Modelling daytime thermal infrared directional anisotropy over Toulouse city centre

Lagouarde, J.-P.; Hénon, Aurélien; Kurz, Britta; Moreau, Patrick; Irvine, Mark; Voogt, James A.; Mestayer, P.G.

doi:10.1016/j.rse.2009.08.012

Cited by 111 publications

(80 citation statements)

References 35 publications

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“…The error becomes increasingly large as sensors deviate from the vertical, as is often the case with airborne and satellite sensors that have off-nadir viewing capabilities. Selected studies have attempted to quantify this effect (Lagouarde et al, 2004;Voogt, 2008;Lagouarde et al, 2010) for given cities using airborne measurements from different views. Nevertheless, most applications and studies simply neglect the resulting errors of radiometer placement and view direction on remotely sensed surface (brightness) temperatures of urban systems.…”

Section: Introductionmentioning

confidence: 99%

The effect of radiometer placement and view on inferred directional and hemispheric radiometric temperatures of an urban canopy

2015

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Abstract. Any radiometer at a fixed location has a biased view when observing a convoluted, three-dimensional surface such as an urban canopy. The goal of this contribution is to determine the bias of various sensors views observing a simple urban residential neighbourhood (nadir, oblique, hemispherical) over a 24 hour cycle under clear weather conditions. The error in measuring a longwave radiation flux density (L) and/or inferring surface temperatures (T 0 ) is quantified for different times over a diurnal cycle. Panoramic time-sequential thermography (PTST) data were recorded by a thermal camera on a hydraulic mast above a residential canyon in Vancouver, BC. The data set resolved sub-facet temperature variability of all representative urban facets in a 360• swath repetitively over a 24-hour cycle. This data set is used along with computer graphics and vision techniques to project measured fields of L for a given time and pixel onto texture sheets of a three-dimensional urban surface model at a resolution of centimetres. The resulting data set attributes L of each pixel on the texture sheets to different urban facets and associates facet location, azimuth, slope, material, and sky view factor. The texture sheets of L are used to calculate the complete surface temperature (T 0,C ) and to simulate the radiation in the field of view (FOV) of narrow and hemispheric radiometers observing the same urban surface (in absence of emissivity and atmospheric effects). The simulated directional (T 0,d ) and hemispheric (T 0,h ) radiometric temperatures inferred from various biased views are compared to T 0,C . For a range of simulated off-nadir (φ) and azimuth ( ) angles, T 0,d (φ, ) and T 0,C differ between −2.6 and +2.9 K over the course of the day. The effects of effective anisotropy are highest in the daytime, particularly around sunrise and sunset when different views can lead to differences in T 0,d (φ, ) that are as high as 3.5 K. For a sensor with a narrow FOV in the nadir of the urban surface, T 0,d (φ = 0) differs from T 0,C by +1.9 K (day) and by −1.6 K (night).Simulations of the FOV of hemispherical, downwardfacing pyrgeometers at 270 positions show considerable variations in the measured L and inferred hemispherical radiometeric temperature T 0,h as a function of both horizontal placement and height. The root mean squared error (RMSE) between different horizontal positions in retrieving outgoing longwave emittance L ↑ decreased exponentially with height, and was 11.2, 6.3 and 2.0 W m −2 at 2, 3, and 5 times the mean building height z b . Generally, above 3.5 z b the horizontal positional error is less than the typical accuracy of common pyrgeometers. The average T 0,h over 24 h determined from the hemispherical radiometer sufficiently above an urban surface is in close agreement with the average T 0,C . However, over the course of the day, the difference between T 0,h and T 0,C shows an RMSE of 1.7 K (9.4 W m −2 ) because the relative contributions of facets within the projected FOV of a pyrgeometer do not co...

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Section: Introductionmentioning

confidence: 99%

The effect of radiometer placement and view on inferred directional and hemispheric radiometric temperatures of an urban canopy

2015

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“…In most of these previous studies, thermal anisotropy was caused by the high roughness levels and complex structures of observed objects [7,[32][33][34] or by atmospheric effects [35]. Although we cannot refute that the earth's surface is a Lambert body in other cases (e.g., low roughness earth surfaces), the objective of this study is to demonstrate whether the ground surface is Lambertian in thermal infrared regions.…”

Section: Introductionmentioning

confidence: 91%

“…With the output of the IR thermometer, we are able to calculate thermal radiance from the ground surface, using Equation (8). In order to compare the radiance from the ground in different viewing angles for the determination of the ground's Lambertian property, we mounted the IR thermometers in 7 Figure 2). Before observations were conducted in the field, we performed calibration of the thermal IR thermometers to keep their measurements comparable.…”

Section: Experimental Observation System Designmentioning

confidence: 99%

“…(2) The other reason may be the fluctuations of the water surface, which make the different thermal emissions observed from different directions. Many studies found that different levels of solar irradiance received by different parts of objects cause radiance directionality [7,12,17]; therefore, radiance directionality is influenced by direct sunlight irradiance during the daytime. For higher roughness observation objects, such as grass and bare soil, the radiance directionality caused by solar irradiance is more obvious.…”

Section: Post Hoc Multiple Comparison Testsmentioning

confidence: 99%

“…Thermal infrared anisotropy has been widely examined in many studies (e.g., the directional anisotropy of thermal infrared measurements over urban areas [6][7][8][9][10][11]; row crop canopies or soil and vegetation (to differentiate these parameters via temperatures) [12][13][14][15][16][17][18][19][20]; over forest or tree cover [21,22]; over soil [23]; and large area targets [24,25]). …”

Section: Introductionmentioning

confidence: 99%

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Identifying the Lambertian Property of Ground Surfaces in the Thermal Infrared Region via Field Experiments

Qin

Yang

et al. 2017

Remote Sensing

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Abstract:Lambertian surfaces represent an important assumption when constructing thermal radiance transfer equations for remote sensing observations of ground surface temperatures. We identify the properties of ground surfaces in thermal infrared regions as Lambertian surfaces via field experiments. Because Lambertian surfaces present homogeneous thermal emissions levels in hemispheric directions for a specific ground surface under specific kinetic temperatures and emissions, we conducted a series of field experiments to illustrate the properties of such ground surfaces. Four typical ground surfaces were selected for the experiments to observe thermal emissions: bare soil, grass, water, and concrete. Radiance thermometers were used to observe ground emissions from seven directions: 30 • , 45 • , 60 • , 90 • , 120 • , 135 • , and 150 • . Solar zenith angles were considered for the observation of ground emissions. Experiments were conducted in five different regions of China (Beijing, Nanjing, Xilinguole, Yongzhou, and Jiangmen) during both daytime and nighttime. To determine whether different observation angles have significantly different effects on radiance, statistical analyses (ANOVA and Friedman test) were conducted. Post hoc multiple comparison tests and pairwise multiple comparisons were also conducted to examine the various pairings of observation angles and to measure the radiance differences. Roughly half of the radiance groups of all observed sites were tested via an ANOVA, and the remaining groups with unequal variances were subjected to the Friedman test. The results indicate that statistically significant differences in the radiance levels occurred among the seven angles for almost all of the sites (39 of the 40 groups). The results of our experiments indicate that the selected ground surfaces, especially the grass and the bare soil, may not behave with Lambertian properties in the thermal infrared region. This is probably attributed to the roughness of the selected surface, because we found that roughness is an important factor affecting the observed magnitude of thermal emission from different directions of the ground surface under study. Therefore, whether or not a terrestrial surface can be assumed to be a Lambertian surface should be based on their geometric structure. When the surface is relatively smooth, we can say that it is close to the Lambertian property in thermal emission.

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Assessing the impact of urban geometry on surface urban heat island using complete and nadir temperatures

Yang

Menenti

et al. 2020

Intl Journal of Climatology

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The surface urban heat island intensity (SUHII) when using nadir-viewing radiometric and complete surface temperature (T r and T c) was evaluated. The urban areas of the Kowloon peninsula and Hong Kong Island were selected and four daytime Landsat TM images and two nighttime ASTER images were collected to retrieve T r and then model T c based on a semi-empirical model. SUHIIs were estimated using both the retrieved T r and modelled T c. High spatial resolution (HR) airborne thermal images (0.2 m) observed at 12:10 noon on Oct 24, 2017 were used to retrieve T c directly. Results based on HR data and satellite data were consistent and indicated that the geometry of the built-up space had a larger impact on SUHII when using T c (SUHIIc) than T r (SUHIIr). During daytime SUHIIc decreased while SUHIIr showed a very slight increase with building density. Both SUHIIc and SUHIIr decreased with higher building height but the rate of decrease of SUHIIc was higher than SUHIIr. Both SUHIIc and SUHIIr decreased with increasing building height variance and increased with increasing sky view factor (SVF). The rate of decrease with building height variance for SUHIIc was larger than SUHIIr. The rate of increase of SUHIIc with SVF was higher than SUHIIr. During nighttime, geometry effects on SUHIIc and SUHIIr were different from daytime. Both SUHIIc and SUHIIr increased with building density, while the rate of increase of SUHIIc with building density, as well as with building height, was much higher than SUHIIr. Both SUHIIc and SUHIIr decreased with SVF, but the rate of decrease of SUHIIc was higher than SUHIIr. Both SUHIIc and SUHIIr initially increased with building height variance and then remained Abbreviations: SUHIIc, The difference between the complete surface temperature of reference rural areas and the complete surface temperature of urban areas; SUHIIr, The difference between the radiometric surface temperature of reference rural areas and the radiometric surface temperature of urban areas; UHII, The difference between air temperature of reference rural station and the air temperature of urban stations.

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Modelling daytime thermal infrared directional anisotropy over Toulouse city centre

Cited by 111 publications

References 35 publications

The effect of radiometer placement and view on inferred directional and hemispheric radiometric temperatures of an urban canopy

The effect of radiometer placement and view on inferred directional and hemispheric radiometric temperatures of an urban canopy

Identifying the Lambertian Property of Ground Surfaces in the Thermal Infrared Region via Field Experiments

Assessing the impact of urban geometry on surface urban heat island using complete and nadir temperatures

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