QIRT Implementation of an infrared camera for road thermal mapping. July 27-30, 2010, Québec (Canada)

Transcription

1 10 th International Conference on Quantitative InfraRe Thermography July 27-30, 2010, Québec (Canaa) Implementation of an infrare camera for roa thermal mapping by M. Marchetti*, M. Moutton*, S. Luwig*, L. Ibo**, V. Feuillet** an J. Dumoulin*** * CETE e l Et-ERA 31, 71 rue e la Grane Haie, TOMBLAINE Nancy, France, Mario.Marchetti@eveloppement-urable.gouv.fr ** CERTES-UPEC, Univerité Pari Et, 61 avenue u Général e Gaulle, Créteil Ceex, France, ibo@univ-pari12.fr *** LCPC, MACS, Route e Bouaye - BP 4129, Bouguenai Ceex, France, jean.umoulin@lcpc.fr Abtract Thermal mapping ha been implemente ince the late eightie to etablih the uceptibility of roa network to ice occurrence with meaurement from a raiometer an ome atmopheric parameter. They are uually one before awn uring wintertime when the roa energy i being iipate. The objective wa to etablih if an infrare camera coul improve the etermination of ice roa uceptibility. Data analyi obtaine from the raiometer an the infrare camera ha hown great imilaritie. A comparion wa mae with promiing perpective. The meaurement rate to analye a given roa network coul be increae by a factor two. 1. Introuction Thermal mapping ha been implemente ince the late eightie to meaure roa pavement temperature along with ome other atmopheric parameter to etablih the uceptibility of roa network to ice occurrence [1-9]. Meaurement are mainly one uing a vehicle circulating on the roa network in given roa weather conition (clear weather, clouy, wet pavement, ). Thee meaurement are both ue for the etermination of a winter rik inex bae on the comparion of roa urface temperature with ew point over the roa network, an a an input for roa weather forecat moel bae on energy balance. If the ew point temperature i below roa urface temperature there i a rik of ice occurrence an therefore a lo of grip for circulating vehicle. Roa urface temperature i mainly obtaine with an infrare raiometer proviing meaurement at a given patial frequency whatever the pee of the vehicle wa ue to it inertion in traffic flow. The evice i either intalle outie or inie the vehicle. To avoi too much influence of the un, an to ee the thermal behavior of the pavement enhance, thermal mapping i uually one before awn uring wintertime. That i when the energy accumulate by the roa uring aytime i mainly iipate (by raiation, by conuction an by convection) an before the roa tructure tart a new cycle. The length of a roa network range between a few hunre of kilometre an up to everal thouan kilometre when it come to multiple lane highway an an analyi in the two irection of a roa. Thi analyi i mainly one when a new roa network i built, when ome major pavement change are mae, or when moification in the roa urrouning took place that might affect the thermal heat balance. Thi help roa manager to intall enor to monitor roa tatu on pecific location ientifie a angerou, or imply to intall pecific roa ign. A et of roa event are collecte by the operator (preence of brige, urban area, woo on roa ie, pavement nature change, ) that might help in the analyi of roa thermal repone. Meaurement are run at pee allowe on the roa network an ranging from a few km/h an up to 110 km/h. They are anyhow time-conuming. Inee, a whole roa network can harly be analye at once, an ha to be partitione in tretche that coul be one in the open time winow to avoi temperature artefact ue to a riing un. The LRPC Nancy ha been uing a vehicle for thermal mapping ince the early eightie. The vehicle i illutrate on figure 1. Although the whole evice ha great performance, uch raiometer coul only analye one lane at a time. Furthermore, meaurement being run before awn, all roa event are uually obtaine making meaurement uring aytime. The roa urface temperature obtaine i then ue to etablih a rough cooling pee. Fig. 1. : Vehicle for thermal mapping

2 The objective of the work wa to etablih if the implementation of an infrare camera on a thermal mapping vehicle coul improve the etermination of roa network uceptibility to ice occurrence by analying everal lane in a ame eion. The analyi of roa urface temperature obtaine from the raiometer an the infrare camera are howing great imilaritie. Comparion wa mae on an area locate between the wheel track. Promiing perpective appeare to increae by a factor two the meaurement rate to analye a given roa network. 2. Decription of the experimental evice 2.1. Infrare raiometer PRT5 an atmopheric parameter The infrare raiometer i a PRT5 from Barne pyrometer, with a 20 fiel of view (FOV). It i mounte on the front bumper of a car, in a compartment which temperature i regulate aroun 18 C. The compartment i locate at about 40 cm above the roa urface. The characteritic of the raiometer are given in table 1. In our tuy, thi raiometer wa choen ha a reference for ata analyi. Table 1. Characteritic of PRT5 raiometer Detector type bolometer etector Spectral banwith µm Thermal range -40 C to + 70 C Senitivity 0.1 C below 0 C, 0.05 C above 0 C Accuracy ± 0.5 C FOV 20 time repone 50 m NET for a time repone of 50 m on a boy at 25 C During the meaurement, uual atmopheric parameter uch a air temperature, relative humiity an atmopheric preure were monitore. Meaurement were provie by a probe eigne to be intalle on moving vehicle, incluing aircraft wing [10] Infrare camera FLIR S65 an thermal image A FLIR S65 camera wa ue. Thi camera ha an uncoole 320x240 FPA etector in ban III. The camera i intalle in a compartment attache to a winow on the right ie of the vehicle. The camera wa plugge to a computer through an IEEE1394 firewire interface. The camera wa turne at leat 30 minute before tarting the meaurement to make ure the whole electronic ytem ha reache a thermal equilibrium. The characteritic of the camera are ummarize in table 2. Table 2. Characteritic of FLIR S65 camera Detector type Microbolometer etector uncoole IRFPA of 320x240 enitive element Spectral banwith µm Thermal range ue -40 C to C Senitivity 0.08 C Accuracy ± 2 % of the meaurement FOV 24 x18 (HxV) (focal len 35 mm) IFOV 1,3 mra lower image acquiition frequency 1 Hz Vieo output Up to 50 Hz non interlace The camera FOV wa uch that each thermal image woul embrace everal element of the cene, from the roa pavement an up to the ky. In uch configuration, the roa i analyze at a near grazing angle. A mirror wa intalle in the FOV of the camera, along with a urface painte with Nextel , which emiivity i coniere a table an equal to 0.97 [11]. The one of the mirror ha been etermine to [12]. Due to the grazing angle, the meaurement area for the infrare camera wa locate ahea of the raiometer one. There i o a itance offet between the temperature meaurement obtaine from the raiometer an the one from the

3 Environment infrare camera at the ame time. Thi offet obviouly epen on the area of the thermal image that woul be invetigate. The farther the area from the front of the vehicle, the greater the offet. Infrare image obtaine with the camera were analyze with ThermaCam Reearcher 2.9. Several region of interet (ROI) were efine on the mirror, on the Nextel coating an on the roa pavement. Thi lat one wa uch that no thermal interference ue to circulating vehicle wa inclue in the region of interet. A ketch of the intrument configuration along with an infrare image i given on figure 2. In the choen configuration for the ata analyi, the itance offet wa of 12 m. Thi value i the itance between the point where the raiometer i making a meaurement an the mile of the pavement ROI. IR camera vehicle raiometer 24 camera axi 1.3 m 7 pavement ROI pavement 2 m 4.5 m ~ 9 m 5.5 m Fig. 2. : Sketch of intrument configuration (left) an thermal image from the vehicle with ROI (right) 2.3. Data acquiition Data acquiition for atmopheric parameter i performe every 3 m with a pee taying below 110 km/h uing a oftware interface evelope uner LabVIEW. Pavement emiivity wa firt uppoe to be equal to one an to behave a a black boy. A et of roa event are collecte by the operator (preence of brige, urban area, woo on roa ie, ) that might help in the analyi of roa thermal repone. A oftware interface for ata acquiition, alo evelope uner LabVIEW uing a pecific FLIR SDK toolkit, wa mae. The coe wa written to procee in a naphot moe for thermal image acquiition. To cope with the camera time integration an limit with ata tranfer, thermal image were only acquire every 24 m, at pee taying below 70 km/h, an uing FLIR native format. Depite the naphot function, the microbolometer matrix an the whole electronic part of the infrare camera have an integration time of a few milliecon. Thi time caue a light blur in the thermal image when the vehicle i moving (trace behin object equivalent to two pixel at 70 km/h in our meaurement configuration). Thi apect i compenate by a choice of ROI for analyi which ize excee the blur effect. All the atmopheric parameter meaure by the ifferent enor uch a air temperature an relative humiity were ue a input parameter for the infrare camera when recoring thermal image. The oftware interface i given on figure 3. Fig. 3. : French oftware interface for ata acquiition with atmopheric an infrare parameter

4 2.4. Roa network pavement The roa network choen for the tet wa almot 30 km long an the meaurement late nearly 30 minute. It inclue everal configuration, from ingle lane roa to multiple lane highway, paing above an below brige, with an without tree on the roaie. Meaurement were run without un raiation to avoi artefact, with a light clou cover. The vehicle remaine in the right lane when the riving wa one on highway. A large itance with the vehicle right before wa maintaine to avoi it thermal ignature. In uch a configuration, there were many variation in the material that coul be ue for roa pavement manufacturing. Furthermore, ue to aging pavement an repair, a wie variety of ituation were met along thee 30 km. Therefore, a fixe an contant emiivity value coul harly be efine. The pavement emiivity coul be coniere a cloe to 1 for meaurement cloe to the normal of the urface [11, 16]. Bae on the literature [13-15], the emiivity ecreae a the obervation angle get cloer 90 with repect to the normal of the analye urface. Neverthele, in thi firt approach, pecularity of the pavement material wa neglecte. So ifference houl be oberve between raiometer an infrare camera ata. 3. Reult an icuion Atmopheric an pavement meaurement are given on the following figure. Pavement temperature obtaine with the infrare raiometer along with the one from the camera are rough ata before any treatment an environment correction. An offet wa oberve between temperature meaure, the camera temperature being ignificantly coler. Neverthele, the pavement temperature profile evolution eem correlate. Furthermore, in both cae, major element of the roa environment uch a brige were properly etecte by both intrument. Before any meaurement correction, thermal amplitue wa larger with the camera (11 C) than it wa with the raiometer (6 C) (ee Fig. 4). Fig. 4. : Surface temperature meaure with the raiometer an the infrare camera, an air temperature a a function of itance before any correction The raiance balance of the whole ytem coul be written a Eq. (1). L meaure ( ε pavement ). Lenvironment + (1 atmophere). Latmophere = τ atmophere. ε pavement. Lpavement + τ atmophere.1 τ (1) In the choen configuration the itance between roa an infrare camera i aroun fifteen meter for the mot itant point were a meaurement i one. The meteorological ituation wa uch that neither clou, nor fog were preent uring the meaurement. The atmopheric tranmiion coefficient τ atmophere wa equal to one. The part ue to the atmophere coul therefore be neglecte. The infrare camera meaurement were one coniering boie in it fiel of view emitting infrare raiation a black boie. Eq. (1) then become Eq. (2) without coniering the pecularity. The raiance from the environment wa obtaine thank to the mirror intalle in the fiel of view of the infrare camera. A ecribe in the previou paragraph, meaurement were one with the camera having a grazing angle with repect to pavement urface. In uch a ituation, the emiivity i below the conventional 0.95 to 0.98 value for non-metallic material in general an aphalt concrete in particular [11, 16]. An emiivity value of 0.77 wa electe, conitent with the literature [15]. Such a choice wa mae to fulfill the grazing angle ituation. It alo allowe getting temperature meaurement from the infrare camera matching the value from the PRT5 raiometer choen a a reference. Thank to Eq. (2), pavement temperature with an environment correction coul be obtaine.

5 Environment T 4 meaure 4 ( 1 ε ). T = ε (2) 4 pavement. Tpavement + pavement environment Once the raiative correction complete, a econ one wa performe to take into account the itance offet between ytem, a illutrate on figure 2 where the meaurement with the infrare camera i ahea of the one of the raiometer. Reult preente in figure 5 how a goo concorance between temperature iue from both intrument once inclue thee correction. A partition of the whole itinerary wa et to eae it legibility. (a) 0 to 7000 m (b) 7000 to m (c) to m () to m Fig. 5. : Temperature meaurement a a function of itance after emiivity an itance offet correction With thi et of correction, the itribution of pavement temperature an of pavement temperature ifference T between the two infrare intrument were etablihe an reult hown in figure 6. The pavement temperature ifference itribution i centere above 1 C, with a tanar eviation of 1.8 C. Bae on the value given in table 1 an 2, ata wa clearly within the enitivity an accuracy of the intrument. Fig. 6. : Pavement temperature itribution an ifference T =T (PRT5)-T (FLIR)

6 Many poibilitie exit in the calculation of the winter rik WR of an itinerary. In France, average meaure parameter (air temperature, relative humiity, pavement temperature, ew point) are commonly ue to analye icing rik of an itinerary. WR i then efine accoring to Eq. 3: WR = 2.WR(T ) + WR(T ), with WR(T ) = 0 if 0 an WR(T ) = 0 if 0,average,average T < 0.5 C;1if 0.5 T < 0.5 C;1if 0.5,average,average T < 1 C;... T < 1 C;... (3) The winter rik wa then calculate uing pavement temperature meaurement of the PRT5 raiometer a uually one, an with ata from the infrare camera, once the emiivity an itance offet correction one. They are illutrate in figure 7, with a partition of the whole itinerary. The global WR hape wa repecte, though value were clearly ifferent from one intrument to the next. Such ifference ha to be moerate becaue of the metho choen for WR calculation. Furthermore, a illutrate on figure 6, the pavement temperature itribution from both intrument are greatly ifferent though gauian in both cae. WR i greatly enitive to the average obtaine. In the cae of the PRT5 raiometer, the average temperature i lightly above -0.7 C, while it i near -1.3 C in the cae of the FLIR camera. Average value for ue point i the ame in both cae. Therefore, a ifference will appear in the WR evaluation. The meaurement with the infrare camera wa bae on many element from the roa environment, enhancing the thermal amplitue of the ROI. The one ue for pavement temperature ha a given patial extent. An ue to the grazing angle, pavement point farther from the vehicle appeare coler than the one near the vehicle. A temperature ifference up to 2 C wa recore along thermal image bae on figure 2 pavement ROI. Thi alo contribute to increae the thermal amplitue within the ROI. Thi coul be correcte coniering an emiivity itribution within the intea of attributing a contant emiivity. Inee, emiivity rop quickly when it come to uch low obervation angle (below 10 ). So, once the average pavement temperature wa calculate for WR, variation aroun it were enhance with the infrare camera an thi clearly affecte the WR which appeare greater that the one wa obtaine with the raiometer. (a) 0 to 7000 m (b) 7000 to m (c) to m () to Fig. 7. : Winter rik obtaine with infrare raiometer an the camera

7 Environment 4. Concluion The objective of thi work wa to etablih the poibility to implement an infrare camera (FLIR S65) on a thermal mapping vehicle to have at a ame time multiple-lane analyi in one hot an for an extene roa urface. Once complete, uch meaurement configuration wa compare to current meaurement ytem in ue (PRT 5 raiometer) to compute the inex of uceptibility of roa network to ice occurrence. To o o, a 30 km-long itinerary wa choen, incluing ifferent roa configuration (highway, urban area, brige, tree,...). The infrare camera wa intalle on boar of a pavement monitoring vehicle. Simplifie raiometric correction were one to take into account the inclination of infrare camera with repect to roa urface. Furthermore, roa ata patial offet between the two meaurement ytem wa correcte. A LabVIEW interface wa evelope for ata acquiition, incluing atmopheric parameter an infrare image. Roa urface temperature analyi obtaine from the raiometer an the infrare camera have hown imilaritie. A comparion wa mae on an area locate between the wheel track. Once raiometric an itance offet correction performe, there wa a goo agreement between the urface temperature meaurement. Data from the infrare camera inicate greater thermal amplitue. Thi coul be explaine by the grazing angle that houl inuce an emiivity correction with a itribution over the region of interet, an not only a ingle value a performe in a firt approximation. The winter rik calculation wa conucte accoring to a very traitional an implitic way. Becaue of the greater thermal amplitue obtaine with the camera an the ifference between pavement temperature average from both intrument, a larger winter rik wa euce along the network with repect to the one obtaine with the raiometer. A a concluion, the feaibility of performing thermal mapping with an infrare camera wa etablihe. Thi woul improve the performance by meauring pavement temperature in everal roa lane at the ame time. The poition of the camera ha to be optimize accoring to it fiel of view. Although the thermal image acquiition frequency i comfortable, a reuction from 24 to 12 m woul eae ata analyi. Thi coul be performe acquiring ata only in the region of interet intea of the whole image, reucing it volume. A compromie ha to be foun to get information about roa urrouning, an to avoi raiation from paing vehicle. REFERENCES [1] Thorne, J.E. The preiction of ice formation on motorway in Britain. Unpublihe PhD Thei, Department of Geography, Univerity of Lonon, UK., [2] Thorne, J. E. Thermal mapping an roa-weather information ytem for highway engineer. Highway Meteorology, A. H. Perry an L. J. Symon, E., E an FN Spon, pp , [3] Belk D.G., "Thermal mapping for a highway gritting network", Ph D thei, Univerity of Sheffiel, ISBN z , [4] Shao J., Liter P.J., Pearon H.B., "Thermal Mapping: reliability an repetability", Meteorol. Appl. 3, pp , [5] Shao J., Swanon J.C., Patteron R., Liter P.J., McDonal A.N., "Variation of winter roa urface temperature ue to topography an application of Thermal Mapping", Meteorol. Appl. 4, (1997). [6] Gutavon T., Thermal mapping a technique for roa climatological tuie. Meteorological Application, 6, pp , [7] Chapman, L., Thorne, J.E. & Braley, A.V. Moelling of roa urface temperature from a geographical parameter atabae. Part 2: Numerical. Meteorological Application 8, pp , [8] Chapman, L. & Thorne, J.E. A geomatic bae roa urface temperature preiction moel. Science of the Total Environment 360: 68-80, [9] Chapman L., Thorne J.E., Small-cale roa urface temperature an conition variation acro a roa profile. Proceeing of the 14 th SIRWEC conference, WIRELESSCOM,. r. o. (Prague, Czech Republic), ISBN , [10] [11] Ibo L., Marchetti M., Bouenne A., Datcu S., Canau Y., Livet J., Infrare emiivity meaurement evice: principle an application, Mea. Sci. Technol., 17, pp , [12] Dactu S., Ibo L., Canau Y., Mattei S., Improvement of builing wall urface temperature meaurement by infrare thermography, Infrare Phyic & Technology, 46, pp , [13] Malague X.P.V., Theory an Practice of Infrare Technology for Nonetructive Teting, John Wiley & on, Inc., 684 p, [14] Gauorgue G., La thermographie infrarouge. Technique et Documentation (France), 386 p., [15] Hanbook of Military Infrare Technology, Office of Naval Reearch Department of the Navy (Wahington D.C., USA), 906 p,1965. [16] Marchetti M., Ibo L., Valérie Muzet, Pitre R., Bouenne A., Datcu S., Canau Y., Livet J., Emiivity Meaurement of Roa Material, QIRT Journal, Volume 1, Iue 1, pp. I.2.1-I.2.7, 2004.