Air Photo Interpretation

There’s a lot you can tell just by looking at an air photograph.

However, you shouldn’t just be a “tourist” when you look at air photos. Below, we’ve listed the top professions that benefit from air photo interpretation.

Professions That Benefit From Air Photo Interpretation

Infrastructure management professions: Quickly find out the extent of degrading infrastructure (eg. roads), infrastructure money-pits (eg. expensive boat mooring maintenance), or areas that should be subject to special treatment (eg. areas with soils that are aggressive to buried assets such as water or gas pipes).

Environmental scientists: Easily discover the spatial extents of vegetation dieback, plant communities, or animal habitats.

Social scientists: In times of water shortage how common is lawn watering? Defining the spatial extents of lower and higher income areas.

Environmental

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You can interpret socio-economic, engineering and environmental themes from this photo

  1. The inlet: The inlet is obviously supported by some sort of wall. You can see that the sand is backed up against it. The build-up of sand on the south-west entrance suggests that the weather and currents are dominantly from this direction.
  2. Water depth: The river is deep. Otherwise boats would not be able to get to their moorings up here. Also, the river is almost certainly dredged at its entrance – you can see a straight line of deeper water.
  3. Groins: This beach has a problem with disappearing sand. Otherwise there wouldn’t be groins all the way along it.
  4. Inundated areas:
    • This area is swampy. Otherwise there would be no need to drain it.
    • The drains are not natural because they’re so straight.
    • The presence of drains suggests that the landscape is flat.
    • Drainage is very important to the land managers here because otherwise they would not bother building so many drains (agriculturists or drainage engineers may have dug them).
    • Its also likely that the soils are very heavy clays because otherwise there wouldn’t be such drainage problems.
Vegetation condition can be used as a surrogate for soil type. This photo was taken in summer because the shadows are small. Also, the infrastructure in the area is likely to be aging because there are cracks in the road.

Vegetation condition can be used as a surrogate for soil type. This photo was taken in summer because the shadows are small. Also, the infrastructure in the area is likely to be aging because there are cracks in the road.

  • Sandy soils:
    • Other areas in the photo are sandy – otherwise the trees and lawns in figure 2 wouldn’t be so burnt off.
    • Some people water their lawns. We know this because the green coincides with property boundaries in many places.
  • Timing of photo: This photo was taken in summer. You can tell that because the shadows are so slight.

Socio-economic indicators

In combination with other information (eg. census, various government databases, property value databases, interviews, etc), air photos can provide clues to an area’s socio-economic makeup.

  • Home size and structure:
    • Possible lower income areas: Most homes away from the waterfront are single storey. You can tell this because they cast small shadows compared to some other homes in the area. Quantum GIS was used to measure one home and it was 128 square meters (around 13 squares).
    • Possible higher income areas: Many waterside homes in the area cast longer shadows, suggesting that they are two story. Moorings are also common suggesting that there is enough surplus wealth to support recreational boating
  • Age of area: This is probably an older area because the roads seem to have lots of cracks in them. The lines across the road in figure 2 are not shadows cast by trees, because we can see that tree shadows elsewhere in the photo look quite different.

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Using Google as an extra resource: In the last few years, google Street View (within google maps) has become very commin in GIS. The two screen captures above confirm the air photos – there are areas where dominantly the houses seem to be small and single story, and in other places the houses are larger.

Street View can either confirm air photos you are looking at, or supplement field work you’ve already done.

We could go into so much detail on further uses of air photos – what green lawns mean for various government policies, vegetation dieback, socioeconomic status, etc. However, the purpose of this article is just to give you an insight into how useful air photo interpretation can be.

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