Abstract:
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In this work, a new GPS carrier phase-based
velocity and acceleration determination method is presented
that extends the effective range of previous techniques. The
method is named ‘EVA’, and may find applications in fields
such as airborne gravimetry when rough terrain orwater bodies
make difficult or impractical to set up nearby GPS reference
receivers. The EVA method is similar to methods such
as Kennedy (Precise acceleration determination from carrier
phase measurements. In: Proceedings of the 15th international
technical meeting of the satellite division of the Institute
of Navigation. ION GPS 2002, Portland pp 962–972,
2002b) since it uses L1 carrier phase observables for velocity
and acceleration determination. However, it introduces
a wide network of stations and it is independent of precise
clock information because it estimates satellite clock
drifts and drift rates ‘on-the-fly’, requiring only orbit data
of sufficient quality. Moreover, with EVA the solution rate
is only limited by data rate, and not by the available precise
satellite clocks data rate. The results obtained are more
robust for long baselines than the results obtained with the
reference Kennedy method. An advantage of being independent
of precise clock information is that, beside IGS Final
products, also the Rapid, Ultra-Rapid (observed) and Ultra-
Rapid (predicted) products may be used. Moreover, the EVA
technique may also use the undifferenced ionosphere-free
carrier phase combination (LC), overcoming baseline limitations
in cases where ionosphere gradients may be an issue
and very low biases are required. During the development of
this work, some problems were found in the velocity estimation
process of the Kennedy method. The sources of the problems were identified, and an improved version of the
Kennedy method was used for this research work. An experiment
was performed using a light aircraft flying over the Pyrenees,
showing that both EVA and the improved Kennedy
methods are able to cope with the dynamics of mountainous
flight. A RTK-derived solution was also generated, and
when comparing the three methods to a known zero-velocity
reference the results yielded similar performance. The EVA
and the improved-Kennedy methods outperformed the RTK
solutions, and the EVA method provided the best results in
this experiment. Finally, both the improved version of the
Kennedy method and the EVA method were applied to a network
in equatorial South America with baselines of more
than 1,770 km, and during local noon. Under this tough scenario,
the EVAmethod showed a clear advantage for all components
of velocity and acceleration, yielding better and more
robust results. |