By Mark Gilberg
Recent advances in infrared technology, including the development of inexpensive infrared cameras, have led to the development of exciting new applications.
One such application is the use of infrared technology to detect and locate subterranean termites in buildings and structures. Termites are an important structural pest in the United States, costing the public billions of dollars each year.
Subterranean termites are particularly destructive and are a significant threat to historic buildings given the traditional use of wood as a building material. Termite damage is both costly and irreversible and can diminish the historic significance of a structure through the loss of original building fabric.
Subterranean termites construct nests that house the colony. Termite nests generate heat as a consequence of the metabolic activity of millions of individual termites as well as the presence of fungi within the nest. It is this temperature differential between the nest and its environment that makes it possible to locate subterranean termite activity in buildings using thermal imaging devices such as infrared cameras.
In addition, subterranean termites also bring considerable amounts of moisture into a building to construct their nests and mud tubes. This moisture readily absorbs and re-emits infrared radiation thus contributing to the temperature differential.
Over the past year, NCPTT, in conjunction with Real Time Thermal Imaging, the New Orleans Mosquito and Termite Control Board, and Dow Agro Sciences Thermal Imaging Puts Termites in the Red has been exploring the use of thermal imaging using infrared cameras as a tool for locating subterranean termite nests in historic buildings. These trials, conducted at St. Alphonsus Catholic Church in New Orleans yielded some very encouraging results, suggesting the potential widespread application of this new technology.
St. Alphonsus Church
St. Alphonsus is located at 2045 Constance Street in New Orleans, a short walk from the French Quarter. It was constructed in 1855 by the Redemptorist Fathers to serve the religious and social needs of the many Irish Catholic immigrants who settled in the area in the 1840s. St. Alphonsus forms part of what was once referred to as Ecclesiastical Square, a complex of religious structures associated with the Catholic Church that occupied five adjacent city blocks. Designed in the Italianate style, St. Alphonsus is constructed of brick and is noted for its magnificent frescoes, paintings and stained glass windows imported from the studio of F.X. Zettler of Munich.
Rising operating and maintenance costs coupled with urban flight to the suburbs led to the closing of St. Alphonsus in the late 1970s. In 1990, a small group of concerned citizens formed the Friends of St. Alphonsus, a nonprofit organization dedicated to the restoration of this magnificent structure. The church is leased from the Archdiocese of New Orleans and now serves as a local community center known as the St. Alphonsus Art and Cultural Center.
Today, St. Alphonsus is just beginning to overcome years of deferred maintenance, which has resulted in a number of problems including extensive termite activity and water damage. Both native subterranean termites, and the St. Alphonsus Church was constructed in 1855 and closed in the 1970s. In 1990, The Friends of St. Alphonsus was formed to restore the historic building. Infrared detection and sophisticated eradication systems are being used to deal with the church’s termite problem. Photo by Ed Freytag Formosan subterranean termite, introduced from Asia after World War II, are present. Formosan subterranean termites, unlike most subterranean termite species, will build nests above and below ground. The above ground nests are typically found in walls and roof voids as is the case for St. Alphonsus. Dow Agro Sciences is presently conducting a series of field trials at St. Alphonsus to establish the extent of termite activity and to assess the effectiveness of their new termite baiting technology that employs both below and above ground bait stations.
Thermal imaging basics
Thermal imaging devices take advantage of the fact that all objects emit infrared radiation.
Devices such as infrared cameras create pictures based on the heat emitted by a viewed object as opposed to ordinary cameras that exhibit images as a result of light reflected off objects. In general, commercial infrared cameras detect radiation within the following range of wavelengths: 3-5 microns (middle wave infrared) and 7-14 microns (long wave infrared).
Infrared radiation outside these wavelengths is absorbed or blocked by particulate matter or gases in the atmosphere and thus cannot be detected. Infrared radiation, like visible light, can be focused and collected using optical devices and converted to an electronic signal. In practice, the latter can be translated into a video signal and assigned a particular shade of gray on a monitor corresponding to different temperature levels. Thus, thermal imaging devices generate images based on differences in temperature of the viewed scene.
The amount of radiation emitted by an object is proportional to the temperature of the object and a material property of the object referred to as emissivity. Emissivity is a measure of a materials ability to absorb and emit infrared energy. The latter is important because objects with different emissivities may appear to have different temperatures even if they are in fact the same temperature.
Thermal imaging analysis of St. Alphonsus
The thermal imaging device used in this field trial was a Palm-IR 250 handheld infrared camera with a spectral response of 7-12 microns . The sensor was an uncooled Ferro electric focal plane array capable of resolving temperature differences of 0.05 degrees centigrade. The real-time images were recorded on a digital video camera. A graphics software program was used to process the different images captured during the trial.
Thermal imaging of the ceiling of St. Alphonsus quickly revealed evidence of considerable water damage, particularly in the southwest corner of the church. Here, the wet, wooden lathes could be clearly seen through the overlying painted plaster.
Thermal imaging of many of the wooden support beams directly above this area in the roof void yielded a number of circular shaped anomalies that later proved to be subterranean termite nests. Similarly-shaped anomalies were observed in other support beams throughout the roof void, though it was not possible to verify the presence of termite nests in every case due to limited access. This was one of the principle advantages of thermal imaging in that it allowed the remote examination of inaccessible areas of the roof void. Excess moisture due to leaks in the roof, however, tended to mask termite activity and rendered the interpretation of thermal images extremely difficult following periods of heavy rainfall.
Thermal imaging has great potential as a quick, nondestructive means of accurately locating termite nests in buildings and as a tool for assessing the effectiveness of subsequent treatment measures. It also holds great promise when used in conjunction with termite baits to ensure the accurate placement of aboveground bait stations.
Thermal imaging is particularly suitable for the examination of historic structures given the need to preserve original building fabric and to minimize damage to historic elements. Moreover, it can be integrated into a total building analysis where it can used to identify water ingress as well as previous restorations.
Mark Gilberg was the NCPTT Applied Research and Technology Transfer Program Director.