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Workspace Method yActive
Description
Replaces yCalc for radar/lidar calculations.
The output format for iy when simulating radars and lidars differs
from the standard one, and yCalc can not be used for such simulations.
This method works largely as yCalc, but is tailored to handle the
output from iyActiveSingleScat.
The method requires additional information about the sensor,
regarding its recieving properties. First of all, recieved
polarisation states are taken from instrument_pol_array. Note
that this WSV allows to define several measured polarisations
for each transmitted signal. For example, it is possible to
simulate transmission of V and measuring backsacttered V and H.
Secondly, the range averaging is described by range_bins. These
bins can either be specified in altitude or two-way travel time.
In both case, the edges of the range bins shall be specified.
All data (including auxiliary variables) are returned as the
average inside the bins. If a bin is totally outside the model
atmosphere, NaN is returned.
The options for iy_unit are:
"1" : Backscatter coefficient. Unit is 1/(m*sr). At zero
attenuation, this equals the scattering matrix value for
the backward direction. See further AUG.
"Ze" : Equivalent reflectivity. Unit is mm^6/m^3. Conversion
formula is given below.
"dBZe": 10*log10(Ze/Z0), where Z0 is 1 mm^6/m^3.
The conversion from backscatter coefficient to Ze is:
Ze = 1e18 * lambda^4 / (k2 * pi^5) * sum(sigma),
where sum(sigma) = 4 * pi * b, and b is the backscatter coefficient.
The reference dielectric factor can either specified directly by
the argument *k2*. For example, to mimic the CloudSat data, *k2*
shall be set to 0.75 (citaion needed). If *k2* is set to be
negative (which is defualt), k2 is calculated as:
k2 = abs( (n^2-1)/(n^2+2) )^2,
where n is the refractive index of liquid water at temperature
*ze_tref* and the frequency of the radar, calculated by the MPM93
parameterization.
A lower limit for dBZe is applied (*dbze_min*). The main reason is to
handle the fact dBZe is not defined for Ze=0, and dBZe is set to the
clip value when Ze < 10^(dbze_min/10).
Authors: Patrick Eriksson
Synopsis
| yActive( | y, y_f, y_pol, y_pos, y_los, y_aux, y_geo, jacobian, atmgeom_checked, atmfields_checked, iy_unit, iy_aux_vars, stokes_dim, f_grid, atmosphere_dim, nlte_field, cloudbox_on, cloudbox_checked, sensor_pos, sensor_los, sensor_checked, jacobian_do, jacobian_quantities, iy_main_agenda, geo_pos_agenda, instrument_pol_array, range_bins, ze_tref, k2, dbze_min ) |
Variables