On Wednesday of this week the Iowa GIS Service Bureau assisted the Iowa DNR with acquiring aerial photos for an EPA wetlands project. The goal of the exercise was to establish a method to identify drainage tiles under row crop farm land using aerial photos.
The plane flew over a six by three mile study area while two passengers worked the cameras. Following a back and forth flight path, the plane covered the entire study area with the two cameras documenting the ground below.
Within the study area were fields known to contain drainage tiles documented in a GIS layer. It was also known that farmers with land within the study area have installed drainage tiles, but confirmation of the location would come after analysis of the aerial photos.
Once the photos are georeferenced in a GIS, a person will be able to compare the aerial images with the drainage tile layer to see if soil condition on the surface corresponds with the drainage system below. After rains, well drained soils contain less moisture and appear lighter in color. If the relationship exists, a person will be able to use aerial photos to identify drainage systems based on the discoloration of soil. In the image you can see the tile network identified by the dry soil on the surface. If you click on the image you can see it more in detail.