Posted on 03/24/2014 10:34:25 AM PDT by don-o
snip
"We looked at the Doppler effect, which is the change in frequency, due to the movement of a satellite in its orbit. What that then gave us was a predicted path for the northerly route and a predicted path the southerly route," explained Chris McLaughlin, senior vice president of external affairs at Inmarsat.
This information was relayed to Malaysian officials by 12 March, but Malaysia's government did not publicly acknowledge it until 15 March, according to the Wall Street Journal. Malaysia began to redirect the search effort that day, to focus on the areas the information described. However, some officials involved with the probe warned that the lost days and wasted resources could impede the investigation.
Meanwhile, Inmarsat's engineers carried out further analysis of the pings and came up with a much more detailed Doppler effect model for the northern and southern paths. By comparing these models with the trajectory of other aircraft on similar routes, they were able to establish an "extraordinary matching" between Inmarsat's predicted path to the south and the readings from other planes on that route.
"By yesterday they were able to definitively say that the plane had undoubtedly taken the southern route," said McLaughlin.
These pings from the satellite – along with assumptions about the plane’s speed – helped Australia and the US National Transportation Safety Board to narrow down the search area to just 3 per cent of the southern corridor on 18 March.
(Excerpt) Read more at telegraph.co.uk ...
Geosynchronous satellites orbits are not perfect circles so their apparent position wanders north and south of the Equator and they drift east and west in an figure-eight pattern. The position at any instant is monitored by ground stations and the offset of transmitted and received signals is compensated for the Doppler a Effect. Inmarsat was able to refine their model by examining not just the exchange of timing signals with MH370 but also with aircraft flying different know courses, speeds and altitudes over the past few weeks.
You are correct. 3 constellations of 10 satellites orbiting at slightly more than 22,000 miles.
"Our satellites"
"We launched the world’s first global mobile satellite communications system to enable merchant ships to stay in touch or call for help in an emergency."
"Today we own and operate three constellations of 10 satellites flying in geostationary orbit 35,786km (22,236 miles) above the Earth. And we remain a pioneer in space communications and the industry leader with the planned launch of our fifth-generation Inmarsat-5 spacecraft in 2013-14."
Man, nobody does hard math like the Brits
Huh?
This’ll be a lost science in the US once our kids get common cored....
but, you see....it goes to eleven.... /spinal tap
Presumably there is also a relativity effect when measuring tiny differences in elapsed time at 22,000 miles above the earth compared to an aircraft flying 7 miles above the earth. I don’t know whether it is big enough to be relevant, but if they are taking into account these tiny variations in the satellite orbit, these must be very small calculations they are making.
The very first use of (low earth orbiting) satellites for search and rescue was proven by ham radio operators in the 1970s and 80s using doppler shift measurements. This led to the development of SARSAT/COSPAS. In this case, it’s the plane that did the moving but physics is physics.
Even GPS satellites aren’t in precise orbits. Their paths are perturbed by gravitational effects (the Sun, moon and mass anomalies of Earth itself) as well as atmospheric drag. Their positions are monitored on every orbit and adjustments are made to the ephemeris (which are loaded into all GPS receivers). In addition, thrusters are used to correct larger drifts from idea position.
I know you can measure “Dopplar” but, assumed they had already done so.
It shouldn’t have taken this long.
That it did seems suspect to me.
What is even more suspect is some former military guy, running his mouth on FoxNews all weekend, claiming “his sources” “confirms” plane landed in Paw Kee Stain.
Boo Chitter.
No better than the hapless and flacid speaking expert they had on this morning.
Wake me when there is some concrete evidence.
http://searchmobilecomputing.techtarget.com/definition/geostationary-satellite
"...the exact position of a geostationary satellite, relative to the surface, varies slightly over the course of each 24-hour period because of gravitational interaction among the satellite, the earth, the sun, the moon, and the non-terrestrial planets."
Yes, there are perturbations and imperfections that are corrected for in the calculations. I considered this as TMI in replying to a person who was unsure about the types of satellites and their orbits.
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
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Apparently they didn’t take into account manmade global warming, so how can the results be taken seriously???
Doppler effect
I thought of that the first day. They should have asked me.
That's the point. I think the Inmarsat spokesman, who is a PR guy and probably not a satellite enginer, misspoke.
We have an aircraft moving at say 500 miles an hour across the surface of the earth.
We have a satellite that is basically stationary with respect to the surface of the earth.
It is not the movement of the satellite with respect to the earth, which is what the spokesman suggested, that is causing the bulk of the Doppler effect.
It’s not relevant on a day-to-day or week-to-week basis ...
“Wake me when there is some concrete evidence.”
Same here.
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