Modeling the performance of a high-speed scan mirror for an airborne line scanner
Abstract
The Digital Imaging and Remote Sensing Laboratory at the
Rochester Institute of Technology is developing a new airborne multispectral
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.)