VLA > General Observing Setup Tool (GOST)

# General Observing Setup Tool (GOST)

For DDT submissions after the Call for Proposals but before the approaching deadline only: start the old GOST version by clicking the DDT version.

## The General Observing Setup Tool (GOST)

### Introduction

The General Observing Setup Tool (GOST for short) is used at the proposal planning stage to specify the anticipated correlator configuration and resources to be used in conjunction with the proposed Karl G. Jansky Very Large Array (VLA) observations.

GOST is a Java application and is updated for the expected capabilities per VLA observing semester as advertised in the Call for Proposals (CfP, see the current OSS). The use of GOST is required for non-default continuum and spectral line observations in order to ensure that planned correlator setups and data rates comply with the capabilities offered for each VLA observing semester. Proposers who define spectral line correlator configurations must ensure that such configurations are, in fact, allowed and that these configurations are correctly communicated to those reading the proposals. GOST helps determining whether a setup is (in principle) possible and whether it falls under Standard, Shared risk, or Resident shared risk observing.

The tool enforces most of the known hardware limitations, such as on the number of subbands and number of channels, but does not include the detailed frequency setup for all subbands. GOST does not replace the careful validation that, including the detailed frequency configuration setup checking, is done in the Resource Catalog Tool (RCT). Note that if a correlator configuration can be configured in GOST, it does not mean that it is wise, or that considerations and restrictions outside the correlator are not equally or even more important. If in doubt, create the full setup in a test resource and validate it in the RCT and/or consult the NRAO Helpdesk.

Proposers must attach the output of this program as a screen snapshot for each of the possible line setups used in the proposal to communicate their intent to the reviewers and the Time Allocation Committee. Continuum and Resident shared risk (RSRO) configurations do not require GOST. Default Continuum resources are integrated into the Proposal Submission Tool (PST) and therefore can be selected directly. RSRO configurations must be described in detail in the appropriate sections of the proposal's Technical Justification.

In the near future it is anticipated that GOST will be replaced by actual resources as defined in the RCT. The RCT is part of the Observation Preparation Tool (OPT).

The rest of this document describes running GOST. For capabilities, definitions and other proposing and observing related content please see the current VLA Observational Status Summary (OSS), the Guide to Proposing for the VLA, the Guide to Observing with the VLA, the Proposal Submission Tool (PST) manual, and the NRAO and VLA science web pages in general. For missing or confusing documentation, etc., please contact the NRAO Helpdesk with your queries and/or suggestions.

### Starting GOST

GOST should only be used to define configurations for Standard and Shared risk observing in non-default continuum and spectral line mode. Plain Continuum can be selected as a default mode in the PST; Resident shared risk configurations must be described in text in the proposal.

To run GOST, a current version of Java webStart needs to be available on the host computer. The Java issues page has solutions for potential problems. The interactive GOST Java application can be launched (left click) or, alternatively, downloaded (right click) as a jnlp-file and selecting Save link as... In the latter case, GOST can be run without an Internet connection from the command line with javaws <downloadDirectory>/latestGOST.jnlp; this has the disadvantage that an older version of GOST may run if it has not been replaced by the newer version. Usually this is not a problem if the jnlp-file is downloaded just before running it.

This is the default view of GOST when first launched (click the images to enlarge in a new tab or window).

 Figure 4.1.1: At the top left hand side there is an option menu (Subbands, View and Help) (see figure left), but more importantly there is a configuration designation in colored font in the top center field (see figure above). At the bottom a Save button will save a screen shot to disk which then should be attached to the proposal in the PST (see figure below). Fields shown in blue font are editable and thus under control of the proposer; fonts in black are derived from the selections made.

### Configuration Designation

In the center of the menu bar is a box that contains one of four (five) possible designations for the correlator configuration. The designations are:

 Standard The configuration conforms to the general capabilities of the VLA for this proposal cycle. Standard (with Justification) As above, but additional justification needs to be added to the text (currently this only applies to data rates exceeding a certain boundary rate). Shared Risk The configuration goes slightly beyond the general and tested capabilities of this proposal cycle and therefore has an element of risk associated with it. Shared risk proposals will not be given the highest scheduling priority due to the unverified nature of the setup, but will otherwise be handled like a general proposal such as being scheduled dynamically. Resident Shared Risk This configuration goes significantly beyond the general capabilities of this proposal cycle. NRAO asks that observers proposing with this type of configuration spend a significant amount of time in Socorro to help develop and test this advanced capability. Invalid This configuration has a technical problem and cannot be proposed for. When this is the case, the Save button is disabled. This kind of configuration should not be saved nor attached to the proposal in the PST. Please try again.

For designations other than Standard, the labels of the triggered warnings are displayed in colored bold type with a prefix marker (e.g., "[!]", not shown in subband columns). When this is the case, please use the Why? button (which will appear next to the configuration designation) for more information as to why the software has chosen this designation. It is then left to the proposer to either change the parameters in GOST back to Standard capabilities or to accept the newer designation.

Clicking the Save button will save a screen shot of the parameters set in GOST to an image file. Please choose a directory location and a unique name for the image file. The system will automatically append a .png suffix. Save one image file for each configuration to be included in the proposal. The PST will accept these images as attachments to the proposal.

On smaller screens (e.g. laptops) pressing Save in GOST will only save the visible part of the window. If the window does not fully fit the screen, one can use the options under the View menu to adjust the size of GOST: F4 to show only A/C, F5 to show only B/D, F6 to show both A/C and B/D (default). If only a few subbands are filled, one can use the Show Unused Subbands (F7 key) to reduce the size of the screen. Note, however, that the PST only takes a single screen shot as input per resource. If two or more screen shots have to be taken to capture all the information for a resource, one needs to combine them in some other program to a single png before uploading (e.g. in xfig).

Note that GOST parameters cannot be saved! Whenever GOST is re-started, all the input parameters are set to their default values. If several closely-related configurations need to be constructed, do so in a single GOST session, saving a snapshot of each configuration when completed. Exiting the tool will require to start over again from scratch.

Special note for users with multiple monitors. Tests in the past have shown problems with the screen capture mechanism for users who have more than one monitor. After saving a GOST screen shot image to a file, please open that file to ensure it took a correct snapshot. If it did not, try moving GOST to another monitor (tests indicate that the first monitor is more likely to give proper results). If the screen capture does not properly work on any monitor, please use a third party tool to take the snapshot and save it in png format only.

## Getting Started

GOST help pages with screen shots follow first. Jump directly to GOST usage hints below.

### Spectral Line Input Help

GOST allows VLA observers to concentrate correlator capabilities on several narrow regions of frequency space (i.e., in subbands placed in basebands). The VLA offers two different samplers to the community: An 8-bit sampler with 2 basebands of 1 GHz bandwidth each (A0/C0 and B0/D0 for the two polarization pairs), and a 3-bit sampler with 4 basebands of 2 GHz baseband each (A1/C1, A2/C2, B1/D1, B2/D2). While the 3-bit sampler provides more bandwidth, the 8-bit sampler is better suited for high dynamic range experiments. The 8-bit samplers are, per frequency interval (e.g. for spectral line work), also more sensitive than the 3-bit samplers at any frequency.

For a more detailed description of basebands, subbands, baseline board pairs, etc., and their restrictions for use, please consult the WIDAR section in the OSS, the Spectral line section in the Guide to VLA observing, and the RCT section in the OPT manual.

The baseband setup fields of GOST summarizes the receiver to be used and the global setup of each baseband property. In the lower portion, the subbands tables (up to 2 by 2 sub-tables), summarize the setup of the subband properties in each of the active basebands.

Below follows the description and help for the parameter fields of each of these tables.

#### Baseband Setup Fields

Figure 4.2.1: Baseband setup fields: plain 3-bit (top) and 8-bit (bottom) views.

The observing bands labeled with the receiver names are ordered from lowest to highest frequencies. Choose the one to be used for this setup. Note that at this time 4/P-bands are not included in the drop down as only the default P-band setup is offered as non-shared risk mode and this P-band observing setup does not require GOST.

A/C and B/D Basebands
The baseband samplers to be used, either 3-bit or 8-bit. Note that mixed settings no longer result in a Shared risk configuration. 8-bit samplers require one baseband center frequency per polarization pair, 3-bit samplers require two (see Baseband Center Freq. next).
Baseband Center Freq (GHz)
Depending on the chosen sampler, these are the one or two input fields for the baseband center frequencies in GHz for AC and BD each. For 3-bit, note that the A1/C1 and A2/C2 baseband centers must be separated by less than 2.5 GHz; the same also holds for the B1/D1 and B2/D2 baseband centers. For restrictions in absolute baseband center frequencies between AC and BD, for both the 8-bit and the 3-bit system, see the OSS. Typically only Ka-band baseband center frequency settings turn out to be problematic, but it is best to check anyway.  If a baseband is not going to be used, i.e., remains without any subbands in the subband table, please set the frequency center similar to the one in the other baseband.

Dump Time (s)
Enter a time in seconds to select the correlator back-end integration time, which is the resulting visibility integration time. The advised and/or mandatory default integration times are posted in the OSS. To view the defaults as a function of frequency band and array configuration, clicking on [defaults] will open up a separate browser window pointing to the relevant section in the documentation. Any dump time below 50ms will cause this configuration to become a Shared risk configuration. The dump time entered influences the data rate (see Total Data Rate, next), with shorter dump times leading to higher data rates. High data rates may also cause this configuration to become a (Resident) Shared risk configuration as described in the CfP.
Note that integration times less than the defaults, as discussed in the OSS, require special justification in the text of the proposal. OTF will generally need shorter integrations (dump times) and is a valid justification as such. For OTF, however, special justification is required when the total data rate exceeds the boundaries for Standard, Standard (with Justification), and Shared risk.

Note that the minimum dump time stated in the CfP assumes a recirculation factor of one. When recirculation is enabled, the minimum dump time will increase with the recirculation factor, e.g., a minimum of 50ms would become a minimum of 200ms if a factor of four recirculation is applied in any of the subbands of the entire setup.

Total Data Rate
This is a display field that totals the data rates from the subbands defined in each of the basebands. There are different data rate boundaries at which a Standard setup becomes Standard (with Justification), Shared risk and Resident shared risk. Consult the CfP (and OSS) for the exact limits for each of these boundary data rate limits for this proposal cycle. To easily view the limits as function of designation, clicking on [limits] will open up a separate browser window pointing to the relevant section in the documentation. As the calculations are made for a full array (27 antennas, 351 baselines), for resources to be used in a subarray configuration, the total data rate displayed here should be scaled with the relative allocation of baselines. Notify the NRAO Helpdesk how to handle the GOST image upload when GOST persists in designating a different Shared risk, etc., mode than intended. Note that enabling recirculation may increase the total data rate above current limits.

Channels x Polarization Products Used
A display field that illustrates the consumption of the correlator capacity in terms of correlator products by this configuration. The product of the number of polarization products produced for one subband and the number of channels (also known as spectral points) into which that subband is divided, summed over all subbands, should be less than the maximum value of 16,384 (without recirculation). Another way to look at this is to say that summing over all subbands used, the correlator can produce 16,384 channels with a single polarization product; 8,192 channels at dual polarization; or 4,096 channels at full polarization.

Baseline Board Pairs Used
A display field that illustrates the consumption of the correlator capacity in terms of baseline board pairs (BlBPs) by this configuration. The correlator consists of 64 pairs of baseline boards that perform the correlations. The value displayed here is the total number of board pairs used by the active subbands in the baseband configurations.

Figure 4.2.2: Baseband fields and subbands table header views: plain 3-bit (top) and 8-bit (bottom).

(Frequency) Range
With the chosen baseband centers, these are the lowest and highest frequencies covered by this baseband. Basebands are actually either 1.024 GHz (8-bit) or 2.048 GHz wide (3-bit). This is the entire frequency range covered by the baseband and available for subband placement. The correlator does not write out data corresponding to this entire frequency range unless a set of subbands are chosen which cover that entire range (NRAO supplies these default continuum setups and GOST is not required). Note that the baseband edges are not as sensitive as the central part and subbands placed near the edges may not produce the best spectral line observations. If two lines are separated by 900–1024 MHz, it is probably best to choose one line to be observed properly, using a subband in the central part of the baseband, over putting each line at the opposite ends of a single baseband. Remaining basebands may be available to properly observe the other line.

Data Rate
The combined data rate for the subbands defined in this baseband. See the description of Total Data Rate above.

#### Subbands Table

Caution! GOST does not require or allow users to specify the center frequencies of the individual subbands. The proposal itself must discuss which lines are to be targeted. Whether a specific frequency setting of individual subbands and basebands is valid can only ultimately be verified by entering the entire setup in the RCT, including all baseband and subband frequency information as well as the Doppler settings for individual sources.

In the description below, changing a parameter in GOST is done by either selecting from the drop down menu options or by clicking on the relevant blue value of the subband row in the subband table. Adding a single subband in a baseband is done by clicking on the subband index number in the SB column. Deleting a single subband is done by clicking on the subband index number that needs to be removed. If a column is not wide enough to display the full entry value, simply drag the column separator in the header to widen the column of interest.

Filling/deleting many subbands:
If the subband setups repeat themselves, one may use the Fill option under the Subbands menu item to bulk fill subbands in basebands. The template menu item selection allows for defining parameters (explained below) for a template subband that can be used to fill a single, all, or part of the basebands with this template; simply close the template setup before using it. Either 16 or 32 subbands can be filled per baseband in 8-bit sampler mode. Using 32 subbands per baseband is not available in 3-bit sampler mode; only the Fill-16 should be used.

SB (subband index)
Click the numbered button in this column to either add or remove a subband. NRAO would like the subbands to be entered consecutively. GOST encourages this by deactivating buttons that should not yet be used to add a subband. It does not, though, entirely prevent one from creating configurations with gaps in the table.

Velo Cov (velocity coverage)
Displays the approximate total velocity coverage (from the total bandwidth selected in the next column, which equals the number of channels times the channel velocity width) of this subband, adopting the baseband center frequency for the calculation.

BW (bandwidth)
Choose a bandwidth for this subband; the widest is 128 MHz, the narrowest is 31.25 kHz. Each option, from widest to lowest, is half the width—or a factor of two—less than the previous. The subband bandwidth is completely independent of the number of polarization products and spectral channels used for the subband, but there are restrictions in combination with recirculation. The maximum recirculation factor is 128 divided by the subband bandwidth in MHz.

Prod (polarization products)
Choose from the list. Full means all four polarization products (RR, RL, LR, LL); dual means the two parallel-hand polarization products (RR & LL). Changing this value will change the number of spectral channels available without changing the number of baseline board pairs or recirculation factor: single polarization gives twice as many channels as dual, and dual gives twice as many as full. Per baseline board pair without recirculation, the number of channels is the product of the number (1, 2 or 4) of polarization products and 64, or the equivalent to 256 divided by the number of polarization products.

Recirc (recirculation factor)
Choose from the list. Recirculation is a term to describe the method to increase the number of spectral channels using correlator software as opposed to baseline board stacking which uses correlator hardware. Recirculation is currently achieved by limiting the subband bandwidth, as opposed to visibility integration time, and only available for subbands less than 128 MHz wide; the maximum recirculation factor for a subband is 128/(subband bandwidth in MHz).
By default, GOST will not enable recirculation: the entry in the column labeled Recirc is 1. Recirculation higher than one, in powers of two, can be used for subband bandwidths less than 128 MHz to increase the number of channels (spectral resolution) without straining the hardware limits imposed by the maximum number of baseline board pairs (see below). Recirculation up to a factor 64 is Standard and subject to other configuration restrictions such as total data rate. For help with recirculation, please contact the NRAO Helpdesk.

BlBP (baseline board pairs)
Choose from the list. It displays the number of baseline board pairs (BlBPs) dedicated to this subband (with a minimum of 1). This number of BlBPs is a priori allocated by this subband and cannot be shared with other subbands. See the description of Baseline Board Pairs Used (above) or the general correlator capabilities in the OSS. The number of BlBPs used may affect the number of subbands available in this or any other baseband. This is correctly handled by GOST. See the OSS for details if this is an issue. Note the difference between BlBP stacking and recirculation to increase spectral resolution (number of channels): recirculation is preferred over stacking as, in principle, less hardware is used and thus may provide more individual subbands and/or help in the scheduling logistics.

Ch Wd (v) (channel width in approximate velocity)
Displays the approximate width of a single channel of this subband in units of velocity, calculated for the center of the baseband with the selection of bandwidth, recirculation, and baseline board pairs. Actually, this is the separation between adjacent spectral points, before any spectral smoothing—these channels are not truly independent.

Ch Wd (f) (channel width in frequency)
Displays the fixed frequency bandwidth of a single channel of this subband with the selection of bandwidth, recirculation, and baseline board pairs. Again, this is the separation between adjacent spectral points, before any spectral smoothing—these channels are not truly independent.

Channels (spectral points)
The values represent the number of spectral points per polarization product into which this subband will be divided. Note that the number of polarization products, recirculation factor, and number of baseline board pairs chosen in the columns to the left all influence the final value.

MB/s (data rate in MB/s)
Displays the data rate associated with this single subband. See the description of Total Data Rate above.

Figure 4.2.3: Example of a Standard (with Justification) setup. Note that clicking the Why? button (in GOST) next to the green Standard (with justification) configuration designation will expose why the justification is needed (in this case because data rate exceeds the Standard limit of 25 MB/sec).

### GOST Usage Hints

Setting up a resource in GOST is simply done by first modifying the template (Menu -> Subbands -> Template) and activating the individual subbands by clicking on the subband ID number in the leftmost column (top to bottom). The activating of individual subbands is done after selecting the receiver band, baseband samplers (3-bit or 8-bit), and baseband center frequencies in the active basebands. The latter can be adjusted at any time, as can the dump time (visibility integration time). Default dump times for the different array configurations can be viewed by clicking the [defaults] link which refers to information maintained in the OSS.

 Figure 4.2.4: Shown left is the default template subband view. Design your template by modifying the columns with the blue headers to obtain the required channel frequency width. It may be useful to first fill in a subband in the subband table to derive the parameters at the observing frequency for that baseband (i.e. converting frequency into velocity). Close the template window when done; each new active subband will be filled with this template.

Then, per subband created, select (click) the bandwidth, required polarization products, and number of channels in which the subbands needs to be divided. Repeat (or see below) until all active subbands are defined. If the product of the polarization products and number of channels in a single subband is larger than 256, more than one baseline board pair (BlBP) is allocated. If the total number of BlBPs allocated reaches 64, and not all exposed subbands are activated/defined, no additional subbands can be added. If more subbands are required then reduce the number of BlBPs in select subbands to enable recirculation (see above). Recirculation allows use of more channels given limitations in hardware, but this may designate the configuration away from Standard for higher factors of recirculation.

If many subbands with almost the same setup are required, the use of a template subband is recommended. The template is used as default for every new subband that is activated. When whole basebands need to be filled out with subbands similar to the template, the suggested setup sequence becomes:

1. Set up a template subband:
• In the upper left corner click: Subbands -> Template
• select a bandwidth
• select the polarization products
• select the number of channels
• Perhaps adjust the number of BlBP (which enables recirculation!)
• close the template window
2. In the upper left corner click: Subbands -> Fill -> [subbands to fill, e.g., A1/C1]
• this fills as many subbands with the template as allowed (16 subbands/baseband, 64 BlBPs)
3. Adjust individual subbands for select properties.
4. Check the configuration designation. If not the desired configuration designation, adjust parameters or start anew until happy.
5. If subbands and BlBPs remain (and within the desired total data rate), create additional (template) subbands, check configuration designation, adjust parameters or start anew until done (and happy).

When done with a GOST setup, do not forget to click the Save button! Also, when a new setup to be created resembles this previous one, do not exit GOST, but continue after save to secure the image for the PST attachment, and adjust the current view.

### If GOST Fails...

It is not impossible that GOST fails to configure or mis-designate a specific complicated spectral line setup, or even has problems with a mode that is advertised as Standard or Shared risk. In such a case, the ultimate reference of the possible capabilities is the RCT. The RCT knows the details about frequency tuning (not known to GOST, so especially for Ka band, it is worth checking in the RCT) as well as some more complicated correlator resource allocation details that are not available to GOST. When a setup is required that is not handled properly by GOST, please let the NRAO Helpdesk know. In such a case, it is acceptable that a png snapshot of the Validation Tab is uploaded to the PST instead of a GOST image. Note that, as with small monitor screen shots above, only one png can be uploaded per resource; some image gluing may be needed to provide the whole Validation Tab page information.