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THERMAL MAPPING FOR A HIGHWAY GRITTING NETWORK by David GrahamBelk fo LL wa ,1 Submitted in fulfilment of the requirementsfor the degreeof PhD Department of Civil and Structural Engineering, University of Sheffield December 1992 To Lin VOLUME 1 ABSTRACT Thermal mapping, the measurementof road surface temperatures (RSTs) with an infra-red thermometer (IRT) mounted in a moving vehicle, seeks to identify a 'characteristic and repeatable' thermal fingerprint (temperature profile) for any stretch of road. A number of useshave been suggestedfor the process, including ice detection sensor network design and identifying stretches of road for selective gritting, with potential financial and environmental benefits due to reduced salt usage. The project 'Thermal Mapping for a Highway Gritting Network' has resulted in the most extensive survey yet undertaken. The aims were to investigate the reliability/repeatability of fingerprints and establish confidence limits. Comprehensive mapping of Sheffield roads took place during winters 1988/89- 1991/92. Significant errors (+/-3°C) in RST readings were identified after the first winter. Laboratory and road tests confirmed errors were produced due to warming/cooling of the IRT. Operating the IRT in a temperature control box eliminated these errors. Seven Sheffield routes were mapped during winters 89/90 and 90/91 with route 1 fingerprints (100) used for most of the analysis. The main factors affecting the variation in RSTs were confirmed as altitude and land-use with localised peaks occurring under bridges and by trees and tall buildings. The occurrenceof cold air drainageon clear/calm (extreme') nights resultedin 'low' RSTsat relatively low altitudes. Differences were identified between what should have been identical extreme fingerprints. Thesewere related to variationsin the behaviourof cold air drainage from night to night and variations in wind direction/speed interacting with local relief. Confidencelimits for extreme fingerprints and maps, taking into accountpossible errors in mapping and differences between fingerprints, were +/-20C and +/- 2.5°C respectively.With important decisionsconcerning gritting madewhen RSTs are +/-5°C confidencelimits of this magnitudehave important implications for thermal mapping. Future use should be restricted to sensornetwork design and assessment/re-designof gritting networks. ACKNOWLEDGEMENTS I would like to take this opportunity to thank SERC and Sheffield City Council Works Department for supporting this research project. In particular, the help, support, encouragement and patience of John Charlton was much appreciated. Special thanks to my supervisors Robert Ashworth (Civil and Structural Engineering) and Peter Smithson (Geography) for their guidance during the course of the research and preparation of this thesis. The support and encouragementof family and friends have been vital. Grateful thanks to the following who have helped out on many occasions in many different ways with apologiesto anyoneI may haveforgotten: Tim Departmentof Civil and StructuralEngineering - especiallyJeanne Cheetham, Robinsonand Kev Spence. Departmentof Geography. Employeesat Sheffield City Council Works Department- especiallyLes Goulding. TraversMorgan Maintenance- equippingvan for thermal mapping. PeterBanham, Micron Techniques/PalmMicrosystems. free Land infrared Ltd - especiallyRoy Barber and for conductingemissivity tests of charge. Brian Parmenter at TRL - loan of KT-17. John Thornes at Birmingham University. CONFERENCE PAPERS 'TheMeasurement of Road SurfaceTemperatures with Infra-RedThermometers (Thermal Mapping)'.Presented at the 24th Universities'Transport Study Group AnnualConference, University of Newcastle-upon-Tyne,6-8th January 1992. The Measurementof Road SurfaceTemperatures with Infra-Red Thermometers(Thermal Mapping)'. Presented at the PTRC European Transport, Highways and Planning 20th Summer Annual Meeting, 14-18th September 1992, UMIST. Published in Highways. Proceedingsof SeminarH, pp. 161-174. iv CONTENTS VOLUME 1 page Abstract i Acknowledgements iii Conferencepapers iv Contents v List of figures xiii List of tables xix List of photos xxil Chapter1 INTRODUCTION 1 1.1. Thesis Outline 1 1.2. Highway Winter Maintenance 2 1.2.1. Weather forecasting and winter maintenance 4 1.2.2. Forecastingroad surfacetemperatures 5 1.2.3. Automated road weather sensors 7 1.2.4. Thermal mapping 9 1.2,5 The developmentof the UK national ice prediction system 9 1.3. Thermal Mapping Theory and Practice 12 1.3.1. The principles of thermal mapping 12 1.3.2. Thermal mapping in practice 16 1.3,3. Factors affecting road surfacetemperatures 20 1.3.4. Types of thermal fingerprint observed 23 1.4.The Developmentof ThermalMapping and Literature Review 24 V 1.4.1.The developmentof thermalmapping as an aid to winter maintenanceoperations 25 1.4.2. Critical researchand comments 32 1.4.3. Applied climatology for increasedtraffic safety and road maintenance 38 1.5. ResearchProposals and Project Aims 40 1.5.1. Background to the project 40 1.5.2. Detailed proposals 42 Chapter 2 STUDY AREA, THE CITY OF SHEFFIELD 43 2.1. Location and Demographic Characteristics 43 2.2. Sheffield'sPhysical Environment 45 2.2.1.Relief 45 2.2.2. Climate 46 2.3. WeatherConditions During the ResearchProject 49 2.3.1. Winter 1988/89 50 2.3.2. Winter 1989/90 52 2.3.3 Winter 1990/91 54 2.3.4 Sheffield 56 2.4. Route Selectedfor Detailed Study 59 ha er 3 THERMAL MAPPING EQUIPMENT AND PROCEDURE AND MAPPING WINTER 1988/89 61 3.1. Thermal Mapping Equipment 61 3.1.1. Thermal mapping hardware 61 3.1.2. Thermal mapping software 63 3.1.3. Testing of thermal mapping equipment 64 vi 3.2. Thermal Mapping Procedure 66 3.2.1. Methods of data collection winter 1988/89 67 3.3. Mapping Winter 1988/89 68 3.4. Performanceof the Infra-Red ThermometerWinter 1988/89 69 3.4.1. Consistencyof temperaturereadings 70 3.4.2. Accuracy of temperaturereadings 72 3.4.3. Implications for thermal mapping 78 Chapter 4 THE PRODUCTION OF ERRORS IN ROAD SURFACE TEMPERATURE READINGS WHILE THERMAL MAPPING 80 80 4.1. PossibleSources of Error 4.1.1. Infra-red thermographyliterature 83 84 4.2. Laboratory Tests on the Compac 3 Infra-Red Thermometer 4.2.1. Equipment design 85 85 4.2.2. Test procedures 4.2.3. Results 87 4.2.4.Discussion 88 4.2.5. Relationshipbetween warming/cooling rates and magnitude of errorsproduced 89 91 4.3. Laboratory Tests on the HeimannKT-17 Infra-Red Thermometer 91 4.3.1. Test procedure 4.3.2. Results 93 4.3.3. Discussion 93 4.4. Road Tests (December 1989) 94 4.4.1. Procedure 95 4.4.2. Results 95 4.4.3. Discussion 97 4.5. How Errors Are Produced 98 vii 4.5.1. Internal Reflection 100 4.5.2. Glare (reflection from surrounds/background) 101 4.6. Explanation of Errors/Inconsistenciesin Thermal Fingerprints and TemperatureData 1988/89 (Chapter 3 Section 3.4.2) 104 4.6.1. Thermal fingerprints 104 4.6.2. Differences between air and road temperatures 105 4.6.3. Runs at different times of the night 106 4.6.4. Comparisonbetween IRT readingsand icelert data 106 4.7. Elimination of Errors While Thermal Mapping 107 4.7.1. Modifications to the temperaturecontrol box and van 107 4.7.2. Mapping procedurewinter 1989/90 109 4.7.3. New temperaturecontrol box winter 1990/91 110 4.7.4. Warming/cooling of the IRT while in the temperature control box 112 4.8. Conclusionsand Summary of MappingUndertaken During Winters 1989/90 and 1990/91 113 ha er5 TYPES OF THERMAL FINGERPRINT OBSERVED AND FACTORS AFFECTING ROAD SURFACE TEMPERATURES 115 5.1. Types of Fingerprint Mapped Along Route 1 116 5.1.1. The extreme fingerprint(s) 116 5.1.2. The dampedfingerprint 118 5.1.3. The intermediatefingerprint 119 5.1.4. Other fingerprints 121 5.2. Factors Affecting Road SurfaceTemperatures in Sheffield 123 5.2.1. Altitude 124 5.2.2. Housing/industry 130 5.2.3 Topography 133 Viii 5.2.4. Other features 137 5.3. Conclusions 140 Chapler6 THE RELIABILITY AND REPEATABILITY OF THERMAL FINGERPRINTS 142 6.1. The Variation in the Amplitude of Thermal Fingerprints 143 143 6.1.1. The measurementof the amplitude of thermal fingerprints 145 6.1.2. Variation of amplitude with cloud and wind during a run 6.1.3. The effect of weather conditions during the earlier part 147 of the night (ie.before 043Ohrs) 6.1.4. Other factors affecting the variation in amplitude of thermal fingerprints 150 152 6.1.5.Combined effect on amplitude 6.1.6.Factors influencing the variationin the amplitudeof 159 extreme fingerprints 6.1.7.Factors influencing the variationin the amplitudeof dampedfingerprints 160 6.1.8. Conclusions 161 161 6.2. Cooling Rates of Air and Road SurfaceTemperatures 163 6.2.1. Observedcooling rates 6.3. Factors Producing Differences in Thermal Fingerprints 165 166 6.3.1. Length of cooling period 6.3.2. Wind speedand direction 171 6.3.3. Potential solar receipt 175 6.4. Conclusions 176 ix Chapter 7 THERMAL MAPS OF SHEFFIELD, POSSIBLE ERRORS IN VEHICLE-BASED THERMAL MAPPING AND CONFIDENCE LIMITS FOR THERMAL FINGERPRINTS AND MAPS 178 7.1. Thermal Maps of Sheffield'sPrincipal Highway Network 178 7.1.1. Preparation of the thermal maps 179 7.1.2. The thermal maps 180 7.1.3. Comparisonof the extreme thermal map with 1992 fingerprints and icelert data 183 7.2. PossibleErrors in Vehicle-BasedThermal Mapping 185 7.2.1. Assessmentof errors 186 189 7.2.2. Magnitude of errors discussedabove (7.2.1) 7.2.3.Possible errors due to variationsin the emissivityof road 190 surfaces 7.3 ConfidenceLimits for ThermalFingerprints Maps 195 . and Chapter8 OVERALL CONCLUSIONS AND RECOMMENDATIONS 197 197 8.1. Principal Findings of the Project 8.1.1. Accuracy of the IRT 197 8.1.2. Factors affecting road surfacetemperatures 198 199 8.1.3. The reliability and repeatability of thermal mapping 8.1.4. Errors in vehicle basedthermal mapping and confidence limits 200 8.2.