Infrared at the Bottom of the World

Gary Phetteplace, PhD, PE Consulting Engineer Jason Weale, PE US Army Cold Regions Research and Engineering Laboratory

ABSTRACT

In 1997, the National Science Foundation (NSF) began construction of a new 80,000 square feet station at the geographic South Pole in Antarctica. As this $150 million project nears completion, there are concerns about the level of heat loss from the station, specifically associated with infiltration/exfiltration. The US Army Cold Regions Research and Engineering Laboratory (CRREL) was retained by NSF to conduct infrared surveys of the new South Pole Station, and has done so during both the 2005-2006 season and the 20062007 season. To place this in perspective, one must consider the impact of heat loss is not only amplified by the severe climate (approximately 42,000 heating degree days at 65 °F base), but also that all fuel is currently flown in. Each delivered gallon of fuel costs of approximately $20. This paper will focus on some of the technical and logistical challenges inherent in conducting an infrared (IR) survey in temperatures as low as -58°F. These unique conditions required us to fabricate a number of specialty items just to complete our surveys. Sample results from the surveys will also be included.

INTRODUCTION

The United States, via its National Science Foundation (NSF), maintains the largest presence of any nation within Antarctica. The US operates three major bases, as well as a number of field camps. The sole purpose of US presence in Antarctica is to support research that either cannot be accomplished in any other place, or is less expensive to conduct there than in the alternative (outer space). The continent of Antarctica is subject to a treaty established in 1959, originally signed by 12 nations including the US, USSR, France, Japan, and the United Kingdom. Today, 46 nations have signed the treaty. Essentially, this treaty sets Antarctica aside for research purposes, and states that no nation shall have a military presence there.

The largest US base of operation in Antarctica is McMurdo Station, supplied by both air and ship (once per season). However, the most environmentally and logistically challenging US base is located at the geographic South Pole. The US has maintained a continuous presence at the South Pole site since 1957. In that time, three different stations were constructed, including the current station that is still a work in progress. The two prior stations were abandoned either whole or in part because they were constructed either on or below the snow surface and are now buried. Snow accumulation at the site averages 6-8 inches per year, which is aggravated by drifting toward any object that protrudes from the surface. For this reason, the decision was made to construct the newest station above the surface of the snow on an elevated and jackable foundation.

The South Pole is a formidable location in which to conduct any outdoor activity. The average annual air temperature is -56 °F, and the coldest temperature on record is -117 °F. The elevation is about 9,350 feet, but it is equivalent to about 10,600 feet as the atmosphere is less dense at the Earth’s poles. Winds average 12 mph with maximum gusts around 56 mph. Essentially, everything at the South Pole has to be flown in on ski equipped LC-130 aircraft, limiting available construction equipment and making different construction projects incredibly expensive to undertake. Considering these difficulties, let’s look at the provisions necessary to conduct an infrared survey of the new Elevated South Pole Station.

CONSTRUCTION FEATURES OF THE ELEVATED SOUTH POLE STATION

The new Elevated South Pole Station is two stories tall, plus it is elevated approximately one story above the snow surface. This means that the station roof is approximately 40 feet above the snow surface, see Figure

1. The basic structure of the station consists of insulated panels attached to a structural steel frame. In the final stages of construction, the outer surfaces of the panels will have an infiltration barrier and will be clad with siding panels. Some of the siding that has already been installed is visible in the top left hand corner of the elevated station in Figure 1. In an effort to reduce snow drifting, a panel was placed at a 45 degree angle at the juncture of the roof and walls. This panel is referred to as the “chamfer” panel. The presence of this construction detail made it impossible to get a proper perspective for infrared thermography of the roof chamfer panel from either the ground or the roof. Thus, we knew we would need to use one of the cranes available on the site to gain a proper angle. This would also allow us to gain a better perspective of the walls and areas on the roof. In the next section, we’ll discuss the tools we devised to accomplish thermography from the crane.

Figure 1: United States South Pole Station, 2006-2007 Season.

PROVISIONS FOR INFRARED THERMOGRAPHY AT THE SOUTH POLE

We had done a number of infrared measurements in our cold rooms at CRREL before we were contracted by NSF to conduct the survey at the South Pole. As a result, we were well aware of the limitations of the infrared camera we planned to use for the survey, a FLIR S60. .While conducting another experiment on an instrument shelter we were designing and testing at -50 °C for Antarctic use, we found that the camera would operate for less than a minute before the focusing would slow. Soon after the battery would not produce adequate voltage and the camera would shut down. We knew we would need to operate the camera remotely from a crane to be able to survey the areas at the top of the walls as well as the roof of the facility in appropriate detail. This meant that the camera needed a separate conditioned enclosure. A simple man basket was available for the crane but no weather-proof enclosure was available for it, nor was it deemed reasonable to construct one that could house both the camera and operator. In addition, for the conditions under which the survey needed to take place at the beginning of the 2005-2006 season, -58 °F, NSF policy did not allow people to occupy the man basket because of potential crane failures possible at such low temperatures.

We knew we would have to provide a conditioned enclosure for the IR camera that could be attached to the man basket. In addition, we needed to be able to operate the camera remotely from a conditioned “chase” vehicle on the snow surface. A special insulated box mounted to a heavy duty instrument tripod head was constructed by CRREL’s technicians (see Figure 2). We were uncertain about the heat balance for the box and did not have time for cold room testing, so we had to assume that we could add “hand warmer” packets to the inside of the box as necessary to maintain the temperature within the camera’s operating range. As it turned out, the box was too airtight to add the hand warmers. Fortunately, they were not needed even in -58 °F ambient temperature. The box design allowed for the use of wide angle and telephoto lenses as well as the bare camera with the standard lens. The box included various holes in the mounting plate and foam insulation inserts for each configuration.

Figure 2: Insulated camera enclosure, left photo is top view when open; right photo is closed, but un-mounted.

In addition to the insulated box, we required a special cable assembly to operate the camera. The distances involved (over 100 feet) did not allow for the extension of the FLIR S-60 “paddle” cable, and of 115V power was unavailable so we couldn’t use “fire wire” communication with amplifiers. The solution we chose was to use the FLIR’s PS Remote software and a notebook computer to control the camera as we monitored the images via a separate video cable link. A third cable supplying 12 VDC to the camera for extended operation was also provided. All of these cables were fabricated with wire rated to withstand -50 °C; normally they are constructed with silicone rubber or Teflon insulation and jackets. Figure 3 shows the insulated box mounted on the man basket of the crane but with its top removed and the cable assembly extending from it. Also shown in Figure 3 is the operator station within the chase vehicle. The entire setup is included in Figure 4.

Figure 3: Left photo is camera enclosure mounted on crane man basket, right photo is operator station.

The equipment described above has been used both during the 2005-2006 season and the 2006-2007 to acquire many images of the Elevated South Pole Station as well as a number of other smaller buildings at the South Pole. The only difficulty encountered is that occasionally we have trouble with the video signal being strong enough for our remote monitor, especially in warmer temperatures (~-20 °F). We believe this is due to losses in the video connections and cabling, and we are fabricating a cable assembly with reduced resistance for use during the survey work in the 2007-2008 season.

Most of the wall surveys have been conducted from the snow surface using a Pisten Bully or similar vehicle. Generally, the infrared camera is hand-held and positioned in front of a partially open side window in the vehicle. The operator of the camera is positioned at the back of the vehicle, using the paddle for monitoring and control. A third person takes notes, primarily indexing the locations of the images, in order to speed up the survey. In both the crane mounted and the snow surface surveys, operator and equipment time is a very precious commodity, so conducting the surveys efficiently is of paramount importance.

Figure 4: South Pole infrared survey setup in use at ~ -55 °F.

SAMPLE RESULTS

Often, building thermographers struggle to locate the effects they are looking for due to inadequate temperature differential (∆T) across wall sections. While the ambient temperatures at South Pole provide a challenge to thermography as outlined above, they have also provided us with ∆T’s of 90-120 °F or more during the times we conducted surveys there. Using the equipment outlined above, we have obtained excellent imagery that has identified many areas of exfiltration. Some examples of the imagery taken are included in Figure 5. We have also witnessed the impacts of infiltration by conducting surveys from the inside in the subfloor area. In total, over 750 infrared and digital images have been taken at the Elevated South Pole Station alone.

Figure 5: Example images. On the left is a close-up of a short portion of the roof chamfer panel area. The temperatures are only for reference purposes to establish the relative magnitude of the exfiltration, the long cold objects are the metal straps that retain the chamfer panels; their apparent temperature is from reflected cold sky radiation. The image on the right provides a larger perspective that shows portions of the wall and roof as well.

SUMMARY

Infrared thermography has earned its reputation as a valuable tool in research, manufacturing, diagnostics, and forensics. With the appropriate equipment and carefully conceived procedures, our experience at the South Pole has not altered that reputation. Retrofits to the building envelope of the Elevated South Pole Station have been designed based on the results of our infrared surveys. If they are successful, they promise to save NSF significant time and resources in the future.

ACKNOWLEDGEMENTS

This project was funded by the National Science Foundation’s Office of Polar Programs, with Sandra Singer as the NSF POC. John Rand, Polar Engineering Consultant, was instrumental in defining the scope of the study and guiding our work. Special thanks go to Frank Perron of CRREL who designed and crafted the insulated enclosure and mount and Chris Williams of CRREL who designed and fabricated the low temperature cabling. The lead author would also like to thank his wife, Karen, for tolerating his long and frequent trips to Antarctica over the past few years.

ABOUT THE AUTHORS

Dr. Phetteplace holds a BS in Mechanical Engineering from Northeastern University, a MS in Engineering from Dartmouth College, and a Ph.D. in Mechanical Engineering from Stanford University. From 1975 until his retirement in July 2007 he was employed by the US Army Cold Regions Research and Engineering Laboratory (CRREL), Hanover, NH. His research at CRREL has been concentrated in the areas of: theory and practice of district heating and cooling, heat pump systems, numerical and analytical methods for approximating heat transfer in soil systems including freezing and thawing, and energy conversion. In addition he has done limited research in robotics, vehicle mobility over winter surfaces, and cold weather impacts on humans. Specific to IR imaging, Dr. Phetteplace served as the US Expert on the monitoring group for the first International Energy Agency (IEA) project to assess the potential for quantifying heat losses from buried heat distribution system using IR technologies. On the second IEA project on the same topic he was a participant in the study and conducted experiments in both Denmark and the United States. He has put the research findings into practice by conducting IR surveys of the heat distribution systems and quantifying the heat losses at 7 major facilities owned by DoD, NASA, and others. Dr. Phetteplace later made significant refinements to the methods developed by the IEA projects while serving as a visiting professor at the Technical University of Denmark. He has also served as an interpretative expert on IR surveys done by others for the purposes of quality control or investigative studies. His expertise in the use of IR technologies extends beyond heat distribution systems having used IR imaging to study the accuracy of roadway pavement sensors and most recently during the last two seasons he has made three deployments to Antarctica doing IR survey work on the National Science Foundation facilities at the US South Pole Station. Dr. Phetteplace is a registered professional engineer in four states, an active member in several technical societies, and the author of more than 125 publications.

Jason Weale is a Research Civil Engineer at the US Army Cold Regions Research and Engineering Laboratory (CRREL), Hanover, NH. Mr. Weale earned his BSCE from the University of Vermont in 1995 and joined CRREL as a Research Civil Engineer in 2001. Mr. Weale is the Program Manager for CRREL’s Antarctic Research Program and has conducted work in Antarctica primarily involving logistics including contributing to the effort to identify an over snow route from McMurdo Station to the South Pole traversing the Antarctic continent. Mr. Weale is currently assigned to NSF Arctic Support Services organization through a Memorandum of Understanding between CRREL and NSF. Mr. Weale is a registered professional engineer in Vermont.