[evla-sw-discuss] Atmosphere

[Bryan Butler]

our plan for the weather station has always been to put it behind a MIB. 
whether it is a plain old vanilla MIB or a CMIB remains to be seen (from the 
software point of view).

	-bryan


On 3/29/06 17:23, Wayne Koski wrote:
> This might be a bit of a sidebar:
> 
> I've been planning that at some point we would want to connect the 
> current weather station to the EVLA via a MIB.  At least I have plans to 
> do so, but down the road a bit.  At one time, we tried to instrument the 
> west arm with two additional stations, one in the middle and one at the 
> end antenna, in order to test doing the same to the other arms. As I 
> recall, we went through an entire array cycle (A, B, C, & D) and it was 
> decided that the central station was good enough.
> 
> So I guess my question is, should we think about doing this again?  I 
> think we would just want temperature, dew point, and barometric pressure 
> at either selected array antennas or selected array pads.  Overkill, I 
> guess would be each antenna, but maybe has scientific merit in that each 
> antenna could correct itself???
> 
> The biggest pain was moving the station tower with the antenna every 
> time we moved, so I'd like to avoid that bit of fun.  However, as I 
> recall the junction box that had the electronics in it, moved with the 
> antenna and therefore was straightforward.  It was only when we moved 
> the junction box to a different antenna that made it bothersome to deal 
> with.  The junction box move was done only once due to the antenna 
> moving very near to the central area.  If we could keep the 
> instrumentation on the antenna like we did the junction box, that would 
> be best in my mind.
> 
> -wayne-
> 
> Barry Clark wrote:
> 
>> I've been thinking about what to do with the atmosphere.  I can't really
>> make up my mind.
>>
>> Currently we just let CALC use a model climate.  This, empirically seems
>> to work best for the VLBA, indicating that the upper atmosphere seems 
>> to follow its seasonal average better than it follows what is 
>> happening on the ground.  But for a relatively small array, most of 
>> the atmospheric
>> phase path differences do lie in the lower atmosphere, and the relative
>> importance of the upper atmosphere is much less. 
>> Pointing is handled by a separate mechanism, with the VLA climate 
>> model (clearly inferior to CALC's) being used to predict refraction.
>>
>> It is clear that the VLA does much better than the EVLA antennas in 
>> pointing, and there is some suggestion that it does better with phases
>> as well.
>>
>> I think it is clear that we want to get the meteorological variables 
>> into the pointing calculation.  This is pretty straightforward, although
>> I can't make up my mind about which side of the java/C interface to do
>> it on (the current calculation lives on the C side, but it might be 
>> easier
>> to keep an eye on on the java side).
>>
>> I am much less clear on what we should do about the phase path 
>> calculation.
>>
>> Possibilities:
>>
>> 1.)  Do nothing - follow the current path until driven off of it with 
>> more
>> compelling data.
>>
>> 2.)  Feed the meteorology into CALC.  I'm not very clear what it might 
>> do with it, but it would use it somehow or other.  Since we have only 
>> one barometer, I think we have to fake barometer readings for each 
>> antenna,
>> according to their elevations.  A bit messy.
>>
>> 3.)  Calculate zenith wet and dry phase paths as currently done at the 
>> VLA (again with corrections for the antenna elevations), and use info 
>> from CALC to apply them to the current rays.  (I think I know how to do
>> this, but it might take a bit of learning.)
>>
>> 4.)  Turn off the CALC atmosphere calculation and install the VLA 
>> atmosphere instead.
>>
>> All of these are complicated to some degree or other if we use this 
>> software to drive PieTown.
>>
>> Comments?
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> 
> 
> 
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