SMA

SMA Data Reduction


[PAGES RETIRED - see the RTDC for updated information]

Welcome to the SMA Data Reduction Website

This website describes SMA-supported data reduction software packages which can convert raw SMA data into products suitable for analysis. A detailed description of the process of analyzing data from an astronomical radio interferometer is available here.

Processing SMA data falls into two broad categories - calibration and imaging. Calibration removes the instrumental effects which are present in the raw data, and converts the flux scale to Janskys. Imaging takes the calibrated visibility data which are irregularly sampled on the UV plane, and produces deconvolved images and image products (spectra, moment maps, etc.). There are three software packages which can, by themselves, calibrate SMA data: MIR, Miriad and CASA. There are two packages which can be used to produce images from calibrated data: Miriad and CASA.

MIR is a set of procedures which run within the commercial IDL programming language. IDL requires a license to run, and users who have accounts on the public CfA machines, or the RG division machines, can use our licenses. However if external users do not have access to an IDL license, they cannot use the MIR package. Another caveat for the MIR pathway is that of a track's data must reside simultaneously in RAM. In practice this means that the computer running MIR/IDL must have 3 to 4 times as much RAM as the size of the SMA dataset, if the full resolution of the correlator is needed. In most cases observers will want to reduce the spectral resolution of the track before processing the data with MIR. MIR can calibrate the SMA data, but it cannot make images.

Miriad is a program originally developed for the BIMA array, which has been adopted by several other observatories. It is an open source software package, with no fees of any kind. Several SMA-specific tasks have been added to the Miriad package. Miriad can both calibrate and image SMA data.

CASA is a package of software developed and supported by NRAO. It is the package usually used for processing JVLA and ALMA data. It can be used to calibrate and image SMA data.


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