Innovative calibration methods for strapdown airborne vector gravimetry aboard HALO

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Strapdown airborne vector gravimetry (SAVG) is the determination of the three-dimensional Earth's gravity field from an aircraft using a strapdown inertial measurement unit (IMU).Compared to the classical stabilized-platform spring gravimeters, which are the predominant instrumentation for airborne gravimetry, SAVG offers several advantages:- Strapdown IMUs yield considerable savings in terms of dimensions, weight, power-consumption, and costs. In addition, no operator is required onboard the aircraft.- SAVG enables the determination of deflections of the vertical (vector gravimetry).- Results from recent SAVG campaigns indicate that SAVG can be more robust against turbulence and during manoeuvres.The Physical and Satellite Geodesy group at the Technische Universität Darmstadt (TUDa) proposes to participate in the ANTHALO-BI campaign (cf. separate mission proposal) in scope of this project, providing the instrumentation and an on-site operator. For the SAVG part, the ANTHALO-BI campaign can be seen as scientific feasibility study for the larger ANTHALO Antarctica campaign (scheduled for 2020/21). For both campaigns, the SAVG experiment of TUDa shall contribute the following:- Scalar gravity measurements at the 1 mGal-level (levelled: 0.5 mGal),- deflections of the vertical (DoV), aiming at 0.5 arc seconds precision, and- high-precision, high-rate attitude and heading outputs (expected precision: 3 and 20 arc seconds, respectively).A crucial part of SAVG is an apropiate modelling of the inertial sensor errors. Recent work at TUDa showed, that offline IMU calibration methods can significantly improve the overall SAVG performance, yielding scalar gravity at the level of 1.0-1.4 mGal for recent SAVG campaigns (0.5-0.6 mGal after applying a cross-over adjustment). This is an excellent performance, reaching the accuracy level of the classical spring gravimeters.A particular challenge for SAVG in view of the ANTHALO-BI and ANTHALO campaigns is the inertial sensor stability over long ranges. Therefore, the main objective of this project is the design and evaluation of novel calibration techniques tailored to long-range SAVG, aiming at a higher long-term stability, and also at a greater robustness in dynamic situations, as during manoeuvres and strong turbulence.For this, extended parametric error models including bias, scale factors, and sensor cross-couplings, each as a function of the sensor temperature will be taken into consideration, as well as sample-based (non-parametric) error models. For the evaluation, existing SAVG data sets, which are or will become available to TUDa will be used in addition to the ANTHALO-BI strapdown data sets.This basic research is expected to be a step towards establishing strapdown airborne gravimetry as the default method for airborne gravimetry in the future.