... (GDF3.1
A binary format made of a header plus an array whose dimension is between 1 and 4 
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... Number3.2
The CLASS/CLIC is a "radio Julian date" (or "Jansky Julian date"), which starts as $-2^{15}$ on the date of the first radio observation by Karl Jansky. It is thus the Modified Julian date minus 60549. That choice was made to maximize the time interval over which radio astronomical data could be usefully stored in an integer*2, back when 2 bytes of header space per spectrum were a significant consideration. This date has little meaning outside the rather sparse community of souls gathered around the CLASS and CLIC programs, however... 
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... ratio3.3
Indeed, low signal-to-noise ratio is a condition where imaging and deconvolution steps are very delicate. 
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