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projects:jupiter:first [2019/09/06 16:27] wucknitz |
projects:jupiter:first [2019/09/09 09:19] (current) wucknitz |
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| For the first real calibration tests, we concentrate on one second of data near 20:16:10.5 UTC, which is at 971 sec offset from the beginning. | For the first real calibration tests, we concentrate on one second of data near 20:16:10.5 UTC, which is at 971 sec offset from the beginning. | ||
| - | Here are 100 sec around that time (only one baseline as overview, reduced frequency range): | + | Here are 1000 sec around that time (only one baseline as overview, reduced frequency range): |
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| + | {{:projects:jupiter:first_overview_1000sec.png?direct&1000}} | ||
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| + | (Most plots here are displayed with reduced resolution. Click on them, maybe twice, for full size.) | ||
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| + | The horizontal blue structures near 12 MHz are RFI, but the red ones just below 20 MHz are real. | ||
| + | The vertical green dashed lines indicate times with jumps in the integer-sample delay, white areas are missing data. | ||
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| + | Here are 100 sec around that time: | ||
| {{:projects:jupiter:first_overview_100sec.png?direct&1000}} | {{:projects:jupiter:first_overview_100sec.png?direct&1000}} | ||
| - | The vertical green dashed lines indicate time with jumps in the integer-sample delay, white areas are missing data. | ||
| - | (Most plots here are displayed with reduced resolution. Click on them (maybe twice) for full size.) | ||
| Here are 10 sec around that time: | Here are 10 sec around that time: | ||
| Line 34: | Line 42: | ||
| FIXME: The calibration process will be described in detail at a later time. For the moment I just want to present some results. We use all these stations for an eigenvalue decomposition, but later exclude CS002,DE604,UK608 from the interferometry, because their parameters are inconsistent with the rest. This is most probably due to bad station calibration, which causes polarisation leakage of the order 1. | FIXME: The calibration process will be described in detail at a later time. For the moment I just want to present some results. We use all these stations for an eigenvalue decomposition, but later exclude CS002,DE604,UK608 from the interferometry, because their parameters are inconsistent with the rest. This is most probably due to bad station calibration, which causes polarisation leakage of the order 1. | ||
| - | The eigenvalue decomposition is also used as basis for labelling good signals from either hemisphere: | + | The eigenvalue decomposition is also used as basis for identifying good signals from either hemisphere: |
| {{:projects:jupiter:first_eigendecomp.png?direct&1000}} | {{:projects:jupiter:first_eigendecomp.png?direct&1000}} | ||
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| ==== Expectation ==== | ==== Expectation ==== | ||
| - | This is based on the magnetic field model of Connerney et al. (2018). As a very first guess I follow the field lines from the actual position of Io (retarded for light time to the Earth) towards both poles. Once it reaches the point at which the local cyclotron frequency equals the mean frequency of the signal, I determine the position and its frequency derivative. The following plot shows Jupiter coloured according to the magnetic field strength at the surface. The points above the surface correspond to the surface of cyclotron frequency equal to observing frequency. Green is foreground, red behind the planet and yelow foreground with an angle between field and line of sight in the range 50 to 80 deg. Io and its field line are shown in black. Note that no correction for the lag along Io's orbit or for the wobble of the plasma torus with Jupiter's rotation was applied. | + | This is based on the magnetic field model of Connerney et al. (2018). As a very first guess I follow the field lines from the actual position of Io (retarded for light time to the Earth) towards both poles. Once it reaches the point at which the local cyclotron frequency equals the mean frequency of the signal, I determine the position and its frequency derivative. The following plot shows Jupiter coloured according to the magnetic field strength at the surface. The points above the surface have cyclotron frequency equal to observing frequency. Green is foreground, red behind the planet and yellow foreground with an angle between field and line of sight in the range 50 to 80 deg. Io and its field line are shown in black. Note that no correction for the lag along Io's orbit or for the wobble of the plasma torus with Jupiter's rotation was applied. |
| - | {{:projects:jupiter:first_magmod.png?direct&500}} | + | {{:projects:jupiter:first_magmod.png?direct&700}} |
| ==== Analysis resolved in time and frequency ==== | ==== Analysis resolved in time and frequency ==== | ||
| - | FIXME | + | Because the fit of the relative positions and shifts looks so plausible, I continued to try and determine positions as function of time and frequency. As origin for the absolute coordinates I used the middle between the signal from both hemispheres. In the Jupiter's N-S direction this is probably not too far from the centre of the planet, but in the E-W direction it is a very bad approximation. |
| + | Nevertheless, just as illustration, for a limited time range: | ||
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| + | {{:projects:jupiter:first_posfits_abs.png?direct&1000}} | ||
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| + | The upper panels show X, the lower Y coordinates, left is southern hemisphere, right is northern hemisphere. These values are dominated by the general offset between both hemispheres. We can also subtract the mean offset to make the motion with time/frequency more visible (note the different colour scale): | ||
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| + | {{:projects:jupiter:first_posfits_motion.png?direct&1000}} | ||
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| + | This is now dominated by the linear drift with frequency. Finally we also subtract the linear drift as function of frequency to show deviations from this overall effect (note the again different colour scale): | ||
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| + | {{:projects:jupiter:first_posfits_resid.png?direct&1000}} | ||
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| + | There are still significant residuals, but this does not necessarily mean that the motion really has strong non-linear components. It could also be that the southern (LH) signal is not really produced along one field line, but is a steady continuum along a range of field lines. There is then no reason to expect a simple shift with frequency. Because I only measure //relative// positions, this would also affect the apparent motion of the S-burst signals from the northern hemisphere. And then there are of course residual calibration errors, which may be related to polarisation leakage in the signals. | ||
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| + | Very intriguing is evidence for a position gradient //across// the S-burst linear features. This can not be explained so easily by calibration problems, but it is too early to take this gradient very seriously. Luckily such effects can also be measured without a calibration of absolute position, so that we can study this potentially very interesting features also for individual hemispheres, and then potentially with stronger signals. | ||
