High Precision Kinematic GNSS Observations Up to 50 S/s for Airborne Gravimetry

Andrea Stürze, Gerd Boedecker

Abstract:	The paper is dealing with GNSS positioning accuracy for airborne gravimetry under highly dynamic conditions. Usually, airborne gravimetry makes use of twin engine aircraft and (stabilized) platform scalar gravimeters. Our focus is on utilizing one engine light aircraft at low flight altitudes for strapdown airborne vector gravimetry and therefore high sampling rate high precision positioning; the attitude problem is discussed elsewhere. A 50 S/s GNSS sampling means 1 observation per ~1m flight trajectory, therefore receivers capable of up to 100 S/s are essential. Also, in view of time differentiation, low noise is essential. Hence, two receivers with appropriate specifications have been acquired, Javad Navigation Systems’ single frequency board JGG100 and Novatel’s dual frequency board OEM4-G2 and test flights were conducted. Additional tests were executed on a test bed with controlled dynamics and true heights to ±0.02 mm at 50 S/s under varying conditions and using a reference station. The GNSS observations were processed along the sequence: i. Position determination using Trimble Total Control software based on double difference method. ii. Heights referred to ground truth. iii. Modeling of deterministic parts of reduced height values by polynomial plus potential periodic terms. This step also permits insights to multipath phenomena. iv. “Kriging” for outlier substitutions. v. EARMA modeling. The EARMA model is an ARMA model complemented by white observation noise. The analysis of the residual heights by EARMA models of different orders (p,q) permits the assessment of the performance of the receivers under different dynamic conditions and using different receiver parameter settings (loop orders and bandwidths). Hence it enables us to tune the receivers for given dynamics depending on aircraft type and air turbulence. The L1 accuracy specifications for the Novatel receiver could be confirmed The EARMA modeling input uses height values resulting from mixing several receiver channels and including environmental noise components. For this reason, it provides a deep insight into the total positioning process performance. However, a system identification of individual receiver channels is not possible due to the composite data.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	1382 - 1391
Cite this article:	Stürze, Andrea, Boedecker, Gerd, "High Precision Kinematic GNSS Observations Up to 50 S/s for Airborne Gravimetry," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 1382-1391.
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