The source detection module in the WSDS Multiframe Pipeline (MDET) operates by searching for local maxima which exceed a specified SNR threshold on a quadrature sum of matched-filtered detection images built from coadded Atlas Images and Uncertainty maps in all four WISE bands. A detailed description of the MDET algorithm and design is given in section IV.4.b of the WISE All-Sky Explanatory Supplement. Two significant updates were made to the MDET module for production of the AllWISE Source Catalog and Reject Table.
The detection threshold on the summed, match-filtered images was set at SNR=2.4 for AllWISE data processing. This is considerably lower than the threshold of SNR=3.5 that was used for the All-Sky and 3-Band Cryo data releases.
MDET utilizes a two step detection process. In step 1, high SNR detections are identified. Large areas around each entry of this preliminary bright source list, from brighter to fainter, are blanked out when constructing the slowly-varying background estimate used for step 2, the final detection step. The blanking is limited to 33% of the detection image pixels. Step 1 is also where MDET estimates the saturation radii for bright sources with saturated cores. The saturation radii are used to expand the fitting radius used later in the profile-fit extraction process (WPRO). In the version of MDET used to produce the earlier WISE data releases, when the 33% area blanking limit is reached, no more saturation radii were estimated even though there may be many saturated sources remaining, causing WPRO to behave non-optimally. This was corrected in the AllWISE version of MDet. Now, even after the 33% blanking limit is reached, fainter, but still saturated sources continue to have their saturation radii estimated.
Last Updated: 2013 October 28