Getting Started

This is a simple introduction to using iLiSA for high-level LOFAR standalone operations and visualizations. Here I introduce some basic concepts, some prerequist configurations, and some one-line commands to run observations and finally how to visualize the data you recorded.

LOFAR station resource basics

iLiSA is designed so that it can run one or more telescope resources remotely. Look at the following diagram

This shows a typical layout topology consisting of a local control unit (LCU) that performs the actual observations, a data recording unit (DRU) where recorded data ends up and a central control unit (CCU) from which you control and monitor the LCU and DRU. Note that the CCU and DRU could be the same physical node, since these are only logical nodes. For security reasons, the LCU will be on another network than the other resources, and this necessitates a gateway portal. In what follows in it assumed that this topology has been setup already, often this will mean enabling ssh tunnels and port configurations, so that the iLiSA user is able to ssh without password into the LCU and DRU from the CCU.

Setting up station access

In order for iLiSA to work, it needs to know how to access your local LOFAR station, i.e., its LCU and DRU. This is done under your home directory, in ~/.config/ilisa/. In particular the file access_lclstn.conf should contain information on the name of the station, the user account, and the its hostname:

LCU :
  stnid : "SE607"      # Station ID
  user : "user6"       # username on LCU (all LCU processes will run as this)
  hostname : "se607c"  # internet hostname of LCU
DRU:        # This is the machine where LCU data ends up and might process it
  hostname : localhost  # or ip address
  LOFARdataArchive : "/data/LOFAR/SE607/"    # Top path to final data archive
  BeamFormDataDir :  "/mnt/lane?/BF/SE607/"  # Path to record BFS data

This is a yaml file with sections for LCU and DRU using the Swedish SE607 LOFAR station as an example.

Basic Recording

The simplest way to use a LOFAR station is to record data using the command line interface called ilisa_rec. For let’s say you want to record XST data for Cassiopeia-A. You do this on the CCU command line (which has the prompt [CCU]$) as follows:

[CCU]$ ilisa_rec xst 55e6 10 Cas-A
[CCU]$ ls /data/LOFAR/SE607/xst/
scan_59632.40269
[CCU]$ ls /data/LOFAR/SE607/xst/scan_59632.40269
SCANREC_INFO.yml  SE607_20220222_093955_spw3_sb230_int1_dur30_dirCas-A_xst

Running Scan Sessions

In practice so-called iLiSA scan sessions are more useful. You write an yaml file with a list of scans that can look like this:

# Save this file as 'bst_scnses.yml'
scans:
  - beam:
      freqspec: '52e6:148e6'
      pointing: Cas-A
    rec: [bst]
    integration:  1
    duration: 60

This is a minimal example where a beam is set up to point towards Cassiopeia-A with a frequency range between 52-148 MHz for 60 s and the beamlets power data is recorded. This scan session can be executed using the follow command:

[CCU]$ ilisa_obs -t 2022-04-26T11:15:00 bst_scnses.yml

where the last argument was the name of the yaml file shown previously and the -t flag specifies when the scan session should start. After the start has occured, the scan session will execute and after 60 s the BST data will be recorded, along with metadata, on the DRU under the path specified in the config file.

Visualizing LOFAR station data

iLiSA also has commands to visualize LOFAR station data. One simply types:

[CCU]$ ilisa_view

In this case the latest, potentially realtime, data is plotted. Otherwise one can type

[CCU]$ ilisa_view /data/LOFAR/SE607/xst/SE607_20220222_093955_spw3_sb230_int1_dur30_dirCas-A_xst

which will browse through the XST data which is shown as covariance matrices. If one wishes to see the sky image maps, one can use the command:

[CCU]$ calim_image bf /data/LOFAR/SE607/xst/SE607_20220222_093955_spw3_sb230_int1_dur30_dirCas-A_xst

where bf argument implies using the beamform imaging algorithm. The result should look something like:

There is also a nearfield nf for imaging RFI sources around the station.