Land cover

I can be contacted at E-mail address:- web@g3tvu.co.uk

Using Land cover data:

For Land cover merges, the file 'UMD1km_L.img' needs to be present on your computer. This can be downloaded from the Internet (as per Roger's elevation data page), from UMD1km_L.zip , and unzipped into my Land cover folder at 'C:\Radio Mobile\Land cover'.

This zip file is 36Mb, but when extracted the data is ~890Mb!

however, by setting your Land cover folder 'Advanced' options in Windows XP to 'compressed', it then only requires ~110MB of space.

1) Merging 'Land cover' with pictures

2) Incorporating 'Land coverage' into propagation plots

1) Merging Land cover data with pictures

If present on your machine, you can browse to the Land cover file location using the Browse button before using.

Pressing the 'Draw' button and 'keeping in new picture' will then produce the following plot, but see below for a description of the legend:

where the Land cover data can be seen, with the colour legend illustrating the ground cover type and height. The data is based on 1km by 500m resolution areas at my latitude.

2) Incorporating 'Land coverage' data into Propagation plots

Land cover data can be incorporated into propagation plots, where the length of the radio path impinging the coverage, and the density of the coverage, are both used to calculate the additional path losses incurred.

Opening the 'Options/Elevation data' pane, and selecting the 'Land Cover' button produces this pane, where 'Include Land cover height' can be checked to add the data into path plot calculations. It is necessary to 'Browse' to your Land cover data file location at the bottom of the pane to activate this feature.

The colours reflect those shown on the legend in the merged picture shown above. In this pane the heights of the various layers and their RF density value can be adjusted from the defaults shown to meet local requirements and calibrations. These User values can be saved and reloaded as required.

By opening the 'Toolbar Options' pane (by a right click on the toolbar), a 'Land cover' button can be selected and displayed at the end of the Toolbar. This button will have a Red background if the Land cover file is not available on your computer - or if the use of Land cover is disabled! Where Land cover is enabled for use in propagation calculations the button background is Green. A click on the button will toggle between the Green 'in use' and Red 'disabled' conditions.

Effects of incorporating Land cover:

The effect of invoking the Land cover data into propagation plots may be illustrated by utilising this Radio Link pane - in this case Land cover is not invoked:

and the Link details are:

On this second Radio Link pane, Land cover has been invoked and is shown on the ground profile. The added 2.4dB losses are due to the radio path passing through foliage on the top of the second hill, plus the small urban loss near the transmit site.

whilst the Link details show:

To produce the above screen records, with the pane active, using 'Alt+Print Screen' will place a copy of the pane on the clipboard for insertion into a photo program.

As an alternative, where only the path details are required rather than the full 'Radio Link' pane, using 'View/Large window' produces a large window of the path on the main program screen. This can then be saved to the clipboard using 'Edit/Copy'.

Placing the cursor at an intermediate point on the Radio path, and saving the Large window as above, shows the link details and the type of Land cover at that point in the bottom data region of the window.

However, if Land Cover isn't invoked, the details of the additional losses aren't displayed.

The effects of using Land cover can be seen by comparing the following Polar plots between two low power units, this first plot has had land cover disabled:

Whilst the second plot below, with the same settings, has land cover enabled:

Comparing the 1μV boundary of both plots, shows the reduced area of coverage when applying the additional Land coverage losses.

These are Roger's notes relating to the use of Land cover.

The Land Cover is now part of the propagation model.
If you have a proper path to the land cover file on your computer,
and activate the Land Cover in Elevation Data options, the program
will evaluate the type of terrain and automatically adjust the
percentage of forest and urban on the path, at the condition that
the percentage in the Network properties is set to zero.
The various types of forest or grass are all using the forest model,
but with a height and a density factor. The actual values are based
on my own initial approximations, but you can edit those parameters
and save them as various test cases.
Use the Details in Radio Link to see the resulting losses in dB.
The graphical view in Radio Link will show the clutter if present.
The penetration through clutter depends on the first Fresnel zone
front, so you may observe some losses even if the radio beam is
above the canopy.
An additional toggle button as been added to the toolbar
options.

***Warning***
The implementation of the Land cover effect in Radio Mobile is based
on a mix of empirical methods and wave theory. Parameters such as
the height of canopy or buildings are based on an estimation for the
average case. Considering that, and considering also the 1km
resolution of the world land cover file, the model is best fit for
communication systems with large coverage.

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9th June 2008