While calculating the Point Ahead Angle we work with Tangential Velocity vector component and to calculate the Doppler shift i.e changes in frequencies, we work with Radial Velocity Vector component.
Correct me if I am wrong, we calculate radial and tangential velocity like the picture above of it (Figure 1). But is this correct way to find out the radial velocity of both satellite while calculating the Doppler shift in changes in frequencies, because we also need to find out the relative radial velocities of both satellite, or the picture below (Figure 2) this is the correct one? where radial velocity component is just opposite of the line of sight of the both satellite.
Because, I looked at the picture below of it (Figure 3) where radial component Vp is as with Line-of-sight of both satellite, then I become confused how should I put my vector components?
Any sort of leads would be much helpful. Please let me know what I am missing here. Thanks in advance.