CFD Utilities Files

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!
   program los_attenuation
!
!  Description:
!
!     For the input line of sight data (los.g and los.f in Plot3D format) and
!     mission-specific radio frequency, calculate a measure of the expected
!     radio attenuation.  The formulation used initially here is that employed
!     by program Radio_Attenuation, c. 2016, which exploited the existence of a
!     substantial aerothermal database for the Orion spacecraft.  It generated
!     a secondary database for all signal directions from multiple antennas.
!
!     This version can also read los.dat (point-order Tecplot file), and it
!     allows for variable function numbers for p, T, eND, and (later) sigma.
!
!     The original design choice that assumed each atmosphere would require a
!     different attenuation method is flawed.  Therefore, the choice of method
!     is now by number with no obvious order.
!
!  Original Reference:
!
!     Mitigation of Communication Blackout During Re-entry Using Static Magnetic
!     Field, Neha Mehra, Rajesh K. Singh, and Subhash C. Bera,
!     Progress in Electromagnetic Research B, Vol. 63, pp. 161-172, 2015
!
!  Formulation Correction From Radio_Attenuation:
!
!     03/17/2016    Rick Thompson determined that plasma frequency
!                   omegap is an angular frequency in radians/sec.
!                   Therefore, the radio frequencies should be in
!                   the same units, so multiply Hz by 2 pi.
!
!  Possible Issues:
!
!     Is this (original) formulation Earth-specific in its use of p and T?
!     Now included is an electron number density-only method that should be
!     applicable to any atmosphere, and is invoked via atmosphere = 'any',
!     since changed to method = 1.  Most recently, Trevor Hedges' formulation
!     using conductivity sigma to compute collision frequency in place of
!     the formulation involving p and T (which appears to be a decent approx-
!     imation at Earth and Mars) is also expected to apply to any atmosphere.
!
!  Namelist Controls (attenuation.inp; omit trailing comments)
!
!     $attenuation
!     los_form                                   (1|2 = los.g + los.f | los.dat)
!     time = 50.5                                            (BET time, seconds)
!     bp = 1.23 2.34 3.45 30. 0. (x,y,z,cone,clock coords. of radio transmitter)
!     receiver = 'MRO'                (receiving asset; 'DTO' = direct to Earth)
!     method = 3                (1 = eND only; 2 = p & T & eND; 3 = sigma & eND)
!     frequency  = 400.                                                    (MHz)
!     ip = 1                                    (function numbers for p, T, eND)
!     iT = 2
!     ie = 3
!     isigma = 4                       (function number for conductivity, sigma)
!     $end
!
!  LOS data:
!
!     The initial formulation expects p, T, electron number density as functions
!     1, 2, 3 in los.f, in SI units.  Any further functions will be ignored.
!     [This has now been generalized via ip, iT, ie which default to 1, 2, 3.]
!     [And isigma has since been introduced for reading conductivity directly.]
!     Other forms of the attenuation calculations may require a different set of
!     functions, including eND alone.
!
!     Since the plottable outputs contain p and T, they should be included in
!     the LOS dataset whether the attenuation calculation uses them or not.
!
!  Output:
!
!     o  Teclotable file of LOS data and the integrand, integrands.dat:
!
!        # time (s): 50.5
!        # bp x/y/z (m): 1.23 2.34 3.45 30. 0.
!        # receiver: 'MRO'
!        # method: 3
!        # frequency (MHz): 400.
!        # attenuation 1(dB): 50.
!        # eNDmax  (per m^3): 1.234e20 
!        # eNDcrit (per m^3): 1.012e20 
!        variables=arc[m],p[Pa],T[K],eND[m^-3],integrand[dB/m]
!        0.000000E+00 4.123456E+01 3.456789E+03 1.234567E+18 1.234567E-04
!        1.123456E-05  :            :            :            :
!         :            :            :            :            :
!
!  History:
!
!     Jan-Jul 2016  D.A.Saunders  Radio_Attenuation implementation for Orion.
!     08-07-2022      "     "     Design of single-LOS adaptation.
!     08-10-2022      "     "     Allow for atmosphere specifics; initial code.
!     08-12-2022      "     "     Realized that a planet name may not be
!                                 sufficient to define what is expected in the
!                                 los.f file.  See discussion above.
!     08-17-2022      "     "     Critical density was set in the wrong place.
!                                 Allow for reading the line of sight data as a
!                                 point-order Tecplot file, los.dat.  Allow for
!                                 variable function numbers for p, T, eND.
!     08-19-2022      "     "     Introduced the electrons-only method shown in
!                                 slides by summer intern Trevor Hedges, and
!                                 invoked with atmosphere = 'any'.  This meant
!                                 moving a bunch of constants up to the top
!                                 level so that variations of the attenuation
!                                 formulation can share them.
!     08-21-2022      "     "     Initial testing completed.
!     08-23-2023      "     "     Incorporated the option to read conductivity
!                                 (sigma) as an input function (newly available
!                                 from a version of DPLR), and the formulation
!                                 from Trevor Hedges that uses sigma directly:
!
!                                                    eND * echarge**2
!                     electron collision frequency = ----------------
!                                                      emass * sigma
!
!                                 in place of Mehra's expression of electron
!                                 collision frequency as a function of p and T.
!     08-25-2023      "     "     Replaced the flawed use of atmosphere as a
!                                 method mechanism with a simple integer choice.
!
!  Author:  David Saunders, AMA, Inc. at NASA Ames Research Center, CA
!
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