Article Exploring delay causes of road construction projects in Egypt

It seems you didn't understand my question.

It seems that the vertical delays are VTECs observed over IPPs surrounding an IGP . These vTECs values are gathered in the observation vector I_v,ipp and needs to be developed in planar-fit expansion using a local Cartesian frame whose origin is at the IGP and whose x-axis aligns with the East direction at the IGP and whose y-axis aligns with the North.

I have solved for Vertical delay as per the equations given in the Appendix D.

But what is the bias error ?

sigma_bias_i,j is the measurement noise corresponding to the pair satellite(i)-receiver(j). The bias is the difference between planar fit estimator's expected value over IPP (sat i and receiver j) and its observed vTEC value.

thank you so much sir