Page 1
An Introduction to Simdata
Scott Schnee (NRAO)
Victoria Workshop – Jan 18, 2011
Page 2
What is Simdata Good For?
• Number of antennas• Antenna configuration• Length of observation• Noise
Take a model image and find out how it would look if observed with ALMA
Page 3
Model Image30Dor Spitzer IRAC 8um image from SAGE
Page 4
Model ImageResized and now at 230 GHz
Page 5
Fourier Transforms of Images
From http://carmilumban-ap186.blogspot.com
Page 6
Scales Measured by ES ConfigurationAntenna Placement uv-coverage synthesized beam
2 hour observation
Page 7
Scales Measured by FS CompactAntenna Placement uv-coverage synthesized beam
2 hour observation
Page 8
Scales Measured by FS ExtendedAntenna Placement uv-coverage synthesized beam
2 hour observation
Page 9
Model Image in ES Configuration
Model Image Convolved Model “Observed” Image
2 hour observation
Page 10
Model Image in FS Compact
Model Image Convolved Model “Observed” Image
2 hour observation
Page 11
Model Image in FS Extended
Model Image Convolved Model “Observed” Image
2 hour observation
Page 12
Basic Simdata Inputs
• Image / model of target• Observing time• Antenna configuration
Page 13
Basic Simdata Inputs
Page 14
FITS Image Basics
• Coordinates• Brightness• Observing Frequency• Resolution (angular and spectral)• Polarization (if needed)
Page 15
modifymodel
• modifymodel = True• skymodel = “30dor.fits”• inbright = ”0.1mJy/pixel”• indirection = "J2000 10:00:00 -40:00:00”• incell = "0.25arcsec”• incenter = "230GHz”• inwidth = '2GHz'
Page 16
setpointings
• integration = '600s’• mapsize = "”• pointingspacing = ""
Page 17
predict
• repodir = os.getenv("CASAPATH").split(' ')[0]• antennalist = repodir+"/data/alma/simmos/alma.early.250m.cfg"
Page 18
Simdata Output
• analyze = True• showarray = True• showconvolved = True• showdifference = False• showfidelity = False
Page 21
Simdata Output - Viewer
Page 22
Other Simdata OptionsThermal Noise
• thermalnoise = ‘tsys-atm’• image = True• vis=‘$project.noisy.ms’
Page 23
Other Simdata OptionsThermal Noise
Convolved Model Thermal NoiseNo Thermal Noise
Page 24
Other Simdata OptionsPhase Noise
Convolved Model No Phase Noise Phase Noise
Page 25
Other Simdata OptionsPhase Noise
• Create measurement set with simdata• Use the “toolkit” to add phase noise– http://casa.nrao.edu/docs/CasaRef/CasaRef.html– http://casaguides.nrao.edu/index.php?title=Corrupt– sm.openfromms("simPN.ms")– sm.settrop(mode='screen',pwv=1.0,deltapwv=0.15)– sm.corrupt()– sm.done()
• Use clean (in CASA) to make the image
Page 26
Your Turn
• Find a fits file of an object you want to image• Use simdata to see how it would look if
observed with ALMA– Rescale image if necessary– Try different antenna configurations– Add noise if interested
• Don’t be afraid to ask for help!