aboutsummaryrefslogtreecommitdiffstats
path: root/fg21sim/galactic/synchrotron.py
blob: f2de2ce10651504a90a3f5a16e727b3f68510a1c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
# Copyright (c) 2016-2017 Weitian LI <weitian@aaronly.me>
# MIT license

"""
Diffuse Galactic synchrotron emission (unpolarized) simulations.
"""

import os
import logging

import numpy as np
import healpy as hp

from ..share import CONFIGS
from ..sky import get_sky


logger = logging.getLogger(__name__)


class Synchrotron:
    """
    Simulate the diffuse Galactic synchrotron emission based on an
    existing template.

    Parameters
    ----------
    configs : `~ConfigManager`
        An `ConfigManager` object contains default and user configurations.
        For more details, see the example config specification.

    Attributes
    ----------
    sky : `~SkyBase`
        The sky instance to deal with the simulation sky as well as the
        output map.

    References
    ----------
    ???
    """
    # Component name
    compID = "galactic/synchrotron"
    name = "Galactic synchrotron (unpolarized)"

    def __init__(self, configs=CONFIGS):
        self.configs = configs
        self._set_configs()

        self.sky = get_sky(configs)
        self.sky.add_header("CompID", self.compID, "Emission component ID")
        self.sky.add_header("CompName", self.name, "Emission component")
        self.sky.add_header("BUNIT", "K", "[Kelvin] Data unit")
        self.sky.creator = __name__

    def _set_configs(self):
        """
        Load the configs and set the corresponding class attributes.
        """
        comp = self.compID
        self.template_path = self.configs.get_path(comp+"/template")
        self.template_freq = self.configs.getn(comp+"/template_freq")
        self.indexmap_path = self.configs.get_path(comp+"/indexmap")
        self.add_smallscales = self.configs.getn(comp+"/add_smallscales")
        self.smallscales_added = False
        self.lmin = self.configs.getn(comp+"/lmin")
        self.lmax = self.configs.getn(comp+"/lmax")
        self.prefix = self.configs.getn(comp+"/prefix")
        self.output_dir = self.configs.get_path(comp+"/output_dir")
        # output
        self.frequencies = self.configs.frequencies  # [MHz]
        self.filename_pattern = self.configs.getn("output/filename_pattern")
        self.clobber = self.configs.getn("output/clobber")
        #
        logger.info("Loaded and setup configurations")

    def _load_maps(self):
        """Load the template map and spectral index map."""
        logger.info("Loading template map ...")
        self.template = self.sky.open(self.template_path)
        logger.info("Loading spectral index map ...")
        self.indexmap = self.sky.open(self.indexmap_path)

    def _add_smallscales(self):
        """
        Add fluctuations on small scales to the template map.

        NOTE:
        Only when the input template is a HEALPix map, this function
        will be applied to add the small-scale fluctuations, which assuming
        a angular power spectrum model.

        XXX/TODO:
        * Support using different models.
        * This should be extensible/plug-able, e.g., a separate module
          and allow easily add new models for use.

        References
        ----------
        [1] M. Remazeilles et al. 2015, MNRAS, 451, 4311-4327
            "An improved source-subtracted and destriped 408-MHz all-sky map"
            Sec. 4.2: Small-scale fluctuations
        """
        if (not self.add_smallscales) or (self.smallscales_added):
            return
        if self.template.type_ != "healpix":
            logger.warning("Input template map is NOT a HEALPix map; " +
                           "skip adding small-scale fluctuations!")
            return

        # Parameters to extrapolate the angular power spectrum
        gamma = -2.703  # index of the power spectrum between l [30, 90]
        sigma_tp = 56  # original beam resolution of the template [ arcmin ]
        alpha = 0.0599
        beta = 0.782
        # angular power spectrum of the Gaussian random field
        ell = np.arange(self.lmax+1).astype(np.int)
        cl = np.zeros(ell.shape)
        ell_idx = ell >= self.lmin
        cl[ell_idx] = (ell[ell_idx] ** gamma *
                       1.0 - np.exp(-ell[ell_idx]**2 * sigma_tp**2))
        cl[ell < self.lmin] = cl[self.lmin]
        # generate a realization of the Gaussian random field
        gss = hp.synfast(cls=cl, nside=self.template.nside, new=True)
        # whiten the Gaussian random field
        gss = (gss - gss.mean()) / gss.std()
        hpmap_smallscales = alpha * gss * self.template.data**beta
        self.template += hpmap_smallscales
        logger.info("Added small-scale fluctuations to template map")

    def _outfilepath(self, frequency, **kwargs):
        """
        Generate the path/filename to the output file for writing
        the simulate sky images.

        Parameters
        ----------
        frequency : float
            The frequency of the output sky image.
            Unit: [MHz]

        Returns
        -------
        filepath : str
            The generated filepath for the output sky file.
        """
        filename = self.filename_pattern.format(
            prefix=self.prefix, frequency=frequency, **kwargs)
        filepath = os.path.join(self.output_dir, filename)
        return filepath

    def preprocess(self):
        """
        Perform the preparation procedures for the final simulations.

        Attributes
        ----------
        _preprocessed : bool
            This attribute presents and is ``True`` after the preparation
            procedures are performed, which indicates that it is ready to
            do the subsequent simulations.
        """
        if hasattr(self, "_preprocessed") and self._preprocessed:
            return

        logger.info("{name}: preprocessing ...".format(name=self.name))
        self._load_maps()
        self._add_smallscales()

        self._preprocessed = True

    def simulate_frequency(self, frequency):
        """
        Simulate the emission at requested lower frequency by
        extrapolating the template map using the power-law model and
        the spectral index map.

        Parameters
        ----------
        frequency : float
            The frequency where to simulate the radio emission.
            Unit: [MHz]

        Returns
        -------
        sky : `~SkyBase`
            The simulated sky image as a new sky instance.
        """
        logger.info("Simulating {name} map at {freq:.2f} [MHz] ...".format(
            name=self.name, freq=frequency))
        sky = self.sky.copy()
        sky.frequency = frequency
        ff = frequency / self.template_freq
        data = self.template * ff ** (-np.abs(self.indexmap))
        sky.data = data
        logger.info("Done simulate map at %.2f [MHz]." % frequency)
        return sky

    def simulate(self, frequencies=None):
        """
        Simulate the synchrotron map at the specified frequencies.

        Parameters
        ----------
        frequencies : float, or list[float]
            The frequencies where to simulate the foreground map.
            Unit: [MHz]
            Default: None (i.e., use ``self.frequencies``)
        """
        if frequencies is None:
            frequencies = self.frequencies
        else:
            frequencies = np.array(frequencies, ndmin=1)

        logger.info("Simulating {name} ...".format(name=self.name))
        for freq in frequencies:
            sky = self.simulate_frequency(freq)
            outfile = self._outfilepath(frequency=freq)
            sky.write(outfile)
        logger.info("Done simulate {name}!".format(name=self.name))

    def postprocess(self):
        """Perform the post-simulation operations before the end."""
        logger.info("{name}: postprocessing ...".format(name=self.name))
        logger.info("^_^ nothing to do :-)")