Research On Image Smear And Distortion Compensation In Long Focus Slope Aerial Camera

As one of new discipline developed in the20th century, aerial imaging andmeasurement techniques are used to detect ground telemetry and scene informationby airborne optical system and optical coupling device. It is used in pre-war andpost-war military strike military reconnaissance assessment. The significance is veryimportant for the development of our defense. The differences between spaceborneoptical equipment and aerospace equipment are large aircraft maneuverability, flightvibration and attitude instability which cause remote sensor axis to sway. Axis cannot point to a fixed target in the exposure time, and so the same scene image indifferent CCD pixels. That produces smear and distortion resulting in a lower flightresolution.Although shock absorbers are equipped between the aerial camera and carrieraircraft, generally the effect of passive damping is obvious for high-frequencydisturbance, but unobvious for low-frequency disturbance. The isolation requirementof long focal length optical system cannot be meeted. For smear problem, this papernot only analyzes the causes of smear and builds a mathematical model, but alsoanalyzes quantitatively the effects of smear on modulation transfer function. Fordistortion problem, this paper builds a mathematical model to indicate therelationship betweenlight speed, altitude, target angle and pitch axis compensation speed, and analyzes the effect of image distortion on the outside disturbance. Thedynamic and steady-state performance indicators and the robust of pitch axis controlsystem are educed from model establishment and parameter analysis.For sinusoidal disturbance, dynamic compensator is built and control law ofdisturbance rejection is got, then the optimal solution for the presence of disturbancerejection controller resistance is proved out. The law of LQR without interferefeedback, LQR with interfere feedback algorithm and dynamic feedback interferencefeedback are compared by simulation experiments. The results show that thedynamic feedback algorithm for external sinusoidal perturbation has a strong rubust.The issue of visual axis motion compensation comes down to the issue ofapproximate optimal output tracking. Dynamic compensator is built and control lawof disturbance rejection is got by solving matrix. State feedback law, feedforward-feedback method and dynamic feedback algorithms were compared throughsimulation. The results show that external sinusoidal perturbation is minimal by thedynamic feedback algorithm.The effects of smear and distortion on synchronization of the space-time areanalyzed in this paper. Three methods of line signal are introduced:1. based onencoder subdivision method;2. based on Hilbert-Huang Transform method;3.encoders and gyro optimization method. The applicability of each method andinterference effects are analyzed.When the pitch moves0.8°/s,0.2Hz sinusoidal, the dynamic compensationmethod depresses the standard output to0.0688°/s by signal interference. Thedetector can distinguish58.4lp/mm; when the camera image under the magnitude ofthe vibration input2G, the dynamic compensation algorithm depresses the remainsof pitch axis velocity to0.14°/s. The detector can distinguish43.89lp/mm. Whenvibration table vibrates0.5G, the signal generator output of the robust of encoder isnot the magnitude. The detector can distinguish58.4lp/mm. When vibration tablevibrates2G, the method can not suppress interference. But under2G vibrations, theoutput of gyro significantly reduces by Hilbert-Huang Transform, which weakens 0.12°/s. The transfer of the signal line frequency range narrows to2KHz. Thefiltering effect is very obvious. The detector can distinguish49.3lp/mm. Theoptimized method improves the signal to external vibration environment adaptability,robustness, and real-time performance. It will not appear on the image compression,tension phenomenon and smear phenomenon. The detector can distinguish55.2lp/mm. When flight altitude is15,863meters, railway sleepers (ties spacedabout0.3m) can be distinguished by flight test. As the focal length is1.5m, theresolution is better than45lp/mm.The work shows that the method in this paper compensates effectively theinterference caused by image smear and distortion. It is important to improve theimage quality of the camera.