<HTML> <BODY BGCOLOR=#ccccdd LINK=#0000aa VLINK=#0000ff ALINK=#ff0000 ><BASE TARGET="bottom_target"><PRE>
!
! Spectral_Units_Conversion
!
! Module containing functions to convert between various spectral units.
!
!
! CREATION HISTORY:
! Written by: Paul van Delst, 14-Jan-2002
! paul.vandelst@noaa.gov
!
!
<A NAME='SPECTRAL_UNITS_CONVERSION'><A href='../../html_code/crtm/Spectral_Units_Conversion.f90.html#SPECTRAL_UNITS_CONVERSION' TARGET='top_target'><IMG SRC="../../gif/bar_purple.gif" border=0></A>
MODULE Spectral_Units_Conversion 7,2
! -----------------
! Environment setup
! -----------------
! Module use
USE Type_Kinds
, ONLY: fp
USE Fundamental_Constants, ONLY: C => SPEED_OF_LIGHT
! Disable implicit typing
IMPLICIT NONE
! ------------
! Visibilities
! ------------
PRIVATE
PUBLIC :: GHz_to_inverse_cm
PUBLIC :: inverse_cm_to_GHz
PUBLIC :: micron_to_inverse_cm
PUBLIC :: inverse_cm_to_micron
! -----------------
! Module parameters
! -----------------
! Version Id for the module
CHARACTER(*), PARAMETER :: MODULE_VERSION_ID = &
'$Id: Spectral_Units_Conversion.f90 29405 2013-06-20 20:19:52Z paul.vandelst@noaa.gov $'
REAL(fp), PARAMETER :: ZERO = 0.0_fp
REAL(fp), PARAMETER :: ONE = 1.0_fp
CONTAINS
!------------------------------------------------------------------------------
!:sdoc+:
!
! NAME:
! GHz_to_inverse_cm
!
! PURPOSE:
! Function to convert frequencies in units of gigahertz (GHz) to units
! of inverse centimetres (cm^-1)
!
! CALLING SEQUENCE:
! Wavenumber = GHz_to_inverse_cm( Frequency )
!
! INPUTS:
! Frequency: Frequency in gigahertz. Must be > 0.0
! UNITS: GHz
! TYPE: REAL(fp)
! DIMENSION: Scalar or any rank array
! ATTRIBUTES: INTENT(IN)
!
! FUNCTION RESULT:
! Wavenumber: The frequency in inverse centimetres.
! Value is 0.0 for an input frequency < or = 0.0.
! UNITS: cm^-1
! TYPE: REAL(fp)
! DIMENSION: Same as input argument.
!
! PROCEDURE:
! The relationship between wavelength and frequency is given by,
!
! c
! l = --- metres .....(1)
! f
!
! where c = speed of light in m.s^-1
! f = frequency in Hz (s^-1).
!
! The conversion of wavelength, l, to frequency, v, in cm^-1, is given by,
!
! 1
! v = ------- cm^-1 .....(2)
! 100 l
!
! where the factor of 100 converts l from metres to centimetres.
! Substituting (2) into (1) gives,
!
! f
! v = ------- cm^-1 .....(3)
! 100 c
!
! If f is expressed as gigahertz, then (3) becomes,
!
! 10^9 f
! v = -------- cm^-1
! 100 c
!
! f
! = 10^7 --- cm^-1
! c
!
! Therefore the conversion factor from GHz to inverse centimeters is
! 10^7/c where c is in m.s^-1.
!
!:sdoc-:
!------------------------------------------------------------------------------
<A NAME='GHZ_TO_INVERSE_CM'><A href='../../html_code/crtm/Spectral_Units_Conversion.f90.html#GHZ_TO_INVERSE_CM' TARGET='top_target'><IMG SRC="../../gif/bar_green.gif" border=0></A>
ELEMENTAL FUNCTION GHz_to_inverse_cm( Frequency ) RESULT( Wavenumber )
REAL(fp), INTENT(IN) :: Frequency
REAL(fp) :: Wavenumber
REAL(fp), PARAMETER :: SCALE_FACTOR = 1.0e+07_fp
IF ( Frequency < EPSILON(ONE) ) THEN
Wavenumber = ZERO
RETURN
END IF
Wavenumber = SCALE_FACTOR * Frequency / C
END FUNCTION GHz_to_inverse_cm
!------------------------------------------------------------------------------
!:sdoc+:
!
! NAME:
! inverse_cm_to_GHz
!
! PURPOSE:
! Function to convert frequencies in units of inverse centimetres (cm^-1)
! to units of gigahertz (GHz)
!
! CALLING SEQUENCE:
! Frequency = inverse_cm_to_GHz( Wavenumber )
!
! INPUTS:
! Wavenumber: Frequency in inverse centimetres. Must be > 0.0
! UNITS: cm^-1
! TYPE: REAL(fp)
! DIMENSION: Scalar or any rank array
! ATTRIBUTES: INTENT(IN)
!
! FUNCTION RESULT:
! Frequency: The frequency in gigahertz.
! Value is 0.0 for an input wavenumber < or = 0.0.
! UNITS: GHz
! TYPE: REAL(fp)
! DIMENSION: Same as input argument
!
! PROCEDURE:
! The relationship between frequency and wavelength is given by,
!
! c
! f = --- Hz (s^-1) .....(1)
! l
!
! where c = speed of light in m.s^-1
! l = wavelength in m.
!
! The conversion of wavelength, l, to frequency, v, in cm^-1, is given by,
!
! 1
! v = ------- cm^-1 .....(2)
! 100 l
!
! where the factor of 100 converts l from metres to centimetres.
! Substituting (2) into (1) gives,
!
! f = 100 c.v Hz
!
! = 10^-9 . 100 c.v GHz
!
! = 10^-7 . c.v GHz
!
! Therefore the conversion factor from inverse centimeters to GHz is
! 10^-7.c where c is in m.s^-1.
!
!:sdoc-:
!------------------------------------------------------------------------------
<A NAME='INVERSE_CM_TO_GHZ'><A href='../../html_code/crtm/Spectral_Units_Conversion.f90.html#INVERSE_CM_TO_GHZ' TARGET='top_target'><IMG SRC="../../gif/bar_green.gif" border=0></A>
ELEMENTAL FUNCTION inverse_cm_to_GHz( Wavenumber ) RESULT( Frequency )
REAL(fp), INTENT(IN) :: Wavenumber
REAL(fp) :: Frequency
REAL(fp), PARAMETER :: SCALE_FACTOR = 1.0e-07_fp
IF ( Wavenumber < EPSILON(ONE) ) THEN
Frequency = ZERO
RETURN
END IF
Frequency = SCALE_FACTOR * C * Wavenumber
END FUNCTION inverse_cm_to_GHz
!------------------------------------------------------------------------------
!:sdoc+:
!
! NAME:
! micron_to_inverse_cm
!
! PURPOSE:
! Function to convert wavelengths in units of microns (10^-6 m) to
! frequencies in units of inverse centimetres (cm^-1).
!
! CALLING SEQUENCE:
! Wavenumber = micron_to_inverse_cm( Wavelength )
!
! INPUTS:
! Wavelength: Wavelength in microns. Must be > 0.0
! UNITS: um (10^-6 m)
! TYPE: REAL(fp)
! DIMENSION: Scalar or any rank array
! ATTRIBUTES: INTENT(IN)
!
! FUNCTION RESULT:
! Wavenumber: The frequency in inverse centimetres.
! Value is 0.0 for an input wavelength < or = 0.0.
! UNITS: cm^-1
! TYPE: REAL(fp)
! DIMENSION: Same as input argument
!
! PROCEDURE:
! Given a wavelength of l microns, the frequency, v, in terms of
! inverse length is its reciprocal, i.e. the number of wavelengths
! that "fit" within a certain length dimension,
!
! 1
! v = --- . 10^6 m^-1
! l
!
! where the 10^6 converts the microns to metres. A factor of 100
! is introduced to produce units of inverse centimetres,
!
! 1 10^6
! v = --- . ------ m^-1
! l 10^2
!
! 10^4
! = ------ cm^-1
! l
!
!:sdoc-:
!------------------------------------------------------------------------------
<A NAME='MICRON_TO_INVERSE_CM'><A href='../../html_code/crtm/Spectral_Units_Conversion.f90.html#MICRON_TO_INVERSE_CM' TARGET='top_target'><IMG SRC="../../gif/bar_green.gif" border=0></A>
ELEMENTAL FUNCTION micron_to_inverse_cm( Wavelength ) RESULT( Wavenumber ) 1
REAL(fp), INTENT(IN) :: Wavelength
REAL(fp) :: Wavenumber
REAL(fp), PARAMETER :: SCALE_FACTOR = 1.0e+04_fp
IF ( Wavelength < EPSILON(ONE) ) THEN
Wavenumber = ZERO
RETURN
END IF
Wavenumber = SCALE_FACTOR / Wavelength
END FUNCTION micron_to_inverse_cm
!------------------------------------------------------------------------------
!:sdoc+:
!
! NAME:
! inverse_cm_to_micron
!
! PURPOSE:
! Function to convert frequencies in units of inverse centimetres (cm^-1)
! to wavelengths in units of microns (10^-6 m).
!
! CALLING SEQUENCE:
! Wavelength = inverse_cm_to_micron( Wavenumber )
!
! INPUTS:
! Wavenumber: Frequency in inverse centimetres. Must be > 0.0
! UNITS: cm^-1
! TYPE: REAL(fp)
! DIMENSION: Scalar or any rank array
! ATTRIBUTES: INTENT(IN)
!
! FUNCTION RESULT:
! Wavelength: The wavelength in microns.
! Value is 0.0 for an input wavenumber < or = 0.0.
! UNITS: um (10^-6 m)
! TYPE: REAL(fp)
! DIMENSION: Same as input argument
!
! PROCEDURE:
! Given a freqency of v inverse centimetres, the wavelength is its
! reciprocal,
!
! 1 1
! l = --- . ------ m
! v 10^2
!
! where the 10^2 converts the centimetres to metres. A factor of 10^6
! is introduced to produce units of microns (10^-6 m),
!
! 1 10^6
! l = --- . ------ um
! v 10^2
!
! 10^4
! = ------ um
! v
!
!:sdoc-:
!------------------------------------------------------------------------------
<A NAME='INVERSE_CM_TO_MICRON'><A href='../../html_code/crtm/Spectral_Units_Conversion.f90.html#INVERSE_CM_TO_MICRON' TARGET='top_target'><IMG SRC="../../gif/bar_green.gif" border=0></A>
ELEMENTAL FUNCTION inverse_cm_to_micron( Wavenumber ) RESULT( Wavelength )
REAL(fp), INTENT(IN) :: Wavenumber
REAL(fp) :: Wavelength
REAL(fp), PARAMETER :: SCALE_FACTOR = 1.0e+04_fp
IF ( Wavenumber < EPSILON(ONE) ) THEN
Wavelength = ZERO
RETURN
END IF
Wavelength = SCALE_FACTOR / Wavenumber
END FUNCTION inverse_cm_to_micron
END MODULE Spectral_Units_Conversion