What was found
ABOUT 5 TO 10 MINUTES IN CRUISE FLIGHT AT FL340 I NOTICED WITH MY OVERHEAD SCAN THAT THE GREEN HYD QUANTITY WAS MID WAY IN THE YELLOW. I THEN LOOKED AT THE GREEN HYDRAULICS ON THE ECAM AT IT SHOWED 440 PSI. FROM THERE IT WAS A FEW MINUTES AND WE GOT THE ECAM NOTIFICATION AND THE QUANTITY NEEDLE WAS AT RED DOT, WITH CORRESPONDING LOW PRESSURE. WE TURNED THE GREEN PUMPS OFF IN ABOUT 30 SECONDS AND COMPLIED WITH ALL ECAM AND QRH PROCEDURES EXCEPT THE LANDING GEAR GRAVITY EXTENSION QRH PROCEDURE WHILE AT CRUISE FLIGHT. WE CALLED RAMP AND LET THEM KNOW WE WERE INBOUND AND WE WILL BE AN EMERGENCY AIRCRAFT AND STOPPING AND SHUTTING DOWN ON RW 18R AND NEEDING A TOW TO THE RAMP. WE DECLARED AN EMERGENCY WITH CENTER FOR THE DESCENT WITH NORMAL GRAVITY EXTENSION AND LANDING. FOUND GREEEN HYD PRESSURE TRANSMITTER LEAKING.REMOVED AND INSTALLED GREEN HYDRAULIC PRESSURE TRANSMITTER PER AMM 29-11-12-04, QTY AND PRESS WITHIN LIMITS, OPS CKS NORMAL, NO LEAKS NOTED AT THIS TIME.