Communications, Radar & Electronic Warfare (201.. - Index of

166Communications, Radar and Electronic Warfare200160I 1201::OJ.@ 80I4020.040 0 60 0 80.0 100.0Range (km)Figure 10.6A terrain profile as generated and displayed using the AREPS software. Reproduced bypermission of SCC Pacific and the Atmospheric Propagation Branch.communications is possible. Close to the ground and beyond the peak of the hills, theshade is lighter, showing that communications are impossible. This is because thetenain is blocking much of the signal. The energy that does anive at a receiver close tothe ground in this region is diffracted over the tenain.The scenario is shown in Figure 10.S. A transmitter on the left of the picture isradiating at VHF omni-directionally. The receiver is on the right hand side. There is noI1::OJ@IFigure 10.7 This shows a communications plot from AREPS using the terrain shown in Figure 10.6. Itlooks different because of the sl ant range dIsplay. The lighter colour shows that communications are notpossible for a receIver close to the ground. This is not due to range; otherwise the darker colour that showseffective coverage would not be present for higher altitude targets. Instead, this is due to the terrainblocking the signal . The only RF energy aVaIlable in this regime is due to diffraction over the terrain.Reproduced by permission of SCC Pacific and the Atmospheric Propagation Branch.