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You need to acquire at minimum three different satellites transmissions, ideally four for the onboard computer to calculate your coordinates. Even if the same chipset is used, there may be differences in the antennae etc, that might result in one or the other being better; but as with the many GPS units I've used you may find that completely dependent on where you are one may be better or worse than another at acquiring and calculating your position from a cold start.
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Also, was that a typo.....did you mean use a PLB (when) in danger?
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One small correction though, whereas the GPS is calculated by the EPIRB/PLB, the Doppler effect estimation by the Cospas is actually calculated by a ground terminal and only requires 1 non-geosynchronous satellite to produce the calculation.
I think given the very real possibility in delayed rescue I wonder if the procedure should be to pop it off at the first sign of significant trouble
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Can you please advise:
- What is the maximum and average time for a broadcast to be received by a satellite and broadcast to a ground station to be actioned ?
- Are these times the same globally or is NZ better served than other locations in this regard ?
Good afternoon David and thank you for your queries below. The notification time from beacon activations has been reduced considerably with the introduction of the MEOSAR (Medium Altitude Earth Orbit Search and Rescue) satellite system. This system now has a total of 20 United State GPS satellites and twelve Galileo satellites which are in continuous earth orbits. These satellites, when in view of a transmitting beacon, independently send the beacon identification to ground station antenna. If three or more satellites receive the beacon signal a ground location can be determined. If only the identification of the beacon is provided from one satellite, and it is registered, then a SAR response can be initiated. In New Zealand we have installed a six antenna ground station north of Taupo and in collaboration with Australia we now receive beacon alerts within two to five minutes. Normally a response would be commenced, at least into the planning stage, within ten minutes. The time to have a SAR asset at the location of the distress beacon can vary considerably and can be affected by the availability of a SAR asset and the weather, sea state or terrain.
The earlier LEOSAR (Low Earth Orbit Search and Rescue) satellite system is still functional and in use. This system currently has five satellites in orbit and the rotate around the earth in north/south polar orbits about every 105 minutes. They have an equatorial spacing of approximate 25 degrees between satellite orbits so at times it can be a long as four hours between suitable passes depending on your location within our Search and Rescue Region. With these satellites they determine position using a doppler technique and provide two positions equally spaced either side of the satellite track on each beacon activation. As a consequence we also need two passes to resolve the positional data that is provided. RCC operational response to the first message received is as with the MEOSAR system – if it is registered then it is normally possible to eliminate options and concentrate on one of the first two locations provided and then the planning cycle commences. If not registered, and there is no other indication of a distress situation, then we have to wait for the second satellite pass to confirm which of the two positions is the likely location of the beacons activation before dispatching any SAR resources.
In response to your second question I would like to think that we are better than the rest but in fairness I would say that the response that you would receive here in NZ is similar to what you could expect from most countries that maintain a Joint Rescue Coordination Centre.
Now days it is normally the registration of (or not) of the beacon and the availability of a suitable SAR response asset that determines the time between when we receive the beacon alert to when you are rescued.
Hope this helps.
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robin.mousley wrote:
When searching for a surfski in conditions where the sea is covered with breaking waves, a 2mi accuracy is almost completely useless.
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When notified the rescuers use the embedded 121.5 signal as an omnidirectional beacon to hone in on the exact position within that 2-3 mile space where they began
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One more precaution for those who are redundant safety minded is to take a vial of safety dye/marker with them. I am in helicopters trying to spot relatively small objects frequently. The green/yellow dye makes that job much easier (though it is still surprisingly difficult, even when you know where the object is supposed to be). The yellow/green color is by far the most visible, much more than safety orange or red.
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I only have an extremely local answer for that one... Here in Cape Town you can get them from Orka Paddling.Slightly off topic, but does anyone know where people are getting the large bright stickers for their boats?
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