
IR thermometer

inserted into the casing pipe. The outer of the threaded

however, it had been confirmed that this condition did not affectconnection between the cylindrical spacer and the conical tip

the soil temperature measurement. Another type of IR

was tapered for setting of an O-ring, and when tightened thethermometer (Sato Keiryoki Mfg. Co., Ltd, SK-8210) with aconnection, the attached O-ring is pushed outward. Thiswide view angle was also used in this study. In a case of IR

mechanism was designed for preventing sand particles fromthermometers with a wide view angle, it was necessary to place

entering the clearance between the casing pipe and the spacer;

the sensor close to the target. Therefore, the sensor was inserted

however, the soil used in this study did not require thisto the casing pipe and placed close to the target depth. The

mechanism. The tip of the casing pipe was also tapered to match

sensor with outer diameter of 23 mm was attached inside the tip

the conical shape of the spacer tip with cone angle of 60°. The

of a plastic pipe with an outer diameter of 27 mm and a wallmaterial of the spacer was polyvinyl chloride, which has low

thickness of 2 mm. And then, it was inserted into the casing pipe

thermal conductivity, so that the temperature of the target soil

with the length of 900 mm, resulting in the distance of 320 mm

would not change before the temperature measurement.

between the tip of the casing pipe and the sensor. In thisThe IR thermometer mainly used in this study was a type withcondition, the field of view has a diameter of 30.3 mm, which

a narrow view angle (HORIBA IT-450F), which can focus onmeans that the measurement is performed on almost the entire

the thermal radiation from a distanced target. It was not affectedsurface of the opening at the tip of the casing pipe. The

by the casing pipe wall even if the sensor and the target have a

difference in temperature measurement methods between using

distance. The IR thermometer was set with a socket placed on

narrow view angle type and wide view angle type IR

the top of the casing pipe to centralize the view direction. Whenthermometers is illustrated in Figure 2. Both the IR

the IR thermometer was mounted on a 900 mm long casing pipe,

thermometers have a measurement resolution of 0.1°C.

it had a target distance of 855 mm and a field of view diameter

The procedure of quick soil temperature measurementof 32.4 mm. This means that the casing pipe wall with an inner

illustrated in Figure 1 is described below. In Step 1, the casing

diameter of 31 mm was slightly included in the field of view;

pipe with inserted spacer was penetrated the soil until the center-5-

Figure 4. Temporal variations of air and soil temperatures measured by self-recording thermistor thermometers.
depth of the conical tip of the spacer reached the target depth.

little sunlight, but Site 2 received plenty of sunlight. In order toWhen the soil was too hard for the spacer to be penetrated bymeasure the soil temperature at multiple depths at the same point,

hand pushing, the upper part of the spacer was lightly tapped

the measurement depth was increased step by step using thewith a shockless hammer for penetration. In Step 2, only thesame drilled hole as illustrated in Figure 3. The measurement

spacer was extracted from the casing pipe, which was remained

depths were the ground surface (GL ±0 mm), GL –100 mm, GL

in the soil, and then in Step 3, the IR thermometer was quickly–200 mm, GL –300 mm, and GL –400 mm, and the above

set inside the casing pipe and the soil temperature was measured.

procedures from Step 1 to Step 3 were repeated at eachTemperature measurements were conducted from earlymeasurement depth. In order to compare with the soil

September to mid-November in 2017 at two field locations (Sitetemperature quickly measured by the IR thermometer, self-

1 and Site 2) on the west side of the Faculty of Engineering,recording thermistor thermometers (ONSET TidbiT v2 UTBI-

Hokkaido University, Japan. The two sites are approximately

001) were installed at GL –100 mm, GL –200 mm, GL –300 mm,

110 m apart. Site 1 was in the shadow of a building and receives

GL –400, and GL –500 mm to record continuous temperature-6-

Figure 5. Measurement results of narrow view angle type IR thermometer on the ground surface at Site 1: (a) the IR thermometermeasurement values superimposed on the temporal variation of measured values with the self-recording thermistor thermometers,(b) Comparison between the IR thermometer and thermistor thermometer measurements.

variations. When the self-recording thermistor thermometers

every one to two weeks to ensure that the soil as the target ofwere installed, gravel particles larger than 5 mm in thetemperature measurement is homogenous.

surrounding soil including the measurement range of the IR

In the following, due to space limitations, the fieldthermometer were removed, so as not to obstruct the penetration

temperature measurement results obtained using the narrowof the casing pipe with spacer. Measurements with the IRview angle type IR thermometer will be mainly described withthermometer were basically conducted three times a day, in thedetails. The field temperature measurement results obtained

morning, at noon, and in the evening. Note here that theusing the wide view angle type IR thermometer and the soil

temperature on the ground surface was not measured at Site 2.

temperature measurement results obtained in the soil containers
will be shown briefly.

In addition, from mid-October 2021 to mid-December 2021,

Main specifications of each thermometer used in this study isquick soil temperature measurements using a soil container with
295 mm in diameter and 345 mm in height was also conducted.

described below:

Six plastic containers filled with soil, in which self-recording

HORIBA, IT-450F

thermistor thermometers were installed on the surface of the soil

 Measuring range: –50 to 500°C (correction is required below
0°C)

layer and at depths of 100 mm and 200 mm, were prepared. Then,
5 plastic containers were placed in 5 different locations with Output: 4 to 20 mA corresponding to 0 to 500°C

different temperatures, respectively, inside the building of the Accuracy: ±(3°C+0.1% of output range) or smaller(emissivity 1.000)

Faculty of Engineering, Hokkaido University, and 1 plastic
container was placed outside the building (in winter, it was Measured wavelength: 8 to 16 μm

moved to the windbreak room of the building entrance to Response time: 0.4 s (95%)

prevent it from freezing). The soil temperature was quickly Operation ambient: 0 to 55°C, 35 to 85%rh without
condensing

measured irregularly with the IR thermometer. Temperature
measurements were conducted on the soil surface using theSato Keiryouki Mfg. Co., Ltd, SK-8210

narrow view angle type and at depths of 100 mm and 200 mm

 Measuring range: 0 to 400°C

using both the narrow and wide view angle types.

 Accuracy: ±2°C or ±2%rdg, whichever is larger (emissivity
0.95)

The holes used for measurement with the IR thermometer
were not left in open but were buried by breaking up the Response time: 0.300 s (90%)

surrounding soil. In addition, since the soil was gradually Detector: Thermopile

compacted due to repeated measurements in a limited area, the Measured wavelength: 8 to 14 μm

soil around the measurement point is dug up and buried again

 Output: 4 to 20 mA corresponding to 0 to 400°C-7-Figure 6. Measurement results of narrow view angle type IR thermometer at GL –100 mm at Site 1: (a) the IR thermometermeasurement values superimposed on the temporal variation of measured values with the self-recording thermistor thermometers,(b) Comparison between the IR thermometer and thermistor thermometer measurements.

Figure 7. Measurement results of narrow view angle type IR thermometer at GL –300 mm at Site 1: (a) the IR thermometermeasurement values superimposed on the temporal variation of measured values with the self-recording thermistor thermometers,(b) Comparison between the IR thermometer and thermistor thermometer measurements.

measured with a self-recording thermistor thermometer are Operation ambient: 0 to 70°C, less than 90%rh without

shown in Figure 4. Here, Figure 4(a) is for Site 1, and Figure

condensing
ONSET TidbiT v2 UTBI-001

4(b) is for Site 2. Because the air temperature was not measured

 Measuring range: –20 to 70°C

at Site 2, the air temperature measured at Site 1 is shown as a

 Accuracy: ±0.21°C

reference value. From the end of summer to the beginning of Resolution: 0.02°C

winter, temporal variations of soil temperatures in response to Response time: 5 minutes in water; 12 and 20 minutes in air

seasonal and diurnal variations of air temperature in Sapporo are
successfully captured. The soil temperatures tend to decrease

moving 2 m/sec and 1 m/sec, respectively (90%)

with the change of seasons from autumn to winter. When the air

3. Measurement results in the field

temperature decreases significantly as a diurnal variation, thedeeper the soil temperature measurement depth, the slower the

3.1 Results of continuous measurements

response in soil temperature. At the depth of GL –100 mm, theTemporal variations in air temperature and soil temperatures

response of soil temperature with diurnal temperature-8-

Figure 8. Comparison between the data observed by the IR thermometer (narrow view angle type) and the data observed by thethermistor thermometers (all data from Site 1)
fluctuations can be seen; however, at the depths of GL –200 mm

the temporal variation of the soil temperature measured

and GL –300 mm, the diurnal variation gradually decreased, andstationarily by thermistor thermometer buried at GL –100 mm.

below GL –400 mm, only little diurnal variation was observed.

At this depth, the soil temperature is also fluctuating under the
influence of the diurnal variation of air temperature. The data

3.2 Results of narrow view angle type IR thermometerfor the middle 12 days are shown in the inset by enlarging the

3.2.1 Results at Site 1

horizontal axis, and the measured values using the IR

Measurement results of the ground surface temperature at Sitethermometer correspond to the diurnal temperature fluctuation

1 is shown in Figure 5. Figure 5(a) shows the results of thestationarily measured by the thermistor thermometer. The

ground surface temperature measured by the IR thermometercomparisons between the measured value of the IR thermometersuperimposed on the temporal variation of air temperatureand the measured value of the self-recording thermistor

measured stationarily by the thermistor thermometer at GL +100

thermometer are plotted in Figure 6(b). The data were plotted

mm. The data for the middle 12 days are shown in the inset byaround a straight line with a slope of almost 45°, and a highenlarging the horizontal axis, and the measured values using thedetermination coefficient (R2 value) of 0.9557 was calculated.

IR thermometer correspond to the significant diurnalThis indicates that the quick soil temperature measurement at atemperature fluctuation. The comparisons between thedepth with the IR thermometer was sufficiently reliablemeasured value of the IR thermometer and the measured value

compared to the measured value of the continuous measurementof the self-recording thermistor thermometer are plotted inof soil temperature with the self-recording thermistor

Figure 5(b). The data were plotted around a straight line with athermometer.

slope of almost 45°, and a high determination coefficient (R2

The measured soil temperature at GL –300 mm at Site 1 isvalue) of 0.9557 was calculated. This indicates that the quick

shown in Figure 7. Figure 7(a) shows the results of soil

soil surface temperature measurement using the IR thermometer

temperature measured by the IR thermometer superimposed on

was sufficiently reliable compared to the measured value of thethe temporal variation of the soil temperature measured

continuous measurement of air temperature with the self-

stationarily by thermistor thermometer buried at GL –300 mm.

recording thermistor thermometer.

At this depth, the soil temperature shows almost no effect ofThe measured soil temperature at GL –100 mm at Site 1 isdiurnal variation of air temperature. The data for the middle 12

shown in Figure 6. Figure 6(a) shows the results of soildays are shown in the inset by enlarging the horizontal axis, andtemperature measured by the IR thermometer superimposed on

the measured values of the IR thermometer correspond to the-9-Figure 9. Measurement results of the narrow view angle type IR thermometer at GL –100 mm at Site 2: (a) the IR thermometermeasurement values superimposed on the temporal variation of measured values with the self-recording thermistor thermometers,(b) Comparison between the IR thermometer and thermistor thermometer measurements.

Figure 10. Measurement results of narrow view angle type IR thermometer at GL –300 mm at Site 2: (a) the IR thermometermeasurement values superimposed on the temporal variation of measured values with the self-recording thermistor thermometers,(b) Comparison between the IR thermometer and thermistor thermometer measurements.

diurnal temperature fluctuation stationarily measured by the

The comparison between measured values of the IR

thermistor thermometer at the depth of GL –300 mm. The

thermometer and the measured values of the self-recording

comparisons between the measured values of the IR

thermistor thermometer consisting of 743 data recorded on thethermometer and the measured values of the self-recording

ground surface and at the depths of GL –100 mm, GL –200 mm,

thermistor thermometer are plotted in Figure 7(b). The data wereGL –300 mm, and GL –400 mm at Site 1 is shown in Figure 8.

plotted around a straight line with a slope of almost 45°, and a

The data were plotted around a straight line with a slope ofhigh determination coefficient (R2 value) of 0.9625 wasalmost 45°, and a high determination coefficient (R2 value) of

calculated. This indicates that the quick soil temperature

0.9458 was calculated. The standard deviation (SD) of themeasurement with the IR thermometer at depths deeper than thatmeasured values of the IR thermometer against theof Figure 6 was also sufficiently reliable, compared to theapproximated relationship corresponding to the measured

measured value of the continuous measurement of soil

values of the thermistor thermometer is 0.934 °C. In the range

temperature with the self-recording thermistor thermometer.

where the temperature did not fall below 0°C, the quick soil

- 10 -

Figure 11. Comparison between the data observed by the IR thermometer (narrow view angle type) and the data observed by thethermistor thermometers (all data from Site 2)

Figure 12. Comparison between the data observed by the IR thermometer (narrow view angle type) and the data observed by thethermistor thermometers (all data from both Site 1 and Site 2)
temperature measurement with the IR thermometer was

IR thermometer correspond to the diurnal temperaturesufficiently reliable to be comparable to the stationarily

fluctuation stationarily measured by the thermistor thermometer.
The measured soil temperature at GL –300 mm at Site 2 ismeasured value of self-recording thermistor thermometer.

shown in Figure 10. Figure 10(a) shows the results of soil
3.2.2 Results at Site 2

temperature measured by the IR thermometer superimposed on

The measured soil temperature at GL –100 mm at Site 2 isthe temporal variation of the soil temperature measured

shown in Figure 9. Figure 9(a) shows the results of soil

stationarily by the thermistor thermometer buried at GL –300

temperature measured by the IR thermometer superimposed on

mm. As shown in Figure 7 for Site 1, although the soil

the temporal variation of the soil temperature measured

temperature shows almost no effect of diurnal variation of air

stationarily by thermistor thermometer buried at GL –100 mm.

temperature at this depth, the measured values of the IR

As shown in Figure 6(a) for Site 1, the measured values of thethermometer correspond to the diurnal temperature fluctuation- 11 -

Figure 13. Comparison between the data observed by the IR
thermometer (wide view angle type) and the data observedby the thermistor thermometers (all data from both Site 1 andSite 2)

Figure 14. Comparison between the data observed by the IR
thermometer (narrow view angle type) and the data observedby the thermistor thermometers (all data from the 6 soil
containers)

stationarily measured by the thermistor thermometer. The
comparisons between the measured value of the IR thermometerand the measured value of the self-recording thermistor
thermometer are plotted in Figure 10(b). The data were plottedaround a straight line with a slope of almost 45°, and a highdetermination coefficient (R2 value) of 0.9727 was calculated.
Even the quick soil temperature measurement with the IR
thermometer at deeper depths than that of Figure 9 was
sufficiently reliable, compared to the measured value of thecontinuous measurement of soil temperature with the selfrecording thermistor thermometer.
The comparison between measured value of the IR
thermometer and the measured value of the self-recording
thermistor thermometer consisting of 551 data recorded at
depths of GL –100 mm, GL –200 mm, GL –300 mm, and GL –Figure 15. Comparison between the data observed by the IR
thermometer (wide view angle type) and the data observedby the thermistor thermometers (all data from the 6 soil
containers)

400 mm at Site 2 is shown in Figure 11. The data were plottedaround a straight line with a slope of almost 45°, and a highdetermination coefficient (R2 value) of 0.9695 was calculated.
In the range where the temperature did not fall below 0°C, thequick soil temperature measurement with the IR thermometerdata deviate from the straight line with a slope of 45° degree.

was sufficiently reliable to be comparable to the stationarily

This is because the installed position of the thermistor

measured value of the continuous measurement with the self-

thermometers and the measurement positions of the IR

recording thermistor thermometer.

thermometer are not the same. In addition, the diurnal variation

As described above, regarding the data measured at Site 1 andof soil temperature was significant at shallower depths. Here, allSite 2, it was shown that the values measured quickly by the IR

the data, including the data corresponding to this large variation

thermometer are highly correlated with the values stationary

are plotted, resulted in some deviation from the regression line.

measured over time by the buried thermistor thermometer. Some

The coefficient of determination was close to R2 = 0.95, even

- 12 -

though some of the data show deviation. The standard deviation

cement is hardened, temperature measurement using IR(SD) of the measured values of the IR thermometer against thethermometer can be conducted. Also, even if the target depth isapproximated relationship corresponding to the measured

in a deeper portion, temperature measurement with wide view

values of the thermistor thermometer is 0.586 °C.

angle type IR thermometer can be conducted using a longer
casing pipe and spacer, and a longer rod connecting to the wide

3.3 Comparison between the narrow and wide view angle

range type IR thermometer as well, because the wide range typetypes

IR thermometer can be inserted to the casing pipe.

The comparison between the measured values of the IR
thermometer (narrow view angle type) and the measured values

3.4 Measurement results in the soil containersof the self-recording thermistor thermometer consisting of 1294

The comparison between measured values of the IRdata recorded at both Site 1 and Site 2 is shown in Figure 12.

thermometer (narrow view angle type) and the measured values

The data were plotted around a straight line with a slope ofof the self-recording thermistor thermometer consisting of 659

almost 45°, and a high determination coefficient (R2 value) ofdata recorded in the 6 soil containers is shown in Figure 14.

0.9502 was calculated. The standard deviation (SD) of the

Similar to the data measured by the narrow view angle type IR

measured values of the IR thermometer against thethermometer described above (Figure 12), the data were plotted

approximated relationship corresponding to the measured

around a straight line with a slope of almost 45°, and a highvalues of the thermistor thermometer is 0.925 °C.

determination coefficient (R2 value) of 0.9702 was calculated.

The comparison between the measured values of the IR

The standard deviation (SD) of the measured values of the IR

thermometer (wide view angle type) and the measured values ofthermometer

the self-recording thermistor thermometer consisting of 1294

corresponding to the measured values of the thermistor

data recorded at both Site 1 and Site 2 is shown in Figure 13.

thermometer is 0.664 °C.

againsttheapproximatedrelationship

Similar to the data measured by the narrow view angle type IR

The comparison between the measured values of the IR

thermometer described above (Figures 4 to 12), the data were

thermometer (wide view angle type) and the measured values ofplotted around a straight line with a slope of almost 45°;the self-recording thermistor thermometer consisting of 594

however, because of a large data variation, determination

data recorded in the 6 soil containers is shown in Figure 15.

coefficient (R2 value) calculated for this is 0.9263, which is

Similar to the measured data with the wide view angle type IR

rather small. In addition, the standard deviation (SD) of thethermometer described above (Figure 13), the measured value

measured values of the IR thermometer against thein voltage was converted to the temperature by approximating it

approximated relationship corresponding to the measured

with a non-linier quadratic function based on the calibration

values of the thermistor thermometer is 1.307 °C, which is rather

results. Regardless the type of IR thermometer, the data

large. This is a matter of the recommended temperature range (–measured by the wide view angle IR thermometer were plotted

50 to 500°C for narrow view range type and 0 to 400°C for widearound a straight line with a slope of almost 45°, and a highview range type) for the IR thermometers, rather than the effectdetermination coefficient (R2 value) of 0.9547 was calculated.

of the view angle itself. The narrow view angle type IR

The standard deviation (SD) of the measured values of the IR

thermometer used in this study maintained a linear relationshipthermometereven when the temperature approached down to 0°C, whereas

corresponding to the measured values of the thermistor

the wide view angle type IR thermometer used in this study

thermometer is 0.775 °C.

againsttheapproximatedrelationshipshows larger variation when the temperature was below 10°C.

Note here that the data set shown in Figures 14 and 15 are

The measurement using both the narrow view angle type andplotted in two groups: one is around 20 to 25°C corresponding

the wide view angle type are available even round 5°C or a little

to locations inside the building, and the other is lower than 20°C

below that. This fact indicates that these measurement

corresponding to outside of the building from autumn (mid-techniques are useful in temperature management for cement

October 2021) to winter (mid-December 2021).

treated soils placed in winter season in cold region, because
cement treated soils do not harden under very cold temperature.

3.5 Summary of measurement results

At the beginning stage of curing before the mixture of soil andAs described above, each temperature measured with IR- 13 -

thermometer was compared with the temperature measured withcalibration.

thermistor thermometer buried near the target depth of the IR

These findings are useful in temperature measurement ofthermometer, resulted in a good agreement with a highcement treated soils placed in winter season in cold region

determination coefficient (R2 value) of 0.95 or higher (except

where temperature control (heating system) is often required if

0.92 for a case of data including temperature below 5°C.

necessary because cement treated soils do not harden under

Although the accuracy of IR thermometers written in theirfreezing temperature (it should be taken care at temperatures

specification is larger than 2 or 3°C, quickly measured

below 5°C).

temperature with IR thermometer shows practically sufficientAcknowledgement

accuracy compared to stationary measurement very accurate
temperature with thermistor thermometer (accuracy of 0.21°C
with resolution of 0.02°C).

The series of soil temperature measurements in the field in2017 was conducted by Mr. Toshiya Yano and Ms. Akane

4. Conclusions

Yoneda, who were graduate students, and by Mr. Masaki Kanari,
Mr. Takahiro Kato and Mr. Hyuga Suzuki, who were

In this study, aiming to develop a quick soil temperature

undergraduate students at Hokkaido University at the time. In

measurement method applicable to efficient and accurate

addition, the series of soil temperature measurements in the soil

measurement at multiple depth at each investigation point overcontainers in 2021 was conducted by Ms. Hana Kobayashi, Mr.

a wide area avoiding damage to the thermometer body and

Kyoichi Shida, and Ms. Tomoka Togiya, who were

problems of a long time for thermal equilibrium, a quick soil

undergraduate students at Hokkaido University at the time. The

temperatureauthor would like to thank their contribution to conduct themeasurement

with

an

infraredradiation

temperature measurements in this study.

thermometer (IR thermometer) using a predrilled hole up to the(Received on Nov. 6, 2023)

target depth was attempted. The findings from this study are
written hereunder.

References

1) A casing pipe with a spacer made of polyvinyl chloride waspenetrated from the ground surface to a target depth. Afterremoving the spacer, the IR thermometer was set into the1) Bispo, A., Andersen, L., Angers, D.A. Bernoux, M., Brossard,

casing pipe, and then, soil temperature was measured

M., Cécillon, L., Comans, R.N.J., Harmsen, J., Jonassen, K.,

quickly in about 5 seconds. A stable measurement was

Lamé, F., Lhuillery, C., Maly, S., Martin, E., Mcelnea, A.E.,

successively conducted. Although the measured temperature

Sakai, H., Watabe, Y., Eglin, T.K.: Accounting for Carbon

with the IR thermometer does not have the accuracy of a

Stocks in Soils and Measuring GHGs Emission Fluxes from

mercury-in-glass thermometer, which takes time inSoils: Do We Have the Necessary Standards?, Frontiers inmeasurement for thermal equilibrium, it was confirmed thatEnvironmental Science, Vol.5, Article 41, 12p, 2017.

it is sufficiently accurate based on a comparison with thetemperature

measuredbyself-recording

2) Hattori, S.: Accurate measurements of practical temperature,

thermistor

Chemical Education, Vol.25, Issue 1, pp. 29–35, 1977.

thermometer.

3) Taylor S.A. and Jackson, R.D.: Temperature, Methods of Soil

2) Both measuring methods using the narrow view angle type

Analysis, Part 1. Physical and Mineralogical Methods-

IR thermometer setting at the top of the casing pipe with aAgronomy Monograph. No.9 (2nd Edition), pp. 927-940,

longer distance from the target depth and the wide view

1986.

angle type IR thermometer setting inside of the casing pipe4) HORIBA, Ltd.: All about radiation thermometers, 2008.

with a shorter distance from the target depth can measure5) World Meteorological Organization: Chapter 2 Measurement

soil temperature with sufficient accuracy.

of Temperature, Prat I: Measurement of Meteorological3) Because the linearity between the actual temperature and the

Variables, Guide to Meteorological Instruments and Methods

displayed temperature possibly tends to be lost particularlyof Observation, pp. I.2–1- I.2–17, 2006.

in a low temperature range, it is necessary to pay attention to
the measurable temperature range of the IR thermometer by- 14 -

港湾空港技術研究所資料

No.1412２０２３．１２

編集 兼発 行人

国立研究開発法人海上・港湾・航空技術研究所

発

港 湾 空 港 技 術 研 究 所

行

所

横 須 賀 市 長 瀬 ３ 丁 目 １ 番 １ 号
TEL. 046(844)5040 URL. https://www.pari.go.jp/

C （2023）by MPAT
Copyright ○All rights reserved. No part of this book must be reproduced by any means without the written
permission of the President of MPAT
この資料は、海上・港湾・航空技術研究所理事長の承認を得て刊行したものである。したがって、
本報告書の全部または一部の転載、複写は海上・港湾・航空技術研究所理事長の文書による承認を得ずしてこれを行ってはならない。