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MODULE cov_cutoff

Contact: Jeff Anderson
Revision: $Revision: 2801 $
Source: $URL: http://subversion.ucar.edu/DAReS/DART/trunk/cov_cutoff/cov_cutoff_mod.html $
Change Date: $Date: 2007-04-04 22:11:48 -0600 (Wed, 04 Apr 2007) $
Change history: try "svn log" or "svn diff"

OVERVIEW

Computes the weight with which an observation should impact a state variable that is separated by a given distance. The distance is in units determined by the location module being used.




OTHER MODULES USED

types_mod
utilities_mod
location_mod



PUBLIC INTERFACE

use cov_factor_mod, only : comp_cov_factor

Optional namelist interface &cov_cutoff_nml may be read from file input.nml.




PUBLIC COMPONENTS


var = comp_cov_factor(z_in, c [,obs_loc] [,obs_kind] [,target_loc] [,target_kind] [,localization_override])
 real(r8)                                  :: comp_cov_factor
 real(r8), intent(in)                      :: z_in
 real(r8), intent(in)                      :: c
 type(location_type), optional, intent(in) :: obs_loc
 integer, optional, intent(in)             :: obs_kind
 type(location_type), optional, intent(in) :: target_loc
 integer, optional, intent(in)             :: target_kind
 integer, optional, intent(in)             :: localization_override
 

Description

Returns a weighting factor for observation and a target variable (state or observation) separated by distance z_in and with a half-width distance, c. Three options are provided and controlled by a namelist parameter. The optional argument localization_override controls the type of localization function if present. The optional arguments obs_loc, obs_kind and target_loc, target_kind are not used in the default code. They are made available for users who may want to design more sophisticated localization functions.

var    Weighting factor.
z_in    The distance between observation and target.
c    Factor that describes localization function. Describes half-width of functions used here.
obs_loc    Location of the observation.
obs_kind    Observation kind.
target_loc    Location of target.
target_kind    Kind of target.
localization_override    Controls localization type if present. Same values as for namelist control.




NAMELIST

We adhere to the F90 standard of starting a namelist with an ampersand '&' and terminating with a slash '/'.

namelist / cov_cutoff_nml /  select_localization
Contents Type Description
select_localization integer Selects the localization function.
1 = Gaspari-Cohn 5th order polynomial with halfwidth c.
2 = Boxcar with halfwidth c (goes to 0 for z_in > 2c).
3 = ramped boxcar. Has value 1 for z_in < c and then reduces linearly to 0 at z_in = 2c.



FILES




REFERENCES

Gaspari and Cohn QJRMS, 125, 723-757. (eqn. 4.10)

ERROR CODES and CONDITIONS

RoutineMessageComment
comp_cov_factor Illegal value of "select_localization" in cov_cutoff_mod namelist Only values 1 through 3 select a localization function.



KNOWN BUGS




FUTURE PLANS




PRIVATE COMPONENTS

Discussion