Aerospace and Electronic Systems Magazine August 2017 - 20

Flight Data Assessment of Tightly Coupled PPP/INS

ACKNOWLEDGMENT
This work was supported through a subcontract with the California
Institute of Technology JPL. The authors thank NOAA NGS for
providing the flight data sets.

REFERENCES
[1]
[2]

[3]

Figure 9.

Cumulative distribution of attitude error of the real-time forward-filter
PPP solutions with INS. Errors are calculated with respect to the onboard real-time NovAtel SPAN estimates as a reference solution.

[4]

if the solutions is intermittently lost midflight because of the loss
of carrier-phase lock, which may occur, for example, during a large
aircraft bank. As such, the performance and sensitivity of tightly
coupled PPP/INS have been presented using two long-baseline
flight data sets to demonstrate the benefits of tight INS with respect to improving the convergence properties of real-time PPP. In
particular, the integrated INS solutions have been shown to speed
up convergence, leading to a reduction in positioning error that
exceeds 30%. Furthermore, the improved solution convergence offered by tight INS has been demonstrated by comparing the realtime estimated zenith tropospheric delay to a postprocessed reference and by comparing the real-time estimated carrier-phase biases
to their estimated steady-state values.
To offer additional insight, this article has presented the sensitivity of the benefit of using tightly coupled PPP/INS while other
typical PPP error sources are reduced through other means. For example, the sensitivity of PPP/INS when using various latency GPS
orbit and clock products (i.e., GPS broadcast orbits and clocks, realtime GDGPS orbits and clocks, and JPL final postprocessed GPS
orbits and clocks) has been presented. From this sensitivity study, it
has been shown that a tight-PPP/INS filters that use real-time GNSS
orbit and clock products, which are known to have centimeter-level
to decimeter-level errors with respect to final orbit and clock products, is able to outperform the positioning solutions that are based
upon GPS-only PPP that uses final postprocessed orbit and clock
products. A similar sensitivity study has been presented with respect to the fidelity of the PPP filter's tropospheric delay modeling
approach. In this case, it has been demonstrated that the benefit of
tightly coupled INS remains consistent, irrespective of the fidelity
of tropospheric delay estimation approach that is adopted.
In summary, for airborne applications that require accurate
real-time solutions and robustness to signal outages, cycle slips,
etc., tightly coupled INS is an important way to compensate for
the slow convergence properties of real-time PPP, and this benefit
remains important even as other PPP error sources, namely, orbit
and clock errors and tropospheric delay errors, are reduced.

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AUGUST 2017

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