1. Hands-On Calibration Ron Maddalena July 13, 2007

2. Preliminaries Change directory: cd /home/scratch/sdscal Start GBTIDL Access data filein,’T_TCAL14MAR07.acs.raw.fits’ summary Note: For 8 GHz receiver, used observing technique of ‘OffOn’ with, for example, scan 6 an observation toward blank sky and scan 7 toward 3C286. Used 4 windows Note: For 12 GHz, dual feed receiver, used observing technique of NOD. Source in feed 1 for scan 31, in feed 2 for scan 32. Used 2 windows. getps,6,ifnum=0 Try different windows to see what’s different header Record elevation, UT date and time getnod,42,ifnum=0 For the adventurous.compile getscalquad.pro

3. Typical Position-Switched Calibration Equation

4. Putting it all together Remove Averaging Solve for Tcal

5. What Do We Need? η from graph, assume gain is elevation independent A p from dish diameter Calculate Air Mass from elevation of observation S from a catalog (e.g., Ott et al 1994, A&A, 284, 331) Table: pp 333-334 Functional fit: p. 335 Note that S will vary significantly across wide bandwidths τ from weather models At Linux prompt, type: cleo forecasts

6. What Do We Need? τ from weather models At Linux prompt, type: cleo forecasts Select “Curves” tab Enter date and UT of the observations Enter frequency range for the receiver (e.g., 7-11 GHz, 11-16 GHz) May want to select ‘Write Out Results’ to create an ASCII file of results Click on ‘Process’ Read opacities off of graph

7. What again are we calculating?

8. How to Calculate (Ref On -Ref Off )/(Sig-Ref) Use the commands ‘emptystack’, ‘select’ ‘avgstack’, ‘copy’, ‘subtract’, ‘divide’, and ‘scale’ Emptystack Clears anything that peviously has been done with the stack Select,scan=6,cal=‘F’,ifnum=0,plnum=0,fdnum=0 Finds all data that meet this selection criteria Avgstack Averages together the data found by ‘Select’ and places into Data Container (DC) zero Copy,0,9 Moves the results to another DC for later use DC 9 will now contain Ref Off Repeat for scan=6, cal=‘T’, place into DC 8 to create Ref On Repeat for scan=7, cal=‘F’, place into DC 7 to create Sig Off Repeat for scan=7, cal=‘T’, place into DC 6 to create Sig On

9. How to Calculate (Ref On -Ref Off )/(Sig-Ref) Summary: DC 9 contains Ref Off DC 8 contains Ref On DC 7 contains Sig Off DC 6 contains Sig On Create Sig and place into DC 10: Add,7,6,10 Scale,0.5,10 Similarly create Ref and place into DC 11 Create Sig-Ref and place into DC 12 Subtract,10,11,12 Similarly create Ref On -Ref Off and place into DC 13 Create (Ref On -Ref Off )/(Sig-Ref) and place into DC 14 Divide,13,12,14 Show,14

10. What again are we calculating? Finally, scale DC 14 by η, S, … to determine Tcal. For example, using fictitious values: scale, 0.5*1234/2*22, 14 scale, 1/1.38e-16*exp(-0.12/sin(33*180/!pi)), 14 etc. show,14

11. Check for non-linearity If system is linear, than (Sig On -Sig Off ) – (Ref On -Ref Off ) = 0 Model the response curve to 2 nd order: P out = B * P in + C * P in 2 Our observations provide: P out = Ref off when P in =T sys P out = Ref on when P in =T sys +T cal P out = Sig off when P in =T sys +T A P out = Sig on when P in =T sys +T A +T cal It’s easy to show that: C = [(Sig on - Sig off )-(Ref on - Ref off )]/(2T A T cal ) Try to estimate a value for C using ‘subtract’, ‘divide’ and ‘scale’ Things are really a bit more complicated since we really measure P out and want to determine P in. Must invert 4 simultaneous linear equations.

12. Now for the real easy way… Getscal,7,6,ifnum=0,plnum=0,fdnum=0,tau=0.05, ap_eff=0.55,smth=1 Show,13 (T cal, assuming linearity) Show,3 (T cal, assuming non-linearity) Show,15 (T sys, assuming linearity) Show,5 (T sys, assuming non-linearity) Show,11 (Source flux)