ARTS built-in documentation server
Workspace Method iyRadioLink
Description
Radiative transfer for (active) radio links.
The method assumes that ppathagenda* is set up to return the
propagation path between the transmitter and the receiver. The
position of the transmitter is given as rte_pos, and the
"sensor" is taken as the receiver.
The primary output (y) is the received signal, where the signal
transmitted is taken from iy_transmitter_agenda. That is, y
is a Stokes vector for each frequency considered. Several other
possible measurements quantities, such as the bending angle, can
be obtained as the auxiliary data (see lost below).
If it is found that no link can be obtained due to intersection of
the ground, all data are set to zero. If no link could be
determined for other reasons (due to critical refraction or
numerical problems), all data are set to NaN.
This method is just intended for approximative calculations for
cases corresponding to relatively simple ray tracing. A detailed,
and more exact, treatment of several effects require more advanced
calculation approaches. Here a simple geometrical optics approach
is followed. See the user guide for details.
Defocusing is a special consideration for radio links. Two
algorithms are at hand for estimating defocusing, simply denoted
as method 1 and 2:
1: This algorithm is of general character. Defocusing is estimated
by making two path calculations with slightly shifted zenith
angles.
2: This method is restricted to satellite-to-satellite links, and
using a standard expression for such links, based on the
vertical gradient of the bending angle.
Both methods are described more in detail in the user guide.
The argument *defocus_shift* is used by both methods.
The following auxiliary data can be obtained:
"Pressure": The pressure along the propagation path.
Size: [1,1,1,np].
"Temperature": The temperature along the propagation path.
Size: [1,1,1,np].
"VMR, species X": VMR of the species with index X (zero based).
For example, adding the string "VMR, species 0" extracts the
VMR of the first species. Size: [1,1,1,np].
"Absorption, summed": The total absorption matrix along the
path. Size: [nf,ns,ns,np].
"Absorption, species X": The absorption matrix along the path
for an individual species (X works as for VMR).
Size: [nf,ns,ns,np].
"Particle extinction, summed": The total particle extinction
matrix along the path. Size: [nf,ns,ns,np].
"PND, type X": The particle number density for particle type X
(ie. corresponds to book X in pnd_field). Size: [1,1,1,np].
"Mass content, X": The particle content for mass category X.
This corresponds to column X in particle_masses (zero-
based indexing). Size: [1,1,1,np].
* "Impact parameter": As normally defined for GNRSS radio
occultations (this equals the propagation path constant,
r*n*sin(theta)). Size: [1,1,1,1].
* "Free space loss": The total loss due to the inverse square
law. Size: [1,1,1,1].
"Free space attenuation": The local attenuation due to the
inverse square law. Size: [1,1,1,np].
* "Atmospheric loss": Total atmospheric attenuation, reported as
the transmission. Size: [nf,1,1,1].
* "Defocusing loss": The total loss between the transmitter and
receiver due to defocusing. Given as a transmission.
Size: [1,1,1,1].
* "Faraday rotation": Total rotation [deg] along the path, for
each frequency. Size: [nf,1,1,1].
* "Faraday speed": The rotation per length unit [deg/m], at each
path point and each frequency. Size: [nf,1,1,np].
* "Extra path delay": The time delay of the signal [s], compared
to the case of propagation through vacuum. Size: [1,1,1,1].
* "Bending angle": As normally defined for GNRSS radio
occultations, in [deg]. Size: [1,1,1,1].
where
nf: Number of frequencies.
ns: Number of Stokes elements.
np: Number of propagation path points.
The auxiliary data are returned in iy_aux with quantities
selected by iy_aux_vars. Most variables require that the method
is called directly or by iyCalc. For calculations using yCalc,
the selection is restricted to the variables marked with *.
Authors: Patrick Eriksson
Synopsis
| iyRadioLink( | iy, iy_aux, ppath, diy_dx, stokes_dim, f_grid, atmosphere_dim, p_grid, lat_grid, lon_grid, z_field, t_field, vmr_field, abs_species, wind_u_field, wind_v_field, wind_w_field, mag_u_field, mag_v_field, mag_w_field, refellipsoid, z_surface, cloudbox_on, cloudbox_limits, pnd_field, use_mean_scat_data, scat_data_array, particle_masses, iy_aux_vars, jacobian_do, ppath_agenda, ppath_step_agenda, propmat_clearsky_agenda, iy_transmitter_agenda, iy_agenda_call1, iy_transmission, rte_pos, rte_los, rte_pos2, rte_alonglos_v,
ppath_lraytrace, defocus_method, defocus_shift ) |
Variables