In this subtitle the following words have the meanings indicated. “Airport” means any airport licensed by the Administration. “Cumulative noise exposure” means a calculated or measured value for the exposure to aircraft noise in a 24-hour period at a given location. “Impacted land use area” means an area within a noise zone occupied by a land use with a limit for cumulative noise exposure that is less than the actual cumulative noise exposure in that area. “Limit for cumulative noise exposure” means the maximum cumulative noise exposure for a given land use that is compatible with that land use. “Noise zone” means an area of land surrounding an airport within which the cumulative noise exposure is equal to or greater than the lowest limit for cumulative noise exposure established by the Executive Director. “Substantially alter” includes reconstruct, rebuild, replace, or substantially change or repair.