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Old 04-08-2013, 16:01   #751
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Look how disparate signals are! Cherie

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Old 04-08-2013, 16:51   #752
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Re: Schooner Nina - MERGED 3 THREADS

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Look how disparate signals are! Cherie

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What was the source of these signals and the locations? Satphone? If so, satphones don't usually send location information, and so any position estimates can be quite imprecise.
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Old 04-08-2013, 16:56   #753
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It appears from Sat Phone Iridium positions. Thought Iridium used GPS??
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Old 04-08-2013, 17:01   #754
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It appears from Sat Phone Iridium positions. Thought Iridium used GPS??
TIMES LOCAL

IRIDIUM MAY 29 1632 -34.9500 173.9900 Poor
IRIDIUM JUN 1 1637 -32.1717 174.2326 Poor
IRIDIUM JUN 1 1644 -31.9095 159.9110 Poor
IRIDIUM JUN 2 2333 -33.4598 167.0595 Poor
IRIDIUM JUN 3 2141 -34.1130 161.4239 Poor
IRIDIUM JUN 4 1150 -33.8327 169.6894 Poor


SPOT MAY 29 1215 -35.17056 174.14554 Excellent
SPOT MAY 30 1145 -34.13174 173.02081 Excellent
SPOT MAY 31 1448 -33.43472 171.892000 Excellent
SPOT JUN 2 1248 -33.599333 168.524667 Excellent- Last known SPOT
MCDAV JUN 3 -33.000000 165.000000 Fair (Estimate only- no position recorded) phone call to Bob McDavitt asking for weather.
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Old 04-08-2013, 17:10   #755
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Re: Schooner Nina - MERGED 3 THREADS

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It appears from Sat Phone Iridium positions. Thought Iridium used GPS??
The latest versions of the Iridium phone include a GPS, but the GPS can be turned off to save batteries, and it can take a while to acquire its position when you turn it on. Even then, the position isn't sent unless the user specifically sends a tracking message.

If these positions came from a GPS-equipped Iridium phone, as actual position reports, then they should generally be accurate. However, if the GPS has not yet acquired its position when the message is sent, then I believe that the last valid position will be used (or none at all?). If the phone, or GPS, have been turned off for a while, that previous position could be quite far from the actual position.

Do you have the actual text from these Iridium messages?

I am guessing here, but if these positions came from Iridium as estimates based on the location of the Iridium satellite at the time of the call, then the boat's actual position could be anywhere within a circle with a radius of 2200 miles. This circle is the satellites "footprint".
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Old 04-08-2013, 17:14   #756
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Re: Schooner Nina - MERGED 3 THREADS

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TIMES LOCAL

IRIDIUM MAY 29 1632 -34.9500 173.9900 Poor
IRIDIUM JUN 1 1637 -32.1717 174.2326 Poor
IRIDIUM JUN 1 1644 -31.9095 159.9110 Poor
IRIDIUM JUN 2 2333 -33.4598 167.0595 Poor
IRIDIUM JUN 3 2141 -34.1130 161.4239 Poor
IRIDIUM JUN 4 1150 -33.8327 169.6894 Poor


SPOT MAY 29 1215 -35.17056 174.14554 Excellent
SPOT MAY 30 1145 -34.13174 173.02081 Excellent
SPOT MAY 31 1448 -33.43472 171.892000 Excellent
SPOT JUN 2 1248 -33.599333 168.524667 Excellent- Last known SPOT
MCDAV JUN 3 -33.000000 165.000000 Fair (Estimate only- no position recorded) phone call to Bob McDavitt asking for weather.
So did these Iridium position reports come from Iridium as position estimates based on satellite location, or were these actual position report messages sent from Nina? This will make a big difference. As I mentioned previously, if these are estimates based on satellite position there could be an error of +/- 2200 miles.

The Spot reports should be good, since these reports come from the GPS that is built into the Spot device aboard Nina.
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Old 04-08-2013, 17:21   #757
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from_unixtime(received_time): 2013-06-03 23:50:25 status: UNDELIVERABLE src_addr: 881623425743 dest_addr: *2 short_message: THANKS STORM SAILS SHREDDED LAST NIGHT, NOW BARE POLES. GOINING 4KT 310DEG WILL UPDATE COURSE INFO@ 6PM

That's the only text. Was one from meteorologist don't have
Cherie
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Old 04-08-2013, 17:33   #758
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Re: Schooner Nina - MERGED 3 THREADS

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from_unixtime(received_time): 2013-06-03 23:50:25 status: UNDELIVERABLE src_addr: 881623425743 dest_addr: *2 short_message: THANKS STORM SAILS SHREDDED LAST NIGHT, NOW BARE POLES. GOINING 4KT 310DEG WILL UPDATE COURSE INFO@ 6PM

That's the only text. Was one from meteorologist don't have
Cherie
OK, that's not a standard Iridium GPS position report. I would ask the Iridium people how they arrived at the position estimate. If it's as I suspect, the accuracy won't be very good. That's not because the system is broken, or they're not trying, it's just the way that these satphone systems work.

But check with Iridium. I am making some assumptions here...
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Old 04-08-2013, 17:36   #759
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Re: Schooner Nina - MERGED 3 THREADS

If you need help discussing this technical stuff with the Iridium folks, I would be happy to help. Let me know if you would like me to make a phone call, or send some email.
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Old 04-08-2013, 17:39   #760
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I'm not even going there with Iridium! It took a top ranking officer from the US State Dept to get this one!!!

Cherie
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Old 04-08-2013, 18:03   #761
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Re: Schooner Nina - MERGED 3 THREADS

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It appears from Sat Phone Iridium positions. Thought Iridium used GPS??
I never get gps coords from Iridiums. My clients must enter their coords from their gps manually as an sms. Actually, what my Iridium carrying clients do most often is the send a tick with their location devices (yellowbrick/spot/etc). But Spot is patchy in some parts of the world so we fall back on manually input gps coords via Iridium sms at times.

I get gps coords with some Inmarsat smss.

I might be wrong if the boat carries the newest Iridium phone that I have not used yet.

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Old 04-08-2013, 18:07   #762
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Re: Schooner Nina - MERGED 3 THREADS

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(...) The Spot reports should be good, (...)
Yes and if any one is off the pack, tick it off the list - at times Spot reports WRONG position (or else their web interface wrongly displays a correct one, I cannot tell which case it is).

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Old 04-08-2013, 18:24   #763
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Hey I don't know what they had.. I just paid bills:--))
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Old 04-08-2013, 20:54   #764
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Re: Schooner Nina - MERGED 3 THREADS

The positions come from Doppler analysis of the time shift on the Iridium signal. The data is not normally available and known to be grossly inaccurate. Two positions taken 7 minutes apart but 700 miles out is hardly trustworthy. There is a lot written on this on the internet but RCC NZ were apparently ignorant of this inaccuracy. They should be asking themselves why they never knew this, why was their training inadequate and what other SAR agencies may also be ignorant of this problem. Asking these kind of questions could save lives in the future.

So for whatever reason, they chose to use a crappy Iridium position rather than the text position from Evi who was an experienced sailor, a meticulous and careful navigator and a math professor. Only her text position agreed with the weather maps, by the way. They finally shifted their searches to Evi's text position on July 1 after learning "new information" from myself and others. Seems like a co-incidence to me. All their prior drift modelling was based on an incorrect position 220 miles to the east and I and others have the emails from them to prove it.

So in summary, the SAR people made a huge mistake trusting and using the Iridium positions over the much more reliable text or verbal positions, especially when you match it to the weather data from Nina. This is not the forum to really get into it but it is obvious to anyone with all the data that they totally screwed up. Right now they are more interested in covering their mistakes than telling the truth. I know it is harsh criticism. RCC NZ are normally the best and the Orion crews are fantastic but the crews in the plane need to be told the right place to search. In this case, it my opinion that RCC NZ totally boned it, particularly with the liferaft searches. Using drift modelling that is 220 miles out for a liferaft search is totally unacceptable. In fairness, it could have been an honest mistake but I am fed up with their a$$ covering and media BS saying they did nothing wrong. This is unacceptable. If you made a mistake, live up to it, learn from it, and stop being such a bureaucrat.

Finally, I can tell you that there will probably be more on this in the future but now is not the time....the families are being kind and diplomatic and trying to work with RCC NZ and the other authorities. As far as I know RCC NZ is giving them what they need and they are concentrating on doing everything they can to keep searching based on new drift modelling from Evi's (correct) text position. They should be supported.
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Old 04-08-2013, 21:00   #765
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Re: Schooner Nina - MERGED 3 THREADS

One question I ask myself is if the accuracy improves if it is a long transmission time. A short data burst like one from an SMS text may be much worse in accuracy than as written in the following. The two positions 700 miles apart yet taken only 7 minutes apart seem to support this theory.

Iridium accuracy references...

First Reference....
https://en.wikipedia.org/wiki/Iridium_Communications
Tracking transceiver units[edit]
Without an extra global navigation satellite system, receiver tracking is difficult, but not impossible, as the position of a mobile unit can be determined using a Doppler shift calculation from the satellite. These readings however can be inaccurate with errors in the tens of kilometers.[33] Even without using Doppler shifts, a rough indication of a unit's position can be found by checking the location of the spot-beam being used and the mobile unit's timing advance.
The position readings can be extracted from some transceiver units and the 9505A handset using the -MSGEO AT command.[45] In the past, Iridium has used this method of tracking to block service to U.S. embargoed countries, such as North Korea and other politically unpopular regions, such as Northern Sri Lanka. It is also used to stop geographically bounded plans from being used outside the designated area.
The Iridium Extreme phone introduced in 2011 has a GPS location service embedded in the device, which the user can use to locate themselves or include in SMS messages. It can also be used to provide advanced services like Geo-fencing. A red emergency button on the top of the unit can be pressed to send the unit's position to emergency rescue agencies or other number pre-programmed by the user or distributor.

Second Reference....
NAL - Network Reference - Iridium Subscriber Unit
The Iridium network makes calculations of the geographical location (geo-location) of an ISU each time a call is placed. The technique employed to determine the geo-location of an ISU is based on measurements of the ISU and satellite propagation delay and Doppler frequency shift. These measurements are used to estimate cosines of spherical angles that identify the ISU's location relative to the satellite by the gateway. The Iridium geo-location process proceeds as follows:
The ISU sends the satellite an uplink geo-location burst, saving the delay and Doppler corrections needed to send the message.
When the satellite receives the uplink geo-location burst from the ISU, it measures the time and frequency offsets of the burst relative to its time and frequency standards.
The satellite then responds with a downlink burst, which the ISU uses as an acknowledgement that the satellite has received the previous uplink geo-location burst.
When the downlink burst arrives, the ISU checks to see if it is satisfied with its estimates for the timing and Doppler. If so, it then transmits an uplink ACCHL message to the satellite that includes the propagation time and Doppler frequency offsets that were used by the ISU during the last geo-location uplink burst. If the ISU did not receive a response, or if the ISU is not satisfied with the accuracy of the exchange, the ISU will repeat the process again at step 1.
The Iridium network can locate an ISU to within 10 km only about 78% of the time. The location accuracy can be much higher; however, the information is not available to commercial users. The so-called error ellipse can have a large eccentricity with the major axis oriented in the azimuth dimension and the minor axis oriented in the radial dimension. The position of the ISU in the radial dimension relative to the satellite can almost always be determined to within 10 km with just one measurement. Errors in the azimuth dimension relative to the satellite are largest along the satellite's ground path and tend to increase with distance from the satellite. Geo-location errors in the east-west dimension, therefore, are sometimes more than 100 times greater than in the north-south dimension.
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