Full text: XVIIIth Congress (Part B7)

  
spatial locations of trench boundaries. This assistance would 
provide the needed information for site remedial investigations. 
The following is a discussion of the techniques and results of this 
effort. 
2.2 Data Collection 
Remotely sensed data were collected through several DOE-HQ 
sponsored programs that involved multiple U.S. government 
agencies. Primary data collection programs included the 
Government Applications Task Force (GATF), the Environmental 
Task Force (ETF), and the Strategic Environmental Research and 
Development Program (SERDP) Waste Site Study. Each had a 
mission to demonstrate the utility of remotely sensed imagery to 
detect and locate buried waste trenches under a variety of 
conditions and to analyze the phenomenology underlying the 
signatures observed on thermal imagery. Data collected included 
a combination of historical imagery, multispectral remote sensing 
data, and "ground truth" data to evaluate the accuracy of remotely 
sensed data and to understand the thermodynamics of trench 
cooling/heating. 
Historical data were obtained from Federal photographic archives 
and included both high and low spatial resolution aerial 
photography and remote sensing data. This data did not provide 
a complete historical perspective, but did include random 
coverage of the period 1942 (prior to DOE occupation of the site) 
to the present. 
Thermal imagery collection was used to detect differential thermal 
patterns that would be indicative of the differences in soil density 
and moisture that are characteristic of trench disposal. 
Multispectral remote sensing from instrumentation, such as the 
Daedalus 1268, which was used to obtain thermal imagery. 
Daedalus 1268 data was obtained during 1992 and 1994 by 
EG&G Energy Measurements using DOE-owned equipment. 
Spatial resolution of 1.5 to three meters per pixel were obtained. 
"Ground truth" experiments were conducted during 1994 and 
involved extensive measurements of soil temperature, soil 
moisture, and meteorological conditions. These data were 
collected and analyzed to understand the physical processes that 
produced the trench signature observed on thermal imagery. 
Arrays of ground sensors were set up at the SWSA-4 study site to 
collect data on the surface and near-surface conditions in the 
trench and in an adjacent control location. The choice and 
configuration of sensors were: 
° Soil Temperature: Measurements of soil temperature were 
recorded at several points inside and outside the trench at 
depths of one inch and a vertical profile at four, six, and 10 
inches. 
° Thermal Radiance: Infrared transducers were used to assess 
the emitted energy in the longwave Infrared band (8-14 
microns) over the trench and non-trench areas. 
° Soil-Moisture: An array of instruments recorded soil water 
potential (i.e., moisture) at two-inch depth, both inside and 
outside the trench. 
2.3 Results 
Through analysis and fusion of the combination of historical 
photography, thermal imagery, and “ground truth” data, the Oak 
Ridge Operations Remote Sensing Program was able to derive an 
accurate trench map of SWSA-4 that could be used by the 
92 
Remediation Manager to delineate trench boundaries. A 
reproduction of this map is shown in Figure 1. 
Statistical analysis of the “ground truth” data indicated the nature 
of the thermal signature of the trench areas. Both the thermistor 
and radiometer data showed that the differences between a trench 
area and the control area (i.e., non-trench area) was most evident 
at night, with the trenches typically cooler. Soil moisture 
measurements showed that the trench area generally exhibited 
greater soil moisture than the control area, which may account for 
the observed thermal differences. The data also showed that the 
spatial variation in temperature within a trench was larger than the 
variation between trenches, suggesting the need for multiple 
observations. During the daytime hours, the thermal difference 
was not readily discernible. 
The SWSA-4 results indicate that nighttime thermal imagery can 
be successfully employed to help delineate waste trench areas at 
known sites under a variety of conditions; however, one must 
consider site ground cover when planning a thermal survey. 
SWSA-4 is characterized by mowed grass fields and similar 
ground cover for both the trench and non-trench areas. This 
simplifies data interpretation. Similar studies at other DOE sites 
with non-homogeneous surface conditions (varying species of 
vegetation) indicate that analysis of thermal behavior is more 
complex and that thermal image signatures are difficult to predict. 
Consistent thermal signatures are associated with sites where the 
surface conditions are more homogeneous, whereas sites with 
mixed and complex vegetation can exhibit different behavior. 
Furthermore, even if no buried waste was present, disturbed soil 
typically exhibited the thermal signature observed at the trenches. 
Thermal imagery must be co-analyzed with other historical and 
“ground truth” information to provide positive confirmation of 
trench presence or absence. 
2.4 Summary 
The results of this study have benefited DOE in two ways. First, 
the study provided information that will be used directly in the 
remediation and monitoring of SWSA-4. Second, the project 
demonstrated a method for using thermal imagery to assist in the 
detection and location of buried waste trenches. The methods 
demonstrated in this project should be applicable to buried waste 
at, potentially, hundreds of similar sites in the coming years. 
Previous ground-based field investigation at SWSA-4 identified 
two individual seep areas that contribute over 90-percent of the 
radioactive strontium releases from the study area. The trench 
map derived from remote sensing data was the key factor in 
pinpointing localized sources feeding these major seeps. Current 
remedial actions are focusing on controlling these few sources and 
will provide a cost-effective interim action to reduce Strontium-90 
releases and off-site risk. Without the remote sensing results, the 
ability to quickly and effectively pinpoint the locations of the 
individual sources would have been lost. The alternative for 
controlling releases (i.e., cap the whole site, collect and treat 
surface water) would cost in excess of $5 million more than the 
current action of directly controlling the sources. 
The procedures demonstrated here can be applied to numerous 
other waste sites where remedial action is necessary to stop the 
migration of contaminants from burial trenches. Candidate sites 
of this type exist at numerous DOE reservations and military 
facilities. The alternative to employing remote sensing technology 
is to rely on extensive and costly ground sampling to precisely 
locate the hazardous material. Direct boring into contaminated 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996 
 
	        
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