A measurement apparatus comprising: a plurality of first electrodes comprising a linear array of first electrodes extending in a direction of flow of a material, each of the first electrodes being spaced apart by at least a first predetermined spacing; a plurality of second electrodes comprising a linear array of second electrodes extending in the direction of flow of the material, each of the second electrodes being spaced apart by at least a second predetermined spacing less than the first predetermined spacing, wherein the linear array of second electrodes is separate from the linear array of first electrodes; an energisation source arranged to energise at least one of said first electrodes so as to cause an electric field to be established between at least one pair of said first electrodes, and to energise at least one of said second electrodes so as to cause an electric field to be established between at least one pair of said second electrodes; a monitor arranged to monitor an electrical parameter at at least one of said first electrodes in response to said energisation of at least one of said first electrodes and to monitor an electrical parameter at at least one of said second electrodes in response to said energisation of at least one of said second electrodes, wherein each of the plurality of first electrodes and the plurality of second electrodes is switchably connected to the energisation source and the monitor; and a controller arranged to generate data indicative of a property of the material within a first region extending a first distance from the first electrodes, and to generate data indicative of a property of the material within a second region extending a second distance, less than the first distance, from the second electrodes, based upon said monitored electrical parameters. a plurality of first electrodes comprising a linear array of first electrodes extending in a direction of flow of a material, each of the first electrodes being spaced apart by at least a first predetermined spacing; a plurality of second electrodes comprising a linear array of second electrodes extending in the direction of flow of the material, each of the second electrodes being spaced apart by at least a second predetermined spacing less than the first predetermined spacing, wherein the linear array of second electrodes is separate from the linear array of first electrodes; an energisation source arranged to energise at least one of said first electrodes so as to cause an electric field to be established between at least one pair of said first electrodes, and to energise at least one of said second electrodes so as to cause an electric field to be established between at least one pair of said second electrodes; a monitor arranged to monitor an electrical parameter at at least one of said first electrodes in response to said energisation of at least one of said first electrodes and to monitor an electrical parameter at at least one of said second electrodes in response to said energisation of at least one of said second electrodes, wherein each of the plurality of first electrodes and the plurality of second electrodes is switchably connected to the energisation source and the monitor; and a controller arranged to generate data indicative of a property of the material within a first region extending a first distance from the first electrodes, and to generate data indicative of a property of the material within a second region extending a second distance, less than the first distance, from the second electrodes, based upon said monitored electrical parameters.