| abstract |
A system (1000) comprising: an inflatable membrane (1002) having a surface; a supply (1016) of a medium (1018) that absorbs more a first wavelength of light than a second wavelength of light, wherein the supply is coupled to the inflatable membrane to allow selective input of the medium to the membrane inflatable; a light source (1020) arranged to illuminate the inner surface of the inflatable membrane; a sensor (1024) located within the inflatable membrane, arranged to measure an intensity of the first wavelength and an intensity of a second wavelength reflected at a location on the surface, when said surface is illuminated by the light source ; and a processor (1026) programmed to determine a thickness of the medium, in a direction of the location on the surface, along the optical path of return to a particular location of the sensor, based on a function of the intensity of the first wavelength and the intensity of the second wavelength. |