'Light fighter' communications

Terrain analysis for the battalion S-6

by CPT John Hinkel

Signal terrain analysis is the key component to producing a viable, flexible communications plan that supports the commander�s scheme of maneuver. Without a viable and flexible plan, the commander won�t adequately exercise command-and-control over subordinate units. A detailed Signal terrain analysis is the key.

Early in the military decision-making process, the battalion S-6 must conduct a mission analysis. The S-6 initially completes the Signal estimate during mission analysis. A component of the Signal estimate is Signal terrain analysis. In bygone days, the S-6 would conduct Signal terrain analysis using a map, ruler and 4/3 graph paper. This was tedious, cumbersome and impractical to use while in the field. Some Signal officers today still use this method minus the 4/3 graph paper.

Many S-6s look at a map and convince themselves this hill or that ridge would be good places for the battalion tactical-operations center, but does the S-6 really "see" the extent of the battalion�s C2 coverage? More importantly, can he determine the radio-signal deadspaces in the battalion�s operations area? Finally, how does he convey this information to the battalion commander, staff and company commanders? Can the Signal terrain-analysis methods of yesterday satisfy the demands of our current MDMP, where commanders are making informed decisions more quickly?

A thorough Signal terrain analysis using computer programs will depict the battalion�s C2 coverage graphically and will help the S-6 show the battalion commander, staff and company commanders the coverage�s extent. Undoubtedly there are several computer programs that will conduct Signal terrain analysis. However, to the exclusion of others, I�ll concentrate my effort on a tried-and-true terrain-analysis program fully supported by the Army�s Corps of Engineers. This program is called TerraBase, and it�s available for download from http://www.wood.army.mil/TVC/.

TerraBase has the capacity to perform gross calculations replicating radio-wave propagation over terrain, and it produces a graphical output that may be incorporated into Microsoft Word or PowerPoint. TerraBase uses standard digital-terrain-elevation data Levels 0 through 3 and controlled imagebase photos to produce its results. The digital terrain data TerraBase uses is available from http://www.geoengine.nima.mil/.

TerraBase is a compact program that�s easy to learn and will run from computers using Windows 95 and NT. Until a specific application is developed for a maneuver battalion S-6, it�s perhaps the most accessible and supported program available. Many battalion S-2s and task-force engineer officers use this program, so it can usually be found already loaded on a computer in the battalion�s TOC.

TerraBase will quickly analyze terrain from a Signal perspective and produce a graphical result depicting projected radio coverage. However, since this program was originally designed for terrain visualization of the battlefield, the parameters required for Signal terrain analysis aren�t obvious and so the S-6 must pay careful attention to the program settings.

TerraBase offers several types of maps, but perhaps the easiest to use in visualizing terrain is a reflectance map. The following example uses a reflectance-map background; however, any background will produce similar results. It�s a matter of personal preference.

After opening the DTED and selecting the AO, the S-6 will see a screen similar to the figure below.

Operations area on TerraBase screen TerraBase screen: operations area.

For TerraBase to calculate frequency-modulation radio coverage, it needs a weapon fan that replicates an FM radio. The S-6 will create this radio weapon fan by clicking on the weapon-fan button and entering appropriate values similar to the following figure.

Screen for weapons fan boxes TerraBase screen: replicating FM by entering values in the weapons-fan boxes.

The S-6 must now enter values to make the program replicate a radio. With a little thought, this is easy. Weapon range becomes radio range. Weapon AGL becomes transmitting-antenna height. Target AGL becomes receiving-antenna height. Left and right boundary correlate to antenna-transmission direction. (Omnidirection is 0 to 360 degrees.) Ray spacing and point spacing determine how many radials and how much spacing along the radials the program will use in its calculations.

Finally, there is curvature. TerraBase uses three types of earth curvature, of which only one replicates the radio horizon. Ensure you use radio curvature.

Now comes the tricky part: the "k" value.

The "k" value represents the local refraction of the earth�s atmosphere. The value of "k" varies with time of day, altitude, weather, season, latitude and humidity. For a standard refraction, "k" has a value of 1.33. For a worst-case value, "k" approaches 0.4. Typically the standard value of k=1.33 will suffice for gross planning.

The next step is to determine the point or points of interest and to allow the program to complete its calculations. Example results follow.

Operations area screen with radio coverage TerraBase operations-area screen with radio coverage overlaid.

The preceding figure uses three radio sites. By creating a weapon fan that replicates a radio�s characteristics and by using a radio horizon, TerraBase has calculated radio coverage. Radial lines projecting from each site show radio coverage. Ray spacing in the weapon-fan setup determine spacing between radials. Radio deadspace is depicted where there�s a break in the ray or where the ray ends. Intersections of rays from different sites show mutual coverage. Lack of a ray from any site depicts radio deadspace. Radio deadspace in the battalion�s AO may require the S-6 to reposition assets or, at a minimum, alert the commander, staff and subordinate commanders of radio deadspace in the AO.

For a more detailed look, the battalion S-6 can use TerraBase to perform a point-to-point line-of-sight analysis. The S-6 will select both a left and right side of the LOS profile. The first time the S-6 performs a LOS analysis, he�ll have to change settings and enable fresnel-zone calculations. He can do this by right-clicking on the initial LOS diagram TerraBase provides. He�ll see a screen similar to the one following.

Fresnel zone dialog box on TerraBase Setting TerraBase up for fresnel zones.

To see fresnel zones, ensure the box is checked next to that option. Since fresnel zones are directly proportional to radio frequency, TerraBase will prompt the operator for a transmit frequency. Since the single-channel ground and airborne radio system�s frequency hops between 30 megahertz and 87.975 mhz, a frequency near the center of SINCGARS� operating spectrum will suffice for gross planning.

So what is a fresnel zone? Visualize a radio transmission in free space as concentric bands of expanding energy (following figure). Zone 1 is in the center of the wavefront and is a direct wave to the receiver. All other zones would travel an indirect route to the receiver.

fresnel zones The fresnel zones. A battalion S-6 is only concerned with Zone 1.

The battalion S-6 is only concerned about Zone 1. TerraBase calculates Zone 1 when using the fresnel-zone-calculation option.

What do the results mean?

Sixty percent of fresnel Zone 1 must clear all obstacles between the transmitter and receiver for establishment of radio LOS. Also, there must not be any obstruction of the fresnel zone during the first and last kilometer. TerraBase visually depicts the first fresnel zone in maroon, displaying it as the outer ellipsoid. The battalion S-6 must focus his attention on the topmost maroon ellipsoid and ensure that at least 60 percent remains free from obstruction. If more than 60 percent is blocked, he should choose another site.

In the maps I�ve shown, the first fresnel zone is clear and these sites, as calculated, are within radio LOS of each other.

Now, the battalion S-6 has a great deal more information to use to complete his Signal estimate, but how does he interpret all the results without getting bogged down? Carefully and with practice. The following figure shows how a battalion S-6 might interpret TerraBase results with respect to a simple sketch of the battalion�s operational graphics.

TerraBase screen with radio coverage charted TerraBase with radio coverage, including deadspace, charted.

In this example, checkered areas depict radio deadspace. Through a careful examination of coverage provided by the proposed communication sites, the battalion S-6 can determine retransmission lines that coincide with operational phase lines.

Does the battalion S-6 hand out this diagram or include it as part of the Signal annex? No, it�s much more information than the commander, staff or subordinate commanders desire. A simple sketch showing TOC location, retrans locations, retrans lines and deadspace in the AO would suffice. The preceding figure is meant as an example of how the S-6 can use TerraBase�s results to complete his Signal annex and eventually formulate a viable and flexible plan that he takes to the battalion�s course-of-action analysis.

The Signal terrain analysis the battalion S-6 can accomplish using TerraBase greatly speeds the process and allows the S-6 to better inform the commander, staff and subordinate commanders of the battalion�s C2 coverage. It visually depicts radio deadspace in the AO and, if used smartly, will greatly enhance the commander�s ability to C2 his subordinate units. Computerized Signal terrain analysis is the key to the S-6�s success in formulating a viable and flexible plan.

CPT Hinkel is the combat Signal trainer at the National Training Center, Fort Irwin, Calif.

Acronym QuickScan
AO � area of operations
C2 � command and control
DTED � digital terrain-elevation data
FM � frequency modulation
LOS � line of sight
MDMP � military decision-making process
Mhz � megahertz
SINCGARS � single-channel ground and airborne radio system
TOC � tactical-operations center

dividing rule

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