The Noise of IMU in EKF

Hello guys,

 When I learn the EKF of px4----->ekf_att_pos_estimator, I have some questions.

 I know the  dax_b、day_b、daz_b、dvx_b、dvy_b and dvz_b are IMU 's noise,  but  can I  treat  dax_b、day_b、daz_b 、dvx_b、dvy_b and dvz_b as daxCov、dayCov、dazCov、dvxCov、dvyCov and dvzCov?

  I find  d--Cov  has  initial value, but the initial value of  d--_b  is 0. 

  Can you tell me  the difference or same of them?

Thank you.

@Paul_Riseborough can you tell me?

Please provide Github links to the specific lines in code. I do not have the time to search through eh code for the variables you are referring to. 383 lines ----->void AttPosEKF::CovariancePrediction(float dt)

*_b are bias states which are initialised to zero. *Cov are state covariances.

I know it. *_b are always zero in ekf process???

No, if you had looked further down you would see they are copied form the states at line #449