Focussed beam reflectance measurement is a technique that shows some promise as a technique for the online characterisation of floc size and structure. A scanning laser is focused into process fluid and the reflected intensity is measured as a function of time. This light intensity signal is normally processed to return chord length measurements which contain combined information on particle size and shape. This study shows that the unprocessed signal can be expected to encode information about the texture of the particle being scanned in addition to size and shape. For the purpose of characterising floc structure, a power law exponent can be recovered from the Fourier transform of the unprocessed signal and this in turn is related to the mass fractal dimension of flocs. The technique is demonstrated with computer generated floes and with flocculated polystyrene latex of a primary particle size of 5 mu m and a mass fractal dimension of D-m = 2.5 as determined by the volume obscuration method. Results obtained through simulation studies into scanning of computer generated floes demonstrate that a correlation exists between the power law exponent and the mass fractal dimension. Loose structures with mass fractal dimension of D-m = 1.64 returned a power law exponent of beta = -1.77 whilst a tighter structure of mass fractal dimension of D-m = 2.34 returned a power law exponent of beta = - 1.92. Results obtained through scanning of polystyrene latex floes of mass fractal dimension of D-m = 2.49 returned a power law exponent of beta = -2.00 which appears not to be in quantitative agreement with the simulation results. (c) 2005 Elsevier B.V. All rights reserved.