Photo interpretation vs. “Photo Reading”
The late Thomas Eugene Avery was one of the longstanding pioneers in teaching applications of photogrammetry in the sciences and many professions such as forestry, biology, urban planning, environmental studies and archaeology. In the fifth edition of his book Fundamentals of Remote Sensing and Airphoto Interpretation, he defines photo interpretation, and contrasts it with what he calls “photo reading.”
“Photo interpretation is defined as the process of identifying objects or conditions in aerial photographs and determining their meaning and significance. This process should not be confused with photo reading, which is concerned with only identifications. As such photo interpretation is both reading the lines and reading between the lines. (Avery 1992, p. 51).
Ebert & Associates’ approach to environmental photointerpretation follows Avery’s definition (although he makes it two words) of “photo interpretation.” Many approaches we’ve seen to environmental sites using aerial photographs consist largely of simply identifying “what something is” on a photo – “drums,” “building,” “pits,” “fence,” and the like – and making overlays that show such words with arrows pointing to the features. Such “photo reading” may be fine for certain purposes, for instance the EPA’s preliminary photo reports indicating the locations of industrial plants, dumps, and other properties such as CERCLA sites.
Environmental litigation, however, requires a more complex approach than using historic aerial photographs simply to “read the lines” to determine environmentally problematical activities that were going on through time, not only on but between the air photo dates.
Third Edition of Introduction to Environmental Forensics Published
This comprehensive textbook on Environmental Forensics contains a chapter written by Dr. Ebert which details current uses of photogrammetry, photointerpretation, and digital mapping in environmental legal research. Drawing upon his 35 years of experience as a testifying forensic photogrammetric expert, as well as an even longer career in employing photogrammetry and remote sensing in archaeological research, his chapter outlines the uses of these techniques in environmental forensics in simple, understandable terms.
Stereo in the Courtroom: A “Virtual” Necessity for presenting Aerial Photographic Evidence
One of the most important techniques for extracting information from aerial photographs is stereo photo analysis. Stereoscopic aerial photos are snapped as an aircraft flies along straight flight lines, and are taken sequentially so that each frame overlaps the last by 60%. This insures that everything covered by the aerial photos is seen from two different camera locations.
By viewing one of the overlapping photos with one eye, and the adjacent one with the other eye, the photo analyst sees the terrain, as will as industrial plants or dump sites, irrigated areas, roads and buildings, or any other legally relevant features of the landscape, 3-dimensionally. And this 3-D view is crucial to interpreting human activities and their effects on the environment.
Optical stereoscopes ranging from small thirty dollar “pocket” viewers, to high-magnification precision instruments costing tens of thousands of dollars, have traditionally been used by photogrammetrists to view stereo.
The advent of digital imaging made another way of viewing stereo– which can be used to great advantage in courtroom exhibits –easily available. Called anaglyphic viewing, this method allows the viewing of the stereo image with glasses with red (left) and blue (right) lenses. The result is 3-D stereo without a stereoscope. The anaglyphic image can be seen on a computer screen, or projected with a computer projector. In situations where computer facilities might not be available, or where lighting can’t be completely controlled, digital prints of the anaglyphs provide the same effect. Poster-sized anaglyphic prints are perhaps the most spectacular way of viewing stereo, however, and are ideally sized for courtroom use.
Presenting and explaining interpretations made from stereo photographs requires being able to show aerial photos 3-dimensionally to judges and juries, rather than just holding up “flat” aerial photo enlargements. Anaglyphs literally captivate the courtroom, giving participants in the judicial process something far more interesting to look at than a dark-suited expert witness. And in a very real way they let everyone there feel as though they too are involved in the photointerpretive process.