Fixed-point Measurements Research Articles

Assessing the urban heat island effect of different local climate zones in Guangzhou, China

The urban heat island (UHI) effect has significant implications on urban development, human health, and climate change. Local climate zones (LCZs) provide an objective and systematic classification of field sites for studying the UHI effect. Accurately characterizing the UHI features in each LCZ is fundamental to mitigating the UHI effect. This study aimed to analyze the UHI effect in six LCZs in Guangzhou. Temperature data were collected simultaneously using fixed-point measurements over 405 days from October 1, 2019 to March 31, 2022. The UHI characteristics of the LCZs under various weather conditions were analyzed by examining the hourly, daily, and seasonal UHI intensities (UHIIs). Consistent diurnal variation patterns were observed in the daily average UHII under different weather conditions but with varying peak values. Ideal days with weak winds and clear skies significantly contribute to the development of maximum UHII, occurring most frequently between 18:00 and 23:00 with a frequency of 45%. In comparison, UHI events on precipitation days have a lower frequency. Furthermore, UHI effects varied significantly among different LCZs, with higher UHII observed in high-density built-up LCZs compared to open low-rise LCZs. Variations were particularly pronounced during the night in autumn and winter with a maximum UHII mean of 5.30 °C. UHI event frequencies and hourly warming/cooling rates were also examined to provide a more comprehensive assessment of the UHI effects on LCZs. This study is of great significance for understanding the UHI characteristics within Guangzhou, and for guiding urban planning and management to mitigate UHI in LCZs.

Experimental Investigation of Helicopter Noise While Approaching an Elevated Helipad

The present paper describes a test campaign performed to investigate the noise footprint emitted by a helicopter in an idealised urban context, reproducing the approach to an elevated helipad. The test campaign was performed in Politecnico di Milano’s anechoic chamber and was finalised to investigate the effects produced only by helicopter noise. The set up consisted of a two-blade main rotor helicopter model and an aluminium rectangular prism model reproducing the landing building. Ground observer perceptions were recorded by means of a surface microphone and a realistic landing trajectory was approximated as a succession of fixed point measurements. Collected data were analysed through acoustic spectra and sound maps. Spectra were used to comprehend physical phenomena, such as reflection, diffraction and shielding, and to analyse the different contributions of helicopter noise. A sound map analysis enabled us to obtain a global perspective of the involved phenomena and to understand th extent to which people close to a building are stressed by a helicopter approaching an elevated urban helipad. Moreover, the experimental database, obtained over a free geometry, can be considered a useful tool for the validation of aeroacoustic solvers with different levels of fidelity.

Assessing the synergies between heat waves and urban heat islands of different local climate zones in Guangzhou, China

Urban heat island (UHI) effects and heat waves (HWs) increase, posing a threat to human health and urban ecological systems. However, the synergistic mechanisms of UHI and HWs are yet to be fully elucidated. This study aims to assess the characteristics of UHI under HWs in different Local Climate Zones (LCZs) using temperature observations from Guangzhou, China. Fixed-point measurements were employed to simultaneously collect air temperature from nine LCZs in 2021. The results showed a localised interplay between HWs and UHI. During HWs, the UHI effect was significantly amplified in built-type LCZ, where the UHI intensity (UHII) was amplified by 0.1–0.5 °C throughout the day, 0.4–1 °C at night, but slightly reduced by 0–0.4 °C during daytime. The UHII was significantly reduced in land-cover type LCZ, and the urban cold effect was amplified during HWs. Furthermore, with strong solar radiation and low wind speed in HWs, the daily maximum UHII of LCZs increased 0.4–1.1 °C. Finally, correlations between UHII and morphological characteristics of LCZs are examined in HWs and non-heat waves (NHWs). During HWs, the increase in impervious surface fraction (ISF) and building surface fraction (BSF) and the decrease in sky view factor (SVF) exacerbate UHII, particularly at night. The augment in surface vegetation fraction (Fveg), does not significantly contribute to reducing the UHI and is less effective than NHWs at night. Therefore, different measures should be taken in different LCZs to mitigate UHII amplification during HWs. This study can serve as a reference for preventing responses to climate extremes.

Experimental Study on Wind Noise Distribution Law of Transmission Lines

Aiming at the problem of wind noise generated by transmission lines under windy weather conditions, this paper selects three groups of transmission lines in Shandong Province, China. Through the fixed-point measurement of the wind noise pressure of the conductor at the ground projection point of the side, phase conductor sags as the starting point, and the outward extension of 50 m as the endpoint, the frequency spectrum curve characteristics of the wind noise of the transmission line, the predominant frequency, the cut-off frequency, and the overall A sound level are analyzed. The results show that the transmission line conductor wind noise is mainly concentrated in the range of 500 - 2000 Hz, and its predominant frequency is around 650 Hz, which belongs to low-frequency noise. The wire wind noise attenuates with the increase of the distance from the projection point, and the attenuation is completed at 50m, and the wind noise fixed-point measurement decreases by 8 dB.

Radiation imaging of a highly contaminated filter train inside Fukushima Daiichi Nuclear Power Station unit 2 using an integrated Radiation Imaging System based on a Compton camera

ABSTRACT The Fukushima Daiichi Nuclear Power Station (FDNPS) suffered a meltdown in the aftermath of the large tsunami caused by the Great East Japan Earthquake that occurred on 11 March 2011. A massive amount of radioactive substance was spread over a wide area both inside and outside the FDNPS site. In this study, we present an approach for visualizing a radioactive hotspot on a standby gas-treatment system filter train, a highly contaminated piece of equipment in the air-conditioning room of the Unit 2 reactor building of FDNPS, using radiation imaging based on a Compton camera. In addition to fixed-point measurements using only the Compton camera, data acquisition while moving using an integrated Radiation Imaging System (iRIS), which combines a Compton camera with a simultaneous localization and mapping device and a survey meter, enabled the three-dimensional visualization of the hotspot location on the filter train. In addition, we visualized the hotspot and quantitatively evaluated its radioactivity. Notably, the visualized hotspot location and estimated radioactivity value are consistent with the accident investigation report of the FDNPS. Finally, the extent to which the radioactivity increased the ambient dose equivalent rate in the surrounding environment was explored.

Inter-laboratory comparison analysis of noise measurement in 91 occupational hygiene technical service organizations

Objective: To understand the comparability of noise measurement results of various occupational hygiene technical service organizations in Guangdong Province by conducting inter-laboratory comparison of measuring instruments and personnel operation. Methods: In October 2020, the instrument comparison and personnel comparison among 91 occupational hygiene technical service organizations engaged in noise measurement in Guangdong Province were carried out in the form of fixed-point measurement and simulated workplace measurement, and the results were analyzed and evaluated by using the robust z-ratio score. Results: In the instrument comparison, 6 organizations had 1 or 2 outliers in their z-ratio scores, 2 organizations had 2 problematic values in their z-ratio scores, and a total of 8 organizations (accounting for 8.8%) were judged as unqualified; A total of 83 organizations (accounting for 91.2%) with satisfactory z-ratio scores or only one problematic value were judged as qualified. In the personnel comparison, there were 11 organizations with 1 or 2 outliers in the z-ratio score, and 1 organization with 2 problematic values in the z-ratio score. A total of 12 organizations (13.2%) were judged as unqualified and 79 organizations (accounting for 86.8%) with satisfactory z-ratio scores or only one problematic value were judged as qualified. Through comprehensive judgment, 20 organizations (22.0%) were judged as unqualified, and 71 organizations (78.0%) were judged as qualified. There was no statistically significant difference in the qualified rates of instrument comparison results, personnel comparison results and comprehensive evaluation results of non-private organizations and private organizations (P>0.05). There was no significant difference in the qualified rates of instrument comparison results and comprehensive evaluation results of qualified organizations and unqualified organizations (P>0.05), there was significant difference in the qualified rate of personnel comparison results (P<0.05) . Conclusion: The noise measurement results of some occupational health technical service organizations in Guangdong Province are generally comparable. To carry out inter-laboratory comparison of noise instrument performance and personnel operation ability of occupational hygiene technical service organizations, can comprehensively evaluate the testing process of each organization and find out the problems existing in each organization.

Quasi-steady circulation regimes in the Baltic Sea

Abstract. Circulation plays an essential role in the creation of physical and biogeochemical fluxes in the Baltic Sea. The main aim of the work was to study the quasi-steady circulation patterns under prevailing forcing conditions. A total of 6 months of continuous vertical profiling and fixed-point measurements of currents, two month-long underwater glider surveys, and numerical modeling were applied in the central Baltic Sea. The vertical structure of currents was strongly linked to the location of the two pycnoclines: the seasonal thermocline and the halocline. The vertical movements of pycnoclines and velocity shear maxima were synchronous. The quasi-steady circulation patterns were in geostrophic balance and highly persistent. The persistent patterns included circulation features such as upwelling, downwelling, and boundary currents, as well as a sub-halocline gravity current. The patterns had a prevailing zonal scale of 5–60 km as well as considerably higher magnitude and different direction than the long-term mean circulation pattern. A northward (southward) geostrophic boundary current in the upper layer was observed along the eastern coast of the central Baltic in the case of southwesterly (northerly) wind. The geostrophic current at the boundary was often a consequence of wind-driven, across-shore advection. The sub-halocline quasi-permanent gravity current with a width of 10–30 km from the Gotland Deep to the north over the narrow sill separating the Fårö Deep and Nothern Deep was detected in the simulation, and it was confirmed by an Argo float trajectory. According to the simulation, a strong flow, mostly to the north, with a zonal scale of 5 km occurred at the sill. This current is an important deeper limb of the overturning circulation of the Baltic Sea. The current was stronger with northerly winds and restricted by the southwesterly winds. The circulation regime had an annual cycle due to seasonality in the forcing. The boundary current was stronger and more frequent northward during the winter period. The sub-halocline current towards the north was strongest in March–May and weakest in November–December.

Grid-based calculation of the Lagrangian mean

Lagrangian averaging has been shown to be more effective than the Eulerian mean in separating waves from slow dynamics in two time scale flows. It also appears in many reduced models that capture the wave feedback on the slow flow. Its calculation, however, requires tracking particles in time, which imposes several difficulties in grid-based numerical simulations or estimation from fixed-point measurements. To circumvent these difficulties, we propose a grid-based iterative method to calculate the Lagrangian mean without tracking particles in time, which also reduces computation, memory footprint and communication between processors in parallelised numerical models. To assess the accuracy of this method several examples are examined and discussed. We also explore an application of this method in the context of shallow-water equations by quantifying the validity of wave-averaged geostrophic balance – a modified form of geostrophic balance accounting for the effect of strong waves on slow dynamics.

Radiation imaging using an integrated Radiation Imaging System based on a compact Compton camera under unit 1/2 exhaust stack of Fukushima Daiichi Nuclear Power Station

ABSTRACT The Fukushima Daiichi Nuclear Power Station (FDNPS) went into meltdown after being hit by a large tsunami caused by the Great East Japan Earthquake on 11 March 2011. Measuring and understanding the distribution of radioactive contamination inside the FDNPS is essential for decommissioning work, reducing exposure to workers, and ensuring decontamination. This paper reports the visualization tests of radioactive contamination in the Unit 1/2 exhaust stack of the FDNPS using a compact Compton camera. Fixed-point measurements were conducted using only a Compton camera and moving measurements using an integrated radiation imaging system (iRIS) that combines a Compton camera with a simultaneous localization and mapping device. For the moving measurements, an operator carrying the iRIS acquires data continuously while walking in a passage near the stack. With both types of measurements, high-intensity contamination was detected at the base of the stack, and detailed three-dimensional (3D) visualization of the contamination was obtained from the moving measurement. The fixed-point measurements estimated the source intensity of the contamination from the reconstructed contamination image acquired by the Compton camera. Furthermore, workers can experience the work environment before actual work by importing a 3D structure model into a virtual reality system displaying the contamination image.

Pt-40%Rh Versus Pt-6%Rh Thermocouples: An emf-Temperature Reference Function for the Temperature Range 0\xa0\xb0C to 1769\xa0\xb0C

The paper describes the metrological characterization of the highly stable Pt-40%Rh/Pt-6%Rh thermocouples to determine their reference function in the temperature range between 0 °C and 1769 °C. The preparation of the Pt-40%Rh/Pt-6%Rh thermocouples is described, as well as the measurement procedures and the measurement results of comparison and fixed point measurements for the determination of the reference function with low uncertainties.

Analysis of Three-Dimensional Morphological Differences in the Mandible between Skeletal Class I and Class II with CBCT Fixed-Point Measurement Method.

This study was aimed at determining the three-dimensional differences in the mandible morphology between skeletal class I and II patients, at exploring the pathogenic mechanisms and morphological characteristics of skeletal class II, and at providing clinical references. The subjects were assigned to two groups according to the size of ANB angle: skeletal class I (2° < ANB angle < 5°) and skeletal class II (5° < ANB angle < 8°). After cone-beam computed tomography (CBCT) scanning, 31 landmarks and 25 measurement items were determined by In Vivo Dental 5.1 software (Anatomage, CA) for statistical analysis. The results were as follows: Co-Go, Go-Me, and CdM-CdD in skeletal class II cases were smaller than those in skeletal class I, and GoR-Me-GoL, GoR-Me-CoL, and, Ig-Men were larger than those in skeletal class I cases. In conclusion, there were significant differences in the three-dimensional morphology of the mandible between skeletal class I and class II patients. The vertical growth of the ramus, the horizontal growth of the mandibular body, and the condyle in skeletal class II patients were smaller than those in skeletal class I cases. In skeletal class II, the growth of the anterior part of the mandible in the vertical direction was larger than that in skeletal class I, and the shape of the mandible was more extended.

Non-stationary Boundary Layers

The literature includes a wide variety of definitions or perceptions of non-stationarity. Non-stationarity can be expressed in terms of turbulence statistics or variability of the forcing of the turbulence such as time changes of the wind vector, the horizontal pressure gradient, or the surface heat flux. Our survey emphasizes the development of non-equilibrium turbulence caused by non-stationary forcing. The degree of non-equilibrium of the turbulence is most reliably evaluated following the local flow rather than using the more available fixed-point measurements. We survey methods to eliminate non-stationary records or partially filter out the non-stationarity. We also summarize issues with parametrization of the non-stationarity. Non-stationarity over the sea can be complex due to time-dependent wave state and surface roughness. The impact of non-stationarity is generally less understood in the stable boundary layer compared to the unstable boundary layer.

Research of Dynamic Azimuth Gamma Instrument while Drilling for Mine

In view of the problems that the existing gamma logging instruments in coal mines can only carry out static fixed-point measurement and are not suitable for rotary drilling, this paper, based on the analysis of the characteristics of measurement while drilling in coal mines and the principle of gamma logging, designs and realizes the dynamic gamma azimuth instruments for mines by means of power line carrier, rotation positioning and gamma measurement technology, which can measure the intensity of natural gamma ray in two directions around the borehole in real time, effectively reflect the changes of different radioactive strata, and guide the geosteering while drilling in coal mine.

Use of Multi-Rotor Unmanned Aerial Vehicles for Fine-Grained Roadside Air Pollution Monitoring

With increasing numbers of motor vehicles, vehicle exhaust gas has become one of the most important sources of urban air pollutants. After being emitted from the motor vehicle, exhaust gas spreads through the air along the road and is gradually deposited in the surrounding area, having an adverse impact on pedestrians and residents. At present, most research on vehicle exhaust directly measures the total emissions from the exhaust pipe or monitors the time variation of air pollutants at the roadside by setting roadside monitoring stations. The spatial resolution of these two methods is very low, however, and it is impossible to describe accurately the diffusion patterns of exhaust gas in the atmosphere after discharge. Some scholars have conducted research on the quality of roadside air by hand-held portable devices, but these are limited by the speed of travel, and the spatial and temporal resolution of the acquired data is also very low. By using multi-rotor unmanned aerial vehicles (UAVs) and portable equipment, this study demonstrates an atmospheric environment monitoring system based on multi-rotor UAV by designing corresponding hardware circuits and software programs. With flexible requirements for takeoff or landing sites and high maneuverability of multi-rotor UAVs, the system increases the capability for high resolution spatial and temporal monitoring of the diffusion of traffic-emitted pollutants. The system can conduct fixed-point measurement by hovering, and can also measure air pollutants in complex urban terrain, providing an innovation in the study of vehicle exhaust gas diffusion.

Measurement of ambient dose equivalent rates by walk survey around Fukushima Dai-ichi Nuclear Power Plant using KURAMA-II until 2016

Ambient dose equivalent rates in various environments related to human lives were measured by walk surveys using the KURAMA-II systems from 2013 to 2016 within an 80-km radius of the Fukushima Dai-ichi Nuclear Power Plant. The dose rate of the locations where the walk survey was performed decreased to about 38% of its initial value in the 42 months from June 2013 to the December 2016, which was beyond that attributable to the physical decay of radiocaesium. The ecological half-life of the slow decreasing component was evaluated to be 4.1 ± 0.2 y. The air dose rates decreased depending on the level of the evacuation areas, and the decrease in the dose rates was slightly larger in populated areas where humans are active. The dose rates as measured by walk surveys exhibited a good correlation with those by car-borne surveys, suggesting that car-borne survey data are reflecting the air dose rates in living environments surrounding roads. The comparison of walk survey data with car-borne survey data indicated that the air dose rate varies largely even within a 100 m square area, and the variation is enhanced by human activities. The dose rates measured by the walk surveys were estimated to be medial of those along roads and those of undisturbed flat ground, and they were found to be decreasing quickly compared with the air dose rate from the flat ground fixed-point measurements.

Decreasing trend of ambient dose equivalent rates over a wide area in eastern Japan until 2016 evaluated by car-borne surveys using KURAMA systems

As part of the investigation of the distribution of ambient dose equivalent rates around the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), car-borne surveys using Kyoto University RAdiation MApping (KURAMA) systems have been conducted over a wide area in eastern Japan since 2011. The enormous volume of measurement data collected until 2016, including those until 2012 which were reported in the previous paper, was analyzed, and dependencies of the decreasing trend of the dose rates in regions within 80 km of the FDNPP on land-use categories, evacuation order areas and magnitude of the dose rates were examined. The air dose rates within 80 km of the FDNPP tended to decrease considerably with respect to the physical decay of radiocaesium. The decrease of the dose rate in the “forest” was slower than its decrease in other regions, while that in “urban area” was the fastest. The decrease in the air dose rate from 2011 was the fastest outside the evacuation order area until 2015, and it was the slowest in the “difficult-to-return zone”. However, the decreasing trend starting from 2013 showed that the decrease in the “zone in preparation for the lifting of the evacuation order” and in the “residence restriction area” was the fastest. It was found that the air dose rates decreased depending on the magnitude of the dose rates and elapsed time from the FDNPP accident, i.e. the decrease in air dose rates in areas with relatively low dose ranges (such as 0.2–0.5 μSv/h) was the largest during a period relatively early after the accident, and the decreasing rate in the dose rate ranges of 1.9–3.8 and 3.8–9.5 μSv/h were the fastest after 2013. The averaged ratios were analyzed to obtain the ecological half-lives of the fast and slow decay components, and those in whole area within 80 km of FDNPP were estimated to be 0.44 ± 0.05 y and 6.7 ± 1 y, respectively. The ecological half-lives with respect to the land use categories, evacuation order areas and magnitude of the dose rates were also evaluated. The decrease in the dose rates obtained by the car-borne survey was larger than that obtained on flat ground with few disturbances using the NaI(Tl) survey meter during approximately 1.5 y after the FDNPP accident. Thereafter, the difference of decreasing tendencies in the air dose rates between both the measurements was negligibly small, with the ratio of dose rates by the car-borne survey to those by the fixed-point measurement of 0.72–0.77.

Scanning of skin gloss by a diffractive optical element-based handheld glossmeter

Skin specular gloss (referred to as “gloss’’) determination is important in dermatology and cosmetic industry as it gives an indication of the skin health and beauty. Its accurate determination is, therefore, necessary. Commercially available glossmeters typically employ large incidence angle geometry, large illumination area, and fixed point measurements making them impractical regarding measurement of curved and complex non-planar objects or surfaces as well as low gloss regime such as the skin. In this study, we have demonstrated the novel application of a diffractive optical element-based handheld glossmeter with scanning capability, overcoming the disadvantages of conventional glossmeters, in the accurate determination of skin gloss and gloss profile for different skin types under different measurement conditions. Different parts of the body (back of the hands, the inner part of the arm and the forehead) of four volunteers with light, dark and intermediate skin types were scanned (also in different directions) to obtain the skin gloss profile and the statistical average skin gloss. Additionally, the skin surface was modified by arm extension and scanned as well. Our preliminary results showed that the statistical average skin gloss reading increased with the increasing lightness of skin. Areas with higher sebaceous glands (forehead) showed higher gloss reading than the other body parts (inner arm and back of the hand). However, the roughness of the skin surface decreased the statistical average skin gloss reading. The handheld scanning skin glossmeter allows for the accurate determination of skin gloss with sensitivity to small variation in the skin surface roughness with high repeatability.

Automatic cruise system for water quality monitoring

The range of unit fixed-point measurement on water quality monitoring system is limited, and the cost for multipoint measurement is high. In order to solve these problems, the automatic cruise system for water quality monitoring was designed. Sage-Husa adaptive Kalman filtering algorithm was adopted to correct the error in GPS positioning. The boat was equipped with ship control module, water quality parameters acquisition module, power-supply module, GPS module and GPRS-DTU packet data transmission module. An Android application was developed so that individual users can use smartphone to communicate with the boat at all time and places. The results show that the boat can basically cruise in the set route to monitor the water quality. In a 4 m2 aquatic plants areas, the dissolved oxygen monitored in different time were about 10.2%, 8.5% and 8.3%, respectively, higher than other areas, and the pH values were 4.1%, 3.8% and 3.7% higher than those in other waters, which shown that plants photosynthesis released oxygen consumption of carbon dioxide will affect the dissolved oxygen content and pH value. This system can widen the measurement range, and lower the measuring cost that can be widely used in the water quality monitoring in aquaculture and river management. Keywords: water quality monitoring, GPS, automatic cruise, Android mobile client DOI: 10.25165/j.ijabe.20181104.2658 Citation: Zhu C Y, Liu X Q, Chen H L, Tian X. Automatic cruise system for water quality monitoring. Int J Agric & Biol Eng, 2018; 11(4): 244-250.

Decreasing trend of ambient dose equivalent rates over a wide area in eastern Japan until 2016 evaluated by car-borne surveys using KURAMA systems

As part of the investigation of the distribution of ambient dose equivalent rates around the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), car-borne surveys using Kyoto University RAdiation MApping (KURAMA) systems have been conducted over a wide area in eastern Japan since 2011. The enormous volume of measurement data collected until 2016, including those until 2012 which were reported in the previous paper, was analyzed, and dependencies of the decreasing trend of the dose rates in regions within 80 km of the FDNPP on land-use categories, evacuation order areas and magnitude of the dose rates were examined. The air dose rates within 80 km of the FDNPP tended to decrease considerably with respect to the physical decay of radiocaesium. The decrease of the dose rate in the “forest” was slower than its decrease in other regions, while that in “urban area” was the fastest. The decrease in the air dose rate from 2011 was the fastest outside the evacuation order area until 2015, and it was the slowest in the “difficult-to-return zone”. However, the decreasing trend starting from 2013 showed that the decrease in the “zone in preparation for the lifting of the evacuation order” and in the “residence restriction area” was the fastest. It was found that the air dose rates decreased depending on the magnitude of the dose rates and elapsed time from the FDNPP accident, i.e. the decrease in air dose rates in areas with relatively low dose ranges (such as 0.2–0.5 μSv/h) was the largest during a period relatively early after the accident, and the decreasing rate in the dose rate ranges of 1.9–3.8 and 3.8–9.5 μSv/h were the fastest after 2013. The averaged ratios were analyzed to obtain the ecological half-lives of the fast and slow decay components, and those in whole area within 80 km of FDNPP were estimated to be 0.44 ± 0.05 y and 6.7 ± 1 y, respectively. The ecological half-lives with respect to the land use categories, evacuation order areas and magnitude of the dose rates were also evaluated. The decrease in the dose rates obtained by the car-borne survey was larger than that obtained on flat ground with few disturbances using the NaI(Tl) survey meter during approximately 1.5 y after the FDNPP accident. Thereafter, the difference of decreasing tendencies in the air dose rates between both the measurements was negligibly small, with the ratio of dose rates by the car-borne survey to those by the fixed-point measurement of 0.72–0.77.

Measurement of ambient dose equivalent rates by walk survey around Fukushima Dai-ichi Nuclear Power Plant using KURAMA-II until 2016

Ambient dose equivalent rates in various environments related to human lives were measured by walk surveys using the KURAMA-II systems from 2013 to 2016 within an 80-km radius of the Fukushima Dai-ichi Nuclear Power Plant. The dose rate of the locations where the walk survey was performed decreased to about 38% of its initial value in the 42 months from June 2013 to the December 2016, which was beyond that attributable to the physical decay of radiocaesium. The ecological half-life of the slow decreasing component was evaluated to be 4.1 ± 0.2 y. The air dose rates decreased depending on the level of the evacuation areas, and the decrease in the dose rates was slightly larger in populated areas where humans are active. The dose rates as measured by walk surveys exhibited a good correlation with those by car-borne surveys, suggesting that car-borne survey data are reflecting the air dose rates in living environments surrounding roads. The comparison of walk survey data with car-borne survey data indicated that the air dose rate varies largely even within a 100 m square area, and the variation is enhanced by human activities. The dose rates measured by the walk surveys were estimated to be medial of those along roads and those of undisturbed flat ground, and they were found to be decreasing quickly compared with the air dose rate from the flat ground fixed-point measurements.