A method of monitoring the accumulation of matter on an external surface of an aircraft, comprising the steps of: applying varying electric fields to the aircraft surface; a sensor monitor receiving a time-series of measurements of a temperature of the aircraft surface and a phase and a magnitude of a current induced in an electric field sensor of an electric field sensor unit from the varying electric fields, the electric field sensor unit being mounted proximate the aircraft surface, the time-series of the measurements varying in accordance with an instantaneous accumulation of matter on the aircraft surface; and the sensor monitor generating an assessment of an accumulation of the matter on the aircraft surface from a correlation of the time-series of the measurements with at least one predetermined matter accumulation profile, each said predetermined matter accumulation profile comprising a corresponding time-series of current phase, current magnitude and temperature measurements, wherein the electric field sensor comprises: an insulating substrate; a plurality of non-contacting electrodes disposed on the substrate and extending parallel to each other on the substrate, each said electrode having an electrode end, the electrodes comprising a plurality of first non-contacting electrodes and a plurality of second non-contacting electrodes interleaved and non-contacting with the plurality of first electrodes, wherein the plurality of first electrodes extend across the substrate from one end of the substrate, and the plurality of second electrodes extend across the substrate from an opposite end of the substrate; and a plurality of conductors coupled to the electrodes and extending transversely through the substrate, wherein the conductors comprise a plurality of first conductors and a plurality of second conductors, wherein each of the first conductors are coupled to the electrode end of a respective one of the first electrodes proximate the one substrate end, and each of the second conductors are coupled to the electrode end of a respective one of the second electrodes proximate the opposite substrate end. applying varying electric fields to the aircraft surface; a sensor monitor receiving a time-series of measurements of a temperature of the aircraft surface and a phase and a magnitude of a current induced in an electric field sensor of an electric field sensor unit from the varying electric fields, the electric field sensor unit being mounted proximate the aircraft surface, the time-series of the measurements varying in accordance with an instantaneous accumulation of matter on the aircraft surface; and the sensor monitor generating an assessment of an accumulation of the matter on the aircraft surface from a correlation of the time-series of the measurements with at least one predetermined matter accumulation profile, each said predetermined matter accumulation profile comprising a corresponding time-series of current phase, current magnitude and temperature measurements, wherein the electric field sensor comprises: an insulating substrate; a plurality of non-contacting electrodes disposed on the substrate and extending parallel to each other on the substrate, each said electrode having an electrode end, the electrodes comprising a plurality of first non-contacting electrodes and a plurality of second non-contacting electrodes interleaved and non-contacting with the plurality of first electrodes, wherein the plurality of first electrodes extend across the substrate from one end of the substrate, and the plurality of second electrodes extend across the substrate from an opposite end of the substrate; and a plurality of conductors coupled to the electrodes and extending transversely through the substrate, wherein the conductors comprise a plurality of first conductors and a plurality of second conductors, wherein each of the first conductors are coupled to the electrode end of a respective one of the first electrodes proximate the one substrate end, and each of the second conductors are coupled to the electrode end of a respective one of the second electrodes proximate the opposite substrate end. an insulating substrate; a plurality of non-contacting electrodes disposed on the substrate and extending parallel to each other on the substrate, each said electrode having an electrode end, the electrodes comprising a plurality of first non-contacting electrodes and a plurality of second non-contacting electrodes interleaved and non-contacting with the plurality of first electrodes, wherein the plurality of first electrodes extend across the substrate from one end of the substrate, and the plurality of second electrodes extend across the substrate from an opposite end of the substrate; and a plurality of conductors coupled to the electrodes and extending transversely through the substrate, wherein the conductors comprise a plurality of first conductors and a plurality of second conductors, wherein each of the first conductors are coupled to the electrode end of a respective one of the first electrodes proximate the one substrate end, and each of the second conductors are coupled to the electrode end of a respective one of the second electrodes proximate the opposite substrate end.