Using the Obervation Preparation Tool (OPT)
Building Your SB
Hardware Setup and Doppler Tracking
The "hardware setup" column is very similar; it shows the hardware setup selected if a resource was previously assigned. Click "No Change" to select the exact resource setting of the preceding scan (it must be defined for that preceding scan of course). Click "Change" to get a familiar dialog box to select your resource catalog, resource group and resource from (only) the predefined resources in the RCT. Resources cannot be defined "on the fly". Also here it is useful to specify all hardware resources (and pointing scan setups) in this SB in a single resource catalog (group), but because resource catalogs typically are not as extensive as source catalogs it is less of a hassle if you don't.
Doppler tracking on resources with rest frequencies is currently disabled; see Appendix A! The next paragraph currently is for background information only.
Spectral line resources that were set up with a rest frequency instead of a fixed sky frequency have to be specified with an option for the Doppler tracking in a third table at the bottom of the page. Choices are to use the information in the source catalog for the source used in the scan (typically done if this is your target source scan), to use another source in any of your catalogs (typically one would choose the target source if this is your calibrator scan for that target), or you can specify another direction in the sky and another velocity to track. The recalculated sky frequencies for the starting time of the completed SB will show in the scan listing mentioned further down.
Intents
In the intents you should indicate the intent of the scan. By default it is set to "Observe Target" (for "Standard Observing"), but you can add more than one intent to it. For example for your phase calibrator you would tick "Complex Gain Calibration", for 3C286 you would choose "Flux Calibration" and for any suitable source you intend to use for bandpass calibration you would select "Bandpass Calibration". The most common options are shown, and the more specialized options that you probably would not want to use are hidden behind the "More" button. More than one intent may be ticked, and will be useful for later use, in particular for automated pipelining. Note that if you leave the intent to the default (Observe Target), you will not have calibrator codes with your data which may complicate your data reduction; in particular it will prevent automated pipelining to handle your data.
Introduction
The idea is to define a sequence of scans in the left hand side column, each with a source, a resource, an observing mode, a time interval and some reason (intent). Each time a scan is added you need to specify these items. However, it is not always straightforward to assemble this scan list in the sequence you want the first time around, and you will need to move scans around. This is easily done! That is, there is no need to panic if you make scans (a bit) out of order; it is almost straightforward to add, e.g., an extra bandpass calibration scan, to move some scans to the middle of the observation, or to redefine source loops after the main framework of your schedule is set up.
Scan Timing
The scan timing determines the length of the scan, either in LST (sidereal) or in UT. The difference is about ten seconds in an hour. It is probably best for everyone to leave keep your schedule in LST when observing with the EVLA only. Options are to set the exact time the scan has to end ("Stop Time", only useful for fixed date schedules), the total (maximum) time the scan may take from the end of the previous scan including telescope slewing time ("Duration"), or the time the telescopes should track the source regardless of telescope slewing time ("On Source", previously known as "Dwell"). Dynamically allocated observing time schedules must be in "Duration (LST)". Note that in the end, the duration of the SB should be an integer multiple of 30 LST minutes (or slightly less).
Target Source
The "target source" column either shows you the name of the target source (i.e. telescope pointing direction) or tells you that no source is assigned. A source needs to be specified and if it is not the one you want, press the "change" button. This brings up a dialog box to interact with the source catalogs that are in your SCT data base. Select the source catalog and the group within that catalog you want to extract a predefined source from. Simply tick the source name - you may have to scroll down your list to find the desired one. Note that you cannot define sources "on the fly"; only sources specified previously in a source catalog in the SCT can be selected. You may need to switch to the SCT if you desire to observe a source that was not previously defined and do so at this time.
Figure 4.4: Changing the resource in a scan overview/details page.
As you will be doing this changing of sources potentially for every scan, you probably see that it might be useful to collect all sources that you want to use in this SB in a single catalog (group), i.e., with your target sources but also with your calibrator and tipping sources from, e.g., the "VLA" list. Otherwise you will be switching back and forth and scrolling up and down a lot.
The First Scan
Create a first scan if necessary: FILE - CREATE NEW - NEW SCAN. Select your first scan (click on "[New Scan]" next to the telescope icon and "STD" in the left hand side column); it contains default parameters such as a scan mode "Standard Observing" for 5 minutes "duration" ("on source" is previously known as "dwell time"), and you will notice three tabs at the top. The number of tabs depends on the scan mode. Current scan modes are "Standard Observing" (tracking a sidereal position in the sky), "Interferometric Pointing" (for improving telescope pointing) and "Tipping" (for measuring opacity curves). Each mode has a different code that shows next to the telescope icon: STD, IP and TIP respectively. Next we will describe "Standard Observing" (STD), which is equivalent to"Standard Interferometer" in Jobserve. IP and TIP modes will be described further below.
Selecting Standard Observing
(STD) for "scan mode" displays two tabs: "Overview" and "Comments". In "Overview" you set up the actual scan (Figure 4.4), whereas in "Comments" you may enter anything specific for this scan for your own reference.
Within the "Overview" tab two tables are displayed. In the first, you name your scan. Note that the scan name is just for the scheduling display in this tree (and in the summary); it is the source name specified in the SCT catalog that ends up in your data. It is followed by scan mode ("Standard Observing"), the antenna wrap, whether or not you want to apply the solution from a previous pointing scan, and whether observing "over the top" is acceptable (most likely not!). The antenna wrap and reference pointing are described further below.
The second table contains the actual target source, the hardware setup (with Doppler tracking settings), scan timing and intents with this scan. Each of these fields must be completed, and an error would result if any of these fields is unspecified.
Calibration
Most observers would want to include calibration scans next to their target source scans. Almost always you would schedule one or two scans on a flux density scale ("amplitude" or "primary") calibrator (e.g., 3C286, J1331+3030) somewhere in the schedule where it is convenient. Spectral line observers would also include one or more scans on a bandpass calibrator if the flux density calibrator is not suited for this (if it is, please select both flux density scale and bandpass calibration as "Intents" for this calibrator source). The target source position scan typically is sandwiched between complex gain ("phase" or "secondary") calibrator scans. To increase integration time beyond the coherence time on a target source, at higher frequencies it is customary to do this as a "fast switching" scan in Jobserve, i.e., not to schedule it as a sequence of new individual scans. Whether or not, the resultant procedure is to loop between your calibrator and target sources.
Checking Your SB
When you have created your sequence of scans for this SB, and no errors and warnings need further attention, go back to the SB page (click on the SB name in the tree of the scans). On the second line you will see how much LST time the observing scans in this SB would consume. The total time consumed by this SB from the allocated time in the PB is the time for the SB times the required "counts" (number of repeats) of this SB. If this time is more than your allocated time, modify one or more of the scans in the SB (delete scans or adjust the time for scans). Remember that your SB length should be close to an integer number of 30 LST minutes and absolutely not longer than your allocated time. If the time is within your allocation, select the second tab-page ("SB Summary").
This tab-page summarizes your SB in three tables. The first table displays all unique resources used in this SB, the second shows all unique source-with-resource combinations, and the third table lists the sequence of scans with their details. Obviously, you should check these tables thoroughly for each tiny detail, e.g., whether you applied the reference pointing solutions ("Apply Ref. Ptg.") to the scans where this correction is useful. The table with the scan sequence will show loops (if any) initially in a collapsed form. It is strongly advised to click the expand-icon (![\includegraphics[height=3mm]{psimg/expand.png.ps}](https://e2e.nrao.edu/opt/OPTMANUAL/img89.png){kind=small}
) to show the scan details of the scans in the loop. You can expand all loops in the scan table at the same time using the expand button in the top left hand side corner of the table, and similarly collapse all loops in one go. After verification that all these scans are as intended, the loop may be collapsed again.
Figure 4.7: Web browser screen shots of the Validate & Submit page.
Printing the SB scan listing
can be done from the tab-page that holds the scan listing ("SB Summary"): click "Print" () in the upper left corner at the start of the tab. It will take you to a printer friendly frame from which you can use your browser's printing tool. You probably want to set the printing properties such that it shrinks the page to fit. You also would want to enable printing of background colors if you are interested to see the errors highlighted; offending values are also struck out to identify errors on your printed copy. Both the "SB Summary" page and the remaining error and warning messages from the interface feedback strip (if any) are printed. Loops in the scan listing are not automatically collapsed nor expanded; it will print as selected in the scan listing at the time of printing. To print the page with all loops expanded, use the alternative print icon.
Bulk edit
is available, for example if you notice that you have many scans with the wrong source (position, velocity) or resource. Go to the SCT or RCT to correct your (re)source or to add a modified version of the (re)source. Then highlight the SB and select EDIT - BULK EDIT. Select the old (re)source name that needs to be corrected, select the new (re)source name you want to replace it with and press "search". This will give you the option to (de)select any scan as the "Confirm Each Change" tick-box is selected by default. The (re)source to be replaced and the (re)source that replaces it may have the same name, that is, when the original (re)source in the SCT or RCT now has the corrected values. This will overwrite the previously copied values, the values the (re)source had when creating the scan originally. Make sure you check the changes were actually applied as you intended before submitting. More advanced bulk editing may become available in a later version.
Validation and submission
is offered in the third tab-page of the SB. Validate and fix any errors that may appear. If you find out that you need help, you can request help from NRAO staff by using the text area provided. When help is requested, you will get an email with a copy of your help request. It will take some time for a response, so please be concise and refrain from repeated use until you hear back.
When you have created one or more SBs for this PB, go back to the PB page (click on the PB name in the tree of the SBs). In the table at the bottom you will find a summary of your SBs in this PB, with some accounting of the time each SB has consumed. You should check this before you submit your schedule, because your SBs will not be accepted for scheduling if they are using up more time than allocated for your project, or more than allocated for you fixed-date SB.
Defining Your Project's PB and SB(s)
There should be at least one project in your tree (if not, use FILE - CREATE NEW - NEW PROJECT) with, when you expand it using the plus-icon in the icon menu, a PB, and possibly a SB and a scan. Click on your project, especially if it has no plus-icon in front of it (and thus is not loaded into memory), and give it some descriptive title if it has not been filled in from the PST information. Similarly, click on your PB and name it.
Each PB is defined for an observing trimester, typically a single VLA array configuration with some hybrid configuration and move time configurations. For your PB, if not transferred from the PST, select the array configuration for which this PB is valid by dragging the array configuration name from the right hand side column to the left hand side column. More than one (consecutive) array configurations, or "Any", can be specified. If your project spans more than one clearly different observing runs per trimester, e.g. some southern sources in BnA array and some more northern sources in B array, simply add more PBs to this project using FILE - CREATE NEW - NEW PROGRAM BLOCK. The table at the bottom is a read-only, sortable administrative table. It keeps track of the total time scheduled in the SB(s) in this PB.
Create a first SB if necessary: FILE - CREATE NEW - NEW SCHEDULING BLOCK. When you next click on the SB, you are presented with three tab-pages in the main editing window (Figure 4.2). In the first tab ("SB Details"), name your SB and select whether it is a fixed-date SB or a dynamic SB - the tab-page will change with different scheduling constraints depending on the choice made; they should have self-explanatory labels and fly-over help tool-tips.
Figure 4.3: Web browser screen shots of the SB details page, bottom portion.
For fixed-date allocations you may have to fill out the starting day (VLA day, i.e., modified Julian day number on the VLA schedule) and LST time of your allocation. To schedule in UT time, e.g., for VLBI scheduling, you can use the UTC toggle-box. The "Array Starting Position" is an option to aid you in anticipating a worst case scenario of the antenna wrap, or to calculate the slew time in the unlikely case that you know where the array will be pointing at the end of a previous observation. Only for the latter you may choose "Equatorial" to enter a (J2000) Right Ascension and Declination, but for the former choose "Horizontal" to enter an Azimuth and Elevation of the anticipated array starting position.
For dynamically allocated observing time you are asked if there are any scheduling constraints. Possible constraints are a range of possible (or convenient) LST starting times, a first date of possible observations, and a starting position of the array. Other constraints deal with the weather at the site. Defaults for weather at specific bands are given in the table; see Figure 4.3. Select the description of the weather constraints that you want to apply, or specify your own constraints (supply both wind and atmospheric phase limits). The antennas will stow when the wind speed reaches 18 m/s). Consult Appendix A for more on SBs for dynamically allocated observing time.
This tab-page also contains a field in which you can communicate your notes, requests, concerns, other constraints, etc, to the operator. If your observations for this trimester include sources that cannot be observed in one consecutive time interval in the time allocated, or if you have more than one fixed-date allocations, you can define different SBs for the different LST ranges or fixed-dates, again by using the menu strip at the top: FILE - CREATE NEW - NEW SCHEDULING BLOCK. If your observing runs are very similar, simply copy the SB and adjust the new SB as required (or increase the repetition count).
The other two tab-pages are not relevant at this stage and will be described below. You are now ready to start making scans in this SB.
Exiting
The proper way to exit the OPT web application is to use FILE - EXIT. You will be prompted about saving changes to your catalogs and projects if there are any, and if you have not saved your work previously using FILE - SAVE ALL.
Exiting can also be achieved, or happen, due to a period of inactivity (currently several hours, but this may change). A time out of the tool will collect all unsaved changes in a copy of the project and/or catalogs that were changed. You can recover these changes when you log in again; they are saved in the copy named "Autosave:" with the name of the project or catalog. These "Autosave:" projects and catalogs should also be created in case there is an ungraceful disconnect, i.e., when the Internet connection ceases.
Introduction
Assuming you already have successfully logged in to the OPT web application, and assuming that there is no message in the "Important message banner" that makes you decide to abandon the OPT for the moment, look for the navigation bar at the top. If "Observation Preparation" is not in bold face, but in normal font and underlined, click on it (Figure 4.1).
Figure 4.1: Web browser screen shot of the OPT opening page.
A short introduction to the layout of this tool's page has been given in the introduction (Chapter 1). This chapter uses the information contained in the resource catalogs (Chapter 2) and information contained in the source catalogs (Chapter 3). It is assumed that the contents of these chapters are familiar, and that the information in the (re)source catalogs is correct. There should be at least one project tree visible in the project browser, with a PB, and possibly a SB and a scan. To activate your project (i.e., to load it in memory), highlight it to see a plus sign () appear in front of its name. Do this for the project that you want to be working on. This may take a while if there are many SBs and/or many scans in the SB(s). As with every operation in the OPT web application, please exercise patience.
If you need to define an additional (test) project or if your project was not filled from the PST, use FILE - CREATE NEW - NEW PROJECT. In the latter case, for a non-test project uncheck the "Test Project" check box, in the dialog window and enter your project (legacy) code without spaces (e.g., AS987) and your proposal code (e.g., 09A-191) before clicking "Add". Note that these codes only work if your projects with these codes were previously approved by the schedulers and you were notified of this by email. This should create a new project tree that you can name and edit. Both the slanted names in a project tree and a yellow dot on the icons means that it is unsaved data.
The purpose of the OPT is to combine a source from one of your source catalogs with a resource from one of your resource catalogs, and to specify an observing mode, a time interval and an intent for this combination. Repetitive combinations will build an observing schedule that defines a SB observation which may be executed by EVLA operations. The sequence of scans in a SB will show in the left hand side column in the project (etc.) tree.
It is useful to outline the project in terms of the PB and SBs in advance. Use information from the proposal, etc. (see Chapter 1) and create (re)source catalogs with only the subset of (re)sources that will be used in the SB you are about to create. Having your (re)sources in small personal catalogs is convenient and faster than having large catalogs or switching back and forth between your personal catalog(s) and, e.g., the "VLA" catalog . Also consider exporting and removing (in that order!) all other (re)source catalogs and projects that you don't need. Check the remaining (re)sources for correctness before you continue.
Moving About
The schedule created may not be your most preferred schedule, both in the details of each scan and in the order of the scans. If you desire to rename a scan or a scan loop (or a SB or a PB), at any time select the scan and edit the name or time interval, or reselect a (re)source.
Figure 4.6: Web browser screen shots of the SB scan listing page, scrolling further down.
By using the menu strip or the icon menu it is possible to delete, cut/paste and add any number of individual scans (or scan loops) to any position in the tree at any time. Some handy icons are the arrows that move a selected scan (loop) up or down in the current tree (i.e., keeping loops intact as loops), and in or out of a scan loop. Currently still fragile, but useful, is to drag and drop the scan () or loop (
) icon to the desired location in the tree or loop. If you place the icon on top of another scan, this scan will be highlighted. When you drop the scan on top of another, highlighted scan, the scan will be placed directly after the highlighted scan; be patient when doing this as it will take some time to appear. This dragging only works on the icon, not on the name of the scan (which selects the scan). Always check the result. There seems to be issues with this feature if you are working deeper down in the left hand side column.
Orientation
The left hand side column
in the OPT contains a collection of projects, instead of a list of catalogs. Projects are subdivided in a tree of PBs, each subdivided in SBs, which each contain scans. This column, per SB, thus holds the scan list, i.e., the column represents the observing schedule. In contrast to the RCT and SCT, much of the editing in the OPT will be performed in the left hand side column as well as in the main editing window.
The icon menu
in the OPT has more options than in the RCT and SCT. The common icons have the same functionality as the icons in the RCT and SCT, but as more editing is done in the left hand side column some extra icons (with their fly-over help tool-tip) are added. Only icons valid for the selected or highlighted items (e.g., PB or scan) are displayed. A full list of icons and their meanings is shown in the listing.
| Save projects/catalogs in this tree | |
| Cut (or delete) selected tree item | |
| Copy selected tree item | |
| Copy selected tree item and paste it directly after this item | |
| Paste selected tree item | |
| Icon menu separator (no action) | |
| Promote selected item up, above the current tree branch (out of loop) | |
| Demote selected item down, in the next current tree branch (into loop) | |
| Move selected tree item up in current tree branch (before previous scan) | |
| Move selected tree item down in current tree branch (after next scan) | |
| Icon menu separator (no action) | |
| Collapse/hide all items in the selected tree | |
| Expand/show all items in the selected tree |
The menu strip
options in the OPT are a bit more complicated and at this time some of the options are disabled or non-functional. The options that are currently relevant in creating your schedule are given in the table.
| FILE | CREATE NEW | PROJECT | EDIT | BULK EDIT | HELP | |
| PROGRAM BLOCK | CUT [ITEM NAME] | ABOUT THE OPT | ||||
| SCHEDULING BLOCK | COPY [ITEM NAME] | MANUAL | ||||
| SCAN | PASTE AFTER/INTO [ITEM NAME] | CONTACT INFO. | ||||
| SCAN LOOP | PASTE BEFORE [ITEM NAME] | |||||
| SAVE ALL | ||||||
| EXPORT... | ||||||
| IMPORT... | ||||||
| EXIT |
Figure 4.2: Web browser screen shots of the SB details page, top portion.
Other Calibration Scans
Besides the "Standard Observing" mode on the scan page, you can select "Interferometric Pointing" and "Tipping" scans. These are special observing modes for calibration, typically applied when observing at high frequencies (above ~ 15 GHz).
Pointing Scan
(IP) may be needed at frequencies of about 15 GHz and higher (K, Ka and Q band). At these frequencies the antenna pointing accuracy (a few arcseconds) becomes a significant fraction of the primary beam. Observing with an inaccurate pointing thus may degrade the signal by a significant fraction. The antenna pointing is a function of the shape of the reflective surfaces and is influenced by, amongst others, gravity and temperature. Therefore, observing at high frequencies may require regular pointing scans to determine offsets from the pointing model. These pointing offsets are usually reasonable for target sources within up to 30 degrees in Azimuth or Elevation from the pointing source. Therefore, typically one would redetermine pointing solutions when moving to a different portion of the sky, or roughly hourly when tracking a (group of nearby) target source(s).
Pointing scans are performed as a five-point raster observation on a strong (over 300 mJy) continuum calibrator, in first instance in X band continuum. This "primary reference pointing" scan usually yields sufficiently accurate pointing offsets, but if more accurate solutions are required a "secondary reference pointing" may follow at the (standard) frequency of the observing band. Secondary pointing is also performed in continuum mode (to be as sensitive as possible to the continuum source) in an attempt to improve the antenna pointing in the band of interest. However, local lore is that although this might improve the pointing a bit toward the pointing source, subsequent slews and with time passing by, this secondary pointing in general does not yield a long lasting improvement on the primary pointing. In addition there is the risk that for some antennas the secondary solution fails. The resources for secondary pointing scans are available, but whether the extra time spent to perform a secondary pointing scan is worthwhile is debatable. Determining pointing solutions using spectral line sources, e.g., with SiO masers in Q band, has not been tested.
Default pointing resources are included in the "NRAO defaults" catalog in the group "Pointing setups" for your convenience. You may want to copy the resources and pointing sources you wish to use from the standard catalogs to your personal catalog. Do not forget to select "Interferometric Pointing" for the observing mode and an "on source" time of at least 2.5 (LST) minutes. You want to start a block of high frequency observations with a pointing scan, and tick the "apply reference pointing" in the first tab-page of the scans in this block thereafter. This tick-box will actually apply the offsets that were determined in a previous pointing scan; if you forget you will be using the (most likely less accurate) default pointing model. Your very first scan may be a pointing scan, but as you don't know in what Azimuth the array starts, you want to allow for ample slewing time or anticipate a worst case scenario using the Azimuth starting conditions on the SB page.
If the pointing scan has not finished by the stop-time of this scan, no valid solutions can be applied. If it has determined a pointing solution before the stop-time has been reached it will continue with another five-point raster, which may or may not yield new solutions (which will be averaged with the first raster solutions). For "secondary reference pointing" scans, apply the solutions of the preceding "primary reference pointing" scan.
A pointing scan is for real-time calibration and, while very useful for real-time calibration, usually does not yield useful data for your project. The data is however included in the observations, be it that you need special switches to load the data in your data reduction package. You may study this data for reference, but the real-time corrections are already applied and cannot be undone.
Tipping Scan
(TIP) may be needed if you are concerned about calibrating the absolute flux density of your target source(s). The atmosphere absorbs some of the radiation, and the fraction of the absorbed radiation depends on the opacity, the transparency of the atmosphere. It is mainly dependent on the content of water vapor between the target source and the antenna(s), and can be derived from a series of system temperature measurements at various elevations. One would redetermine the opacity on the time scale in which significant changes are expected, i.e., the time scale in which the water vapor content of the atmosphere above the telescopes changes. This is a strong function of baseline length and actual weather and no real guideline on time scales is available. Use common sense in the trade-off between overhead and usefulness of the scans in post-processing.
Figure 4.5: Web browser screen shots of the SB scan listing page, top portion.
Tipping scans are performed toward an Azimuth direction close to your sources at about the observing frequency. The scan samples seven elevations between about 20 and 60 degrees for a system temperature and can be directed from top to bottom (down) or from bottom to top (up). When you select an Azimuth for your tipping scan, be aware that shadowing may occur, especially in C and D array configurations. Avoid the Azimuth directions of the arms, i.e., avoid measuring tips close to the Azimuths of -5, 56, 115, 175, 236, 295, 355 and 416 degrees.
You have to select "Tipping" for the observing mode to expose the tipping scan tab pages. Tipping scans are set up using one of your resources and probably are best done with the widest bandwidth available; make a new resource if you need it. You do not need a physical source. The "on source" time is fixed to 5 (on source LST) minutes, because it takes this much time to complete your tipping scan (in one direction, up or down). In the "Details" tab you will have to set the Azimuth and direction; do not forget this as otherwise you will be slewing to the default Azimuth of 0 degrees (North) and may hit a wrap constraint. It can consume half an hour of your observing time to return to your science observing. Always set the Azimuth.
You may place any number of tipping scans anywhere in your schedule as you feel fit to monitor the opacity during your observations, although you may want to do this close to your block(s) of high frequency observations. Your very first scan may be a tipping scan, but as you don't know in what Azimuth the array starts, you want to allow for ample slewing time or anticipate a worst case scenario using the Azimuth starting conditions on the SB page.
If the tipping scan has not finished by the stop-time of this scan, the data will contain those elevation samples (out of seven) that were completed. If it has completed the tip before the stop-time, it simply will continue with the next scan until the regular stop-time for that scan - this scan may be used to buffer the difference, e.g., absorb the extra time on your bandpass calibrator.
A tipping scan is for off-line calibration and may or may not yield useful data for your project. The data is included in the observations and you need special switches to load the data in you data reduction package. A "tip" would allow you to determine the opacity of the atmosphere during the tipping scan (i.e., during your observation), and you can use that value to correct for the atmospheric absorption in your data. Read the manual of your data reduction package on how to obtain and apply tipping scan data corrections.
Recap
This chapter should have made you familiar with creating scans from (re)sources, creating and checking an observing schedule (SB), and submitting your SB to operations.
Scan Loops
Setting up a "scan loop" is done using the menu strip: FILE - CREATE NEW - NEW SCAN LOOP. It will show you a "Scan loop details" page in the main editing window; assign a descriptive name to it and specify the number of iterations of this loop. The tick-box for bracketed means to copy the first scan in the loop to the end of the loop, i.e., add another calibrator scan so that the last target scan is also bracketed between two calibrator scans when the first scan in the loop is on a calibrator source. The four tree setups of scans in the table of examples below are equivalent; they all enclose scans on a target with a scan on a calibrator source before and after each target scan, i.e., they all result in the sequence Cal - Target - Cal - Target - Cal.
| No Loop | Normal Loop | Bracketed Loop | |
|---|---|---|---|
| Individual Scans | two different orderings | should start with Cal | |
In the example on the right hand side (the most compact, bracketed loop) the double-star after the loop icon, in front of the number of iterations of this loop, indicates that this loop is a bracketed loop. To achieve bracketing of the target source(s) with scans on the calibrator source, the bracketed loop must begin with the calibrator source scan. Of course one is free in choosing any of the possible scheduling solutions; the resulting observing script is the same either way, but the scan listing summary will differ in compactness and clarity. Also, if there is a long slew to the sources in the loop, the best way to absorb the slew in the scan duration of the first calibrator scan is using "No Loop" or "Loop1", as otherwise this extra slew time is also added to the duration of the loop calibrator scan.
Note that you can NOT use the "No Change" resource option in the first scan of a loop! This is because when unfolding the loop, the "previous scan" in the first source of the loop can refer to the resource of the last scan outside the loop (first occurrence) as well as the last scan inside the loop (any following occurrences).
A loop can contain any number of sources, not necessarily only a calibrator scan and a single target scan. If your target sources are near in the sky and you can get away with a single calibrator for all of these targets you can group them in a loop with more than one, say four, target scans before returning to your calibrator. Keep in mind that the total loop time should be shorter than the anticipated coherence time at our observing frequency. Loops may also contain loops. If your loop is selected, adding a new scan will place this new scan in the scan loop. The only difference with a normal scan is that this scan will be scheduled as many times as the "Loop iterations" specified, consecutively in a loop with the other sources in the loop. When finished with defining a loop, you may want to highlight it and then collapse it (using from the icon menu) for a more compact display in the tree.
Sharing Projects
You can export your project containing your PBs and SBs to a local disk just like you can save the RCT and SCT catalogs (by selecting FILE - EXPORT). It is good practice to do so, and to delete obsolete projects and catalogs when the contents in the OPT web application data base gets large. You will appreciate the increase in speed over the network while you know you can always reload these catalogs and projects when you need them again. By the way, the exported XML file is not used for submitting your schedule, just for you and your collaborators to communicate or keep safe.
Submitting Your SB
Once everything is in order, when you are within your time limits and no errors remain, you can submit your SB schedule using the third tab on the SB page (click on the SB name and select the "Validate & Submit" tab page). It will send the information to the relevant places within EVLA operations and show you a message to that effect. All you need to do now is keep your fingers crossed... Note that you do not send a (observe) file to an NRAO email address as you may have been used to, only press a button. The SB will turn read-only: the SB name will appear in slanted red font.
When you realize you have an error in your submitted SB, simply select the SB in the tree, and navigate to the "Validate & Submit" tab page. You can cancel your SB submission, which creates a copy of the read-only SB in the PB. You can edit the copy, and submit it with your corrections.
While we are commissioning the first use of the WIDAR correlator, your submission will actually put your schedule in a queue that currently is on hold. After we have received your schedule we will check it for technical errors (i.e., not the sequence of scans, but for the WIDAR resources) and release it to the observing queue when it is found to be valid for setting up the WIDAR correlator. This practice will change with experience.
Subsequent Scans
There are a few ways to add extra scans. A blank-slate scan can be obtained using the menu strip: FILE - CREATE NEW - NEW SCAN. It will be inserted after the current highlighted scan in the tree, and will become the active (newly highlighted) scan.
Another way to obtain a new scan is by using the icon menu. It has several icons dealing with creating scans. Using the icons for copy and paste, a new scan can be created from a previously created scan, and be pasted at any position in the scan tree after selecting (highlighting) the scan it has to follow in the tree. The same can be achieved using the icon with the little green dot (), although this will paste the new scan directly after the scan that is copied, which is useful when building your scans sequentially.
You probably want to change your source of the scan if you place the new scan directly after the previous one (otherwise it is the same scan). Please take an effort to fill out the correct scan intent for each scan.
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