User Tools

Site Tools


lbaops:lbacalibrationnotes:pre2010

Data correlated pre-2010

All LBA data correlated before 1 January 2010 have amplitude scaling applied at the correlator based on the nominal SEFD for each telescope. This means that the amplitudes on each baseline from the correlator are roughly in Jy. In order to apply measured Tsys corrections, this factor needs to be “undone” in post-correlation processing. This can be easily done in AIPS task ANTAB by inserting the nominal SEFD applied to each antenna into the denominator of the FT keyword value in the TSYS group in the calibration text file (see the explanation of ANTAB in AIPS).

For all data correlated at Curtin in 2008-2009, the nominal SEFD values used were as listed in the table below (from the old vex2config.pl). Note that for the ATCA tied array, it was assumed that 5 antennas were tied, which may not have been the case (see the observers wiki or logs). If less than 5 antennas were used in the tied array, then the nominal scaling factor applied is incorrect. The value applied for each participating telescope is listed in the correlator input file (TSYS keyword) for each experiment, and ideally this should be checked rather than assuming that the values in the table below were used.

Another way to adjust the nominal amplitude scaling (other than in ANTAB as above) is to use AIPS task CLCOR (OPCODE = 'GAIN'). Run once for each antenna as required, specifying CLCORPRM(1) to give the appropriate scaling factor: note that the gain correction factor in CLCOR corresponds to units of square root of antenna SEFD (Jy).

Hypothetical example: A 22GHz LBA dataset correlated in 2009 has 'TSYS: 106' for ATCA listed in the correlator input file. This assumes 5 antennas were tied, but according to the observer's log on the wiki, only two ATCA antennas were included in the tied array. Therefore the a priori SEFD should have been 265 Jy (=530/2).
If the measured Tsys log is available (pre-CABB), this will be correct for the number of antennas in the tied array. The measured Tsys can be converted to the ANTAB input format and used to calibrate the amplitudes. The value for FT should be divided by 106 to undo the nominal scaling applied at the correlator.
If the measured Tsys is not available (which is the case since the CABB correlator has been used at the ATCA), then either ANTAB input can be generated with nominal Tsys values, or alternatively, the gain could be adjusted to the (correct) nominal value using task CLCOR, setting CLCORPARM = 1.58, 0 (= sqrt(5/2)).

Telescope Nominal SEFD (Jy) in each frequency range (MHz)
<1500 1500-1799 1800-2499 2500-4999 5000-6499 6500-7999 8000-9999 10000-14999 >15000
Parkes 40 42 30 110 110 110 43 370 810
ATCA 68 68 106 70 70 170 86 - 106
Mopra 340 340 530 350 350 850 430 1300 900
Hobart 470 420 650 640 - 1240 560 1200 1800
Ceduna - - 400 450 - 550 600 750 2500
Tidbinbilla - 23 16 - - - 25 - 60
Hart - 200 210 290 260 290 340 480 3000
Tigo - - - - - - 7700 - -
O'Higgins - - - - - - 6300 - -
lbaops/lbacalibrationnotes/pre2010.txt · Last modified: 2015/12/18 16:38 (external edit)