Specifying Observation: Difference between revisions
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Created page with '== Specifying what you want to observe and how == * '''project''' is the root file name for <tt>simdata</tt> output (ms, images, will all start with that root) * '''refdate''', …' |
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* '''project''' is the root file name for <tt>simdata</tt> output (ms, images, will all start with that root) | * '''project''' is the root file name for <tt>simdata</tt> output (ms, images, will all start with that root) | ||
* '''refdate''', '''totaltime''', '''integration''' set when you want to observe and for how long. | * '''refdate''', '''totaltime''', '''integration''' set when you want to observe and for how long. | ||
* <font color="green">simdata will recenter the track at transit i.e. the maximum altitude</font>. A long track will see the source rise and set, and placing your model at the appropriate declination can ensure that the source is always low. More flexibility e.g. for snapshot observations through a range of LST, are possible at the tool level. Contact remy at nrao.edu for more information. | * <font color="green"><tt>simdata</tt> will recenter the track at transit i.e. the maximum altitude</font>. A long track will see the source rise and set, and placing your model at the appropriate declination can ensure that the source is always low. More flexibility e.g. for snapshot observations through a range of LST, are possible at the tool level. Contact remy at nrao.edu for more information. | ||
* Mosaic observations will rotate through the mosaic fields during the track defined by '''totaltime''', remaining at each pointing for '''scanlength''' integrations each of duration '''integration'''. No slew time is inserted. | * Mosaic observations will rotate through the mosaic fields during the track defined by '''totaltime''', remaining at each pointing for '''scanlength''' integrations each of duration '''integration'''. No slew time is inserted. | ||
* '''direction''', '''pointingspacing''', and '''relmargin''' specify where you want to observe, and how to space the pointings of the mosaic, since you'll probably do a mosaic. | |||
* '''cell''' and '''imsize''' are the parameters for the output image. Even if you don't care about producing an image, but just want to simulate visibilities, '''<tt>simdata</tt>''' uses these two parameters to set the field of view and lay out mosaic pointings. | |||
* '''startfreq''', '''chanwidth''', '''nchan''' specify the frequency information for the output which will be interpolated from the input. There is no "continuum" mode in ALMA as there was on the old VLA, so you just specify '''nchan''' =1 if you want a continuum simulation. | * '''startfreq''', '''chanwidth''', '''nchan''' specify the frequency information for the output which will be interpolated from the input. There is no "continuum" mode in ALMA as there was on the old VLA, so you just specify '''nchan''' =1 if you want a continuum simulation. | ||
== Checking what you're doing (without waiting a long time) == | == Checking what you're doing (without waiting a long time) == | ||
* | |||
* | * '''checkinputs'''="yes" produces a graphical output with your scaled input model and the primary beams of your desired mosaic overlaid (and the elevation of the source as a function of time and coming in the future a spectral window with atmospheric transmission). | ||
* '''checkinputs'''="only" produces the same window, and then stops before running the time-consuming visibillity calculation and deconvolution. This is recommended if you are trying a new image size, or mosaic parameters, etc. Get it all right and then run the actual simulation. | |||
Revision as of 18:35, 3 December 2009
Specifying what you want to observe and how
- project is the root file name for simdata output (ms, images, will all start with that root)
- refdate, totaltime, integration set when you want to observe and for how long.
- simdata will recenter the track at transit i.e. the maximum altitude. A long track will see the source rise and set, and placing your model at the appropriate declination can ensure that the source is always low. More flexibility e.g. for snapshot observations through a range of LST, are possible at the tool level. Contact remy at nrao.edu for more information.
- Mosaic observations will rotate through the mosaic fields during the track defined by totaltime, remaining at each pointing for scanlength integrations each of duration integration. No slew time is inserted.
- direction, pointingspacing, and relmargin specify where you want to observe, and how to space the pointings of the mosaic, since you'll probably do a mosaic.
- cell and imsize are the parameters for the output image. Even if you don't care about producing an image, but just want to simulate visibilities, simdata uses these two parameters to set the field of view and lay out mosaic pointings.
- startfreq, chanwidth, nchan specify the frequency information for the output which will be interpolated from the input. There is no "continuum" mode in ALMA as there was on the old VLA, so you just specify nchan =1 if you want a continuum simulation.
Checking what you're doing (without waiting a long time)
* checkinputs="yes" produces a graphical output with your scaled input model and the primary beams of your desired mosaic overlaid (and the elevation of the source as a function of time and coming in the future a spectral window with atmospheric transmission). * checkinputs="only" produces the same window, and then stops before running the time-consuming visibillity calculation and deconvolution. This is recommended if you are trying a new image size, or mosaic parameters, etc. Get it all right and then run the actual simulation.
