[Dart-dev] [4144] DART/trunk/observations/gps: Added some info to the html file about local vs non-local operators.

[nancy at ucar.edu]

Revision: 4144
Author:   nancy
Date:     2009-11-11 10:33:12 -0700 (Wed, 11 Nov 2009)
Log Message:
-----------
Added some info to the html file about local vs non-local operators.
Added comments in the source about the overwrite_time option,
about why we don't recommend using it.

Modified Paths:
--------------
    DART/trunk/observations/gps/convert_cosmic_gps_cdf.f90
    DART/trunk/observations/gps/gps.html

-------------- next part --------------
Modified: DART/trunk/observations/gps/convert_cosmic_gps_cdf.f90
===================================================================
--- DART/trunk/observations/gps/convert_cosmic_gps_cdf.f90	2009-11-06 22:24:18 UTC (rev 4143)
+++ DART/trunk/observations/gps/convert_cosmic_gps_cdf.f90	2009-11-11 17:33:12 UTC (rev 4144)
@@ -78,8 +78,8 @@
 
 integer, parameter :: nmaxlevels = 200   !  max number of observation levels
 
-logical  :: local_operator = .true.
-logical  :: overwrite_time = .false.
+logical  :: local_operator = .true.   ! see html file for more on non/local
+logical  :: overwrite_time = .false.  ! careful - see note below
 real(r8) :: obs_levels(nmaxlevels) = -1.0_r8
 real(r8) :: obs_window = 12.0     ! accept obs within +/- hours from anal time
 real(r8) :: ray_ds = 5000.0_r8    ! delta stepsize (m) along ray, nonlocal op
@@ -92,8 +92,14 @@
                                   ray_ds, ray_htop, gpsro_netcdf_file,    &
                                   gpsro_netcdf_filelist, gpsro_out_file 
 
-! could add overwrite_time to namelist
 
+! 'overwrite_time' replaces the actual observation times with the
+! analysis time for all obs.  this is intentionally not in the namelist
+! because we think observations should preserve the original times in all
+! cases.  but one of our users had a special request to overwrite the time
+! with the synoptic time, so there is code in this converter to do that
+! if this option is set to .true.  but we still don't encourage its use.
+
 ! initialize some values
 obs_num = 1
 qc = 0.0_r8

Modified: DART/trunk/observations/gps/gps.html
===================================================================
--- DART/trunk/observations/gps/gps.html	2009-11-06 22:24:18 UTC (rev 4143)
+++ DART/trunk/observations/gps/gps.html	2009-11-11 17:33:12 UTC (rev 4144)
@@ -118,8 +118,7 @@
 Optional namelist interface
 <A HREF="#Namelist"> <em class=code>&amp;convert_cosmic_gps_nml</em> </A>
 may be read from file <em class=file>input.nml</em>.
-</P> 
-<P>
+</P> <P>
 The work directory contains several scripts, including one which downloads
 the raw data files a day at a time (cosmic_download.csh), and one 
 which executes the conversion program (convert_script.csh).  These
@@ -131,14 +130,26 @@
 and do not use the options to automatically delete the input files.
 Keep the files around until you are sure you are satisified with the
 output files and then delete them by hand.
-</P> 
-<P>
+</P> <P>
 The conversion executable, convert_cosmic_gps_cdf, reads the namelist
 from the file 'input.nml', but also reads an analysis time from the
 terminal or the standard input unit.  This makes it simpler to convert
 multiple files without editing the namelist.  The program prompts for
 the time string with the required time format, 
 <em class=code>yyyy-mm-dd_hh:mm:ss</em> .
+</P> <P>
+The namelist lets you select from one of two different forward
+operators.  The 'local' forward operator computes the expected
+observation value at a single point: the requested height at the
+tangent point of the ray between satellites.  The 'non-local' operator
+computes values along the ray-path and does an integration to get
+the expected value.  The length of the integration segments and
+height at which to end the integration are given in the namelist.
+In some experiments the difference between the two types of
+operators was negligible.  This choice is made at the time of
+the conversion, and the type of operator is stored in the observation,
+so at runtime the corresponding forward operator will be used to
+compute the expected observation value.
 </P>
 
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