LWA1 Observation Preparation Directions and Hints
LWA1 is observing by reading commands from a text file called a
Session Definition File (SDF). The SDF consists of a series of
'observations'. For the LWA1 control system, an 'observation' is
defined as observing a source for a set of time. That is, if you are
observing several sources immediately after each other, they each
constitute an 'observation'.
Before scheduling your observations, please read through the current known constraints and issues with the LWA1. More scheduling hints are available at the end of this page.
How to work with the SessionGUI
- Installing and starting SessionGUI: The SessionGUI is a
tool for preparing SDFs. This is a python-based GUI, which requires
the LWA Software Library (LSL) to be installed. After installation, to
open the SessionGUI run the 'sessionGUI.py' program.
Information on how to download the LSL and SessionGUI software can be found at:
Session Schedules: http://fornax.phys.unm.edu/lwa/trac/wiki/SessionGUI
- Creating a new SDF:
- Select 'File/New', and the Observer Information window will
show, where your program basic details should be listed.
- Observer ID number: This number is given to you by the LWA User
Program when your observations are scheduled. If you don't have
one then send a request to Greg Taylor.
- Project ID code: Your LWA project code (e.g., LC012).
- Project comments: Anything you want to convey to the User Programs/Operations (SDF number 1 out of 22 in total etc.).
- Session Information ID: should be an increasing number, defining
the different sessions you will run under the same project ID. Each
SDF should have a different session ID (different beams get different
IDs!). For example, you might decide to run two sets observations of the same
source, using three beams. This means 6 different session IDs.
- Session Comments: Anything you want to convey to the operator (how
many beams you are using, LST range, date constraints and/or other
constraints and special instructions for your SDF). Describe if data can be inegrated in time or averaged in frequency (and if so, to what values) before it will be returned to you.
- Session Type: select whether you are using the TBW, TBN or DRX (beam forming).
- Data Return Method: Depending on your data size, select the method
by which you would like to receive your data. If you are using the
spectrometer, the current number of channels are restricted to
less than 2048 and is also a function of integration time. See
this interactive table,
For the moment it is strongly recommended to keep the number of
channels between 128 and 1024 and the integration time between 0.01
and 0.08 seconds. The tables identify the capabilities of DROSv2’s
spectrometer mode with DP producing the maximum-rate DRX stream. At
filter codes other than than 7, spectrometer performance is limited
only by RAM availability and output data rate, which must remain below
10 MiB/s (hard limit not established). In the tables, the color of the
“N.NNN” text indicates the extent to which DROSv2 is capable in that
mode. Black background indicates that the mode is infeasible for
geometrical or bandwidth-related reasons. Purple indicates that the
mode is infeasible due to algorithmic reasons (would prevent vector
intrinsics usage). Brown indicates that the mode is infeasible due to
memory requirements or timing-considerations. Maroon indicates that
the mode is infeasible due to computational throughput
considerations. Red indicates that the mode is not viable with present
memory complement, but may be possible, with low likelihood, after
adding more RAM. Blue indicates that the mode is not viable with
present memory complement, but may be possible, with high likelihood,
after adding more RAM. Yellow indicates that the mode is nominally
feasible, but likely to “choke” once in a while, but definately would
improve with added RAM. Green indicates that the mode is nominally
feasible, but perhaps not necessarily extensively. Cyan indicates the
mode has not been tested, but is assumed to be feasible. Lastly, Gray
indicates that the mode has not been tested and it is uncertain
whether it would be feasible or not.
A white background indicates
the mode has been tested extensively and is vetted.
- Go to 'Observations/Add' and select whether you will schedule a
TBW, TBN or a DRX 'observation'. The DRX can use regular RA/Dec
tracking, Jupiter tracking or Solar tracking mode, or Stepped mode where
the user points at a fixed point in RA, DEC or ALT, AZ. A line will appear on the GUI, and
you can fill in details for each observation:
- Observation name
- Target name (TBN/TBW default: All-Sky)
- Specific comments (optional)
- Start time in UTC. If you are observing a regular RA/Dec tracking source and you do not know when the observation will take place, enter a dummy time and include in the comments section the observable LST range. The time of observation will be shifted by the operator when your file is to be run.
- Observation duration (hh:mm:ss.s)
- Source RA (J2000) (DRX only)
- Source Dec (J2000) (DRX only)
- Tuning 1 (MHz)
- Tuning 2 (MHz)
- Filter code (DRX filter codes, TBN filter codes)
- max S/N in beam
- Under the 'Observations/Advanced Settings' tab you can specify
details of the observing system. Select the beam number you would
like (with a mild preference for beam 2, 3 or 4 since beam 1
occasionally underflows). Also specify a DRX GAIN setting
for the observation. The default may work if you are using
wide bandwidths at high frequencies, otherwise consult with
- Checking your SDF:
- Go to 'Observations/Session at a Glance' to see that all your sources are
visible at the defined observing time.
- Use 'Observations/Validate All' to run a validator confirming the
schedule file is valid.
- Go to 'Data/Estimate Data Volume' to get an estimate of the size
of your data set. You may want to use this to revise your preferred
method of shipping the data (under the
- Save and submit your SDF:
- Save your file under File/Save As. A good naming convention is
LH004_121117_0600_0045_B2.SDF where in this case the time
of the observation is 06:00 UTC on Nov. 17, 2012, the session ID
is 45 and the SDF is for beam 2. Operators may reassign the
file in time, and switch beams as necessary.
- Submit your SDFs
SDF Submission web page preferably a week, or at least 2 days before your
observations begin. Once a valid set of SDFs has been
submitted an e-mail will go out to lwa1ops.
- If you would like to watch your observations take place then go to
LWA1 Operations Screen.
- Find your observations in the LWA Database:
- Visit the LWA Database and search for recent Sessions
that have your PROJECT CODE (e.g., LH004).
Hints for making LWA1 schedules:
- For beam (DRX) observations the default gain is 6. This is
appropriate for maximum bandwidth (filter code 7 = 19.6 MSPS)
observations and the Split ASP filter configuration. For
observations in the Full ASP filter configuration a higher gain
(perhaps 5) is appropriate. For observations below 30 MHz
during the day when RFI is often strong a gain of 6
may again be appropriate. Users are advised to consult with
LWA1 staff, and then arrane to get a quick look at their data to see if
their selected gain is optimal.
- In the SessionSchedules directory, there are other useful python scripts. In particular, the 'shiftSDF.py' script can shift the SDF in several different ways:
- Shift an existing SDF to a new start date/time
- Move an SDF file to a new UTC date but the same LST
- Switch the session ID to a new value
- Print out the contents of the SDF file in an easy-to-digest manner
- Within the SDF, each 'observation' has to be 1,024
steps or less. If your file contains more steps, please submit your
schedule as a series of shorter observations. (2/1/12)
- The SessionGUI schedules beams/TBN/TBW separately. If you have
more than one beam that may differ only in the tunings, schedule one
beam first. Then copy the resulting text file for the other beams, and
edit the tuning frequency. (2/26/12)
- If your SDF has several observations that are not to be observed
continously, please prepare separate SDFs for the observations, there can be no time gaps in the SDFs.