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docs: review analysers

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Analysers
=========
Analysers do their work before the actual optimisations. They analyse the data
with respect to the problem-dependent expected signal strength for each target
and with respect to the pre-event noise power.
The analyser results are used to weight the data in the following optimisation.
Analysers do their work before the actual optimisations, they analyse the observed data to weigh the :term:`targets <target>` in the following optimisation.
TODO: review, link to the reference, link to papers?
There are two analysers implemented so far, which work on waveform targets:
Grond come with two analysers, which work on waveform targets:
``TargetBalancingAnalyser``:
This analyser balances, based on estimated signal amplitudes, the waveform target contributions to the misfit. This is done with synthetic waveforms from random source models drawn from the model space defined in the problem configuration. Waveforms from stations that are far away from the source will on average have small signal strengths, while targets of stations close to the sources will have larger signal amplitudes. To balance the importance of waveforms the inverse of the mean signal strength is used as a ``balancing_weight``. Like this the effect of simple geometrical spreading or through the radiation pattern is lessened in the misfit evaluation.
This analyser balances the waveform target contributions to the misfit, based on estimated signal amplitudes.
Synthetic waveforms from random source models are drawn from the model space defined in the problem configuration. Waveforms at stations far away from the source will have small signal strengths, while stations close to the sources will show larger signal amplitudes on average. To balance the importance of waveforms the inverse of the mean signal strength is used as a ``balancing_weight``. This compensates dampening effects from geometrical spreading and averages the radiation pattern towards the misfit evaluation.
``NoiseAnalyser``:
This analyser evaluates the pre-event noise for the waveform targets to form empirical target weights. High pre-event noise variance leads to a small target weight for the corresponding target in the misfit calculation. It is assumed that the pre-event noise is random background noise and stationary in the time from the first pre-event sample to the last analysed phase sample. A check for significant earthquakes in the critical time
frame can be enabled.
This analyser evaluates the pre-event noise for the waveform targets to define empirical target weights.
High pre-event noise variance leads to a small :term:`target` weight for the corresponding target in the misfit calculation. It is assumed that the pre-event noise is random background noise and stationary in the time. However, a check for significant earthquakes in the critical time frame can be enabled.
``TargetBalancingAnalyser`` configuration
-----------------------------------------
The balancing of target is problem-dependent. This means the configuration of
the problem also configures the ``target_balancing``. The only extra parameter
needed is
Balancing of target weights depends on the configured problem search space. This means the configuration of the problem also configures the ``target_balancing``. The only extra parameter needed is
``niterations``
an integer number that defines how many random waveform predictions the target-balancing weights are based. A meaningful number will depend on the problem. Large model spaces (loose model parameter bounds) may require a larger number of predictions for more stable average values. For more tightly constrained problems the signal strength at the targets for the not-so-different source models, which are drawn from a small model space, may not vary much. A smaller number may suffice. Of course, the computational effort increases linearly with the number of ``niterations``.
.. code-block :: sh
an integer number defining how many random waveform predictions are modelled. A meaningful number will depend on the problem. Large model spaces (loose model parameter bounds) may require a larger number of predictions for stable average values. Tightly constrained problems can draw from a small model space and may not vary much - here a smaller number is suffice.
The computational effort increases linearly with the number of ``niterations``.
.. code-block :: yaml
analyser_configs:
- !grond.TargetBalancingAnalyserConfig
@ -39,23 +38,23 @@ needed is
``NoiseAnalyser`` configuration
-------------------------------
This analyser is not strongly model-independent. Only the reference time given in 'event.txt' is used to estimate the phase arrivals. These phase arrivals define what `pre-event` is.
This analyser is independent from the problem. Only the reference time given in :file:`event.txt` is used to estimate the phase arrivals. These phase arrivals define where `pre-event` is.
.. glossary ::
``nwindows``
is an integer number. It gives the number of sub-windows in which the noise trace of duration ``pre_event_noise_duration`` is split. If larger than ``1``, the noise variance is in each sub-window and the average noise variance is returned.
is an integer number defining the number of sub-windows of the trace. If larger than ``1``, the noise variance in each sub-window and the total average noise variance is calculated.
``pre_event_noise_duration``
defines how long the pre-event noise trace is in seconds.
defines the trace length of pre-event noise in seconds.
``check_events``
is a boolean value. If ``True`` the iris global earthquake catalogue is looked up to find if phase arrivals of other events may disturb the statistics of the noise.
is a boolean value. If ``True`` the IRIS global earthquake catalogue is searched for phase arrivals of other events, which may interfere with the pre-event noise.
``phase_def``
is a string that defines the reference phase for the pre-event time window.
is a string that defines the reference phase for the pre-event time window. See `Pyrocko's definition of phases <https://pyrocko.org/docs/current/apps/cake/manual.html>`_.
.. code-block :: sh
.. code-block :: yaml
analyser_configs:
- !grond.NoiseAnalyserConfig


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