The POLARIS (Polar Motion Analysis by Radio Interferometric Surveying) network monitors the location of the Earth's axis of rotation using the method of Very Long Baseline Interferometry (VLBI). Extragalactic radio sources are observed to determine polar motion, universal time, precession and nutation. Estimates of x and y components of the position of the pole, and formal uncertainties are tabulated according to observational dates. Currently, the nominal interval between entries is five days. The POLARIS Earth orientation information has applications in high accuracy satellite and space geodesy, geodynamics research, and climatology.
Data are available in machine-readable form from NOAA via telephone modem or through INTERNET - specifically, Earth Orientation Parameters (EOP), UT1 (Rotational Orientation of the Earth), and Length of Day (LOD). The following files are available:
Monthly: IRIS** EOP from current adjustment of IRIS data series, from 9/27/80 UT1MC** UT1 from Intensive series, from 4/24/84 LODR** LOD, uncorrected/corrected for tidal variations, from 1/1/86 Weekly: IRISW* Rapid Calculation of recent IRIS EOP UT1RS* Rapid calculation of recent intensive UT1
(For fuller information on the nature and content of these files, speak with the Technical Contact for this data set.) To access these files from modem, first set your terminal for 1200 baud, full duplex, any parity, and then dial (301) 881-6358. Enter and wait for response. Respond to 'user ID' with IRIS-NGS; to 'password' with NGS. Respond to 'who are you?' your organization name. Finally, respond to : prompt with LI,name where 'name' is the file name. To avoid further interrupts, respond with rather than . Exit with EX before disconnecting the modem. Subscribers to the GE Mark III system may also access these files, and should use their usual system procedures.
These files are now available via INTERNET using FTP protocols. The INTERNET address where the files can be found is 'ray.grdl.noaa.goc' or '18.104.22.168 The user should log in as 'anonymous' and give his/her own name when the system asks for a password. After logging on, the user should change to the appropriate directory with the command 'cd /dist/vlbi' and use the FTP command 'get' to transfer the appropriate files. The file names are identical to those described above (for modem access), but without the asterisks, which can cause difficulty on UNIX systems.
INFORMATION SERVICES BRANCH
NATIONAL GEODETIC SURVEY Phone:
ngs.infocenter at noaa.gov
National Geodetic Survey, NOAA
Information Services Branch
1315 East-West Highway City:
Province or State: