Object Tracking From Aircraft

Hello there,
I am working on object tracking from aircraft. There is Kalman Filter in OpenCV, I am trying to revise it as Extended Kalman Filter. I have a problem at this point. Normally I need to include state model jacobian instead of state transition matrix. Likewise, instead of the measurement matrix, I use its jacobian matrix, but I have a problem with this. I’m having trouble creating a jacobian matrix because the model of the system is not clearly specified in the code. Has anyone worked on this before? What path should I follow?