Long wave infrared detectors are often employed in airborne infrared early warning systems, which are often contaminated the with heavy nonuniformity noises. To correct the nonuniformity and compensate the nonlinearity of detectors, a nonuniformity correction method is proposed. The observation model of radiance nonuniformity is introduced. The correction coefficients are deduced in theory with the reference of a blackbody and a gradient scene. And, an outfield experiment with a proof-of-concept camera is performed to detect the airliners. Experimental results show that the peak value of local standard deviation of the corrected image decreases from 8.57 to 2.39, compared with the two-point correction method based on a blackbody. For the target of Airbus A319 from 50.64 km away, the signal-to-clutter ratio rises from 4.87 to 11.22. The proposed method can decrease the local standard deviation effectively, which has a significant contribution to airborne infrared early warning systems.