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In the focal plane of a pushbroom imager, a linear array of pixels is scanned across the scene, building up the image one row at a time. For the Multispectral Thermal Imager (MTI), each of fifteen different spectral bands has its own linear array. These arrays are pushed across the scene together, but since each band's array is at a different position on the focal plane, a separate image is produced for each band.The standard MTI data products (LEVEL1B R COREG and LEVEL1B R GEO) resample these separate images to a common grid and produce coregistered multispectral image cubes. The coregistration software employs a direct "dead reckoning" approach. Every pixel in the calibrated image is mapped to an absolute position on the surface of the earth, and these are resampled to produce an undistorted coregistered image of the scene. To do this requires extensive information regarding the satellite position and pointing as a function of time, the precise configuration of the focal plane, and the distortion due to the optics. These must be combined with knowledge about the position and altitude of the target on the rotating ellipsoidal earth.We will discuss the direct approach to MTI coregistration, as well as more recent attempts to "tweak" the precision of the band-to-band registration using correlations in the imagery itself.

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