Smoothing GPS carrier phase double differences using inertial measurements for high performance applications

Abstract

This paper will describe an enhancement to the GPS double difference carrier phase measurements on a single airborne platform by smoothing them with inertial measurements while preserving the dynamic bandwidth. This enhancement will reduce the impact of carrier phase multipath and carrier phase noise on baseline determination between multiple antennas on an aircraft when in flight. This type of measurement system has numerous applications where platform pointing and relative body motion must be determined at the mm-level for applications such as sensor stabilization, Synthetic Aperture Radar, long range RADAR (i.e. angle-of-arrival measurements). Lower noise levels (mm-level and below) enable more performance to the stabilized system such as increased aperture for longer range, operation at higher frequencies, and more image resolution. The focus of this paper will be on a technique to provide this enhanced performance for these various applications using the available navigation systems. Additionally, this type of smoothing can effectively remove the additional noise induced by carrier phase measurement differencing. The noise level of a double or triple difference can be reduced below that of the raw measurement. A complimentary synthesized double difference quantity with ultra-low-noise characteristics will be used to smooth the GPS carrier phase double difference measurements without losing dynamic bandwidth since it follows the airborne dynamics. Flight test data will be presented to demonstrate the performance improvement in the midst of aircraft dynamics. Results will show that the noise reduction follows the theoretical prediction.

Carrier phase multipath error characterization and reduction in single aircraft relative positioning

“…It is important to note that the predicted double-difference might contain some error due to imperfect frame calibration and baseline survey as described in (Dickman and Bartone 2008). Therefore, these residuals are not shown to be a zero-mean process.…”

“…In addition, the NL measurement combination exhibits a statistical improvement due to a reduction in the rangedomain noise variance. The NL measurement can then replace the traditional single-frequency double-differenced carrier phase (DDCP) (Cosentino and Diggle 1996;Dickman and Bartone 2008). Typically a metric of of the respective wavelength or reduction of all error sources to about 2.5 mm for the NL solution.…”

“…11. The single-frequency (L1) DD prediction error shown in the first subplot was calculated by subtracting a DD prediction from the DD measurement (Dickman and Bartone 2008). The DD residual in the first subplot contains unmodeled errors such as multipath as is apparent from the DD variation corresponding to the same fading pattern seen in the CNR data.…”

The Inertial Attitude Augmentation for Ambiguity Resolution in SF/SE-GNSS Attitude Determination

“…In 2004, to resolve the problems existing in the GNSS attitude determination application when low-end receivers are used, Wang introduced the gyro-rate measurement into the attitude integration filtering and improved the performance of GNSS attitude determination system [ 17 , 18 ]. In 2008, Dickman studied how to use the inertial measurement to depress the low frequency errors contained in GNSS carrier phase measurements [ 19 ], but this method requires a high IMU measurement precision, hence, it is not applicable to GNSS attitude determination.…”