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Each record in a Miriad dataset organizes its correlation data by spectral windows and so-called wideband channels. Each Miriad spectral window contains data from a band of frequencies, broken up into some number of channels. (Because each channel, then, is fairly narrow in bandwidth, these correlations are often referred to as "narrow-band" data.) The wideband channels, in general, contain single correlations, averaged over some band at potentially arbitrary frequencies; that is, they are bolometer-like measurements.
In Miriad datasets written by the BIMA telescope, the wideband channels are used to store wide-band averages of the spectral windows. More specifically, the first wideband channel contains the average of all spectral windows channels associated with the lower sideband (the first Nwin/2 windows), and the second wideband channel contains the average of the upper sideband windows. The remaining wideband channels contain the averages of each of the spectral windows (in the same order). Thus, if the BIMA Miriad dataset contains Nwin spectral windows, there will be Nwin+2 wideband channels. The first Nwin/2 windows will be from the lower sideband, and the rest, from the upper sideband.
When the Miriad data is converted to an MS, each spectral window and each wideband channel is loaded into a separate MS spectral window. Thus, for a BIMA dataset with Nwin windows, the output MS (by default) will contain Nwin*2+2 spectral windows. If all narrow and wideband data are present, mirfiller will store the relationships into the output measurement set so that they can be used appropriately in the calibration process. The select function can be used to further control the windows that get written.
Which windows that should get passed by default (i.e. where they are not explicitly specified by the select function) can depend on what ``flavor'' visibility dataset it is; that is, more specifically, where its been in its processing history and what the user wants to do with it. For example, if the data is calibrated, then the wideband data is usually no longer needed. (Calibrated or uncalibrated, the window averages are usually not needed.) Furthermore, if it has gone through much processing in Miriad, it is possible that some of the windows or wideband channels may have been discarded; thus, the convention for wideband channels described above is no longer valid. Finally, it's possible that the dataset did not originate from the BIMA telescope, and thus, the convention for wideband channels does not apply. mirfiller attempts to detect the ``flavor'' of the input dataset and adjusts its default window selection accordingly. See the select function for details.