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projects:mkat_sband:pub:noisevar [2022/05/18 12:57] wucknitz |
projects:mkat_sband:pub:noisevar [2022/05/25 11:28] (current) wucknitz |
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| I take the autocorrelations of all antennas. Gaps in the data (between scans) are filled but masked. Data are then normalised (per scan, because different targets can have very different noise levels) as follows: The median of the XX and YY levels are taken (per frequency), and XX and YY are normalised by this. XY is normalised with the geometric mean of the two. This brings the median noise in X and Y to a value of unity. The XY correlation can have arbitrary phase due to delay differences. Because of this, it is rotated using the median of XY (real and imaginary). This means XY will generally be close to positive real. The amplitude can differ from antenna to antenna, but it should be relatively constant. The imaginary part should be constant close to zero. Finally, 1 is subtracted from XX and YY to bring them nominally to zero. | I take the autocorrelations of all antennas. Gaps in the data (between scans) are filled but masked. Data are then normalised (per scan, because different targets can have very different noise levels) as follows: The median of the XX and YY levels are taken (per frequency), and XX and YY are normalised by this. XY is normalised with the geometric mean of the two. This brings the median noise in X and Y to a value of unity. The XY correlation can have arbitrary phase due to delay differences. Because of this, it is rotated using the median of XY (real and imaginary). This means XY will generally be close to positive real. The amplitude can differ from antenna to antenna, but it should be relatively constant. The imaginary part should be constant close to zero. Finally, 1 is subtracted from XX and YY to bring them nominally to zero. | ||
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| + | ===== All results ===== | ||
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| + | [[https://cloud.mpifr-bonn.mpg.de/index.php/s/eHdawNC3DZ6Hex8|Results from all observations that have been processed (for this purpose) so far are available at this link.]] | ||
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| + | A description of the individual plots in the PDF files can be found below. | ||
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| + | In addition to files for each dataset, there is a file [[https://cloud.mpifr-bonn.mpg.de/index.php/s/wnCcqweKcH8rMyg|ALLFIRST_auto_noisevar.pdf]], which consists of the first overview pages from all PDF files (from all data sets). For some reason the colours look a bit strange in this file. | ||
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| + | **Note that displaying the PDFs in the browser may interpolate the colours, e.g. between stations. If that is the case, please download and display offline.** | ||
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| ===== Individual plots ===== | ===== Individual plots ===== | ||
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| {{:projects:mkat_sband:pub:auto_noisevar_1648081798_sdp_l0_freqmed.png?direct&800|median over frequencies}} | {{:projects:mkat_sband:pub:auto_noisevar_1648081798_sdp_l0_freqmed.png?direct&800|median over frequencies}} | ||
| - | The total power measurements in XX and YY are easiest to interpret. Without variation, they would be zero. Over longer scans (marked by vertical green lines), we sometimes see gradients. These can be due to the changing elevation and are not of concern. Some antennas, in this observation particularly in YY, have stronger variations, in particular intermittend high levels and sudden changes of levels. | + | The total power measurements in XX and YY are easiest to interpret. Without variation, they would be zero. Over longer scans (marked by vertical green lines), we sometimes see gradients. These can be due to the changing elevation and are not of concern. Some antennas, in this observation most prominent in YY, have stronger variations, in particular intermittent high levels and sudden changes of levels. |
| real(XY) shows the linear polarisation level of the noise. It is generally relatively constant over time. The orthogonal component, imag(XY), on the other hand, often changes rapidly with the variations in YY. | real(XY) shows the linear polarisation level of the noise. It is generally relatively constant over time. The orthogonal component, imag(XY), on the other hand, often changes rapidly with the variations in YY. | ||
