A method of determining an air data parameter for an aircraft propelled by at least one engine, the method comprising: emitting a first coherent light pulse into a first target volume aft of the aircraft within an engine exhaust flow of the aircraft; receiving a first backscatter light return from the first light pulse interacting with the first target volume; determining a first air data parameter based on the first backscatter light return and at least one of an engine parameter indicative of a condition of the engine and an aircraft parameter indicative of a state of the aircraft; and outputting the first air data parameter to a consuming system of the aircraft; the method further comprising emitting a second coherent light pulse into a second target volume forward of the aircraft; receiving a second backscatter light return from the second coherent light pulse interacting with the second target volume; determining a second air data parameter based on the second backscatter light return; and outputting one of the first air data parameter and the second air data parameter to the consuming system of the aircraft based on a comparison of an intensity of the second backscatter light return to a light intensity threshold; and wherein outputting one of the first air data parameter and the second air data parameter includes outputting the first air data parameter to the consuming system of the aircraft when the intensity of the second backscatter light return is less than the light intensity threshold, and wherein the first air data parameter is a first airspeed of the aircraft and the second air data parameter is a second airspeed of the aircraft. emitting a first coherent light pulse into a first target volume aft of the aircraft within an engine exhaust flow of the aircraft; receiving a first backscatter light return from the first light pulse interacting with the first target volume; determining a first air data parameter based on the first backscatter light return and at least one of an engine parameter indicative of a condition of the engine and an aircraft parameter indicative of a state of the aircraft; and outputting the first air data parameter to a consuming system of the aircraft; the method further comprising emitting a second coherent light pulse into a second target volume forward of the aircraft; receiving a second backscatter light return from the second coherent light pulse interacting with the second target volume; determining a second air data parameter based on the second backscatter light return; and outputting one of the first air data parameter and the second air data parameter to the consuming system of the aircraft based on a comparison of an intensity of the second backscatter light return to a light intensity threshold; and wherein outputting one of the first air data parameter and the second air data parameter includes outputting the first air data parameter to the consuming system of the aircraft when the intensity of the second backscatter light return is less than the light intensity threshold, and wherein the first air data parameter is a first airspeed of the aircraft and the second air data parameter is a second airspeed of the aircraft. <EOS>