Feature/block offsets

NuRadioReco/framework/parameters.py

@@ -57,6 +57,7 @@ class channelParameters(Enum):
     signal_receiving_zenith = 15    #: the zenith angle of direction at which the radio signal arrived at the antenna
     signal_ray_type = 16        #: type of the ray propagation path of the signal received by this channel. Options are direct, reflected and refracted
     signal_receiving_azimuth = 17   #: the azimuth angle of direction at which the radio signal arrived at the antenna
+    block_offsets = 18 #: 'block' or pedestal offsets. See `NuRadioReco.modules.RNO_G.channelBlockOffsetFitter`
 
 
 class electricFieldParameters(Enum):

NuRadioReco/modules/RNO_G/channelBlockOffsetFitter.py

@@ -0,0 +1,256 @@
+"""
+Module to remove 'block offsets' from RNO-G voltage traces.
+
+The function ``fit_block_offsets`` can be used standalone to perform an out-of-band 
+fit to the block offsets. Alternatively, the ``channelBlockOffsets`` class contains convenience 
+``add_offsets`` (to add block offsets in simulation) and ``remove_offsets`` methods that can be run 
+directly on a NuRadioMC/imported ``Event``. The added/removed block offsets are stored per channel
+in the `NuRadioReco.framework.parameters.channelParameters.block_offsets` parameter.
+
+"""
+
+from NuRadioReco.utilities import units, fft
+from NuRadioReco.framework.base_trace import BaseTrace
+from NuRadioReco.framework.parameters import channelParameters
+# from iminuit import Minuit
+import numpy as np
+import scipy
+
+class channelBlockOffsets:
+
+    def __init__(self, block_size=128, max_frequency=51*units.MHz):
+        """
+        Add or remove block offsets to channel traces
+
+        This module adds, fits or removes 'block offsets' by fitting
+        them in a specified out-of-band region in frequency space.
+
+        Parameters
+        ----------
+        block_size: int (default: 128)
+            The size (in samples) of the blocks
+        max_frequency: float (default: 51 MHz)
+            The maximum frequency to include in the out-of-band
+            block offset fit
+
+        """
+        self.sampling_rate = None
+        self.block_size = block_size # the size (in samples) of the blocks
+        self._offset_fit = dict()
+        self._offset_inject = dict()
+        self._max_frequency = max_frequency
+
+    def add_offsets(self, event, station, offsets=1*units.mV, channel_ids=None):
+        """
+        Add (simulated or reconstructed) block offsets to an event.
+
+        Added block offsets for each channel are stored in the 
+        ``channelParameters.block_offsets`` parameter.
+
+        Parameters
+        ----------
+        event: Event object | None
+        station: Station
+            The station to add block offsets to
+        offsets: float | array | dict
+            offsets to add to the event. Default: 1 mV
+
+            - if a float, add gaussian-distributed of amplitude ``offsets``
+              to all channels specified;
+            - if an array, the length should be the same as the number
+              of blocks in a single trace, and the entries will be
+              interpreted as the amplitudes of the offsets;
+            - if a dict, the keys should be the channel ids, and each
+              value should contain either a float or an array to add to
+              each channel as specified above.
+
+        channel_ids: list | None
+            either a list of channel ids to apply the offsets to, or
+            None to apply the offsets to all channels in the station
+            (default: None).
+
+        """
+
+        if channel_ids is None:
+            channel_ids = station.get_channel_ids()
+        for channel_id in channel_ids:
+            channel = station.get_channel(channel_id)
+            if isinstance(offsets, dict):
+                add_offsets = offsets[channel_id]
+            elif len(np.atleast_1d(offsets)) == 1:
+                add_offsets = np.random.normal(
+                    0, offsets, (channel.get_number_of_samples() // self.block_size)
+                )
+            else:
+                add_offsets = offsets
+
+            # save the added offsets as a channelParameter
+            if channel.has_parameter(channelParameters.block_offsets):
+                block_offsets_old = channel.get_parameter(channelParameters.block_offsets)
+                channel.set_parameter(channelParameters.block_offsets, block_offsets_old + offsets)
+            else:
+                channel.set_parameter(channelParameters.block_offsets, offsets)
+
+            channel.set_trace(
+                channel.get_trace() + np.repeat(add_offsets, self.block_size),
+                channel.get_sampling_rate()
+            )
+
+    def remove_offsets(self, event, station, mode='fit', channel_ids=None):
+        """
+        Remove block offsets from an event
+
+        Fits and removes the block offsets from an event. The removed
+        offsets are stored in the ``channelParameters.block_offsets``
+        parameter.
+
+        Parameters
+        ----------
+        event: NuRadioReco.framework.event.Event | None
+        station: NuRadioReco.framework.station.Station
+            The station to remove the block offsets from
+        mode: 'fit' | 'approximate' | 'stored'
+
+            - 'fit' (default): fit the block offsets with a minimizer
+            - 'approximate' : use the first guess from the out-of-band component,
+              without any fitting (slightly faster)
+            - 'stored': use the block offsets already stored in the 
+              ``channelParameters.block_offsets`` parameter. Will raise an error 
+              if this parameter is not present.
+
+        channel_ids: list | None
+            List of channel ids to remove offsets from. If None (default),
+            remove offsets from all channels in ``station``
+
+        """
+        if channel_ids  is None:
+            channel_ids = station.get_channel_ids()
+
+        offsets = {}
+        if mode == 'stored': # remove offsets stored in channelParameters.block_offsets
+            offsets = {
+                channel_id: -station.get_channel(channel_id).get_parameter(channelParameters.block_offsets)
+                for channel_id in channel_ids}
+        else: # fit & remove offsets
+            for channel_id in channel_ids:
+                channel = station.get_channel(channel_id)
+                trace = channel.get_trace()
+
+                block_offsets = fit_block_offsets(
+                    trace, self.block_size,
+                    channel.get_sampling_rate(), self._max_frequency
+                )
+                offsets[channel_id] = -block_offsets
+
+        self.add_offsets(event, station, offsets, channel_ids)
+
+
+def fit_block_offsets(
+        trace, block_size=128, sampling_rate=3.2*units.GHz,
+        max_frequency=50*units.MHz, mode='fit', return_trace = False,
+        tol=1e-6,):
+    """
+    Fit 'block' offsets for a voltage trace
+
+    Fit block offsets ('rect'-shaped offsets from a baseline)
+    using a fit to the out-of-band spectrum of a voltage trace.
+
+    Parameters
+    ----------
+    trace: numpy Array
+        the voltage trace
+    block_size: int (default: 128)
+        the number of samples in one block
+    sampling_rate: float (default: 3.2 GHz)
+        the sampling rate of the trace
+    max_frequency: float (default: 50 MHz)
+        the fit to the block offsets is performed
+        in the frequency domain, in the band up to
+        max_frequency
+    mode: 'fit' | 'approximate'
+        Whether to fit the block offsets (default)
+        or just use the first guess from the out-of-band
+        component (faster)
+    return_trace: bool (default: False)
+        if True, return the tuple (offsets, output_trace)
+        where the output_trace is the input trace with
+        fitted block offsets removed
+
+    Returns
+    -------
+    block_offsets: numpy array
+        The fitted block offsets.
+    output_trace: numpy array or None
+        The input trace with the fitted block offsets removed.
+        Returned only if return_trace=True
+
+    Other Parameters
+    ----------------
+    tol: float (default: 1e-6)
+        tolerance parameter passed on to scipy.optimize.minimize
+    """
+    dt = 1. / sampling_rate
+    spectrum = fft.time2freq(trace, sampling_rate)
+    frequencies = np.fft.rfftfreq(len(trace), dt)
+    n_blocks = len(trace) // block_size
+
+    mask = (frequencies > 0) & (frequencies < max_frequency) #  a simple rectangular filter
+    frequencies_oob = frequencies[mask]
+    spectrum_oob = spectrum[mask]
+
+    # we use the bandpass-filtered trace to get a first estimate of
+    # the block offsets, by simply averaging over each block.
+    filtered_trace_fft = np.copy(spectrum)
+    filtered_trace_fft[~mask] = 0
+    filtered_trace = fft.freq2time(filtered_trace_fft, sampling_rate)
+
+    # obtain guesses for block offsets
+    a_guess = np.array([
+        np.mean(filtered_trace[i*block_size:(i+1)*block_size])
+        for i in range(n_blocks)
+    ])
+    if mode == 'approximate':
+        block_offsets = a_guess
+    elif mode == 'fit':
+        # self._offset_guess[channel_id] = a_guess
+        # we can get rid of one parameter through a global shift
+        a_guess = a_guess[:-1] - a_guess[-1]
+
+        # we perform the fit out-of-band, in order to avoid
+        # distorting any actual signal
+
+        # most of the terms in the fit depend only on the frequencies,
+        # sampling rate and number of blocks. We therefore calculate these
+        # only once, outside the fit function.
+        pre_factor_exponent = np.array([
+            -2.j * np.pi * frequencies_oob * dt * ((j+.5) * block_size - .5)
+                for j in range(len(a_guess))
+        ])
+        const_fft_term = (
+                1 / sampling_rate * np.sqrt(2) # NuRadio FFT normalization
+            * np.exp(pre_factor_exponent)
+            * np.sin(np.pi*frequencies_oob*block_size*dt)[None]
+            / np.sin(np.pi*frequencies_oob*dt)[None]
+        )
+
+        def pedestal_fit(a):
+            fit = np.sum(a[:, None] * const_fft_term, axis=0)
+            chi2 = np.sum(np.abs(fit-spectrum_oob)**2)
+            return chi2
+
+        res = scipy.optimize.minimize(pedestal_fit, a_guess, tol=tol).x
+
+        block_offsets = np.zeros(len(res) + 1)
+        block_offsets[:-1] = res
+
+        # the fit is not sensitive to an overall shift,
+        # so we include the zero-meaning here
+        block_offsets += np.mean(trace) - np.mean(block_offsets)
+    else:
+        raise ValueError(f'Invalid value for mode={mode}. Accepted values are {{"fit", "approximate"}}')
+
+    if return_trace:
+        output_trace = trace - np.repeat(block_offsets, block_size)
+        return block_offsets, output_trace
+
+    return block_offsets

changelog.txt

@@ -13,6 +13,7 @@ new features:
 - added ability to generate high-low-triggered noise on a narrow band but return full-band waveforms
 - phased array noise generation utility class: calculate trigger time and cut trace accordingly
 - use Philox noise generator in noise adder module (this changes the default random sequence)
+- added 'block offset' removal/simulation module for RNO-G
 
 bugfixes:
 - fixed/improved C++ raytracer not finding solutions for some near-horizontal or near-shadowzone vertices