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Surface Temperature Mapping of the University of Northern Iowa Campus Using High Resolution Thermal Infrared Aerial Imageries
Department of Geography, University of Northern Iowa, Cedar Falls, Iowa, USA
Author to whom correspondence should be addressed
Received: 25 July 2008; in revised form: 22 August 2008 / Accepted: 22 August 2008 / Published: 25 August 2008
The goal of this project was to map the surface temperature of the University of Northern Iowa campus using high-resolution thermal infrared aerial imageries. A thermal camera with a spectral bandwidth of 3.0-5.0 μm was flown at the average altitude of 600 m, achieving ground resolution of 29 cm. Ground control data was used to construct the pixel- to-temperature conversion model, which was later used to produce temperature maps of the entire campus and also for validation of the model. The temperature map then was used to assess the building rooftop conditions and steam line faults in the study area. Assessment of the temperature map revealed a number of building structures that may be subject to insulation improvement due to their high surface temperatures leaks. Several hot spots were also identified on the campus for steam pipelines faults. High-resolution thermal infrared imagery proved highly effective tool for precise heat anomaly detection on the campus, and it can be used by university facility services for effective future maintenance of buildings and grounds.
Thermal; infrared; aerial; remote sensing; buildings; steam lines; surface temperature
Heat loss detection is an important aspect of infrastructure maintenance. With fuel prices rising and ecology concerns gaining voice, managers and engineers face the problem of heat loss reduction. One of the common ways to improve energy efficiency is to identify temperature anomalies (“hot spots”) in the existing infrastructure. Defects in building insulation, leakage in underground pipelines and general insulation deterioration are good examples of heat loss sources. Thermal radiation is not perceived by the human eye, which complicates the process of hot spot detection. Thermal remote sensing makes thermal radiation visible, which makes it an excellent solution to the problem of locating hot spots. Thermal infrared sensors can be handheld or fixed on a platform such as an airplane, a satellite or a car. Each of these platforms has its own advantages and disadvantages.
Ground level surveys are very flexible and can easily be performed on demand. They are, however, prohibitively time-consuming when dealing with a large study region [1
]. Another problem is that the results of the ground survey cannot be easily integrated into modern GIS systems. Airborne and satellite-based surveys, on the other hand, provide data that can be easily georeferenced, imported into any GIS system and prepared for automated analysis as described by MacKay [2
Satellite systems have a number of advantages: they offer vast coverage, collect imagery at regular intervals and at lower cost. On the other hand, satellite imagery is not available on request because the orbital path is not easily adjustable. Also, the combination of limited pixel dwell-time and low level of signal in the infrared part of the spectrum only allows for spatial resolution of 60m or worse (60m for Landsat, Band #6 and 90m for Aster, Bands #10 to 14, according to NASA specifications). Finally, sun-synchronous satellites (such as Aster and Landsat) are not suitable for precise heat loss analysis, because it is the heat coming from inside the buildings that is of interest, not the re-emitted heat coming from the sun.
Aerial imagery can be acquired on request (at any time of day and night) and with high spatial resolution because of the much lower altitude of flight. Several papers have demonstrated that aerial imagery can produce temperature measurements accurate to within 0.6-1.7°C [3
]. A number of drawbacks, such as long deployment time (the plane needs to travel to the place of survey) and relatively high cost (costs of $200,000