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Technical Justification
In order for the proposal review committees to judge that the proposed observations are technically feasible and will achieve the scientific objectives, it is necessary for the user to justify the various choices that were made when creating the Science Goal. For example, for a spectral line observation it must be shown that the requested sensitivity and correlator setup will enable the line to be detected with sufficient signal to noise and that the spectral resolution of the correlator mode, perhaps including spectral averaging, is appropriate.
From Cycle 2 onwards, the technical justification is no longer submitted as part of the PDF that contains the scientific case, but is instead created using a node in the Science Goal. This has been designed to help non-expert users in particular in the writing of technical justifications by presenting various calculations based on the SG contents e.g. the signal to noise ratio on the spectral line and the spectral dynamic range. For most projects, the technical justification node is split into four separate sections, each of which has a free-format text box in which the relevant item must be justified. The four sections are:
- Sensitivity: The OT presents a number of signal to noise calculations, depending on whether the SG is targeting spectral lines, continuua, or both. The discussion should convince the technical assessor that the line or continuum is being observed with sufficient signal to noise and that there enough spectral bins across each spectral line to perform the scientific goals.
- Imaging: This should include an explanation of why the specific values of the angular resolution and largest angular scale were requested and discuss whether the arrays selected by the OT will produce a suitable image of the source. Images resulting from simulations that are relevant to this discussion should be attached to the PDF containing the scientific justification.
- Correlator configuration: The main thing to discuss here is the spectral resolution that has been selected and why. Spectral averaging should be mentioned if this has been requested.
- Choices to be justified: There are a number of setup options which, if selected, should be mentioned in the technical justification text. For example, single polarization will normally not be selected as this results in lower sensitivity. However, for a given spectral window width, single polarization gives twice the number of channels and therefore it can be useful when very high spectral resolution is required. As another example, mosaic observations are normally conducted with the individual pointings separated by the Nyquist frequency, but in survey observations where large sources are not being imaged, this is not necessary and larger separations can be used. If this is the case, a brief discussion of the reasons why the non-Nyquist value was chosen can make the job of the technical assessor a lot easier.
The exceptions are VLBI and solar projects where instead only a single free-format text box needs to be completed. As a sensitivity is not entered by the user, the OT cannot display SNR calculations. In all cases, the justification texts must contain a minimum of 50 characters and no more than 4000 are allowed.
Note that it is possible to copy and paste whole technical justifications from one Science Goal to another. This can either be done via the Edit menu, or one can simply drag and drop the node into the destination SG. Alternatively, the contents of individual text boxes can be copied and pasted.
Next: Summary Information
Up: Adding Phase-1 Science Goals
Previous: Time-constrained observing
Contents
The ALMA OT Team, 2018 Sep 25