Young Hikers Missing in Joshua Tree Since Thursday [7/27/17]

General Palm Springs area.

Re: Young Hikers Missing in Joshua Tree Since Thursday

Postby Sean » Fri Sep 01, 2017 6:27 pm

Perry wrote:Sean, I have wondered if dogs that are trained using cadavers from other environments might not search for the same aromatic chemicals and proportions of chemicals of a body in a desert environment. But I would think that the authorities would quickly figure out that the dogs need to be trained specifically using cadavers from a desert environment, if that's necessary. But if it is harder for the dogs in the desert, and Otherhand said he could easily smell remains in Death Valley, then it may be that the aromatic compounds are not uniquely human, so there's too many false positives from dead animals.


I read a couple scholarly articles on the subject. My impression is that these dogs are well-trained before being used in actual cases in the field. Practical problems, though, are often related to human error or ignorance. Trainers, for example, don't fully understand the dog's olfactory abilities. And handlers sometimes fail to recognize the dog's signals. But in this case they also have to contend with non-ideal terrain and weather.

Mr. Mahood found Norman Cox on an open salt flat seven months after the fact. He also benefited from cooperation with the Carson City sheriff, who gave him all the prior SAR data, plus he knew Cox was suicidal from a letter the guy wrote. People looking for the Orange County couple had none of these advantages. The JTree terrain is rocky and hidden, not flat and open. And it's only been a month. I wouldn't expect serious decomp to begin until the weather cools down. Maybe then the dogs and searchers will have better luck.
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Re: Young Hikers Missing in Joshua Tree Since Thursday

Postby bretpct » Sat Sep 02, 2017 12:12 am

Perry wrote:Ric, if authorities knew the exact GPS coordinates near Smith Water, why would they say the ping was near the general parking area in the early days of the search?

Is there an easy way to overlay the coverage splash onto a more detailed map and not cover up the terrain with the colors?
http://www.otherhand.org/wp-content/upl ... ussion.pdf (page 4)


Here's OtherHand's RSSI map overlaid at a low opacity. Notice that the car and SWC lie at just about 10 miles from Serin Tower.

I know in my experience, when I've tried to locate my position on an iPhone with a poor signal, the map will show me within a huge circle (probably 10+ miles). I've also experienced on my iPhone "No Service" in the Angeles Forest, despite being in visual contact with a cell phone tower, only to have a cloud float into the perfect position and give my phone three bars. Then the cloud floated on, and so did my cell service.

The more I read about cell phone pings, the less I trust them for specific locations. Especially when only one tower is in play.
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Re: Young Hikers Missing in Joshua Tree Since Thursday

Postby Ed » Sat Sep 02, 2017 8:25 am

Interesting, thanks for the links, bretpct. I am a faithful reader of the Economist, but must have missed the article mentioned.

But now we have the GPS chips in smartphones. I wonder how long it takes them to get a good three or four satellite location fix. On my GPS unit, it can take quite a long time if it does not have the current almanac. And I think that about 20 minutes is recommended for downloading the almanac. Admittedly, it is an older unit. But it is also a Garmin GPS, not a chip in a smartphone, serving a secondary purpose.
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Re: Young Hikers Missing in Joshua Tree Since Thursday

Postby Ric Capucho » Sat Sep 02, 2017 8:34 am

Perry wrote:Ric, if authorities knew the exact GPS coordinates near Smith Water, why would they say the ping was near the general parking area in the early days of the search?

Is there an easy way to overlay the coverage splash onto a more detailed map and not cover up the terrain with the colors?
http://www.otherhand.org/wp-content/upl ... ussion.pdf (page 4)


Hi Perry,

As inferred previously, there are two ranging methods; the easiest is the cell tower measuring the time it takes for a signal to make the round trip. The more sophisticated is to carefully examine the GPS location data supplied by the cellphone itself and presumably cached somewhere on the cell tower's computer. I can only imagine that the ranging given for the easier tower measurement was consistent with the range to the Maze Loop parking. I guess it was only a day or two later when a specialist took a hard look at the more sophisticated GPS data that the discrepancy became very obvious.

Someone has just pointed out to me that Serin Tower is a Verizon tower, and that other carriers have their own towers located elsewhere. So unless we know Orbeso was a Verizon subscriber, then the splash map for Serin is inconclusive.

Maybe ask Tom how he splashed the Serin coverage in a more easily readable way. I've struggled with Hey What's That for years...

bretpct wrote:
Perry wrote:Ric, if authorities knew the exact GPS coordinates near Smith Water, why would they say the ping was near the general parking area in the early days of the search?

Is there an easy way to overlay the coverage splash onto a more detailed map and not cover up the terrain with the colors?
http://www.otherhand.org/wp-content/upl ... ussion.pdf (page 4)


Here's OtherHand's RSSI map overlaid at a low opacity. Notice that the car and SWC lie at just about 10 miles from Serin Tower.

I know in my experience, when I've tried to locate my position on an iPhone with a poor signal, the map will show me within a huge circle (probably 10+ miles). I've also experienced on my iPhone "No Service" in the Angeles Forest, despite being in visual contact with a cell phone tower, only to have a cloud float into the perfect position and give my phone three bars. Then the cloud floated on, and so did my cell service.

The more I read about cell phone pings, the less I trust them for specific locations. Especially when only one tower is in play.


Hi Brett,

Agree about your concern about the ranging accuracy of cell towers. They can be extremely misleading. However the margin of error of a GPS position even with reflections, limitations of satellite coverage, and anything else that may put a spanner in the works is only a few hundred metres, say half a mile max. So a GPS calculation error that gives a position many miles away from the true position isn't possible. Better not be, as the military use the GPS signals to target missiles onto the bad guys.

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Re: Young Hikers Missing in Joshua Tree Since Thursday

Postby Ric Capucho » Sat Sep 02, 2017 8:37 am

I don't suppose anyone happens to know which airbnb the couple used, and/or its location?

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Re: Young Hikers Missing in Joshua Tree Since Thursday

Postby Ed » Sat Sep 02, 2017 10:00 am

Ric Capucho wrote:So a GPS calculation error that gives a position many miles away from the true position isn't possible. Better not be, as the military use the GPS signals to target missiles onto the bad guys.


Well, we have taken out a few weddings and funerals, plus the Chinese embassy in Belgrade, so I don't think the military relies on perfect information before acting.

More seriously, I have read suggestions that the information stored by the cell phone company and available subsequently can be considerably less than that employed in a 'live' fix.
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Re: Young Hikers Missing in Joshua Tree Since Thursday

Postby zippetydude » Sat Sep 02, 2017 1:46 pm

Ed wrote:Well, we have taken out a few weddings and funerals, plus the Chinese embassy in Belgrade, so I don't think the military relies on perfect information before acting.


:lol: Made me laugh with that one Ed!

BTW, I posted that the forecast for Sunday is the low 80's. The NWS has parts of Joshua Tree showing 83 degrees for the high, then other parts show 93 degrees? 10 degree difference in just a few miles in the middle of the desert? I don't trust it when it's 100 in Palm Springs. Just wanted to clarify that before I accidentally waste someone's afternoon driving all the way to JT only to find it dangerously hot for hiking/searching.

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Re: Young Hikers Missing in Joshua Tree Since Thursday

Postby cynthia23 » Sat Sep 02, 2017 2:18 pm

Here in Palm Springs, it's quite unpleasant even by our standards, with both high heat and humidity.
Q: How many therapists does it take to screw in a light bulb? A: Only one, but the light bulb has to want to change ...
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Re: Young Hikers Missing in Joshua Tree Since Thursday

Postby Wildhorse » Sat Sep 02, 2017 7:02 pm

92 in San Diego downtown today. The government sent a high heat alert. What would ever do without the gov telling us that it is hot outside?
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Re: Young Hikers Missing in Joshua Tree Since Thursday

Postby zippetydude » Sat Sep 02, 2017 8:33 pm

Wildhorse: http://www.trover.com/d/mTfc-ben-nevis- ... d-scotland

You may have already seen this, but it is so very much in accord with the threads we have shared about gps and human beings and the wilderness. I look it up from time to time just to smile again...

8)

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