Spying From Above

A few weeks ago I needed to study the local area using satellite imagery. When I expanded the view centred on my place I was pleasantly surprised. Sometime during the past year Google updated the images for this area. For the first time I have a picture that is almost up to date with construction of my antenna farm. You can click on the image to see it in full resolution -- caption link takes you directly to the source. Indeed, you'll have to to see the finer detail I'll be discussing.

Extracted from Google Maps

Before going into radio stuff I should explain the peculiar patterns. The satellite image was captured during haying season when my neighbour had started on my land after finishing with his own. That dates the image to late July or early August, and the shadows indicate mid-morning. Notice how he deals with the tower base, guys and wire antenna anchors. He's very considerate and careful; after all, he's a guest on my land.

Notice the mind-bending perspective: everything leans right at a 95° bearing. The exact position of the satellite is not known from this, apart from saying that it was a little north of west. A few moments with a ruler and calculator converts the projected linear length of the tower lean to determine the satellite's elevation angle: approximately 63° above the horizon. Algorithmic processing transforms the curved quasi-trapezoidal perspective to rectilinear coordinates. Since the details of objects are unknown their shapes are not corrected. Hence the peculiar image.

With that interesting if irrelevant detail out of the way let's see what we can learn from spying on my antenna farm circa last summer, before the new big tower was planted. One is that you can see that the scars of the cable trenches have not healed. I believe that the trench to the 80 meter vertical array had not yet been back filled, explaining its prominence.

Staying with the 80 meter yagi you can see its orientation by the trench scars running from the central tower -- driven element -- to the 4 parasitic wire elements. Notice that they are not at right angles, allowing me to optimize array directions, which is not possible with a 4-square. As a result the radial field shape is oblong. The radial field is staked and mowed; haying is banned.

Turning to the yagis, you'll notice that some elements are highly visible while others are difficult to pick out or are not visible at all. This is due to the illumination angle, yagi orientation and the resolution limit of the satellite image. Where there is specular reflection very narrow aluminum tubes are prominent despite being well below the image resolution limit. In other cases similarly sized elements are not at all visible.

On the Trylon tower near the house the TH7 elements are quite visible but only the boom of the 6 meter yagi above it is clearly visible. On the 150' tower the largest elements of the top yagis are visible. Their direction appears to have reduced the level of specular reflection and therefore visibility.

The long European (northeast) Beverage in the northeast bush area is of course invisible. Yet there are some short sections along its path that appear fuzzily. My guess is that periodic inspection and service walks along the antenna route create visible scars in the vegetation. On the ground my walking path is only noticable when there is snow. Since I detour around trees the path is not entirely straight.

A curiosity regarding resolution is the central tower of the 80 meter array. Due to the perspective it leans in the same manner as the other towers yet the tower is just a fuzzy smudge. The weathered galvanizing is far less reflective than the white paint on the big tower. The Trylon is a slightly less fuzzy since most of the galvanizing is less weathered and the structural members are wider. The two unpainted galvanized sections in the 150' tower look like gaps for the same reason.

If geology is your interest there is something for you as well. Notice the brown tint in the hay west of the 80 meter array, adjacent to a treed area. This is usually a sign that the topsoil is thin where the bedrock approaches ground level. To protect farm equipment such as plows it is common to leave these areas wild. There are places such as the patch north of the array the bedrock pierces the surface. I have been lucky that none of my tower excavations hit bedrock.

Is any of this useful? As I've written before this can be a good way to satisfy your curiosity or to spy on your competition. For non-contesters it can be informative to study the layout of others' towers and antennas.