In-situ emissivity measurement for land surface temperature determination

Transcription

1 TWENTIETH SYMPOSIUM ON THERMOPHYSICAL PROPERTIES Boulder, CO, USA June 24 29, 2018 In-situ emissivity measurement for land surface temperature determination J.P. MONCHAU 1*, M. MARCHETTI 2, L. IBOS 3, B. SAINTOT 2 1 THEMACS Ingénierie, Champs sur Marne, FRANCE 2 CEREMA, Nancy, FRANCE 3 CERTES Université Paris Est, Créteil, FRANCE * (corresponding author): monchau@themacs.fr 1

2 TWENTIETH SYMPOSIUM ON THERMOPHYSICAL PROPERTIES Boulder, CO, USA June 24 29, 2018 Introduction In-situ emissivity measurement tool Angular correction of directionnal emissivity Prospects and improvement 2

3 TWENTIETH SYMPOSIUM ON THERMOPHYSICAL PROPERTIES Boulder, CO, USA June 24 29, 2018 Introduction In-situ emissivity measurement tool Angular correction of directionnal emissivity Prospects and improvement 3

4 Introduction In-situ emissivity measurement for land surface temperature determination The objective of this study is to have an accurate value of the surface temperature by thermal imaging. To reach this goal it is necessary to have an accurate value of directionnal emissivity. Two exemple of work : Winter risk Land surface temperature determination 4

5 Introduction THERMOCITY : Thermal mapping for winter risk (city of Paris) The experimental dispositive on the roof of a car Measurement in progress during the winter Thermal mapping : City of Paris Example of thermal image Field of view of the camera Radiation of the environnement 5

6 Introduction THERMOCITY : Thermal mapping for winter risk (city of Paris) Example of winter risk evaluation The measurement was made by two vehicles (from THEMACS and CEREMA) and simultaneous an aerial thermography was done by the LNE (National metrology institute in France) with a plane all around the city of Paris 6

7 Introduction Land surface temperature measurement in Namibian desert (ESA project) LST and emissivity measurement in NAMIBIA Surf1 W Alu B Surf2 A Example of temperature calculation from luminance and reference temperature Thermal picture : the temperatures of the surfaces references (White, Black, Alu) are measured. The luminance of the 5 surfaces are measured B Experimental dispositive of measurement. A: reference surfaces B: soil viewing NPL 7

8 Introduction Problem: emissivity depends of the material and the angle of view At 300K 1% error on emissivity = error of 0.75K 8

9 TWENTIETH SYMPOSIUM ON THERMOPHYSICAL PROPERTIES Boulder, CO, USA June 24 29, 2018 Introduction In-situ emissivity measurement tool Angular correction of directionnal emissivity Prospects and improvement 9

10 In-situ emissivity measurement tool Reflectometry with a modulated IR flux Two devices were developped in the CERTES Laboratory. EM1 : Modulation of IR flux by a modulation of temperature EM2 : Modulation of IR flux by a system of rotating screen One device were developped in THEMACS Ingénierie :EM3 10

11 In-situ emissivity measurement tool Reflectometry with a modulated IR flux EM1 Cavity modulated in temperature Modulated reflected flux Modulated incident flux IR detector Flux of the sample =σ.t 4 Sample 11

12 In-situ emissivity measurement tool EM1 : the first emissometre of CERTES Laboratory Radiating part Peltier effect Modulated enclosure Aluminum part Sample Optical system Modulated IR source Optical bench Sample 12

13 In-situ emissivity measurement tool A concept to produce a modulated IR flux at high frequency: Advantages : -The source is still a cavity A 3D chopper -It is possible to control the incidence angle and modulate it at different frequencies -Fast measurement -Easy to transport for field measurement -Low cost design -Patented design 13

14 In-situ emissivity measurement tool EM2 For more information: Infrared Emissivity Measurements of Building and Civil Engineering Materials: A New Device for Measuring Emissivity Int J Thermophys 2013 Jean-Pierre Monchau Mario Marchetti Laurent Ibos Jean Dumoulin Vincent Feuillet Yves Candau 14

15 In-situ emissivity measurement tool EM3 Emissivity measurement in Namibia with EM3 A the measurement head B : measurement on Gobabeb site The device used is the emissivity measuring device EM3 from THEMACS Ingénierie. Two spectral band can be used : 8-14µm or broad band (1-50µm). 15

16 In-situ emissivity measurement tool N measuremen Point Emissivity t 1 Point Point Point Point Point Point Point Point Point Point Point Point Point Point Point Mean standard dev Broadband Emissivity Measurements: In view of the measurements made on this type of soil, an average emissivity of may be considered as the reference value. Emissivity measurement in Namibia with EM3 Point Emissivity point point point point point point point point point point point point point point point Mean standard dev Measurements of emissivity in band III 16

17 In-situ emissivity measurement tool Emissivity measurement in Namibia with EM3 Sensitivity of KT19-85.II from Heitronics documentation DEXTER thermopile documentation documentation 17

18 In-situ emissivity measurement tool Emissivity measurement in Namibia with EM3 Laboratory Spectral Measurements: These measurements were done in the laboratory and not in the field. The spectrometer is a Frontier Perkin- Elmer, with an integrating sphere Pike. Measurements were made separately on sand and gravel (supposed quartz) pieces Reflectance Gravel 1 Gravel 2 Gravel 3 Gravel Reflectance Sand 1 Sand 2 Sand λ (µm) λ (µm) Emissivity for different spectral band Material 2-17µm 8-14µm 8-12µm µm Sand Gravel

19 In-situ emissivity measurement tool Emissivity measurement in Namibia with EM3 Conclusion of this campaign: These measurements help us for land surface temperature but we have to know the bandwith of the radiometer There is always problems with mineral sample (never grey!) 19

20 In-situ emissivity measurement tool The solution is to make in-situ measurement with a portable spectrometer The 4300 Handheld FTIR is the first of its kind employing lightweight ergonomics, ease of use, ruggedness, and flexibility into one system. The 4300 weighs in at approximately 2kg. With its lighter weight and new design, the ergonomics of the system make it ideal for field use and deployment into non-laboratory situations. A variety of sampling interfaces (Diffuse Reflectance, External Reflectance, Grazing Angle, Diamond ATR, Ge ATR) allows the user to easily transition from one sample type to another while on the go, with no alignment or adjustments necessary. Sample types typically include infrared absorbing and scattering surfaces, reflective metal surfaces with coatings and films as well as analysis of bulk materials including powders and granules. 20

21 TWENTIETH SYMPOSIUM ON THERMOPHYSICAL PROPERTIES Boulder, CO, USA June 24 29, 2018 Introduction In-situ emissivity measurement tool Angular correction of directionnal emissivity Prospects and improvement 21

22 Angular correction of directionnal emissivity Problem : Does the angular correction is constant? Solution: Measure the directionnal emissivity at different angle 22

23 Angular correction of directionnal emissivity Experimental device Thermocouple for rear temperature measurement Peltier Sample Power supply 80V/120A Stepper motor IR camera SC7300 SPIDER II instrument Micro-computer Computer Under Labview 23

24 Angular correction of directionnal emissivity Micro-computer Experimental parameters - Periodic thermal excitation applied by 16 thermoelectric coolers - FLIR SC7300 long wave infrared camera (spectral range µm, matrix ) cooled by a Stirling engine. NETD=0.02K - Sampling frequency f e =0.5 Hz - Sampling period of thermal wave : 640s - Observation angles from 0 to 88.5 (goniometer) - Experimental setup controlled by a LabView program Stepper motor Sample IR camera SC

25 Angular correction of directionnal emissivity Experimental device 25

26 Angular correction of directionnal emissivity Thermal excitation (front face of the sample) - Sine wave on Peltier modulus at T=640s Measurements with the camera: 0.5s (25 frames at 50Hz for each angle). Measurement from 0 to 88.5 and from 88.5 to 0 (118 measurements during 236s) Examples of bituminous concrete sample Examples of thermal images with ROIs 26

27 T Source ( C) Angular correction of directionnal emissivity T Source ( C) 45 Angle = 21 Angle = 21 Angle = T App,Surface ( C) t (s) t (s) T Source ( C) T App,Surface ( C) 0 T App,Surface ( C) t (s) t (s) 27

28 T App,Surface ( C) Angular correction of t directionnal (s) emissivity t (s) 28

29 Angular correction of directionnal emissivity n 0.8 ( ) Sample 1 Sample 2 Sample 3 Glass PVC 0 29

30 Angular correction of directionnal emissivity Relative emissivity Absolute emissivity Angle( ) Angle( ) 30

31 TWENTIETH SYMPOSIUM ON THERMOPHYSICAL PROPERTIES Boulder, CO, USA June 24 29, 2018 Introduction In-situ emissivity measurement tool Angular correction of directionnal emissivity Prospects and improvement 31

32 Prospects and improvement To avoid problems with temperature measurement with radiometric method we have to control radiative environnement We are looking for bandwith with «grey behaviour» for pyrometry Spectral reflectance data from JPL (%) λ (µm) 32

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