Multiple spectrum channel, multiple sensor fiber optic monitoring system

A multiple sensor fiber optic sensing apparatus and method for determining physical parameter down a wellbore. It includes an optical fiber having a plurality of first fiber optic sensors and a plurality of second fiber optic sensors deployed along its length. In response to an interrogating pulse, the first fiber optic sensors generate responses in a first optical spectrum window, and the second fiber optic sensors generate responses in a second, different optical spectrum window. The responses in the first optical spectrum window are measured in a first optical spectrum channel, and the responses in the second optical spectrum window are measure in a second, different optical spectrum channel and provide indications of more than one parameter. The bandwidth of the first window is narrower than the second. The first sensors may be fiber gratings and may measure temperature whilst the second sensors may be polarimetric sensors for measuring pressure. Signals received may be selected and processed based on travel time of light pulses through the system. Amplification and spectrum analysis techniques are used.