A sensor apparatus includes a cylindrical sensor window defining an axis and an air nozzle positioned at one end of the sensor window and shaped to direct airflow in a direction parallel to the axis across the sensor window. The air nozzle extends circumferentially relative to the axis around the sensor window. The nozzle is formed of an inner edge and an outer edge each extending circumferentially relative to the axis around the sensor window. The inner edge is circular with a radius at least as great as an outer radius of the sensor window. The outer edge includes a first portion with a semicircular shape with a radius smaller than the outer radius of the sensor window and a second portion that extends circumferentially relative to the axis around the sensor window from the first portion to the first portion at a constant radial distance from the inner edge.