High impedance op-amp using guard ring to drive a shield
By buffering the shield with each input, it reduces ingress of unwanted signals and reduces the capacitance on the coaxial cable as the shield tracks the center conductor signal.  Improved immunity is achieved further with triaxial or double shielded cables.

In the case of coaxial a 1MOhm drain wire provides ground reference to the source to shunt higher impedance low frequency stray fields.  This is done on the outer shield for the triaxial cable on the source side.