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Selected WSDS Prototype Processing Results for December 2007 Sky Simulation Data | |
Ned Wright generated a set of 70 simulated WISE framesets (a frameset consists of the images in the four WISE bands covering the same approximate region on the sky) covering a 1° radius roughly circular area centered near ecliptic coordinates λ=0°, β=+30°. The 70 framesets sample sections of fourteen adjacent WISE scans taken between 08:07 December 15 and 12:13 December 16, 2009 UTC and are laid down on the sky using a realistic mission scanning strategy. The images simulate In Figure 1, the positions of the nominal image centers on the sky are shown as filled red circles.
The simulated images were generated with rotation and reflection between the bands, small position offsets between the bands, and offsets between the nominally reported field centers and true centers on the sky. No distortion was included in these simulations. The simulated images contain unspecified instrumental signatures, but no corrections were made for these in processing because the corresponding dark frames, flat-field frames, etc. were not provided.
The scenes contained in the simulated images include a smoothly varying zodiacal background and a distribution of point sources that were generated assuming a gaussian PRF and using a simulation catalog built on seed objects drawn from the 2MASS All-Sky PSC. Images of asteroids were added to each frameset at the appropriate positions for each image's time of observation. A catalog of "true" source positions and fluxes in the four WISE bands was provided with the simulated images. The distribution of the simulated source positions on the sky is shown by the small black points in Figure 1. The apparent linear feature in the northwestern section of the source distribution result from the presence of uncorrected spurious extractions of the diffraction spikes around the bright star β Pegasi in the 2MASS PSC.
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| Figure 1 - Sky map in equatorial coordinates showing distribution of simulated sources (black points) and nominal simulated image centers (red points) in December 2007 70 Frameset simulation |
The December 2007 70 frameset simulation has been used for unit and system testing in the early development of the WISE Science Data System (WSDS). Although the simulations have been used primarily to test data flow and interfaces at this stage, a number of WSDS subsystems/modules are in advanced prototype stage and are producing results that begin to illustrate the capabilities of the WSDS.
We present here summaries of selected output from the early WSDS unit test processing of the 70 frameset simulation. It is emphasized that these results are intended to be illustrative only, and they do not represent the accuracy that will eventually be achieved by the WSDS.