lofarstationdata: Python interface to Lofar single-station cross-correlation data

This python module provides easy access to Lofar cross correlated station data (XST & ACC). UVWs and data corrected for geometric delay are automatically calculated. It can also write the data out as a Measurement Set. A command line utility is included for converting to Measurement Set.

This was written for international stations but might also work for Dutch HBA stations. It would need modification to work with Dutch LBA - it doesn't know about the configurations (inner, outer, sparse, etc) for the Dutch LBA fields.

Antenna positions are obtained from Lofar's AntennaField.conf files (link). A set is included with this package which will be used by default as long as you specify the station name.

Dependencies

• Python 2.7 or higher
• python-casacore (which in turn depends on casacore)
• casacore-data (see below)
• NumPy

Casacore data:

If you want to maintain your own casacore data directory or use the one from NRAO's Casa package you can specify its location in ~/.casarc Eg:

measures.directory: /opt/casa-release-4.7.0-el7/data

Installation

If you're not doing a system wide install the easiest way to install is with pip:

pip install --user git+https://github.com/sabourke/lofarstationdata

if you don't have pip:

wget https://bootstrap.pypa.io/get-pip.py
python get-pip.py --user

You might need to add ~/.local/bin to your PATH to use the lofar-station-ms converter utility.

Alternatively, for a system wide install (requires write access to Python's module directory):

pip install git+https://github.com/sabourke/lofarstationdata

Usage

The Measurement Set conversion tool is called lofar-station-ms:

$ lofar-station-ms --help
usage: lofar-station-ms [-h] [-c ANTFIELD] [-n STATIONNAME] [-t STARTTIME] -r
                        {3,5,6,7} [-s 0..511] [-i INTEGRATION] [-d DIRECTION]
                        [-x | -a] [-q]
                        indata [msname]

positional arguments:
  indata                Input data file name
  msname                Output Measurement Set name

optional arguments:
  -h, --help            show this help message and exit
  -c ANTFIELD, --antfield ANTFIELD
                        Lofar station AntennaField.conf file
  -n STATIONNAME, --stationname STATIONNAME
                        Station name for MS antenna and observation tables
  -t STARTTIME, --starttime STARTTIME
                        Start time (centre point of first integration),
                        YYYYMMDD_HHMMSS
  -s 0..511, --subband 0..511
  -i INTEGRATION, --integration INTEGRATION
  -d DIRECTION, --direction DIRECTION
  -x, --xst             File is an XST capture (default, unless filename is
                        standard ACC format)
  -a, --acc             File is an ACC capture
  -q, --quiet           Only display warnings and errors

required arguments:
  -r {3,5,6,7}, --rcumode {3,5,6,7}

Example:

lofar-station-ms -r 3 -s 307 -n SE607 20170121_085835_xst.dat test1.ms

Python Examples

There is a directory example code and a XST sample in the examples subdirectory (an ACC was not included because of their size). These will not be installed with pip so you need to clone the repository to get them:

git clone https://github.com/sabourke/lofarstationdata

ACC Example:

from lofarstation.stationdata import ACCData
from casacore.measures import measures

CasA = measures().direction("J2000", "23h23m26s", "+58d48m00s")
CygA = measures().direction("J2000", "19h59m28.3566s", "+40d44m02.096s")

sd = ACCData("20161231_133057_acc_512x192x192.dat",
             station_name="SE607", rcu_mode=3)

# Print time, freq, flux in the direction of CygA
sd.direction = CygA
for i in range(sd.n_time):
    print sd.time[i], sd.frequency[i][0], sd.data[i].mean().real

# Write a MS centred on CasA
sd.direction = CasA
print sd.data.shape
sd.write_ms("CasA.ms")

XST Example:

from lofarstation.stationdata import XSTData
import matplotlib.pyplot as plt

sd = XSTData("20151122_125835_xst.dat", station_name="SE607",
             rcu_mode=3, subband=307, integration_time=1.0)

# Plot UV coverage. No direction was specified, default is zenith
uvw = sd.uvw.reshape((-1,3)) # Standard array shape is N_time * N_ant * N_ant * 3
plt.gca().set_aspect('equal', adjustable='box')
plt.plot(uvw[:,0], uvw[:,1], '.')
plt.show()

# Set direction and plot again
from casacore.measures import measures
sd.direction = measures().direction("AZEL", "45deg", "30deg")
uvw = sd.uvw.reshape((-1,3))
plt.plot(uvw[:,0], uvw[:,1], '.')
plt.show()