Abstract: 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 digitizing detector for recovering the analyzed secondary radiation.