Ground truth

Scouting odonate habitat using Google Earth is quicker and simpler than a site visit, but when you think a new location has potential you still need to “ground truth” what is shown in the remotely-sensed imagery.

For example, the following Google Earth image suggests it should be relatively easy to reach the banks of two tributaries that flow into Dyke Marsh Wildlife Preserve.


Dyke Marsh Wildlife Preserve | interactive image on Google Earth

In contrast, look at the following photorealistic 32-bit HDR composite image of Dyke Marsh as viewed facing southeast from River Towers Condominiums. The banks of one of the streams are choked with dead vegetation, flattened by a recent flooding rain event. In mid-summer, the same location is likely to be a tough slog due to waist-high vegetation!

A 32-bit HDR composite image created from three photos of Dyke Marsh as viewed from River Towers Condominiums, Fairfax County, Virginia USA, +/- two stops of exposure.

29 FEB 2016 | River Towers Condominiums | Dyke Marsh

Look closely at the preceding composite image. Did you notice the beaver lodge? The George Washington Memorial Parkway appears along the base of the tree line shown in the background. You can see a white vehicle that seems to be driving through the marshland, near the center of the image.

Copyright © 2016 Walter Sanford. All rights reserved.

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2 Responses to “Ground truth”

  1. Mike Powell Says:

    Nothing beats a ground reconnaissance for determining the accessibility of a particular location. Vegetation is such a huge factor in the marshy areas we often visit and thorns always seem to grow in abundance.

  2. More Needham’s Skimmer dragonflies | walter sanford's photoblog Says:

    […] Note: This is the same location I described in “Ground truth,” posted on 02 March 2016. As I speculated in the post, by mid-July the banks of the stream […]

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