What DISCOS is¶
DISCOS is the control software produced for the Medicina, Noto and SRT 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 actually implemented for the telescopes (i.e. excluding the huge ACS framework) amounts to > 550000 active lines.
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 observations, as the fully integrated backend available on-site is the analog total power one. Since both the hardware and software implementations are continuously updated, this manual will forcibly undergo frequent 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. Notice: the features not yet available in this release are shown in brackets.
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|
|Beam-parking:||the antenna points to a fixed Azimuth-Elevation position|
|MS:||Minor Servo system, which includes the subreflector|
|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|
|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 2 feeds of the K-band receiver used with the continuum backend produce 2 feeds x 2 polarisations = 4 sections|
|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|
|user-input or schedule commands that are launched to a specific UT time by means of the “@” symbol|
|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’s a celestial target, follows its sidereal motion|