Meteor trails in the single frames can make streaks in the coadded images causing spurious detections in PIXPHOT which result in false point and extended sources, and photometric errors in real point and extended sources which are on or near the meteor track. Since the meteor tracks seldom appear in more than one or two frames, it is possible to blank the affected pixels in those frames and just use the clean frames for imaging and photometry. In the V2 processing, single frame detections (from FREXAS) which are identified as unconfirmed in adjacent frames by POSFRM/PFPREP ('solos'- see here) were thresholded by PIXPHOT and the affected pixels in the single frames were blanked to remove radiation hits and 'hot' pixels. Since a meteor trail also results in sporadic detections in the single frames, a side effect of the solo processing was to remove random portions of meteor tracks, resulting in "technicolor (tm)" stripes in 3-color images.

For 2MAPPS V.3 and the final reprocessing, it was decided to specifically blank the meteor tracks in the single frames prior to coaddition. This was accomplished by identifying meteors using a modification of a streak finding algorithm developed by Tom Jarrett which identified linear features in the working data base using detections flagged as unreliable. Since most meteor streaks also leave easily identified linear features in the single frame detection solos files (which are created prior to coadding the frames in the pipeline), a modification of Tom Jarrett's algorithm can be used on this cleaner data base, and the results can be used to blank the meteor streaks in the single frames prior to coaddition. Identified linear features would be blanked in all three bands from one edge of the frame to the other. There are on the order of 10-20 solos/frame in most of the sky, so searching in the solos file is much more efficient than searching all the single frame detections or comparing the pixels in overlapping frames. The solos from the 3 bands can be combined to increase the number of detections defining the linear features.

The following plots show a typical meteor track in a coadded image, and the corresponding plot of the solos in frame coordinates:

meteor track in solos file-

Analysis is required to resolve the following issues:

The following image pair shows a meteor trail with detections marked with green crosses on the left, and the same image on the right when the meteror trail is blanked in a single frame in all three bands prior to coaddition.

Meteor Trail Blanking Implemented 010206

anomolous blanking due to off-axis bright star (Beta Pegasi)

This type of artifact could be removed by blanking the entire frame. A reliable means of identifying these frames automatically has not yet been devised.

The following image pairs show coadds with meteors from the 2MAPPS V2 processing compared with the sucessfully blanked tracks from the 2MAPPS V3 test processing.

In 971116n, 14 meteor tracks were sucessfully identified and blanked. In 980319s, 15 meteor tracks were sucessfully identified and removed. In 971116n, 4 frames associated with off-axis light from Beta Pegasi had problematic blanking.

Subtle tracks are missed that can be detected by eye in 3 color images. With the exception of the off-axis problem shown above, no problems were evident in the images due to streak blanking triggered by phenomena other than true meteor streaks. The process is not completely reliable, however, and some additional problems will doubtless surface.