A target scene generator for generating a target image, for use in testing pulsed laser sensing apparatus for incorporation in a flying object, the generator comprising: an array of pixel elements, detector means for detecting operation of a pulsed laser, and light source means for generating at least one pulse of light representing a returned laser pulse, characterised in that the generator further comprises: a reconfigurable optical waveguide network selectively coupling said light source means to respective said pixel elements, and a controller means being operative to selectively reconfigure said waveguide network, whereby to present to selected pixel elements said at least one pulse of light and said controller means being operative so that said one pulse is provided with selected time delay characteristics such that light emitted from said pixels represent the returned optical signals from a target illuminated by said apparatus, the network including a plurality of delay elements providing differing delays and said controller means being arranged to selectively incorporate the delay elements in light paths to each pixel element from said laser source means, to represent pulse spreading effects or variations in signal time delay within a scene. an array of pixel elements, detector means for detecting operation of a pulsed laser, and light source means for generating at least one pulse of light representing a returned laser pulse, characterised in that the generator further comprises: a reconfigurable optical waveguide network selectively coupling said light source means to respective said pixel elements, and a controller means being operative to selectively reconfigure said waveguide network, whereby to present to selected pixel elements said at least one pulse of light and said controller means being operative so that said one pulse is provided with selected time delay characteristics such that light emitted from said pixels represent the returned optical signals from a target illuminated by said apparatus, the network including a plurality of delay elements providing differing delays and said controller means being arranged to selectively incorporate the delay elements in light paths to each pixel element from said laser source means, to represent pulse spreading effects or variations in signal time delay within a scene. a reconfigurable optical waveguide network selectively coupling said light source means to respective said pixel elements, and a controller means being operative to selectively reconfigure said waveguide network, whereby to present to selected pixel elements said at least one pulse of light and said controller means being operative so that said one pulse is provided with selected time delay characteristics such that light emitted from said pixels represent the returned optical signals from a target illuminated by said apparatus, the network including a plurality of delay elements providing differing delays and said controller means being arranged to selectively incorporate the delay elements in light paths to each pixel element from said laser source means, to represent pulse spreading effects or variations in signal time delay within a scene.