Help! I’m lost/injured! Rescue me! - a preliminary report

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Posted by Bill S on March 28, 2008 at 9:04:15 pm EDT

In the Friday, March 28, 2008, Wall Street Journal, there is an article about the tracking services available on your cell phone. Most cell phones currently available in the US have a GPS chipset in them, because of the requirement for locating a 911 caller. In addition, the service providers offer various services to provide the closest restaurant, hotel, gas station, or other service to your location, with turn by turn directions. Many offer tracking of children for their parents. The latest LBS (Location-Based Service) is to display on a map on that tiny screen the locations of your “friends”, so you can ping the closest ones to join you for lunch (there are all sorts of “stalker” and other issues, but that’s not the topic here).

Since cell phones work poorly at best in wilderness locations where we usually backpack and climb, there have been a number of discussions on Trailspace about the various types of PLBs (Personal Locator Beacons), EPIRBs (Emergency Position Indicating Radio Beacons), ELTs (Emergency Locator Transmitters, a device for aircraft), etc. I am writing an article for Trailspace on such devices and am in the process of evaluating 2 devices at the low cost end of the scale, the TracMe and the SPOT. I have also looked at the ACR, which is more expensive.

This is a preliminary report to give a slight introduction to the more extensive review.

The TracMe (about $100, with free replacement if it is used in an emergency) is basically like the transmitter part of an ELT or an avalanche beacon. When activated (manually, not automatically like an ELT is activated on impact or continuously on during the trip like an avy beacon), the TracMe transmits a voice "Help...Emergency" message every 15 seconds on FRS channel 1. The lithium battery has a shelf life of 10 years and has enough charge to transmit the help message for 7 days. The message does not give the location. Like an ELT or avy beacon, you have to know that the victim is missing and the general area, and you have to follow a grid-like searching procedure (the standard one taught for SAR and for avalanche rescue). Since the range of FRS is strictly line of sight, you have to search blindly until you are within 1 to 5 miles and can receive the signal, analogous to the 20-50 meters needed to acquire the signal of an avalanche beacon. The company recommends carrying a location-transmitting device, such as the SPOT in most circumstances to alert your emergency contact to the need for rescue - having an emergency 2 days into a 2 week trip means the battery will run out before you get reported as overdue. However, this is an inexpensive device to use with children in your family who might wander off from the group, or with youth groups. If the boy who wandered off from his scout troop in the Uintas a couple years ago had one, he or his remains might have been located, whereas he remains missing. The search is relatively easy if you are carrying and FRS radio. Basically, just proceed in a grid pattern until you pick up the signal, continue in a straight line until the signal reaches a maximum, turn at right angles and follow a straight line to a maximum, and repeat to narrow in (this is oversimplified, of course - you should take a basic SAR course).

The SPOT uses the signals from the Global Positioning System to determine its location, then transmits them to your "team" and/or a commercial international SAR coordinating organization. The device is simple to operate. There are 4 buttons - power on/off, OK, Help, and 911. The power button is obvious - it turns the unit on and off. "OK" has two functions. The first is to send an "OK" message to your "team". The message is a short one that you compose on the SPOT website (http://www.findmespot.com/), saying whatever you want within the 114 alloted characters ("Bill is Ok, just running late as usual"). Pressing the OK button for 3 seconds activates the send mode, which transmits the message to the Globalstar digital messaging system, which relays it in turn to the SPOT company servers, which in turn send an email message or text message to the 5 (maximum) members of your "team" whose email or text addresses you have entered on the website. It can take as long as 20 minutes for the message to get through, due in large part to the limitations of the Globalstar satellite messaging system, but also due to limitations of any GPS receiver under canyon or canopy. In my tests so far, the position has been at the email on my "team's" computers within a couple minutes, though twice it appears to have taken about 10 minutes. The positions have generally been reasonably accurate, considering that the GPS chipset appears to be a less-capable older set and the system only transmits the latitude and longitude to 0.0001 deg (about 36 feet). Given the 7 meter 50% error budget for the User, this sometimes means a single position can occasionally be off by 140 feet (which I have observed - but see my comment on the Help message later). An excellent feature is that the email/text message is the URL that, when clicked, shows the location on GoogleEarth (where you can select the map, satellite view, or a combination). Here is a sample message -

Quote:

Bill S SPOT test. I'm here.
ESN:0-7361118
Latitude:39.3192
Longitude:-120.3532
Nearest Location: Norden, United States
Distance: 0 km(s)
Time:03/08/2008 00:16:54 (GMT)
http://maps.google.com/maps?f=q&hl=en&geocode=&q=39.3192,-120.3532&ie=UTF8&z=12&om=1

The OK button can also be used to compile tracks. To activate Tracking, you hold the OK button down for 5 seconds (instead of 3). A Track point is transmitted every 10 minutes, but at this time, is not sent to your "team". This function is still under development. Your team members, or anyone you provide the username and password to, can sign onto the website and see the track points. But note that 10 minutes at 2 miles per hour is a half kilometer, rather a large spacing if the trail has lots of switchbacks. In addition, the unit appears to be very sensitive to orientation and to where you are carrying it. I have had several hikes of 10 miles and a bike ride of 25 miles with no track points. The Track continues for 24 hours or until cancelled.

The Help function is similar - while the unit is on, hold the help button down for 5 or more seconds, which then activates a repeated transmission of the Help message you programmed in to your "team" (which can be a different set of 5 from your "OK" set). Again, you set up a message of up to 114 characters (a space is a character, remember). The message is repeated every 5 minutes for up to a week or until cancelled (a "Cancel Help" message is sent). To check the accuracy, I set the unit sending "Help" in my back yard for several 1-hour sessions, then averaged the positions. The averaged location was within a meter of the actual location, going from the Google Earth satellite photo (ooops, the official resolution of GoogleEarth is several meters, so I shouldn't have said that). Again, there were occasional points that were off by 140-150 feet.

The 911 function on my test unit is disabled, and a special arrangement would have to be made with the commercial SAR agency to do a test. However, I am assured that, except for the SAR coordination group being notified and in turn notifying the local SAR group, 911 is the same as the Help function.

My preliminary assessment is that SPOT is a good and fairly inexpensive location device to keep your "team" comforted that you are OK, or that you need help, or to call out a professional Search and Rescue team. The unit is $170, plus a subscription that varies in cost depending on whether you only use the 911 service, or add the messaging and tracking services. Note that you are limited to only the two messages - "I'm OK" and "I need help".

I should note that SPOT does not provide worldwide coverage. Because of the limitations of the GlobalStar digital messaging system (which gives better coverage than the satellite voice telephone part of GlobalStar), you are limited to approximately 70 deg N latitude to 70 deg S latitude. The coverage map indicates that there is also a limitation in most of the world to land areas, and there are some land areas in the included latitudes that are not covered. I do not expect to be visiting those areas in the next couple of months and so cannot check.

A more complete evaluation follows later.

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