Apparatus for detecting an anomaly, (e.g the presence of a hydrocarbon seep) at or near a water or land surface comprises means for generating a beam, preferably a pulsed beam, of primary light radiation, preferably ultra-violet light, and directing the beam towards the surface. The beam is sufficiently intense and of such a spectral composition that the beam causes the anomaly, if present, to emit secondary light radiation. The apparatus also comprises means for collecting the secondary light radiation, or means for collecting solar induced secondary light radiation, spectral analysis means for analysing the spectrum of the secondary radiation, and a high resolution, multi-element digitising detector for recovering the analysed secondary radiation. The detector has a plurality of detection channels positioned across the spectrum of the basckscattered primary radiation and emitted secondary radiation, the channels being software configurable and under the control of a digitally addressable computer-operated controller. The concentration of used channels across the plurality of channels is adjustable and increasable in the regions of the spectrum of greatest interest and decreasable in the regions of least interest.