Overview
What DISCOS is
DISCOS is the control software produced for the Italian radio telescopes. It is a distributed system based on ACS (ALMA Common Software), commanding all the devices of the telescope and allowing the user to perform single-dish observations in the most common modes. As of today, the code specifically implemented for the telescopes (i.e. excluding the huge ACS framework) amounts to about 650000 lines. Even VLBI (or guest-backend) observations partly rely on DISCOS, as it must be used to perform the focus selection and the frontend setup.
This guide is meant to help the observer in the use of DISCOS, without dealing with the “behind-the-curtains” complex details of the system. This release focuses on single-dish continuum and spectroscopy observations; the fully integrated backends available on-site are the analog total power one, the XARCOS and SARDARA spectrometers. Since both the hardware and software implementations are still going on at SRT, this manual will forcibly undergo continuous revisions.
Here follows a simple schematization of the observing system, helpful to visualize all the main devices DISCOS deals with and the most important operations it performs.
Note
(1) Frequency switching is possible only manually editing the schedules, as the schedule-creating tool does not foresee this specific mode, yet.
Glossary: terms and abbreviations
- >:
this symbol precedes commands to be given in the operatorInput panel
- $:
this symbol precedes commands to be given in a system shell
- AS:
active surface
- Beam-parking:
the antenna points to a fixed Azimuth-Elevation position
- Bin:
frequency channel
- FWHM:
Full-Width Half-Maximum
- HPBW:
Half-Power BeamWidth
- MF:
Multi-Feed
- MS:
Minor Servo system, which includes the subreflector and the PFP
- Nodding (aka “beam switching”):
it involves two or more feeds. The source is alternatively observed with each of the feeds, so that there is always one feed “on source”
- OTF:
On-The-Fly acquisition. The antenna moves according to user-defined parameters, scanning the sky at constant speed. Data acquisition is active during the scan
- PFP:
Primary Focus Positioner, the servo which allows to put the primary focus receivers in place
- Position switching (aka “on-off”):
the beam is alternatively pointed to the source (on) and to a properly defined offset position (off)
- Preset:
mount mode allowing only beam-parking observations, with no pointing model applied
- ProgramTrack:
mount mode allowing tracking, OTF/raster scans, beam-parking
- Raster:
acquisition is performed via discrete pointings (in tracking or beam-parking mode), planned to sample a certain path/area on the sky
- Section:
acquisition stream (aka “logical channel”). E.g.: the 7-feeds of the K-band receiver used with the continuum backend produce 7 feeds x 2 polarisations = 14 sections
- SF:
Single-Feed
- Slewing:
motion of the antenna when it is going to the target position. Slewing is always performed at maximum speed, with no data acquisition taking place
- Temporised commands:
user-input or schedule commands that are launched to a specific UT time by means of the “@” symbol
- Time-tagged commands:
when commands are not temporised, the philosophy for their execution is asap (as soon as possible), but the system internally schedules them associating each operation to a properly computed time. This is particularly relevant for the positions commanded to the mount, so that the antenna motions take place along a fully controlled path (except in slewing)
- TPB:
Total Power Backend
- Tracking:
the antenna points to a target and, if it is a celestial target, follows its sidereal motion