Variational bias correction for Mode-S aircraft derived winds

Abstract

A variational bias correction (VarBC) technique is proposed within the three-dimensional variational (3D-Var) assimilation system of the Météo-France convective scale model AROME to remove biases present in horizontal wind components derived from aircraft Mode-S data. A set of two predictors derived from the geometry between ground and air speeds has been chosen in order to correct the aircraft speed and heading. Data collected from a set of 8 ADS-B antennas located over France for two periods in 2018 (April and October) have been used to assess the VarBC. Thanks to the availability of anchoring data (radiosoundings, AMDAR aircraft reports), the adaptive bias correction scheme is very efficient for improving the quality of Mode-S derived winds to a level that is similar to those from AMDAR and Mode-S bias corrected by the KNMI. The heading bias correction is the most important one in order to reach background departure values around 2.5 m/s. The behaviour of the VarBC is assessed more precisely for specific aircraft where its capacity to adapt to rapid changes due for example to aircraft maintenance is demonstrated. Moreover, when examining separately predictors for both wind components they appear to converge most of the time towards similar speed and heading corrections. Additional quality controls have allowed to reach background departure values of 2.2 m/s while increasing by a factor of ten the number of aircraft observations to be assimilated in the AROME-France domain.

Keywords:

• aircraft winds
• variational bias correction
• data assimilation
• Mode-S derived data

Acknowledgments

The technical support from F. Guillaume (Météo-France/CNRS) has been very useful during the course of the study. Olivier Henry (Météo-France) provided the plots of magnetic declination difference (Figure 2). S. de Haan (KNMI) is acknowledged for his pionnering work on Mode-S data in the NWP context and for providing a MUAC dataset for our own evaluations. Finally, the UKMO software has been essential to compute derived winds from BDS registers collected by Météo-France antennas with the help of Olivier Traullé, Guillaume Gamelin, and Jean-Marc Lefèvre (Météo-France) to insure data production.

Notes

1 Raw data: non-meteorological quantities recorded onboard the aircraft.

2 See Section 3.1 for active data definition.

3 See Section 3.1 for passive data definition.