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IR survey modes
Standare Dither and Stare
During survey data-taking the telescope moves
continuously in declination at approximately 57/second, while
tracking in hour angle at the sidereal rate. The articulated secondary
executes a sawtooth pattern of motion which freezes the image of the
sky on the focal plane during the frame exposures. The shift between
consecutive images is 1/6 of the array width. The arrays are aligned
to that subpixel steeping is obtained via this geometric tilt.
Each region of sky is observed for 1.3 secsonds with an elaped
time of 1.445 secs. This the total exposure is 7.8 seconds.
The reported observing efficiency is 85% including all overheads.
The survey is carried out by observing strips of 30 degrees in declination
and 12 arcminutes in Right Ascension with an overlap of 2 arcminutes
between consecutive strips. Dithering is via a microscanning mirror.
Each expsoures is 1 sec and there are 9 dithers with a shift of 1/3 pixel
in RA and 7/3 pixels in Dec. Thus the total travel is 3 pixels by
21pixels or 9arcsecs by 63arcsecs.
Drift Scanning
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Richard McMahon,
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Last modified: Sun Mar 12 10:59:40 2006