Calculating model for equivalent consumption efficiency in polarization measurement system of oil-spilled on the sea

•Polarization characteristic of the oil film and seawater is observed.•Analyze the transmission path of polarized light in the samples.•A parameter called equivalent consumption efficiency (ECE) is defined.•The polarization information of oil film and water has obvious difference by ECE.•Experiments on Mueller matrix, depolarization coefficient and ECE prove our model.