120°105°90° 165°150°135°75°60°45°30°15°0°-15°-30°-45°-60°-75°-90°-105°-120°-135°-150°-165°

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30°

45°

60°

75°

-15°

-45°

-60°

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15°

GPS SiteGLONASSSLR SiteVLBI SiteDORIS Site

Fortaleza

Arequipa

Bogotá

Santiago

Brasilia

La Plata

Kourou

Easter Island

Galapagos Islands

Limón

Tahiti

Kokee Park

Mauna Kea St. Croix

Barbados

Key BiscayneMcDonald

North Liberty

Greenbelt

Ottawa

Lac du Bonnet

EnsenadaPie Town

Quincy

Albert HeadAlgonquin

Colorado SpringsWestford

Mammoth Lakes

St. John's

Washington, D.C.Southern California

Integrated GPS Network(over 50 sites)

Churchill

Schefferville

Penticton

Fairbanks

Flin Flon

HolbergNanoose Bay

Priddis

Ucuelet

Whitehorse

Williams Lake

Whistler

Yellowknife Reykjavík Höfn

Thule

Kangerlussuaq

O'HigginsPalmer

Casey

MawsonDavis

McMurdo

Auckland

Hobart

TidbinbillaPerth

Yaragadee (2)

Karratha

Jabiru

TownsvilleNouméaAlice Springs

Macquarie Island

Chatham Islands

PretoriaHartebeesthoek

Sutherland

Rabat

Bahrain

Ascension

Maspalomas

Diego GarciaSeychelles

Cocos Islands

Singapore

Bakosurtanal

Kwajalein

Guam

Taipei

Tsukuba

Shanghai

Kunming

Xi'anWuhan

UsudaTaejonSuwon-shi

Gough Island

AnkaraMadrid

Nicosia

Borowiec

Brussels

Cagliaril'Ebre

KievOndrejov

Grasse

Graz

Herstmonceux

Innsbruk

Bangalore

IrkutskJozefoslaw

Kiruna

Kitab

KootwijkOlsztyn

Malindi

Matera

Mendeleevo

Medicina

Metsahovi

Noto

Yerevan

Ny Ålesund

Oberpfaffenhofen

Onsala

Penc

Mitzpe Ramon

San Fernando

SofiaToulouse

Tromsø

Padova

Villafranca

Westerbork

Zimmerwald

Zweningorod

Zelenchukskaya

Yakutsk

Almaty

Bishkek

Petropavlovsk-Kamchatsky

Lhasa

Magadan

Krasnoyarsk

Sanae

-30°

Kerguélen

Genova

Chesapeake Bay(3 sites)

Bermuda

Eastport

Tiksi

South Pole

Urumqi

Wettzell

Yebes

Effelsberg

Simeiz

KashimaMiuraKoganeiTateyama

Mizusawa

Syowa

Fort Davis

Green Bank

Hancock

Brewster

Los Alamos

Owens Valley

Kitt Peak

Goldstone

Bar Harbor

Potsdam

Maidenak

Riyadh

Helwan

Katzively

Komsomolsk

Changchun

Beijing

Simosato

Mt. Stromlo

Haleakala

Monument Peak

Svetloe

Tokyo

Riga

Quezon CityKaygabok Taal

Bilibino

KumtorkalaTalasKhantau Chumysh

ShamsiGebze

Bucharest

Yamoussoukro

Rio Grande

Cordoba

Salta

Aguascalientes

Riobamba

Ohrid

VeneziaOsijek

Arti

Dubrovnik

Santiago de Cuba

Esteli

Chiliwack

Tegucigalpa

ManaguaSan LorenzoGuatemala City

San Salvadore

Richard's Bay

AmmanMetzoki Dragot

Yuzhno-Sakhalinsk

Noril'sk

Ceduna

Darwin

DiyarbakirTrabzon

Istanbul

Kingston

Libreville

Boras

Marion Island

Tristan de Cunha

Rothera

Amsterdam Island

Sainte-Helene

Cachoeira Paulista

La Reunion

DjiboutiColombo

Mt. Everest

Arlit

Ponta Delgada Dionysos

Cibinong

Dakar

Solcorro Island

Rapa

Richmond

Badary

Purple Mountain

Manila

Futuna

Port Moresby

Terre Adéle

Novosibirsk

Woodinville

Visby

GjØvik

Neustrelitz

Maartsbo

Sèvres Mattersburg

Teddington

WroclawDelft

Mitaka

Lindfield

Brisbane

The Crustal Dynamics Data Information SystemCDDIS — NASA's Space Geodesy Data Archive

Carey Noll and Maurice DubeNASA GSFC

What is Space Geodesy Data?GPS Global Positioning System Source: Military satellites equipped with precise clocks transmitting satellite messages such as ephemeris, clock offsets, etc. Instrument: Dual frequency GPS receiver and antenna Observable: Station to satellite pseudorange, phase delay Yield: 1. Precise satellite ephemerides 2. Relative positions of and distances between observing stations 3. Earth rotation, orientation, polar motion, etc. 4. Time/frequency synchronization

GLONASS GLObal NAvigation Satellite System Source: Russian military satellites equipped with precise clocks transmitting satellite messages such as ephemeris, clock offsets, etc. Instrument: GLONASS receiver and antenna Observable: Station to satellite pseudorange, phase delay Yield: 1. Precise satellite ephemerides 2. Relative positions of and distances between observing stations 3. Earth rotation, orientation, polar motion, etc.

SLR Satellite Laser Ranging Target: Satellite equipped with corner cubes Instrument: Ground-based short-pulse laser transmitter Observable: Round-trip pulse time-of-flight to satellite Yield: 1. Satellite orbit 2. Positions of and distance between observing stations 3. Earth rotation, orientation, polar motion, etc.

VLBI Very Long Baseline Interferometry Source: Quasar (microwave frequencies) Instrument: Radio telescope equipped with X- and S-wideband receivers Observable: Difference in signal arrival times Yield: 1. Correlated delay and delay rate of simultaneous observations as a function of time 2. Positions of and distance between observing stations 3. Earth rotation, orientation, polar motion, atmospheric angular momentum, etc.

DORIS Doppler Orbitography and Radiolocation Integrated by Satellite Target: Satellites equipped with DORIS receiver and uplink hardware Instrument: Beacon transmitting radiofrequency signals Observable: Doppler shift on radiofrequency signals Yield: 1. Precise satellite ephemerides 2. Positions of observing stations

Global GPS, GLONASS, SLR, VLBI, and DORIS Networks

CDDIS Data HoldingsGPS

Temporal coverage: 1990 through present Data volume: On-line: 100 Gbytes +300 Gbyte jukebox Off-line: 200 Gbytes

GLONASS

Temporal coverage: 1998 through present Data volume: On-line: 25 Gbytes Off-line: N/A

SLR

Temporal coverage: 1976 through present Data volume: On-line: 10 Gbytes Off-line: 20 Gbytes

VLBI

Temporal coverage: 1979 through present Data volume: On-line: 30 Gbytes Off-line: 30 Gbytes

DORIS

Temporal coverage: 1992 through present Data volume: On-line: 5 Gbytes Off-line: N/A

Network Stations Continuously operational Timely flow of data

Data Centers Interface to network stations Perform QC and data conversion activities Archive data for access to analysis centers and user community

Analysis Centers Provide products to user community (e.g., station coordinates, precise satellite orbits, atmospheric products, etc.)

Central Bureau Management of service Facilitate communications and coordinate activites

Governing/Directing Board General oversight of the service Future direction

For Further Information:Carey Noll Maurice DubeManager, CDDIS Raytheon ITSSNASA GSFC Lanham, MD 20706Greenbelt, MD 20771 dube@cddis.gsfc.nasa.govnoll@cddis.gsfc.nasa.gov

CDDIS Web Site:http://cddis.nasa.gov or http://cddisa.gsfc.nasa.gov

Data Flow for International Services

Interdisciplinary Uses of CDDIS DataThe majority of CDDIS data sets are utilized for geodetic studies, such as plate tectonics, earthquake displacements, seismisity studies, volcano monitoring, Earth orientation, atmospheric angular momentum, etc. This archive of GPS, SLR, VLBI, DORIS, and GLONASS data are utilized to precisely determine station positions and velocities of the network stations and thus are used to maintain the terrestrial reference frame, the set of points which realize an ideal reference system. As a consequence, user data from single points or dense regional networks can be tied to this global reference frame.

The IGS and ILRS have been generating precise satellite ephemerides on a routine basis for many years. Precise orbits available from the CDDIS for GPS satellites have accuracies of five cm. SLR and DORIS data retrieved from the CDDIS archive are utilized in precise orbit determination (POD) efforts for several international oceanography missions, including TOPEX/Poseidon, ERS-1/2; in the near future, JASON and ENVISAT will join this list of missions deriving precise orbits from SLR and/or DORIS data. GPS flight receiver data, as well as SLR data, are also utilized for POD efforts for international geophysical missions such as GFO-1 and CHAMP and the future GRACE and IceSAT missions.

The GPS network within the IGS consists of globally distributed, continuously operating stations with dual-frequency P-code receivers. By using these two frequencies, the effects of the ionosphere can be determined and used to correct positional measurements. Current ionosphere products derived from GPS data and available through the CDDIS include the vertical total electron content (TEC). The TEC product can be used in the calibration of altimeter data and to correct single frequency GPS data. In 2001, a special campaign will be conducted by the IGS to study the effects of the solar maximum on the ionosphere, particularly in the polar and equatorial regions. High-rate data from the global GPS network will be archived at the CDDIS for a one-week period during April in support of this activity.

The GPS signal is sensitive to the refractive index of the atmosphere, which is a function of pressure, temperature, and moisture. Both space- and ground-based GPS meteorology can contribute to global climate research. Troposphere products generated by IGS analysis centers include precipitable water vapor, derived from zenith path delays. The results are dependent upon meteorological sensors collocated at the GPS sites, and can be a valuable tool in the validation of other meteorological products.

Introduction to the CDDISThe CDDIS is a dedicated data center supporting the international space geodesy community since 1982. The CDDIS provides easy and ready access to a variety of data sets, products, and information about these data. The CDDIS archive includes Global Positioning System (GPS), GLObal NAvigation Satellite System (GLONASS), Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Doppler Orbitography and Radiolocation Integrated by Satellite (DORIS) data and products. The specialized nature of the CDDIS lends itself well to enhancement to accommodate diverse data sets and user requirements.

CDDIS serves as one of the primary data centers for the following services within the International Association of Geodesy (IAG): International GPS Service (IGS) International Laser Ranging Service (ILRS) International VLBI Service for Geodesy and Astrometry (IVS) International Earth Rotation Service (IERS) International GLONASS Pilot Project (IGLOS-PP) International DORIS Service (IDS)

The CDDIS is operational on a dedicated computer facility located at NASA GSFC. This computer facility hosts web sites for the CDDIS, the ILRS, and several other GSFC facilities. The majority of the CDDIS data holdings are accessible via anonymous ftp and the web.

As in past years, the year 2000 saw another increase in the usage of the CDDIS. On average, 1.5M files totaling over 150 Gbytes in size were downloaded from the on-line CDDIS each month. Over 5,400 distinct hosts in over seventy countries accessed and downloaded data from the CDDIS last year. Furthermore, over 150 users accessed the CDDIS on a daily basis to download data. Over 120 institutions in over sixty countries supply data to the CDDIS on a daily basis for archival and distribution to the international user community.

New Thrusts for the CDDISIn 1999, the IGS issued a Call for Participation in the Low Earth Orbiters (LEO) Pilot Project. This activity will start in the summer of 2001. The CDDIS will retrieve, reformat, archive and provide access to data from a ground network of forty to fifty low-latency GPS receivers operating at a one-second sampling rate. The CDDIS will also archive data from GPS flight receivers on board the CHAMP and SAC-C satellites. Analysts will retrieve these data to produce precise orbits of the LEO platforms, which will aid in the generation of other products, such as temperature and water vapor profiles in the neutral atmosphere and ionosphere imaging products. The LEO Pilot Project will test the ability of the various components of the IGS infrastructure to support near real-time acquisition, dissemination, and processing of GPS data.

Efforts are also underway to increase the size of the on-line archive of the CDDIS. A 600-platter CD-ROM jukebox will provide access to the archive of older GPS data.

CEN 04/05/2001

Space Geodesy Network Stations

GPS GLON SLR VLBI DORIS

Operational/Regional Data Centers

Analysis Centers/User Community

Global Data Centers

Compressed Data Files (in data type-specific formats)

Compressed Data Files (in data type-specific formats)

Raw Data

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