Overview¶
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 |
| Bin: | frequency channel |
| DF: | Dual-Feed |
| FWHM: | Full-Width Half-Maximum |
| HPBW: | Half-Power BeamWidth |
| 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 |
| 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’s a celestial target, follows its sidereal motion |