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Remote Eavesdropping

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Eavesdropping enables you to watch the progress of your queue observing while it happens. If you sign up for eavesdropping (at the start of the semester), when your program comes up in the queue the observer may contact you and start a screen-sharing session so that you can see the data come in and help with the quality assessment. Note: observing is a high-pressure activity. Therefore, eavesdropping is at the observer's discretion - they may or may not call. This document lists the main features of the mode. PI Procedures are detailed at the end of this page. First we offer some definitions of the intention behind the mode.

Eavesdropping is:

  1. Ability to see, and comment on, target acquisitions.
  2. Ability to assess data quality quickly enough to allow useful changes to be made in the observing.
  3. Ability to understand what is happening in the observing at any given time.
  4. Added value only. All observations must be executable without eavesdropping, no observation should rely on it.
  5. Initiated by the observatory.
  6. Ability to see: data reduction pipeline products.
  7. Ability to request modifications to observation (change exposure time, re-arrange steps, change wavelength, add a filter, skip a previously included filter, etc). Must not significantly change the nightly queue plan in a way that the observer would not have done and must not redefine the observation in a way which might duplicate some other observation in the database. (Guidelines will be needed for the observer in these cases.)
  8. Ability to interact with raw data for their project (and associated calibrations) stored at the observatory.

Eavesdropping is not:

  1. Ability to override: queue decisions taken by the summit staff and/or QC. All queue choices will be made in the same way as normal. This includes rapid Targets of Opportunity, which will continue to interrupt the current observation even if that observation is being eavesdropped upon. In a marginal case, e.g. very thin cirrus, and where there is no direct impact on higher-priority programs, the PI may be asked if they wish to continue. If they say yes, despite the weather conditions being outside their formal requirements, a “PASS” flag will be placed on the data in the GSA.
  2. Ability to directly execute (start, stop etc.) the sequence.
  3. Ability to directly control the instrument.
  4. Ability to see the summit OT (because of confidentiality of other programs).
  5. Ability of PI to communicate with QC (the observer will do this in case of need).
  6. Allowed to result in additional staff hours at the observatory. In practice this means that it will not be used in classical runs unless the classical programme has already sent the PI or a Co-I to the summit.
  7. Allowed to result in reduced efficiency – emphasis remains on pre-preparation of observations. No preparation is done on the fly at night, and all time spent inspecting acquisition images etc. is charged to the PI’s programme.
  8. Allowed to produce additional work on QCs or staff queue observers.
  9. Applied to short observations (this is to avoid the overhead of contacting the PI, getting the eavesdropping session established etc. for an observation that may only take 15 minutes).

The Mode

All Band 1 and 2 PIs are invited to eavesdropping if they wish, via the PI email announcing that they have been granted time. If a PI chooses to eavesdrop, they enter their range of dates for multiple contact numbers in a google spreadsheet. Observers check this spreadsheet to see if a PI has an available contact for the current night. 

On a given night, should the program come to the top of the queue and be identified in the plan as an eavesdropping program for the night, the PI or designated contact receives a phone call stating that observations are about to begin. They open Skype on a browser, connect to the control room and to a FITS storage server, and take part in the observation, including watching and commenting on acquisitions, inspecting data frames and commenting on whether to continue or terminate an observation. Note that the QCs will not always schedule a program for eavesdropping on a given night, even though it has that "status". For example, they may be guided by the weather forecast and we will also attempt to avoid scheduling sessions back to back to give the observer a breather. So data may be taken on an eavesdropping program without a call being made (this is also consistent with observers having discretion over calling, and with the first point in "IS", above).

To avoid confidentiality issues and debates between PIs In the course of any given night, only one program will be invited to eavesdrop at a time. To ensure quick decision making and as easy as possible a technical interface, only one eavesdropping channel will be open on a given programme at a time.

Brief records are kept (in the night log) of the key points of the dialogue between the observer and the PI.

PI Procedures

Initial contact

PIs will be invited to participate in eavesdropping in the initial PI email announcing they have been allocated observing time.  The deadline for signing up for eavesdropping is the Phase II submission deadline.  If you wish to take part, you will be asked to send the contact details for up to three eavesdroppers:

  • Name
  • email address
  • telephone number

Note that you can designate up to three sets of details; these may be used to give three different contact numbers for yourself, to be used at different times in the semester, three different co-Is to cover different ranges of nights,or some combination of these. We use these to set up our dial-up calls that will be used to make initial contact on any given night. The three contacts are labelled "a", "b" and "c" respectively; please refer to them as such in your emailed response. 

Specifying contact availability

You will receive a link to a google spreadsheet in the initial email. This is where you tell us who is available and when.  The data entry sheet looks like the following:

Google Spreadsheet

All you need to do is locate the "Availability" tab (bottom of the browser window) for the telescope you wish to eavesdrop at, and enter "a", "b" or "c" into each date on which your contacts are available (only one contact per night). Please be sure to consider the target observability and enter contacts, if possible, at the earliest possible date - your program may well be observed as soon as the targets become available.

Notes for Eavesdropping Contacts

In remote eavesdropping, a Contact person (you) for a given program is contacted at night and takes part in target acquisition and data assessment in real time. This page gives information you will need to know in order to take part in an eavesdropping session.


Observing on a queue of high-priority science is intensive and can be intrinsically stressful for the observers. Please be aware of the following points, which seek to ensure that they can do their job:

  • All eavesdropping sessions are done at the discretion of the observer. As noted above, eavesdropping is defined as added value; not necessary to the successful completion of the observation as specified in the OT. The observer has discretion to discontinue an eavesdropping session at any point.
  • Similarly, network connection problems in the course of a session may or may not be fixed. The observers often have their hands full. If you get disconnected, try to call back but don't assume that the observer has time to investigate what happened. They will, by definition, carry on with your observation.
  • The observer may be a staff scientist or a member of the Science Operations Specialists group. They are trained in the use of the instrument but you should not assume that they are familiar with your science.
  • Please don't ask the observer for advice on observing technique or data reduction. Such enquiries, along with questions about Phase I and II preparation, should be directed first to your NGO.
  • The observer and telescope operator work with observing systems and telescope systems as-is. They are not responsible for the properties or efficiency of these systems. If you, as Eavesdropper, wish to critique any aspect of these systems, please do so to the Head of Science Operations during daytime hours. Any attempt to engage the night crew in such discussion will normally result in a swiftly terminated session.
  • The observer is empowered to ensure that an eavesdropping session does not interfere with the nightly queue plan. If, for example, the queue plan states that your observation must stop and some defined time in order to get onto a high-priority observation in the queue, they will stop it at that time.
  • If you are not content with any of the above as it pans out in any given eavesdropping session, you should contact the relevant Head of Science Operations. Do not debate with the observer.


Here we give a brief description of the observing process.

Two people are typically present at the control room: one runs the telescope, the other runs the science program. Eavesdropping adds you. The observing process you are joining in with is described below; the call you receive will normally have gone out between 15 and 30 minutes before the first of these steps.

  1. Observer loads your program in the OT and selects the observation.
  2. Observer sends the observation to the seqexec which then runs it.
  3. Telescope operator slews to the target, while instrument is automatically configuring (can be a few minutes depending on distance to target).
  4. Telescope operator acquires guide star and sets guiding going (up to six minutes total for steps 1 and 2 combined).
  5. Observer, Telescope Operator and Eavesdropper acquire the target (involves taking an image and using "gacq", and iterative offsetting) (instrument specific, see the instrument overhead pages for details).
  6. Observer starts running the seqexec and thus exposing.
  7. First frame comes in and is displayed on the screen sharing session (Eavesdropper and Observer inspect and confirm continuation).
  8. DHS saves data and the Eavesdropper can pick them up from the FITS server.

Contact Person Actions

Once you receive the call, you will normally do the following:

  1. Wake up (sorry!).
  2. Run skype and a browser on your laptop, ipad or other computer.
  3. In skype, contact "gneavesdrop" or "gseavesdrop" and get a video call going. If this is the first time you have eavesdropped, you will need to ask for gseavesdrop or gneavesdrop to allow itself to be added to your contacts before you'll be able to call.
  4. If you want to assess data in real time: in your browser, connect to the gemini gateway (via which you will access the FITS storage server to get quick access to your data). Instructions for the latter are below.

During the Call

The observer will set skype to share the desktop on their machine and display one of the telops workstation screens via it. this is the screen on which they will display the target acquisition. You should be able to see that and comment on the target field as the Observer acquires the target. Once the first data frames come in, you will have two options: either just watch the frames on the skype session, or download them via the gateway session in your browser.

Accessing your Data

The Gemini Observatory Archive is designed to make data available for download within a minute or so of the readout completing, and is now the recommended way to download data during eavesdropping sessions. Data access during eavesdropping is now via the archive the same as regular post observing data access.

Your science data will be proprietary. In order to access proprietary data for your program, you will need to have created an account on the archive and be logged in, and you will also need to have registered your program ID with your archive account. Details of this process are provided here. You are encouraged to do this ahead of time, both so that you don't need to do it in real-time when we've just woken you up and as we're observing your project, and also so you get to see the system ahead of time.

Once logged in, we recommend you put both your program ID and the current UT date in the search form to see your data from tonight. Clicking the "Search" button will update the results. Click the [D] next to a file to download that one file. The [P] gives a jpeg preview of the file if available - the preview for each file may take an extra minute or two to become available, so very recent data may not have a [P] link.