[daip] AIPS Help

[Eric Greisen]

vivianchen wrote:
> Hi,
> 
>  
> 
> I've attached a copy of the amplitude vs. time graph I obtained from the 
> VLA data set AY0192 (A-Array Configuration, C-Band). When I plot either 
> amplitude vs. time or amplitude vs. uv-distance for stokes 'RL' and 'LR' 
> of Sgra*, the plots will have those horizontal lines cutting across. I 
> was wondering whether you have any idea what those horizontal blanks 
> cutting across may be.

Actually, I suspect that this quantization is in the data themselves. 
In the old days, the VLA receivers could not handle a wide range of 
amplitudes so the gain would have to be turned down to observe SgrA*.
This did cause quantization in the recording of the visibilities.  At 
large amplitudes, the quantization in the real and imaginary parts has 
so many states that the amplitudes appear uniform.  But at weak 
amplitudes, the quantization leads to visible gaps.  Try plotting the 
real part or the imaginary part rather than amplitude.  The bottom line 
- the quantization was put in the data as they were recorded and there 
is nothing that can be done about it.  The imaging is not likely to be 
impacted by this since tit combines many samples taken over a wide range 
of u and v.

Eric Greisen