System temperature versus za.


     I've gone through the telescope data sets taken with the correlator (april thru july 2000) and extracted all of the cal on/off pairs (about 15000).The system temperature in the calOff portion of the cycle was computed using the tabulated cal values.
The plots can be found at:

Computing Tsys using the cal onoff pairs.

    calOn/Off pairs typically track a position on the sky  for 10 seconds with the cal on and then continue tracking the same position (on the sky) for another 10 seconds with the cal off.  If the observer was position switching then the sequence is: positionOn, positionOff, calOn,calOff where the calOn/calOff pair tracks the off source position.

   The system temperature is computed using the total power information (0 lag).  If [K] is kelvins and [corTP] are
correlator total power units (linear in power but arbitrary) then:

delta[corTP]= calOn[corTP] - calOff[corTP]  gives the size of the cal in [corTP] units
calTPtoK      = calSize[K]/(delta[corTP]  is the size of the cal in K / size of the cal in  [corTP]  so it
                           will  convert [corTP] to kelvins
Tsys[K]          = calOff[corTP] * calTPtoK is the system temperature.

     Tsys is computed for the calOff scan so  that the cal is not included. When computing (calOn - calOff)  we assume that the difference is only do to the cal. For small cals and high zenith angle, there is a small change  from tsys(za) dependance since we continue to track the same position in the sky for the calon and caloff.

Fitting the system temperature za dependance:

    The beam should start to spill over the dish at 15 deg za and start to leave the ground screen at 17 degrees. Looking at the data there is a linear increase out to 15 degrees za and then it turns up. I fit a linear term to za 0-20 and then a 2nd and 3rd order term for za > 14 degrees. To remove outliers, I did the fit, removed all points greater than N sigma (this is labeled on the plot) and then refit the data.

About the plots:

Figure notes:

Things to think about:

Tsys vs za polynomials:

    The polynomial fits to Tsys vs zenith angle are listed below. The ^2 and ^3 order terms are only used for za > 14 degrees. The za is in degrees.
processing: x101/tsys/Readme for a description
plotting  : x101/tsys/plotall.plt