Total Power Data
Retrieving and Viewing a Total Power Scan
Single beam total power (TP) data is retrieved using gettp() which returns a GBTTPScan total power scan object that is used to calibrate and average the data. First, import the relevant module
>>> from dysh.fits.gbtfitsload import GBTFITSLoad
>>> import wget
>>> import numpy as np
Download the data from GBO
>>> filename = wget.download("http://www.gb.nrao.edu/dysh/example_data/onoff-L/data/TGBT21A_501_11.raw.vegas.fits")
>>> print(filename)
TGBT21A_501_11.raw.vegas.fits
Note
The data used for this tutorial is ~800 MB. Make sure you have enough disk space and bandwidth to download it.
Then load your SDFITS file containing TP data. In this example, we use a GBT SDFITS file downloadable from GBO
>>> sdfits = GBTFITSLoad(filename)
The returned sdfits can be probed for information
>>> sdfits.info()
Filename: TGBT21A_501_11.raw.vegas.fits
No. Name Ver Type Cards Dimensions Format
0 PRIMARY 1 PrimaryHDU 12 ()
1 SINGLE DISH 1 BinTableHDU 245 6040R x 74C ['32A', '1D', '22A', '1D', '1D', '1D', '32768E', '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 summary() of the data
>>> sdfits.summary(show_index=True)
SCAN OBJECT VELOCITY PROC PROCSEQN RESTFREQ DOPFREQ # IF # POL # INT # FEED AZIMUTH ELEVATIO
0 152.0 NGC2415 3784.0 OnOff 1.0 1.617185 1.420406 5 2 151 1 286.218008 41.62843
1 153.0 NGC2415 3784.0 OnOff 2.0 1.617185 1.420406 5 2 151 1 286.886521 41.118134
Retrieve a scan, selecting and IF number and polarization
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.
>>> tpscan = sdfits.gettp(scan=152, ifnum=0, plnum=0)
The GBTTPScan contains the individual integrations. The system temperatures per integration are calculated from the CALON and CALOFF data
>>> print('%s' % (np.array2string(tpscan.tsys, precision=2)))
[17.46 17.47 17.51 17.48 17.27 17.24 17.43 17.51 17.36 17.41 17.27 17.36
17.28 17.31 17.15 17. 17.54 17.21 17.4 17.38 17.49 17.43 17.15 17.2
17.45 17.15 17.31 17.31 17.1 17.48 17.29 17.24 17.52 17.31 17.19 17.1
17.35 17.14 17.38 17.48 17.22 17.5 17.33 17.27 17.41 17.2 17.48 17.21
17.37 17.47 17.25 17.18 17.25 17.17 17.14 17.36 17.25 17.28 17.25 17.19
17.36 17.14 17.48 17.17 17.36 17.43 17.51 17.38 17.29 17.19 17.4 17.63
17.36 17.27 17.19 17.45 17.39 17.48 17.24 17.31 17.13 17.22 17.24 17.42
17.1 17.5 17.38 17.24 17.42 17.32 17.27 17.35 17.29 17.49 17.4 17.18
17.18 17.28 17.26 17.48 17.38 17.35 17.28 17.25 17.28 17.39 17.25 17.24
17.08 17.28 17.28 17.36 17.53 17.38 17.34 17.48 17.43 17.49 17.29 17.44
17.32 17.5 17.11 17.38 17.24 17.2 17.37 17.21 17.19 17.32 17.01 17.48
17.34 17.35 17.5 17.01 17.44 17.45 17.4 17.38 17.18 17.44 17.22 17.25
17.28 17.19 17.38 17.34 17.3 17.26 17.37]
You can time-average the data, in this example with equal weighting per integration, and plot it
>>> tpscan.timeaverage(weights=None).plot()
