Upon further reflection, if you will forgive the pun, I have come to the conclusion that this is solely due to the point of observation, there were no additional devices utilized in creating the picture, and it is naturally occurring.
Imagine if you will the multiple rays of light coming from the sun. The rays are parallel, for all intents and purposes. This will create an even lighting of the ground in all areas that are flat. (Reference all areas outside of the "rainbow" - for lack of a better word.)
No light comes from the area of the shadow, for obvious reasons - it is being blocked by the photographer.
The bright area is reflection from the particles on the ground (water droplets?), and the brightness is evenly distributed within the circle. When we get to the edge of the droplets' ability to reflect the light, we get the bending of each color component in the order of most easily bent (violet) on the inside to least easily bent (red) on the outside. This is representative of the parallel light beams from the sun reflecting on the backside of the droplets in it's dispersion of the spectrum. Outside of the red ring lies beyone the angle in which the sunlight will do anything more than light the surface.
I don't believe that the picture being taken near the solstice or at a particular latitude has much to do with it since the area over which the illusion appears seems to be about 4 feet across, judging by the size of the shadow. In other words, the conditions aren't that much different than on any other day.
scott.ellis@ps.ge.com