MODELING THE PERFORMANCE OF A HIGH-SPEED SCAN MIRROR FOR AN AIRBORNE LINE SCANNER

The Digital Imaging and Remote Sensing Laboratory at the Rochester Institute of Technology is developing a new airborne multi-spectral imaging scanner. One of the most critical components of the scanner system is the scan mirror assembly. The scan mirror must satisfy at least two basic requirements: (1) optical image quality: the image blur caused by deformation of the mirror surface should not exceed the detector size, and (2) mechanical stability: the scan mirror assembly must be dynamically balanced to prevent vibration due to centrifugal force. Due to the large size (6-in. diameter) and high rotation speed (4800 rpm), these two requirements are difficult to meet at the same time. We present a modeling approach for evaluation of mechanical design alternatives using image quality metrics. Several mirror design configurations were evaluated. Each configuration was modeled using a finite element analysis method. The deformation of the mirror surface as well as the centrifugal forces were calculated. The image quality was modeled using optical image formation theory. The modeling approach was validated experimentally. A 3-in. scan mirror was modeled using the same procedures, and the line spread function (LSF) of the scan mirror due to the deformation at high speed was calculated. The actual LSF at that speed was also measured using a CCD linear array camera. The test results obtained with a 3-in. mirror agree with the model within 20% in the width of the LSF. (Approximately 500% error is observed if no distortion is assumed.)