Verifying a High Point Using a Survey¶
This is an example to show how Cambium link planners use a high point survey to refine their estimates of the terrain and obstructions near high points. This builds on the previous example Verifying a High Point Using a Map.
We use the following survey aids:
Map, path profile, Google Earth(TM) aerial photo
Barometric GPS receiver
Clear plastic ruler
Surveyor’s tape measure
Pocket calculator
Binoculars
We follow these steps:
We use the barometric GPS receiver to verify terrain height.
Because air pressure may change frequently, the GPS receiver must be recalibrated near every high point, at a point with a known altitude. The map shows a suitable point for calibration, where the road crosses the 150 m contour near the high point, as annotated on this Google Earth photograph:
We calibrate the GPS at this point.
We go to the high point (or as near to it as possible) and record the terrain height from the GPS: 156 m.
We go to a place where we can observe the trees from a measured (or estimated) distance.
We estimate the height of the highest trees in the clump using the ruler method, as described in Verifying a Link End Using a Survey. We record the height of the highest trees: 20 m. We also record the height of the trees at the edge of the clump: 15 m.
When we return to the office, we update the profile with these results, adjusting the clutter type to Deciduous Forest at 15 m with a slight adjustment in the terrain height and on the outer edge setting the clutter to Light Trees - Shrubs at 5 m with an additional obstruction loss of m.
We now have a more accurate profile of the high point. This will help us to optimize the link and achieve acceptable data throughput.