Satellite imagery and digital processing have revolutionized geotechnology over the past 25 years. However, this revolution still has not solved geotechnology's besetting problem. That problem is a client who says, "We need an immediate environmental assessment of a site so our project can begin, and we haven't budgeted much for this assessment." Visual processing offers a fast and cost-effective solution for this problem.
      The first phase of an environmental clean-up operation is to identify and prioritize sites of contamination and degradation. Moving about at ground level taking random water and soil samples at likely-looking sites is unreliable, whereas painstakingly gathering samples on a grid over a hundred acres or more is slow and prohibitively costly. The obvious solution is strategic sampling based on a detailed property history documented with remotely sensed data. An aerial view frequently reveals features and patterns which cannot be seen at ground level. Aerial photographs and maps contain vast amounts of visual data that can be optimized for quick and accurate assessments. Furthermore, nothing equals a trained human mind for judging the significance of irregular features or peculiar patterns.
      Although considered old-fashioned or inferior by many in the digital world of multispectral or hyper-spectral analysis, aerial photos are the ideal medium when dealing with historical site audits that extend over less than 100 square miles because photography possesses the following three advantages.
      Advantage 1. Archival aerial photos, going back many decades, are quickly and easily obtained. Sources abound at the federal, state or provincial level, and even at the municipal level. Many North American cities, such as the city of Toronto, photograph the entire metropolitan area every year. States and provinces regularly acquire photography for highway alignment and maintenance studies, natural resource evaluation, map revision and other reasons.
      Advantage 2. Aerial photos cost only a few dollars each to reproduce, relatively few are needed for most site audits and they can be quickly interpreted with the right equipment.
      Advantage 3. Aerial photography provides the high spatial resolution required for a proper environmental site assessment.

A Case History
Here is an example of what can be accomplished with optically-enhanced aerial photographs and digital processing. Prior to assessing environmental damage to two adjacent properties in Canada's National Capital Region, the engineering firm of Oliver, Mangione, McCalla and Associates Ltd. retained Gregory Geoscience Ltd. to prepare an environmental site history and establish parameters for a ground study.
      Air photos of the site dating back 25 years were obtained from a national photo archive. The photos were then enlarged and registered to both a site map and a soil map. The prevalent practice among geotechnologists when using aerial photographs is to acquire paper prints. Paper characteristically lacks an ability to reproduce fine details, so the geotechnologist typically is limited to a magnification of five times the original photograph. By optically enhancing transparencies of the photo prior to digitization (see Photo 1), Gregory Geoscience routinely uses photos at 20 or 30 times magnification and sometimes as high as 50 times magnification; this procedure gives superior detail at a comparable cost.
      Analysis of the aerial photography established that the site was in pristine condition in 1976 and mapped significant changes between 1976 and 1979 as a result of a probable change in ownership. In Photo 3, which establishes the original condition of the site (spring 1976), the naked eye can pick out a house, a barn, an equestrian track and some small outbuildings. Photo 4 (spring 1982) is reliably dated and shows tremendous changes to the site. Much of the tree cover is gone, the site is littered with junked equipment, and aggregate has been extracted leaving a number of water-filled pits. Enlargement of the photo up to 72 times (Photo 5) detects a barrel dump standing between the small irregularly-shaped water hole and the oval sand pit in the center of Photo 4. By 1995, this dump was overgrown with vegetation and it blended into the landscape. Yet, in terms of detrimental impact, it probably is the most environmentally-significant feature of the site.
      Using the PROCOM-2 system's optical and digital capabilities, Gregory Geoscience tracked the nature and extent of changes to the site over the succeeding 10 years, as demonstrated by Photo 1 which is a composite of various computer screens captured from the system. Use of different filters and enhancement techniques made possible a count of the number of upright and tipped barrels, and noted that some were open and some were closed (left and right sides Photo 1). Spectral enhancement (center of Photo 1) helped to indicate different types and/or condition of many of the barrels. Ground investigation to date has revealed that many of these barrels contained organic solvents. There has been leakage with some groundwater contamination which is currently being fully remediated.
      Using this photographic evidence and other information discovered from clues in the enhanced photos, Gregory Geoscience was able to guide the process of locating soil and water sample sites even though some of the major causes of contamination were no longer obvious.
      The 1992 photo base map (not shown) will also serve as a template for assessing the progress of remediation activities. This solution was fast, accurate and cost-effective; it also is applicable to an overwhelming proportion of site audits. By taking advantage of skilled interpretation, optical and digital processing and data integration, a comprehensive site history was documented. Anyone can look at remotely sensed data, but the right combination of skill, data and methodology lets you see the wealth of information that it contains.

Another Kind of Case
Satellite data or regional air photography are generally preferred when assessing larger areas, but the combination of optical and digital technology still offers savings in time and costs.
      For instance, a similar project on a much larger scale focused on planning an environmental assessment of an abandoned military airbase in the former Soviet Union. In that case, the departing Soviet forces had simply removed their aircraft and other equipment leaving a significant environmental problem. Safety of the drinking water supply for a large city located near the airport was a prime concern. Therefore, NOTRA Environmental Services of Ottawa and Gregory Geoscience were contracted to carry out an environmental audit.
      Satellite images were preferred in this case because of the size of the area and the importance of spectral analysis. SPOT 20m multispectral image data were acquired for the airbase. The PROCOM-2 was used to integrate the SPOT data quickly with topographic maps, soil profiles and airbase plans. Detailed visual interpretation of the combined data very quickly produced a map of possible contamination sites.
      Using very high resolution digital capture, each identified site was scanned at resolutions between 1500 and 5500 pixels per inch. The resulting raster data were processed and enhanced using the ILWIS (Integrated Land and Water Information System) software package. The ILWIS software was also used to produce a detailed Digital Elevation Model (DEM) for the study site that was used in conjunction with the satellite data (see Photo 2) to determine the transport direction of any possible contaminates.
      This procedure generated a map and a list of sites within the airbase property that required investigation on the ground. This information enabled NOTRA Environmental Services Inc. to conduct a Phase 1 site audit during a visit to the base that lasted less than one week. Phases 2 and 3 of the audit were then defined and the costs of implementing a full site cleanup were determined.

Conclusion
Many tasks in environmental assessment and pollution abatement are dependent on a knowledge of present and past site characteristics. The proper processing and interpretation of aerial photographs or other remotely sensed data can provide the crucial knowledge base for a comprehensive site evaluation and remediation plan. Making the most of our ability to view and interpret the visual data that are so abundantly available can help us to see what we are looking at.

About the Author:
Harold Moore is president of Gregory Geoscience Ltd. in Kanata, Ontario, Canada. He may be reached at 613-599-7465.

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