1. A method of monitoring a subsea pipeline system connecting one or more wells to a floating production system, wherein the subsea pipeline system is at least partially flexible, the method comprising: installing a continuous optical fibre distributed sensor as part of the subsea pipeline system, using the continuous optical fibre distributed sensor to provide a distributed measurement of temperature, vibration, pressure or strain, or any combination thereof along at least a part of the subsea pipeline system; making a discrete measurement of the flow rate in the subsea pipeline system or at the surface on the floating production system; using a computer-based program to: segment the at least part of the subsea pipeline system into a plurality of pipeline system sections; plot the distributed measurement of temperature, vibration, pressure or strain with the plurality of pipeline system sections; combine the distributed measurement for the plurality of pipeline system sections and the discrete measurement to predict the actual condition of the fluid or the subsea pipeline system; feed-back a system model with the distributed measurement of temperature, vibration, pressure or strain; use the system model to predict behavior of the subsea pipeline system; and use the predicted behavior of the subsea pipeline system to determine operation control parameters of the subsea pipeline system, including heating zones of the subsea pipeline system, shut-down/cool-down periods, choke positions and tension in anchor chains.