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.

ESCS overall tasks

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