Plot GNSS TEC

The Global Navigation Satellte System (GNSS) Total Electron Content (TEC) is one of the most valuable ionospheric data sets, given its long and continuous operational duration and expansive coverage. pysatMadrigal currently only supports Vertical TEC (VTEC) data handling through pysatMadrigal.instruments.gnss_tec.

The VTEC measurements are median filtered to fill 1 degree latitude by 1 degree longitude bins. This can be represented with spatially representative coverage as shown in the example below. Start by obtaining the desired data and loading it.

import datetime as dt
import matplotlib as mpl
import matplotlib.pyplot as plt
import numpy as np
import pysat
import pysatMadrigal as pysat_mad

vtec = pysat.Instrument(inst_module=pysat_mad.instruments.gnss_tec,
                        tag='vtec')
ftime = dt.datetime(2013, 1, 1)

if not ftime in vtec.files.files.index:
    vtec.download(start=ftime, user='firstname+lastname', password='myname@email.address')

vtec.load(date=ftime)
print(vtec.variables)

The result of the above command should be ['time', 'gdlat', 'glon', 'dtec', 'gdalt', 'tec'], where 'tec' is the VTEC and 'dtec' is the error in the VTEC. To plot the data on a grid where each value takes up the desired grid size, we need to extend the latitude and longitude coordinates, as the data is specified at the lower edge of each coordinate bin.

coords = {}
for ckey in ['gdlat', 'glon']:
    coords[ckey] = list(vtec[ckey].values)
    coords[ckey].append(vtec.meta[ckey, vtec.meta.labels.max_val])
    coords[ckey] = np.array(coords[ckey])

Now, create a figure using pcolormesh to create a regular grid with VTEC value indicated by color.

fig = plt.figure()
ax = fig.add_subplot(111)

itime = 0
vmin = vtec.meta['tec', vtec.meta.labels.min_val]
vmax = np.ceil(vtec['tec'][itime].max().values / 10.0) * 10.0
con = ax.pcolormesh(coords['glon'], coords['gdlat'],
                    vtec['tec'].values[itime], vmin=vmin, vmax=vmax)

ax.set_facecolor('0.9')
ax.xaxis.set_major_locator(mpl.ticker.MultipleLocator(60))
ax.yaxis.set_major_locator(mpl.ticker.MultipleLocator(30))
ax.set_xlabel('Geographic Longitude ($^\circ$)')
ax.set_ylabel('Geodedic Latitude ($^\circ$)')
plt.colorbar(mappable=con, ax=ax, location='right', fraction=.1, pad=.01,
             label='VTEC ({:s})'.format(vtec.meta['tec',
                                                  vtec.meta.labels.units]))
fig.suptitle('{:s} {:s} at {:s}'.format(
    vtec.platform.upper(), vtec.tag.upper(),
    vtec.index[itime].strftime('%d %b %Y %H:%M:%S UT'), fontsize='medium'))

plt.show()