MOPEX Online Manual

Why MOPEX?

MOPEX provides a general purpose tool to generate mosaics of FITS images and to perform point source extraction. While both of these tasks are needed for many astronomical datasets, MOPEX addresses several complications specific to Spitzer data:

Geometric Distortion and Fast Projection: Spitzer images have significant geometric distortion, described in the FITS header using the World Coordinate System (WCS). Mosaicking and photometry must accurately interpret this information, which is not yet standard in all packages. Moreover, large Spitzer mosaics include many images, so a fast method is required when performing the projection. MOPEX's fast direct plane-to-plane projection is described in Makovoz, D. 2004, PASP, 116, 971-974.




Outlier Rejection: Spitzer data suffer from cosmic rays and other transient artifacts. While some of these effects are mitigated in the BCD pipeline, further outlier rejection is still required while mosaicking. The best algorithm for rejecting these outliers depends upon the observing mode. For example, temporal outlier rejection performs well in the case of highly redundant sky coverage, but it fails in other cases. A combination of temporal and spatial outlier rejection ("dual outlier rejection") has been implemented in MOPEX, along with other options.




Profile Fitting: Spitzer pixels are relatively big relative to point sources, so MOPEX fits with Point Response Functions (PRFs), which take into account intra-pixel sensitivities. For multi-frame photometry, MOPEX does source detection on a mosaic image, but point-source fitting on the original stack of images.

In addition to solving these specific problems, MOPEX provides the standard data analysis functions for mosaicking and source extraction. Mosaicking options include background matching, drizzle interpolation, exposure time weighting, error propagation and residual image generation (command-line mode only). Photometry options include image segmentation (passive and active deblending), aperture photometry, and residual image generation.