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the efficacy of using remote sensing to monitor roof integrity
over long periods of time, but the study may lead to approaches
that could be used in long-term monitoring and detection of
changes in structural roof integrity.
4.2 Data Collection
Investigative efforts to date have focused on comparison of
traditional and remote sensing assessment methods for the K-31
Process Building at the K-25 Site. Remote sensing data is
being examined for possible correlations with roof assessment
measurements made for DOE by Jacobs Engineering using
conventional ground-based methods. Building K-31 was built
in 1944 to cover a process building that housed a 24-hour per
day operation. The roof is a shallow slope, built-up roof with
an area of approximately 68,748 m? (740,000 ft?) and was last
re-roofed in 1980. The Jacobs Engineering roof survey (July
1994) indicated that many sections of the roof were heavily or
moderately saturated with moisture. It was concluded that the
roof condition indicated almost total roof failure, and
recommendations were made for complete replacement.
Land-based measurements of K-31 were made by Jacobs
Engineering during July 1994 using walkover video
thermography. Remote sensing of the thermal infrared
spectrum was conducted by EG&G Energy Measurements
during March 1994 using DOE-owned equipment including a
Daedalus 1268 multispectral scanner. Remote sensing was
conducted at an altitude of 2,000 feet above ground level for a
spatial resolution of 1.5 meters per pixel.
4.3 Results
Since the thermal and structural properties of a roof change
over time as the structure ages and degrades, thermal anomalies
can be indicative of roof decay and intrusion of water into roof
components. Thermal signatures provide thermal
characterization of rooftops, including evidence of moisture,
presence of standing water as pools or in outer roof layers, roof
sag, structural integrity defects and deterioration by thinning
materials, rust, material cracks, etc.
Figure 4 compares a partial map of wet insulation locations for
the western edge of Building K-31 based on the results of an
infrared thermography inspection (July 1994) with Daedalus
1268 nighttime thermal imagery (March 1994). According to
the results of the walkover survey, the western section (Areas
6B, 6A North, and 6A South) contains 40-percent wet
insulation. The suspected wet areas correlate extremely well
with the cooler temperatures (blue/green) in both daytime
thermal imagery (Daedalus Multispectral Band 11) and
nighttime thermal imagery. As a result of the strong visual
correlation, remote sensing data can generate thermal contour
and thermal anomaly maps for each rooftop that substantiate
and compare favorably with video thermography. It should be
noted that the thermography inspection for the K-31 rooftop
was conducted over a time frame of eight evenings and
involved several individuals. The airborne remote sensing
sensor was able to collect rooftop temperature data for all
buildings at the K-25 Site in a single aerial survey (multiple
flight lines).
97
4.4 Summary
Due to the substantial number of large aging DOE roofs and the
shrinking federal budget for addressing these problems, roof
assessment surveys by conventional means may become
increasingly unattractive. The use of a cost-effective alternative
must be developed. The K-31 roof survey, as well as similar
work at the DOE Hanford Site, demonstrates that remote
sensing provides such an alternative. Remote sensing can
obtain the needed data in a fraction of the time required by
conventional means and can be performed safely without
worker risk from walking on roofs of questionable integrity.
In addition to the use of remote-sensed thermography, the use
of micro-topography should also be examined as a tool for
providing evidence of structural deformation, such as roof sag
due to aging, and to characterize the rooftops of individual
buildings. Indirect methods for determining surface
irregularities include using visible wavelength imagery (at low
sun angles), interferometric Synthetic Aperture Radar (SAR),
or infrared (near or thermal) wavelengths (after a rainfall event).
Standing water on a flat roof after precipitation indicates a
depression. Roof leaks may be indicated by depressions
without standing water after precipitation.
5. CONCLUSION
Recent cutbacks in funding and regulatory pressure for less
study and more remedial action have resulted in a need for
substantial changes in remedial investigation methods as
lengthy and/or costly techniques can no longer be tolerated.
The work described in this paper illustrates that remote sensing,
used in conjunction with "ground truth" measurements, can
offer a viable and cost-effective alternative to conventional
land-based methods. The federally-funded demonstration
projects of the early 1990s have proven the merit of remote
sensing. In the coming years, it is our obligation to fully
develop these proven technologies, provide environmental
program managers with procedures for their usage, and to
continue to market and develop their beneficial uses for site
investigations and trending. In Oak Ridge, Environmental
Restoration Program managers, as well as the general Oak
Ridge public, have become increasingly aware of the benefits
and uses of remote sensing. With this wider level of
acceptance, DOE is confident that remote sensing will become
a standard practice for future environmental site investigation
projects.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
