def read_band(self, key, info):
"""Read the data."""
# Read data
tic = datetime.now()
with open(self.filename, "rb") as fp_:
header = self._read_header(fp_)
res = self._read_data(fp_, header)
res = self._mask_invalid(data=res, header=header)
self._header = header
logger.debug("Reading time " + str(datetime.now() - tic))
# Calibrate
res = self.calibrate(res, key.calibration)
# Get actual satellite position. For altitude use the ellipsoid radius at the SSP.
actual_lon = float(self.nav_info['SSP_longitude'])
actual_lat = float(self.nav_info['SSP_latitude'])
re = get_earth_radius(lon=actual_lon, lat=actual_lat,
a=float(self.proj_info['earth_equatorial_radius'] * 1000),
b=float(self.proj_info['earth_polar_radius'] * 1000))
actual_alt = float(self.nav_info['distance_earth_center_to_satellite']) * 1000 - re
# Update metadata
new_info = dict(
units=info['units'],
standard_name=info['standard_name'],
wavelength=info['wavelength'],
resolution='resolution',
id=key,
name=key.name,
scheduled_time=self.scheduled_time,
platform_name=self.platform_name,
sensor=self.sensor,
satellite_longitude=float(self.nav_info['SSP_longitude']),
satellite_latitude=float(self.nav_info['SSP_latitude']),
satellite_altitude=float(self.nav_info['distance_earth_center_to_satellite'] -
self.proj_info['earth_equatorial_radius']) * 1000,
orbital_parameters={
'projection_longitude': float(self.proj_info['sub_lon']),
'projection_latitude': 0.,
'projection_altitude': float(self.proj_info['distance_from_earth_center'] -
self.proj_info['earth_equatorial_radius']) * 1000,
'satellite_actual_longitude': actual_lon,
'satellite_actual_latitude': actual_lat,
'satellite_actual_altitude': actual_alt,
'nadir_longitude': float(self.nav_info['nadir_longitude']),
'nadir_latitude': float(self.nav_info['nadir_latitude'])}
)
res = xr.DataArray(res, attrs=new_info, dims=['y', 'x'])
# Mask space pixels
if self.mask_space:
res = self._mask_space(res)
return res
def test_get_earth_radius(self):
"""Test earth radius computation."""
a = 2.
b = 1.
def re(lat):
"""Compute ellipsoid radius at the given geodetic latitude.
Reference: Capderou, M.: Handbook of Satellite Orbits, Equation (2.20).
"""
lat = np.deg2rad(lat)
e2 = 1 - b ** 2 / a ** 2
n = a / np.sqrt(1 - e2*np.sin(lat)**2)
return n * np.sqrt((1 - e2)**2 * np.sin(lat)**2 + np.cos(lat)**2)
for lon in (0, 180, 270):
self.assertEqual(hf.get_earth_radius(lon=lon, lat=0., a=a, b=b), a)
for lat in (90, -90):
self.assertEqual(hf.get_earth_radius(lon=0., lat=lat, a=a, b=b), b)
self.assertTrue(np.isclose(hf.get_earth_radius(lon=123, lat=45., a=a, b=b), re(45.)))
def _get_metadata(self, key, ds_info):
# Get actual satellite position. For altitude use the ellipsoid radius at the SSP.
actual_lon = float(self.nav_info['SSP_longitude'])
actual_lat = float(self.nav_info['SSP_latitude'])
re = get_earth_radius(
lon=actual_lon,
lat=actual_lat,
a=float(self.proj_info['earth_equatorial_radius'] * 1000),
b=float(self.proj_info['earth_polar_radius'] * 1000))
actual_alt = float(
self.nav_info['distance_earth_center_to_satellite']) * 1000 - re
if self._round_actual_position:
actual_lon = round(actual_lon, 3)
actual_lat = round(actual_lat, 2)
actual_alt = round(actual_alt / 150) * 150 # to the nearest 150m
# Update metadata
new_info = dict(
units=ds_info['units'],
standard_name=ds_info['standard_name'],
wavelength=ds_info['wavelength'],
resolution='resolution',
id=key,
name=key['name'],
platform_name=self.platform_name,
sensor=self.sensor,
time_parameters=dict(
nominal_start_time=self.nominal_start_time,
nominal_end_time=self.nominal_end_time,
observation_start_time=self.observation_start_time,
observation_end_time=self.observation_end_time,
),
orbital_parameters={
'projection_longitude':
float(self.proj_info['sub_lon']),
'projection_latitude':
0.,
'projection_altitude':
float(self.proj_info['distance_from_earth_center'] -
self.proj_info['earth_equatorial_radius']) * 1000,
'satellite_actual_longitude':
actual_lon,
'satellite_actual_latitude':
actual_lat,
'satellite_actual_altitude':
actual_alt,
'nadir_longitude':
float(self.nav_info['nadir_longitude']),
'nadir_latitude':
float(self.nav_info['nadir_latitude']),
},
)
return new_info