Tutorials

The following tutorial will show you how to run a basic data reduction for a Hydra A 13cm / 2 GHz observation.

Data reduction of 2 GHz data.

First we need to read in data from the file we want to process

$ python dran.py -f test_data/HydraA_13NB/2011d285_04h55m29s_Cont_mike_HYDRA_A.fits

This will produce the following output

 1************************************************************
 2# PROCESSING SOURCE:
 3************************************************************
 4# File name:  2011d285_04h55m29s_Cont_mike_HYDRA_A.fits
 5# Object:  HYDRA A
 6# Object type:  CAL
 7# Central Freq:  2280.0
 8# Observed :  2011-10-12
 9************************************************************
10
11- Processing: ON_LCP
12
13
14# No sidelobes detected
15
16
17* Center of baseline blocks on left and right of peak:
18min pos left: [-0.4041615] @ loc/s [160]
19min pos right: [0.391495] @ loc/s [2497]
20scan len: 2699
21
22# Fit the baseline
23************************************************************
24
25# Fit = 0.073x + (-0.034), rms error = 0.0292
26
27# Fit the peak
28************************************************************
29
30# Peak = 2.464 +- 0.030 [K]
31
32# S/N: 86.77
33
34- Processing: ON_RCP
35
36
37# No sidelobes detected
38
39
40* Center of baseline blocks on left and right of peak:
41min pos left: [-0.40816145] @ loc/s [153]
42min pos right: [0.39016168] @ loc/s [2525]
43scan len: 2731
44
45# Fit the baseline
46************************************************************
47
48# Fit = -0.000632x + (-0.0406), rms error = 0.0254
49
50# Fit the peak
51************************************************************
52
53# Peak = 2.493 +- 0.025 [K]
54
55# S/N: 100.69

We are now going to breakdown the results returned

Lines 1 - 9 give us basic details on the source under observation. This includes the name of the file being processed, the object being observed, the type of object it is (CAL = Calibrator or TAR = Target), the observing frequency, as well as the date the source was observed.

Line 11 tells you the drift scan currently being processed, in this case its the LCP On scan drift scan.

Line 14 is a debugging output that lets you know if any large sidelobes were detected, these are sidelobes which are larger than half the peak maximum.

Once the data is loaded and prepped, the program begins processing the data. First it tries to correct or remove any drift in the data that may exists. Using a gradient descent type algorithm, the program fits a spline through the data and detects the location of the lowest minimum locations on either sides of the center of the drift scan.

Line 17 - 20 give us information on the positions selected as the local minimum points. An also gives the length of the scan.

4% of the scan length is then used as the number of points required to get enough data around the local minimum points in order to fit a polynomila therough the data.

The equation of the line that is used to correct the drift in the data is then displayed in line 25.