*************************************************************************** IERS Message No. 7 March 27, 2001 *************************************************************************** ITRF Report 4 on local ties Report on local tie problems in colocation sites as result from ITRF2000 Analysis Zuheir Altamimi IERS ITRS Product Center Institut Geographique National, France Date: March 22, 2001 The importance of local ties in space geodetic colocation sites is no longer to be demonstrated. Their impact on the ITRF solutions is very critical since they represent the key element of ITRF combination. Based on ITRF2000 residual analysis, the current situation of local ties is summarized in the following two tables: Table 1: Missing Local Ties: Sites where local ties between some or all points are missing (information is not available at IERS ITRS Product Center). Table 2: Dubious local ties: Sites where local tie estimates differ from Space Geodesy estimates. The current local ties collected by the ITRS-PC since more than 10 years come from heterogeneous sources and do not always contain quality (precision) information, necessary for rigorous ITRF combination. These local ties are used in ITRF combinations as observations with proper variances. In case where these variances are not available, they are computed using a geodetic formula given in ITRF publications. Note that a dubious local tie is declared as such if its ITRF2000 post fit residuaul is larger than or equal to 1 cm. This threshold of 1 cm is the minimum requirement for a global frame aimed to be good to at least 1 ppb level (6 mm over the Earth's surface). Therefore the ITRF2000 residual analysis is a tool to assess their quality or their level of agreement with Space Geodesy estimates. Dubious local ties are due to at least one of the following reasons: - They are imprecise - They are in error - Space Geodesy estimate is imprecise - Space Geodesy estimate is in error Each one of these two tables is sorted in two categories, according to their importance for ITRF: ***: Highly Important Sites, given their geographic location and/or quality of their geodetic instruments. These critical sites are mostly those where local ties between points observed by at least two different techniques are not available (Table 1), respectively dubious (Table 2). This is the case for example of: - Wuhan (China) where the local tie between the SLR and GPS points is not available. - Fairbanks (ALASKA) where the local tie between the VLBI and GPS points is dubious. * : Very Important Sites, given the quality of their geodetic instruments. These sites are those where SOME local ties are not available (resp. dubious). This is the case for example of: - Tromso (Norway) where the new GPS point is not connected to VLBI, SLR, DORIS or the old GPS points. - Wettzell (Germany) where the local tie connecting the SLR point 8834 (S018) is dubious. In order to remedy this situation, it is recommended to initiate efforts starting with Highly important sites. A useful information (per-site residual summary and plots) highlighting the quality of local ties in ITRF2000 colocation sites is available on the web at: http://lareg.ensg.ign.fr/ITRF/ITRF2000/valsit.html Table 1: Missing Local Ties Sites where local ties between some or all points are missing Missing tie per DOMES Site Name Country Imp Technique (Point) ----- ---------------- -------- --- -------------------------------- Highly Important Sites 10317 NY-ALESUND NORWAY *** VLBI(S003 7331) 12309 MENDELEEVO RUSSIA *** SLR(S001 1870), GPS(M002 MDVO) 12329 YUZHNO-SAKHALINS RUSSIA *** GPS(M003 YSSK), DORIS(S001 SAKA) 12337 SIMEIS UKRAINE *** SLR(M001 7561), SLR(S003 1873) SLR(S006 1893), VLBI(S008 7332) 21602 WUHAN CHINA *** SLR(S003 7236), GPS(M001 WUHN) 21605 SHANGHAI CHINA *** GPS(M002 SHAO), VLBI(S008 7226) 21609 KUNMING CHINA *** GPS(M001 KUNM), SLR(S002 7820) 21612 URUMQI CHINA *** GPS(M001 URUM), VLBI(S001 7330) 21701 KASHIMA JAPAN *** SLR(M002 7335), VLBI(S001 1856) VLBI(S004 1857), VLBI(S006 7334) 21704 KOGANEI JAPAN *** SLR(M001 7328), SLR(S002 7308) S002(S004 7327) 21729 USUDA JAPAN *** VLBI(S001 7246), GPS(S007 USUD) 23903 SUWN-SHI S. KOREA *** GPS(M001 SUWN), VLBI(S001 7353) 21733 MINAMI TORI SIMA JAPAN *** SLR(S001 7300), VLBI(S002 7310) 21739 MIURA JAPAN *** SLR(M001 7337), VLBI(S001 7336) 21740 TATEYAMA JAPAN *** SLR(M001 7339), VLBI(S001 7338) 30302 HARTEBEESTHOEK S.AFRICA *** SLR(M003 7501) 40403 PALOS VERDES USA *** VLBI(M001 7268), GPS(M002 PVEP) 40419 KODIAK USA *** VLBI(M001 7278), GPS(S001 KOD1) 42501 BERMUDA USA *** SLR(M001 7067), VLBI(M002 7294) GPS(S004 BRMU) Very Important Sites 10302 TROMSO NORWAY * GPS(M006 TRO1) 12302 RIGA LATVIA * SLR(S006 1885) 12725 CAGLIARI ITALY * SLR(S013 7548) 13402 SAN FERNANDO SPAIN * SLR(S007 7824) 14201 WETTZELL GERMANY * SLR(M200 7594), VLBI(S100 7593) 21730 TSUKUBA JAPAN * VLBI(S007 7345) 21732 CHICHIJIMA JAPAN * VLBI(S004 7347) 40405 GOLDSTONE USA * GPS(S031 GOLD, current IGS point, Post-Landers) 40437 MAMMOTH LAKES USA * (M001 7259), (M002 CASA) Mobile VLBI - GPS ~4km 40439 OWENS VALLEY USA * VLBA(S006 7616) 40451 WASHINGTON USA * GPS(S003 USNO) 40492 VERNAL USA * SLR(M001 7892), VLBI(M002 7290) (Destroyed) 40499 RICHMOND USA * VLBI(S019 7201), GPS(S020 RCM6) Table 2: Dubious Local Ties --------------------------- DOMES Site Name Country Imp Techniques/points Delta (cm) ----- -------------- -------- --- ---------------------------------- ----- Highly Important Sites 10204 HOFN ICELAND *** VLBI(M001 7635)/GPS(M002 HOFN) 10 12717 NOTO ITALY *** VLBI(7547 S001)/GPS(M003 NOTO) 1 12734 MATERA ITALY *** VLBI(7234 S005)/GPS(M008 MATE) 1 13402 SAN FERNANDO SPAIN *** SLR(S004 7824)/GPS(M004 SFER) 5 13407 MADRID SPAIN *** GPS(MADR S012)/VLBI(1565 S010) 1 20805 ANKARA TURKEY *** SLR(M001 7589)/GPS(M002 ANKR) 30 21601 BEIJING CHINA *** GPS(M001 BJFS)/SLR(S004 7249) 5 21605 SHANGHAI CHINA *** SLR(S001 7837)/VLBI(S009 7227) 5 21732 CHICHIJIMA JAPAN *** VLBI(S001 7316)/SLR(S002 7844) 50 30302 HARTEBEESTHOEK S.AFRICA *** GPS(HART M002, HARK M007, HRAO M004) 1 DORIS(HBLA S005, HBKA S202) 1 40104 ALGONQUIN CANADA *** VLBI(7282 S001)/GPS(ALGO M002) 1 40408 FAIRBANKS USA *** GPS(FAIR M001)/VLBI(7225 S002) 2 GPS/DORIS(FAIA S004, FAIB S005) 1 40440 WESTFORD USA *** VLBI(S003 7209)/GPS(S020 WES2) 2 40451 GREENBELT USA *** GPS(GODE M123)/Other site points 1 50501 GUAM USA *** GPS(GUAM M002)/DORIS(GUAB S001) 3 66006 SYOWA ANTARTICA *** VLBI(7342 S004)/GPS + DORIS 5 66007 ROTHERA ANTARTICA *** GPS(ROT1 M001)/DORIS(ROTA S001) 7 66008 O'HIGGINS ANTARTICA *** VLBI(S001 7245)/GPS(M001 OHIG) 3 91501 PETRELS Is. TERRE ADELIE *** GPS(DUM1 M001)/DORIS(ADEA S001) 3 97301 KOUROU FRENCH GUIANA *** GPS(KOUR M210)/DORIS(KRUB S004) 5 Very Important Sites 10317 NY-ALESUND NORWAY * GPS(NYA1 M003) 2 14201 WETTZELL GERMANY * SLR(8834 S018)/Other site points 1 40405 GOLDSTONE USA * SLR(7085 M001, 7115 M002, 7265 M006) VLBI(1514 S001, 7222 S009, 1513 S014, 1515 S019), DORIS(GOMA S005) 1-5 40439 OWENS VALLEY USA * VLBI(7207 S002)/Other site points 2 40499 RICHMOND USA * VLBI(7219 S001)/GPS(RCM5 S018) 1 ___________________________________________________________________________ R: VLBI, L: SLR, P: GPS, D: DORIS Delta : Difference between local tie and Space Geodesy estimate ***************************************************************************