Hi Daniel, Thanks for the info. I'll look into it more when I get a free moment. And for the cubic thing, I just meant that it appears that the doppler S-curve looks like a third order polynomial over the course of a full pass. After a quick google search, the first image at this link is what I mean (in this case envision time along the y axis and doppler offset along the x axis).
http://www.biology.arizona.edu/biomath/tutorials/polynomial/graphingpolynomi...
But I haven't looked into this fully yet, and it sounds like you might be saying that its not that simple. I was just looking into regression equations for the purposes of curve fitting from a number of discrete doppler offset observations. At a quick glance, the cubic polynomial seemed like the right 'shape' for the regression.
I think what you might be warning about is that, in doing so, because there are a large number of parameters that go into the generation of the doppler (and its s-curve), that we might be losing necessary fidelity in the data by assuming a cubic polynomial? Honestly this all kind of new territory for me, so any and all advice is welcome.
Thanks again for the info, much appreciated.
-Zach, KJ4QLP
Research Associate Ted & Karyn Hume Center for National Security & Technology Virginia Polytechnic Institute & State University Work Phone: 540-231-4174 Cell Phone: 540-808-6305
On 11/9/2015 3:29 PM, Daniel Estévez wrote:
Dear Bob and Zach,
This paper might be worth looking at: http://www.dtic.mil/dtic/tr/fulltext/u2/409103.pdf
As far as I know, it started the whole business of location by measurement of Doppler shift.
Apparently, according to the success of project Transit, it is possible to:
a) Compute the TLEs of a satellite by using just a few minutes of the Doppler curve of the beacon of a satellite, as received on a ground station with known location.
b) Compute the location of a ground station, by using just a few minutes of the Doppler curve of the beacon of a satellite with known TLEs, as received on said ground station.
Of course, several variation on this are possible, such as the one which is discussed here:
Compute the location of a ground station by using the Doppler curve of its transmissions during a pass, as received on a satellite with known TLEs.
It seems that the key point in all this is that the Doopler curve depends independently on all the parameters in question (so not a cubic polynomial, which depends on fewer parameters).
73,
Dani M0HXM/EA4GPZ.
El 09/11/15 a las 17:59, Zach Leffke escribió:
No worries, I thought on it a bit more and I think a cubic polynomial is the right fit. I also found some python tools for regression calculations that I think will be useful for this. Also, I think this is pretty similar to how the COSPAS/SARSAT system used to locate lost ships (EPIRBs) and downed Aircraft (ELTs) before the proliferation of GPS and its inclusion in the locator beacons.