Environmental Image Group, Inc.
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Services Methodology Equipment Aerial Photography Reports Site Map


The most fundamental tool used in the analysis of historic aerial photos, is stereo observation and interpretation following standard practices in the field. These are activities which are not easily duplicated by automated systems such as target cuing software or GIS Programs. This intensive, manual approach is nowadays augmented by Digital Image Processing (DIP) to crop out the site, to enhance the interpretability of the photographs, to do much of the stereo analysis work, and to organize and print the results.

The results of the analysis can take on many different forms, depending on the needs of the case. For example, some cases have consisted largely of answering specific questions about activities on the ground at various times in the past. Often, this has been reported back immediately over the phone, followed up with brief, written reports. Other cases, more typically, have involved broad study of an industrial facility and then the production of a detailed, illustrated report presenting the results from any one set of air photos. Most commonly, these individual reports are forwarded to the client when finished. This promotes immediate use of the information by the rest of the study team, as further historical air photo analysis continues with other years of imagery.

At the conclusion of a typical multi-date investigation, the individual reports may be assembled into a “compendium” report and edited appropriately. Depending on the needs of the client, other features can be added to this compendium report. These might include an executive summary, a list of figures, a table of all annotations from the individual aerial photo reports, or a summary chart of all individual features of the industrial facility. This is done as a spreadsheet, with the columns being the air photo dates, and the rows being the site features. One of the earlier columns would include a zoomed air photo of that feature. As the reader looks over such a chart, the lifetime of each feature will be indicated by the width and position of the comments from each succeeding photo flight in the cells of the spreadsheet.

Another product sometimes created, is a portable, handheld stereogram viewer, either for the historical air photos or for fieldwork photos of the site, if fieldwork was undertaken by the Photo Interpreter. Such fieldwork has several purposes. One is simply to acquaint the analyst with the site (if it still exists!). Another is to provide ground views of the same features described and reported from the aerial photography. And a third purpose is to systematically document, by means of careful procedures, the condition of the site at a given time.





1. Observation of Airphotos by Laypersons

Aerial photos seem, to the layperson, to tell the whole story in a glance. “A picture is worth a thousand words”. However, the reality of this narrow, arcane work is, that results come slowly, and only with significant effort and expense. This is not a job for the layman, or any person expecting the photographs to give up their secrets quickly and easily. In rare cases, the aerial photography will produce a single observation which turns the entire case upside-down. In litigation, this is sometimes referred to as looking for the “silver bullet”, the one piece of clear photographic evidence which reliably establishes the facts. However, in practice—after thirty-six years of part-time legal work with aerial imagery—I have concluded that this is not generally to be expected. In fact, in only two cases did I find a silver bullet, and that took an almost wasteful effort…a long story.

2. Detailed Photo Interpretation by Qualified Specialists

If the photo Interpreter is well matched to the job, a great many unequivocal answers can be produced. Conservative, cautious image analysis reveals facts and opinions which are very hard to argue with. This work will typically produce Photo Interpretaion Reports, sketch maps, diagrams, tables, and, especially, annotated photographs that label the features of interest. Approximate dimensions of ground objects are also a common product, where useful. Depending on the field of expertise of the interpreter, some functional information is also to be expected. The work begins at the lowest level, ideally, with a single film stereopair under a Zoom Stereoscope. In modern times, much of the imagery will only be available as digital scans. Thus, the Photo Interpreter must also have available a methodology for studying these scan files, in detail, in stereo. The results will be reported in descriptive fashion, and/or using charts, diagrams, spreadsheets, whatever, and added to the results from the next films from another year. When enough of this work is completed, a high-level, easy reading summary can be created for the site. If a very balanced procedure is followed with integrity, this will be very hard to argue with (e.g., under cross examination by an aggressive attorney, guided by another qualified Photo Interpreter).

3. Photogrammetric/Engineering/GIS Analysis

This type of work will typically lead to accurate, scaled drawings and maps. Reliable dimensioning of ground objects is also quite normal. Some functional analysis may also be done, if the engineers are qualified in the particular industry. The primary purposes of the application of GIS software are to allow overlays of various georeferenced aerials or maps, and to do more extensive dimensioning of ground features, and to create three-dimensional views and/or videos. Perspective presentation, and fly-through videos of site details will be possible as a result of the three-dimensional models created in the work.

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