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Obtaining CORS Information Using Anonymous FTP
DATE
====
August 2, 2005
INTRODUCTION
============
The National Geodetic Survey (NGS), an agency of the National Oceanic and
Atmospheric Administration, manages the National CORS (Continuously
Operating Reference Station) network. This network currently contains more
than 650 GPS data-collection sites in the United States and its territories,
with a few in foreign countries. The following text describes how to
obtain GPS data from these sites via the Internet using the anonymous file
transfer protocol (FTP) utility. Users may also obtain these GPS data via
the World Wide Web at http://www.ngs.noaa.gov/CORS. While most users should
find the Web more convenient for downloading small amounts of GPS data from
the CORS network, NGS recommends that people use anonymous ftp to download
large amounts of GPS data such as data for more than five days and/or data
for more than ten sites.
See http://www.ngs.noaa.gov/CORS/newsletter2/ for a list of the sites currently
contained in the National CORS network.
NGS also manages the Cooperative CORS network which contains more than 140
additional GPS data-collection sites in the United States. Users need to
download GPS data from these sites directly from the organization that is
responsible for the site. Appropriate Web links are maintained at
http://www.ngs.noaa.gov/CORS/Coop .
CORS sites are operated by a collection of more than 155 organizations,
representing various federal, state, local and foreign government agencies,
as well as various academic and commercial institutions. The CORS network
enables GPS users to determine centimeter-level positional coordinates for
user-selected locations. Additionally, CORS data serve to monitor crustal
motion, the distribution of moisture in the atmosphere, and the distribution
of free electrons in the ionosphere.
DATA FORMATS
==============
NGS uses four types of files to store the GPS data. The following table
provides a summary of these file types. All stored files have been compressed
using the UNIX-Z compression algorithm. Also, all files are either in the
Receiver Independent Exchange (RINEX) format, version 2(1)
( http://www.ngs.noaa.gov/CORS/Rinex2.html ),
or the HATANAKA-compacted RINEX format
( http://sopac.ucsd.edu/dataArchive/hatanaka.html )
____________________________________________________________________________________
| Day 0 | Days 1-30 |
____________________________________________________________________________________
RINEX FORMAT | | Type D1: Daily file |
| | at original |
| | sampling rate |
____________________________________________________________________________________
HATANAKA | Type H: Hourly | Type D2: Daily | Type D2: Daily
COMPACTED | files at original | file, decimated to | file, decimated to
RINEX FORMAT | sampling rate | a sampling rate of | a sampling rate of
| | 30 seconds | 30 seconds
____________________________________________________________________________________
Each Type H file contains one hour's worth of GPS data in the Hatanaka-compacted
RINEX format for an individual CORS. These files contain the data at its
original sampling rate (or sampling interval), that is, at the sampling rate
that the GPS receiver recorded the code and carrier-phase signals from the
satellites. Popular sampling rates include 1 second, 5 seconds, 10 seconds,
15 seconds, and 30- seconds. These files are created only for those CORS
whose data are available to NGS on an hourly or more rapid basis. These files
are created within a few minutes after the data have become available to NGS
(usually within a few minutes after the turn of the hour).
Each Type D1 file contains 24-hours worth (from UTC midnight to UTC midnight)
of GPS data in the RINEX format for an individual CORS at the data's original
sampling rate. These files are created after all 24-hours of data have become
available to NGS (usually within a few hours after EDT/EST midnight). These
files are kept for 30 days.
Each Type D2 file contains 24-hours worth (from UTC midnight to UTC midnight)
of GPS data in the Hatanaka-compacted RINEX format for an individual CORS at a
30-second sampling rate. These files are created after all 24-hours of data
have become available to NGS (usually within a few hours after EDT/EST midnight)
. These files are kept indefinitely.
FILE NAMING CONVENTION
======================
The RINEX file naming convention is as follows:
{ssss}{ddd}{h}.{yy}{t}; where ssss is the four character site identifier, "ddd"
is the day of year, "h" is a letter which corresponds to an hour long UTC time
block, "yy" is the year and "t" is the file type. For daily files, the format
would be {ssss}{ddd}0.{yy}{t}.
Hour long UTC time block identifier (h):
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23
a b c d e f g h i j k l m n o p q r s t u v w x
Ending (t) File Type
_________________________________________________
o Observation
d Hatanaka-compacted observation
n Navigation (satellite orbit)
m Meteorological
s Summary
__________________________________________________
FILE TRANSFER PROTOCOL (FTP)
============================
FTP is a user interface to the File Transfer Protocol. FTP copies files over
a network connection between the local "client" (user) computer and a remote
"server" computer. FTP runs on the client computer.
The user's system must have access to the INTERNET and support the File
Transfer Protocol (FTP). Some useful ftp commands are given below.
ascii set ascii transfer type
binary set binary transfer type
bye terminate ftp session and exit
cd change remote working directory
dir list contents of remote directory
get retrieve one file
help print local help information
mget retrieve multiple files
mput send multiple files
prompt force interactive prompting on multiple commands
put send one file
quit terminate ftp session and exit
show display the contents of an ASCII file
* Actual commands may vary among operating systems.
TO ACCESS CORS FTP DIRECTORIES
==============================
To access the CORS FTP directories, follow the steps below.
Type the "ftp" command followed by the INTERNET address as follows:
ftp cors.ngs.noaa.gov
Respond to the following:
Login: anonymous
Password: your complete e-mail address
You will arrive at the ftp command level indicated by the prompt "ftp>".
Then use the command " cd cors "
If you have trouble, type "help" to print local help information or
review the section FILE TRANSFER PROTOCOL for help with additional
commands.
The following sub-directories contain additional files and information.
coord NAD83 and ITRF positional information for the
CORS sites.
rinex Rinex data files.
station_log Station information, antenna specifications,
and site contacts.
utilities Programs for manipulating the RINEX files.
Plots 60-day Time Series plots of CORS sites.
ACCESS VIA WWW
==============
NGS has developed a home page on the Internet World Wide Web (WWW) for
online access to information on its products, services, and program
activities.
The CORS products and data are available through NGS' home page which is
accessible through either NOAA's home page or by typing in the URL
(Uniform Resource Locator):
http://www.ngs.noaa.gov/CORS
when using a browsing tool such as Internet Explorer (IE) or Netscape.
Browse to find the information you need.
Users may also access the CORS FTP directories via the WWW by typing in the URL
ftp://www.ngs.noaa.gov/cors/ .
DIRECTORY STRUCTURE (FTP)
=========================
| | |
| |-- yyyy --|-- ddd --|--site id--|-- GPS data
|-- rinex --| | | |
| | |
--cors-| |-- global nav file
| |
| |- igs orbits (igs, igr, igp)
|-- select.txt
|
|-- UFCORS.txt
|
|-- Plots
|
|-- README.txt
|
|-- RINEX-2.txt
|
|-- news.let (newsletter)
|
|-- coord
|
|-- station_log --|-- *.log
|
|-- utilities |-- Unix--|-- HPUX -- programs
| | |-- SunOS
| | |-- Solaris
| | |-- SGI
| |
| |-- NT -- |-- programs
| |
| |-- Dos-- |-- interpo.exe
| |-- join24pc.exe
|-- join24.txt
|-- gpscal.exe
|-- gpswk.exe
|-- cato.exe
|-- cato.txt
|-- decimate.exe
|-- decimate.inp
|-- decimate.txt
|-- gzip386.exe
|-- uudecode.exe
|-- uuencode.exe
|-- tar4dos.zip
FILE COMPRESSION
================
All GPS data files are stored in the UNIX compressed format. The compressed
files have the extension ".Z" appended. You may retrieve the compressed files
as is by using the "get or mget" command and the complete file name, including
file name extensions. If you transfer the file in compressed mode, be sure to
set the transfer mode to "binary". Executable program files should be transferred
in "binary" mode, text files should be transferred in "ascii" mode.
UTILITIES
=========
Several DOS based utility programs are available to manipulate the RINEX
data files. Versions also exist for other platforms such as Silicon
Graphics (sgi), Sun Microsystems (sun), and Hewlett Packard (hp).
gzip386.exe Executable file which contains the utility "gzip.exe".
join24pc.exe Utility program to join two or more hourly RINEX
observation or navigation files.
decimate.exe Utility program to decimate 5 second data to a user
specified rate.
interpo.exe Utility program to interpolate between data epochs. Please
read the documentation for this utility for more details.
E-MAIL
======
If you would like to add your name to the NGS CORS e-mail list, please email
your request to ngs.cors@noaa.gov. You will receive
the weekly NGS CORS Newsletter and other special notifications.
ADDITIONAL INFORMATION OR REQUESTS
==================================
For additional information please email ngs.cors@noaa.gov
Or call us at (301) 713-3563.