Subject: [IGSMAIL-4509]: real-time tropo grids for NE U.S.
From: Jim Ray "(NGS" 301-713-2850 "x112)" <[email-masked]>
To: [email-masked], [email-masked]
Cc: [email-masked]
Date: Fri, 18 Jul 2003 08:43:43 -0400 (EDT)

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IGS Electronic Mail      18 Jul 05:44:35 PDT 2003      Message Number 4509
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Author: Seth Gutman, NOAA Forecast Systems Lab (forward by Jim Ray)

Friends and Colleagues,

	As promised, the tools and data needed to calculate the zenith
hydrostatic and wet delays in real time in the Northeast HA-NDGPS Test
Area now available at: 
ftp://ddftp.fsl.noaa.gov/outgoing/gpsdist/zwdgrids/

	The grids are located in the /ndgps directory, and the tools needed to
read them and compute zhd and zwd are located in the /tools directory. 
The README file is printed out below.

If you have any questions or encounter any problems, please contact:

[email-masked]
NOAA Forecast Systems Laboratory
325 Broadway  R/FS3
Boulder, CO 80305-3328
303-497-6795 (Voice)
303-497-6014 (Fax)

or myself at:

Seth I. Gutman
Chief, GPS-Met Observing Systems Branch
NOAA Forecast Systems Laboratory Demonstration Division
325 Broadway R/FS3
Boulder, CO 80305-3328
Phone:  303.497.7031
FAX:    303.497.6014
Email:  [email-masked]
Web:    http://gpsmet.noaa.gov

We are eager to evaluate the utility of this product, so please provide 
us with your comments, feedback, and results as soon as you feel 
comfortable doing so.  We stand ready to support you in every way 
possible in this testing and evaluation effort, and thank you for your 
interest in this effort.

Best regards,

Seth

---------------------------------------------------------------------------

25 June 2003

                         THE HA-NDGPS GRIDS README FILE

This directory contains the experimental zwd and altimeter data computed from
the 20-km RUC run at the NOAA/Forecast Systems Laboratory.
It also contains the GEOID 99 code downloaded from the National Geodetic
Survey (NGS) web site  (http://www.ngs.gov/GEOID/GEOID99/dnldgeo99061.html).
The GEOID99  code has been modified to run in a batch mode.
Please see g1999rme.txt for a description of the GEOID99 code.

The script getDelay.pl obtains the zwd, zhd, and ztd for the hour before 
and the hour after a requested time.  The values at previous hour are
analysis values, and the data for one hour after the requested time is a
2-hr forecast value.  The user can interpolate between
these values to obtain the delays at their specified time.

The build instructions for these modules have been tested on REDHAT LINUX
version 7.3.  This code should build on any LINUX or UNIX platform.

To INSTALL:

1) make a subdirectory on your hard drive.
2) copy all the files in this directory into that subdirectory.
3) type "make all"
4) edit the script getDelay.pl
   line 22 - #my $password
   take out comment (#) and replace userName\@address with your
   username@address

DESCRIPTION OF THE GRIDS
------------------------

The grids are located at the following address:
	ddftp.fsl.noaa.gov
in directory:
 	outgoing/gpsdist/zwdgrids/ndgps/

The grid files are created hourly.  Each grid goes from lower left
(34.40, -84.2) to upper right (47.2, -71.7). The filename defines the data
within the file.  An example GRID name is 0317612.GRID

where 03 is the year
      176 is the day of year
      12 is the hour.

Each grid has 4 associated jpg files:
  031761200.a0.jpg - altimeter contour plot of analysis values valid at 1200 UT
  031761202.a2.jpg - altimeter contour plot of the 2-hour forecast valid at
                     1400 UT
  031761200.z0.jpg - zwd contour plot of analysis values valid at 1200 UT
  031761202.z2.jpg - zwd contour plot of the 2-hour forecast valid at
                     1400 UT

The GRID file contains:
   number of longitudes
   number of latitudes
   lower left longitude
   lower left latitude
   longitude, latitude, zwd@analysis, alt@analysis, zwd@2hr-fcst, alt@2hr-fcst

So, the data in file 0317612.GRID would have values for 12 UT and 14 UT.

This would be the file the user would retrieve if he wanted to obtain delays
for 13 UT.  The user would then interpolate the values returned from the 
program to obtain delays an exact time.

TO EXECUTE PROGRAM:
-------------------

Type ./getDelay.pl lat lon ellipsoid_hgt

or

Type ./getDelay.pl lat lon ellipsoid_hgt year month day hour

SCRIPT getDelay.pl
---------------------------------

DATA INPUT
----------

The input arguments are:
  latitude
  longitude
  ellipsoidal elevation

Optional arguments are:
  year
  month
  day
  hour

PROGRAM FLOW
------------

If the time arguments are not entered, the program defaults to a time
2 hours from "now".  If the time is entered, the program will get a file
containing the analysis data 1 hour before the time entered and a 2-hour
forecast for an hour after the time requested.

The program computes the filename and ftp's the file from the FSL ftp site.

The program then obtains the geoidal height by executing the
NGS GEOID99 program intg.  I have made changes to the FORTRAN code to set
certain parameters so the program can run non-interactively.  Some of the
changes I have made are the following:

-  commented out calls to write interactive prompts
-  pass in name of file containing lat/lon values (ifnam)
-  set iinput = 2 (using input from file)
-  set iform = 2  (free format)
-  set ipos = 1 (positive east)
-  set poseast = 1 (positive east)
-  set outfil = .false. (no output file)
-  set ofyn = 'n' (no output file)
-  changed output to only print the geoid value
-  set dir to . (current directory)

For a comparison of the original code and the version on our site, download
the original code from http://www.ngs.gov/GEOID/GEOID99/dnldgeo99061.html
and run diff on the source files.

After the geoidal height has been calculated, the orthometric height is
computed by subtracting the geoidal height from the ellipsoidal height.

The program then runs the C++ program getSiteDelay and obtains the 
delay values from grid.

DATA OUTPUT
-----------

a string containing the following:

zhd0: 2.2804 zwd0: 0.10516 ztd0: 2.38556 zwd2: 0.12708 zhd2: 2.27839
ztd2: 2.40547

where zhd0 = zenith hydrostatic delay at time 0
      zwd0 = zenith wet delay at time 0
      ztd0 = zenith total delay at time 0
      zhd2 = zenith hydrostatic delay at time 2
      zwd2 = zenith wet delay at time 2
      ztd2 = zenith total delay at time 2

For Questions or Comments please contact:

[email-masked]
NOAA Forecast Systems Laboratory
325 Broadway  R/FS3
Boulder, CO 80305-3328
303-497-6795 (Voice)
303-497-6014 (Fax)

------------------------------------------------------
Seth I. Gutman
Chief, GPS-Met Observing Systems Branch
NOAA Forecast Systems Laboratory Demonstration Division
325 Broadway R/FS3
Boulder, CO 80305-3328

Phone:  303.497.7031
FAX:    303.497.6014
Email:  [email-masked]
Web:    http://gpsmet.noaa.gov