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#274231 - 02/17/15 02:35 AM A Distress Beacon Isn't the Same As Dialing 911
Doug_Ritter Offline

Pooh-Bah

Registered: 01/28/01
Posts: 1966
http://abcnews.go.com/US/wireStory/hampshire-mountain-hiker-activated-beacon-found-dead-29006945

No info yet on what type beacon, but no beacon replaces common sense.
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#274234 - 02/17/15 05:14 AM Re: A Distress Beacon Isn't the Same As Dialing 911 [Re: Doug_Ritter]
James_Van_Artsdalen Offline
Addict

Registered: 09/13/07
Posts: 449
Loc: Texas
Quote:

"Unfortunately, a lot of the coordinates that we received over the night were all over the place within a mile circumference," Fish and Game Lt. Jim Goss told WMUR-TV.

Many years ago I looked up the details on what a SARSAT beacon transmits to the satellites.

The key thing is that there's only so much space in the packet transmitted, and some of the least significant bits/digits of the location are not sent.

My memory is not clear, but I think the digits transmitted amount to a minimum 300' circle. It may be larger, but the point is that it doesn't matter how precisely the beacon's GPS can pinpoint the location: only a limited number of digits can be sent.

In the best conditions a good GPS can get to < 30' precision, but these were not the best conditions. Her GPS may not have been able to calculate a fix even as small as SARSAT's capabilities based on where the beacon was and how the atmosphere was distorting the signals in the storm. And with the wind it's not hard to imagine the beacon being promptly covered by ice, dirt & debris even if the beacon was in a good spot for listening to GPS satellites.

Finally, beacon GPS may not have even come into play. The Fish & Game guy said the error circle was about a mile. That used to be the precision for locating the beacon by "triangulation" from the SARSAT satellites when no GPS data was available. If this capability still exists it's not hard to imagine storm-driven radio distortions causing a satellite fix to wander a lot.

Mount Washington weather is notorious even to non-hikers. A weather radio would have been a good idea.

PS. A GPS receiver generally uses a temperature-compensated oscillator in the timing measurement. It may have been too cold for the GPS receiver to calculate a position!

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#274235 - 02/17/15 05:20 AM Re: A Distress Beacon Isn't the Same As Dialing 911 [Re: Doug_Ritter]
hikermor Online   content
Geezer in Chief
Geezer

Registered: 08/26/06
Posts: 6745
Loc: southern Cal
Yes indeed.Knowledge trumps gear and gadgets
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#274237 - 02/17/15 10:40 AM Re: A Distress Beacon Isn't the Same As Dialing 911 [Re: Doug_Ritter]
Herman30 Offline
Enthusiast

Registered: 08/08/06
Posts: 258
Loc: Finland
Here is a video from the search http://www.wmur.com/news/rescuers-search-for-missing-hiker-near-mt-adams/31294362

At 0:32 is visible the harsh weather condition.

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#274238 - 02/17/15 10:51 AM Re: A Distress Beacon Isn't the Same As Dialing 911 [Re: Doug_Ritter]
Phaedrus Offline
Pooh-Bah

Registered: 04/28/10
Posts: 2197
Loc: Great Plains
It sounds like even with location data accurate to within an inch the rescuers still might not have been able to save her. Knowing where you are is one thing, being able to get to you in time is another.
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#274239 - 02/17/15 04:34 PM Re: A Distress Beacon Isn't the Same As Dialing 911 [Re: Phaedrus]
AKSAR Offline
Old Hand

Registered: 08/31/11
Posts: 1126
Loc: Alaska
Originally Posted By: Phaedrus
It sounds like even with location data accurate to within an inch the rescuers still might not have been able to save her. Knowing where you are is one thing, being able to get to you in time is another.
I think Phaedrus hit the main point. The real issue seems to have been that the conditions were so severe that SAR teams had difficulty even getting into the area.

Modern 406 beacons provide location data both by transmitting GPS coordinates and by Doppler shift. As J_V_A notes above, the GPS coordinates are truncated to an accuracy of 100 meters or so. Doppler shift alone gives a location to about 2 km.

In this case there isn't enough info to know why ".......a lot of the coordinates that we received over the night were all over the place within a mile circumference". It could be the subject was still moving around, desperately seeking shelter. Or perhaps buried under snow where the GPS couldn't get a good fix, but the satellites could still get a Doppler fix on the 5 watt 406 signal. I doubt the cold or weather conditions had much effect on the GPS chip, in Alaska folks regularly use GPS in conditions at least as severe.
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#274243 - 02/17/15 10:16 PM Re: A Distress Beacon Isn't the Same As Dialing 911 [Re: Doug_Ritter]
boatman Offline
Addict

Registered: 03/10/03
Posts: 424
Loc: Michigan
Sometimes no matter what gear you have or what preps you make, when your times up its up. There are no guarantees in life except that it ends. I feel sorry for this person. I also feel sorry for the SAR team. To be so close and have this outcome must be heartbreaking for them. If she was wandering around after activating her beacon it impeded her resque. not much to shelter with on a ridgeline like that. I wonder if she had a bivie bag if it could of helped....

BOATMAN
John

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#274245 - 02/17/15 11:29 PM Re: A Distress Beacon Isn't the Same As Dialing 911 [Re: boatman]
hikermor Online   content
Geezer in Chief
Geezer

Registered: 08/26/06
Posts: 6745
Loc: southern Cal
What was the weather forecast at the time? Setting off in the face of wind and storm like this is not a very good idea, especially solo,and you had better have the capability to dig a snow cave really quick.
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#274246 - 02/18/15 12:57 AM Re: A Distress Beacon Isn't the Same As Dialing 911 [Re: Doug_Ritter]
jshannon Offline
Addict

Registered: 02/02/03
Posts: 585
Loc: North Texas
I'm reading that beacon was ACR ResQLink 375. Another article.

http://dailym.ai/1EMuAzy


Edited by jshannon (02/18/15 12:58 AM)

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#274249 - 02/18/15 09:56 AM Re: A Distress Beacon Isn't the Same As Dialing 911 [Re: Doug_Ritter]
Tjin Offline
Pooh-Bah

Registered: 04/08/02
Posts: 1749
looks like a experienced outdoors person.

In my experience there are a few kinds of persons who will go out despite bad weather forcast:

- People with time and/or money contrains. Do it now or wait/save up for another year.

- Setting your self up for succes type of persons. 'The we, go out despite bad weather forcasts and see how the weather actually is on sight and determine if you turn around or not'. Weather forcasts are just forcasts and it's not really too accurate. Many people, me including have just stayed home when the weather forcasts was bad, just to find out it was pretty good.

- A little bad weather means less congestion on populair routes, which sometimes makes things more pleasant and sometimes even safer.

In all cases, beter get a good bail out plan and bring proper equipment. I do not know her, the area or the weather forcast, but I do get why people do not abord plans when the weather forcast turn bad.
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