MERTIS: using diffractive optical elements for geometrical calibration

Abstract

Geometrical sensor calibration is essential for space applications based on high accuracy optical measurements, in this case for MERTIS. The goal is the determination of interiour sensor parameters. A conventional method is to measure the line of sight for a subset of pixels by single pixel illumination with collimated light. To adjust angles which define the line of sight of a pixel a manipulator construction is used.A new method for geometrical sensor calibration is presented using Diffractive Optical Elements (DOE) in connection with laser beam equipment. This method is especially used for 2D-sensor array systems but can also be applied to the thermal infrared push-broom imaging spectrometer MERTIS.Diffractive optical elements (DOE) are optical microstructures which are used to split an incoming laser beam with a dedicated wavelength into a number of beams with well-known propagation directions. As the virtual sources of the diffracted beams are points at infinity, the object to be imaged is similar to the starry sky which gives an image invariant against translation. This particular feature allows a complete geometrical sensor calibration with one image avoiding complex adjustment procedures which means a significant reduction of calibration effort.