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Downloading The Data

Description

The programs of this software suite can only read RINEX data files. Convertors to RINEX exist and so this should not be an obstacle. Most data distribution centers use this format although the files themselves may be compressed to speed transmission.

Data from a receiver is commonly converted into three files, each with a specialized task. If surface meteorological data is available, a fourth file containing this data could also be created. The formats for these files are described in the RINEX standards. The naming convention for these files is: SSSSDDD#.YYC where

Only the observation files are required with one exception; one broadcast navigation file is also necesary. The navigation file from any one of the sites to be processed could be used. Many data centers also generate a global navigation, composed of many individual nav files and suitable for use with any data set. If multiple broadcast navigation files are present at the start of processing, run_survey will select one, based on the number of satellites included, and continue normally.

This tutorial covers three common data sources:

  1. a local data file
  2. the CORS data center
  3. an IGS global data center

Generally, transfer of data from a data center is done via the Internet. Each data center has a policy on reloading historical data and/or transfer via other media. Contact the data center directly to inquire about those policies.

Tutorial

At the end of the last tutorial, the current directory was ~/tutorial.

Retrieving data taken locally, by one's own group or institution, should be straight forward and may be as simple as copying the file into the appropriate location from somewhere else on the system or uploading the data from a PC. In this example, the data for Solomons Island, MD, SOL1, will be used as the local data file. These data were taken by the Geosciences Research Division (NOAA/NOS/NGS/GRD) as part of the Chesapeake Bay Sea Level Project. GRD makes all its data available via anonymous FTP. Retrieving this data will serve as the first of three examples of downloading files over the Internet.

Change to the working directory, 96_360.
cd 96_360
Retrieve the data from the GRD anonymous FTP site.
ftp gracie.grdl.noaa.gov
Connected to gracie.grdl.noaa.gov.
220 tony FTP server (Version wu-2.4(1) ...
Name (...): anonymous
Guest login ok, send your complete email address as password.
Password: me@my.home.address
... welcome message ...
ftp> bin
ftp> 200 Type set to I.
ftp> prompt
ftp> Interactive mode off.
ftp> cd dist/cignet/d360_96a
ftp> get sol13600.96o.Z
ftp> local: sol13600.96o.Z remote: sol13600.96o.Z
200 PORT command successful.
150 Opening BINARY mode data connection for ...
ftp> bye
ftp> 221 Goodbye.
run_survey recognizes Unix compressed files (indicated by the .Z extension) as a valid file type so no additional actions need to be taken.

Cape Henlopen, DE, CHL1, is a U.S. Coast Guard navigation site. Data from these sites are redistributed by the (NOAA/NOS/NGS) CORS data center. CORS provides data from a diverse network of tracking sites and should be a valuable data resource.
Retrieve the CHL1 data from the CORS anonymous FTP site:
ftp cors.ngs.noaa.gov
Connected to quark.ngs.noaa.gov.
Name (...): anonymous
331 Guest login ok, send your complete email address as password
Password: me@my.home.address
... welcome message ...
ftp> bin
ftp> 200 Type set to I.
ftp> prompt
ftp> Interactive mode off.
ftp> cd rinex/96360/chl1
ftp> 250 CWD command successful.
ftp> get chl13600.96o.gz
local: chl13600.96o.gz remote: chl13600.96o.gz
200 PORT command succesful.
150 Opening BINARY mode data connection for ...
ftp> bye
ftp> 221 Goodbye.

The .gz extension indicates a file compressed with the gzip program. gzip is a freeware compression program gaining widespread use. If it is not available, executables for a wide variety of platforms are available from ???.

run_survey does not recognize gzip compressed files at this time. Uncompress the file:
gunzip chl1360.96o.gz

The final example, data taken at Goddard Optical Research Facility east pier, GODE, will be retrieved from the NASA/Goddard Crustal Deformation Data Information System (CDDIS). The CDDIS also serves as an IGS global data center. The CDDIS generates a global navigation file . This is an excellent resource if no other navigation file is available. The global broadcast navigation file will be retrieved too.

Retrieve the data from the CDDIS anonymous FTP site.
ftp cddis.gsfc.nasa.gov
Connected to cddis.gsfc.nasa.gov.
220 CDDIS.GSFC.NASA.GOV MultiNet FTP Server Process...
Name (...): anonymous
331 anonymous user ok. Send read ident as password.
Password: me@my.home.address
... welcome message ...
ftp> bin
ftp> 200 Type I ok.
ftp> prompt
ftp> Interactive mode off.
ftp> cd gps1:[gpsdata.96360.96o]
ftp> 250 Connected to GPS1:[GPSDATA.96360.96O].
ftp> get gode3600.96o_z
ftp> local: gode3600.96o_z remote: gode3600.96o_z
200 Port ...
Retrieve the global broadcast navigation message file.
ftp> cd ..
ftp> 250 Connected to GPS1:[GPSDATA.96360].
cd 96n
ftp> 250 Connected to GPS1:[GPSDATA.96360.96N].
ftp> get brdc3600.96n_z
ftp> local: brdc3600.96n_z remote: brdc3600.96n_z
200 Port ...
ftp> bye
ftp> 221 QUIT command received. Goodbye.
These files areUnix compressed with a non-standard extension. Rename the files.
mv gode3600.96o_z gode3600.96o.Z
mv brdc3600.96n_z brdc3600.96n.Z


Notes

The directory ~/tutorial/96_360 should now contain four files:

brdc3600.96n.Z chl13600.96o gode3600.96o.Z sol13600.96o.Z.

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January 14, 2000
Steve Hilla