When a cell phone signal is received at two or more towers, the ability to triangulate back upon the signal to a place on the map or landscape is becoming common. This is no different than when a rescuer wants to pinpoint his or her location on a topographic (topo) map by shooting azimuths (bearings) on plainly visible and identified objects, such as mountain tops, TV or radio towers, plainly visible and recognizable buildings, etc. You record the bearing — called an azimuth — to one feature and draw a line on your map. You do the same to one or two other known features and again, draw the lines on your map. Where the two or three lines cross, that is where you are. This is the process of map triangulation. It can show you where you are on a map, and this system works very well, provided you know or recognize the features to which you are aiming and can identify them on your map.
This method of locating yourself on a topo map obviously requires you being able to see and clearly identify distant features to which you are aiming. This is why tall towers and mountaintops work so well. In the flat lands you will likely have to rely upon tall man-made features to use in this process.
Cell tower signals work in much the same way. A cell phone signal emanating from the forest travels outward and is received at two or more towers. The “reverse direction” or back azimuth of the cell phone signal from the two towers will eventually cross each other. This is the general area where the call originated. This location is normally documented by use of latitude-longitude coordinates, very often given in degrees/tenths of degrees format, instead of degrees, minutes and seconds, which is far more useful in terrain mapping programs and in GPS units.
Once your communications center provides you with the cell phone’s coordinates, you can begin the assessment of how your search will need to commence. However, these initial coordinates are usually in a degrees/tenth of degrees format. Converting them to degrees, minutes, seconds format will generally be more useful to you in search operations, and the conversion is performed as follows:
You are provided with these cell phone “ping” latitude/longitude coordinates: 35.40406* north by 82.73901* west
(Note: the symbol * is depicted as the degrees symbol for this article.)
Convert the latitude first. The 35 degrees will remain 35 degrees, so write it down as such. Next, multiply the .40406 x 60 = 24.2436. The 24 now become your “minutes.” Then, multiply the .2436 x 60 = 14.61. This becomes your “seconds.” Therefore the converted latitude is now 35* 24’ 14.61” north. It is as simple as that.
Do the same conversion for the longitude: 82 degrees remains as 82 degrees, and write it down. Multiply .73901 x 60 = 44.3406. 44 become your “minutes.” Multiple .3406 x 60 = 20.43. This becomes your “seconds.”
Your converted latitude/longitude coordinates are now 35* 24’ 14.61” north by 82* 44’ 20.43” west. That’s all there is to the conversion; plain, simple and useable. NOW you can enter these coordinates into your navigation system to pinpoint the cellphone and thus the user of the lost person(s).
There are several quality terrain mapping systems on the market that are useful to rescuers in SAR operations, but the one I have found to be the most simple and user friendly for rescuers — especially those of us who are “electronically challenged” — is Terrain Navigator Pro by MapTech. It just quite simply has so many useful features available in the program that GREATLY assist rescuer command staff in planning and operating a search. You can calculate distances, areas, landform profiles, and easily have the coordinates anywhere on the topo map where the cursor is located. You can see streams, ponds, lakes, dams, buildings, roads and trails of all types, and so much more. You can even display the topo map and the corresponding color aerial photo at the same time and both to scale! As I have taught fire and rescue departments for years, the abilities of this mapping program are limited only by your imagination in the use of the program.
Below is the example of locating the converted cell ping coordinates. You can also use the Google Earth program to obtain aerial photos of the area you are searching, and toggle back and forth between your Terrain Navigator Pro and Google Earth aerial photos.
In many articles I have tried to show you tools that will help you plan, coordinate and document a search operation. From an incident management perspective, perhaps the most useful tools shown are those presented here. Base maps with aerial photos are invaluable in SAR operations. If your department runs searches and you don’t have this mapping capability, I urge you to get it. But to become proficient in any mapping and/or terrain system, you have to train with it, just like in ANY other rescue discipline or tool.
Until next time — BE SAFE.