Hello, > could the same data be acquired by very closely monitoring the > orbit(s) of satellite(s) at many ground stations around the world > (perhaps you could also measure the Doppler shifts of its radio signals) > ? everything is possible, why not? :-) But, this would be very expensive since you need a tracking network which provides continuous orbital measurements. That means a lot of sensor stations on Earth. The efficient way is to measure the gravitational attractions itself by two satellites. > But I suppose there is also the question of an unknown atmospheric > density to the required degree of precision; the GRACE satellites will > both be affected by the atmosphere essentially equally. Drag could > conceivably be confused with a gravimetric gradient. The GRACE satellites have on-board accelerometers to measure non-gravitational effects such as atmospheric drag. Cheers, Sebastian ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/sat/seesat/seesatindex.html
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