SubBeamNod
SubBeamNod scans with the GBT consist of using the subreflector to alternate between an on and an off position between two feeds on a receiver.
Calibrating SubBeamNod Data
For this example we will be using data from a receiver checkout, TRCO_230413_Ka. The data can be downloaded from this link. Or, using wget
>>> import wget
>>> url = "http://www.gb.nrao.edu/dysh/example_data/subbeamnod-Ka/data/TRCO_230413_Ka.raw.vegas/TRCO_230413_Ka.raw.vegas.A.fits"
>>> filename = wget.download(url)
>>> print(filename)
TRCO_230413_Ka.raw.vegas.A.fits
SubBeamNod data is retrieved using subbeamnod() which returns a Spectrum object.
First, import the relevant module
>>> from dysh.fits.gbtfitsload import GBTFITSLoad
Then load your SDFITS file containing SubBeamNod data
>>> filename = 'TRCO_230413_Ka.raw.vegas.A.fits'
>>> sdfits = GBTFITSLoad(filename)
The returned sdfits can be probed for information
>>> sdfits.info()
Filename: TRCO_230413_Ka.raw.vegas.A.fits
No. Name Ver Type Cards Dimensions Format
0 PRIMARY 1 PrimaryHDU 12 ()
1 SINGLE DISH 1 BinTableHDU 245 5280R x 74C ['32A', '1D', '22A', '1D', '1D', '1D', '1024E', '16A', '6A', '8A', '1D', '1D', '1D', '4A', '1D', '4A', '1D', '1I', '32A', '32A', '1J', '32A', '16A', '1E', '8A', '1D', '1D', '1D', '1D', '1D', '1D', '1D', '1D', '1D', '1D', '1D', '1D', '8A', '1D', '1D', '12A', '1I', '1I', '1D', '1D', '1I', '1A', '1I', '1I', '16A', '16A', '1J', '1J', '22A', '1D', '1D', '1I', '1A', '1D', '1E', '1D', '1D', '1D', '1D', '1D', '1A', '1A', '8A', '1E', '1E', '16A', '1I', '1I', '1I']
You can also print a concise (or verbose if you choose verbose=True) summary() of the data
>>> sdfits.summary(show_index=True)
SCAN OBJECT VELOCITY PROC PROCSEQN RESTFREQ DOPFREQ # IF # POL # INT # FEED AZIMUTH ELEVATIO
0 32 1256-0547 0.0 Nod 1 26.5 26.5 1 2 60 2 160.975324 43.884984
1 33 1256-0547 0.0 Nod 2 26.5 26.5 1 2 60 2 161.174093 43.928449
2 34 1256-0547 0.0 Nod 1 30.5 30.5 1 2 60 2 161.589629 44.000491
3 35 1256-0547 0.0 Nod 2 30.5 30.5 1 2 60 2 161.783395 44.041622
4 36 1256-0547 0.0 Unknown 0 0.75 0.75 1 2 120 2 162.124052 44.100404
5 37 1256-0547 0.0 Nod 1 34.5 34.5 1 2 60 2 162.611075 44.183661
6 38 1256-0547 0.0 Nod 2 34.5 34.5 1 2 60 2 162.896506 44.237997
7 39 1256-0547 0.0 Nod 1 37.5 37.5 1 2 60 2 163.333508 44.306385
8 40 1256-0547 0.0 Nod 2 37.5 37.5 1 2 60 2 163.529285 44.343704
9 41 1256-0547 0.0 Nod 1 30.5 30.5 1 2 60 2 164.941425 44.559629
10 42 1256-0547 0.0 Nod 2 30.5 30.5 1 2 60 2 165.139436 44.593378
11 43 1256-0547 0.0 SubBeamNod 1 30.5 30.5 1 2 120 2 165.469522 44.639023
12 44 1256-0547 0.0 Nod 1 30.5 30.5 1 2 60 2 166.48287 44.776997
13 45 1256-0547 0.0 Nod 2 30.5 30.5 1 2 60 2 166.688378 44.808119
14 46 1256-0547 0.0 SubBeamNod 1 30.5 30.5 1 2 120 2 167.026583 44.849753
15 52 1256-0547 0.0 Nod 1 30.5 30.5 1 2 60 2 169.972904 45.179358
16 53 1256-0547 0.0 Nod 2 30.5 30.5 1 2 60 2 170.175815 45.201877
17 54 1256-0547 0.0 SubBeamNod 1 30.5 30.5 1 2 120 2 170.518885 45.232575
The SubBeamNod scans are 43, 46, and 54. Retrieve and calibrate a SubBeamNod scan, then plot it
Note
For each scan in the summary dysh shows the mean of the VELOCITY, RESTFREQ, DOPFREQ, AZIMUTH and ELEVATIO columns, while GBTIDL reports the value of the first integration for a scan. If you use verbo
se=True in dysh you get all the integrations.
>>> sbn = sdfits.subbeamnod(scan=43, fdnum=1, ifnum=0, weights='tsys')
>>> ta = sbn.timeaverage(weights="tsys")
>>> ta.plot()