Bottom backscattering strength versus grazing angle was measured in a deep water abyssal plain in the Mediterranean Sea. The measurements were made with a narrow‐band 365‐Hz‐omnidirectional towed source and a towed linear array. The measuring method takes advantage of the receiving array beamforming capability to accurately discriminate returns at given grazing angles from other interfering returns. The approximations to the evaluation of the backscattering areas are analyzed and discussed. The results indicate that for high to medium grazing angles a specular (facet) reflection model is appropriate whereas for medium to small grazing angles the data follow approximately a Lambert's law relationship. The crossover angle depends on signal type and geometries specific to the experiment. The measured data are compared to previously reported measurements.