5,000,000 Delays -- Some Statistics

arXiv:1102.0665v1 [physics.geo-ph] 3 Feb 2011 5,000,000 Delays—Some Statistics∗ Zinovy Malkin† Institute of Applied Astronomy, St. Petersburg, Russia Abstract 5,000,000 VLBI delays are stored now in the IVS data base and available for sci- entific analysis. This is a remarkable result of more than 20 years of geodetic VLBI history. This paper presents some statistics related to the VLBI observations during almost 25 years of geodetic VLBI. At the end of 2004, the number of VLBI delays obtained in the framework of the geodetic and astrometric VLBI programs reached 5,000,000! This is one of the major milestones in the VLBI history resulting from almost 25 years of heroic efforts by astronomers and physicists, engineers and programmers, network stations and correlator teams. Most of the statistics presented here (when not indicated explicitly) are related to all the observing sessions, independent of their duration. As can be seen from Table 1, only number of sessions substantially depends on the session set taken into account, other statistics are practically the same for all sessions and 24h ones (we consider the session as 24h one if its duration is 18 hours or greater). One can see that most of observations were obtained during the 24h and intensives (< 2h) sessions. The sessions with duration 2–18h were, evidently, rather sporadic. Table 1: Statistics depending on the session duration. Number of observations is given in thousands. Number of stations includes also the experimental ones (KASL, MOJAVLBA, NOTOX, LEFT85 1, VLBA85 3, WIDE85 3). Session duration All ≥18h < 18h < 12h < 6h < 2h Number of observations 5005 4913 92 80 68 64 Number of sessions 8528 3757 4771 4737 4633 4528 Number of stations 159 156 53 40 29 17 Number of baselines 1356 1335 167 94 51 33 Number of sources 2254 2248 406 355 201 119 These observations were collected in 8528 sessions (3757 of them with duration 18h or greater) at 159 stations including experimental ones, on 1356 baselines (there was a misprint in the IVS Newsletter of August 2002, number of baselines 1722 given there should be 1272). ∗In: IVS 2004 General Meeting Proc., Eds. N. R. Vandenberg, K. D. Baver, NASA/CP-2004-212255, 2004, 47–51. †Current affiliation: Pulkovo Observatory, St. Petersburg, Russia 1 Totally, 2254 sources were observed, more the half of them during the VLBA Calibrator Survey program. Figure 1 shows how the overall result was reached. It is interesting to see how much time was needed to get each million observations (Table 2). Apparently, a limit of the capacity of existing IVS network is reached in the late 1990s. Table 2: Time taken to collect each million observations (∆T), the corresponding period of observations (Tbeg −Tend), and number of sessions. Some inconsistencies between ∆T and Tbeg−Tend are due to rounding. Million 1st 2nd 3rd 4th 5th ∆T, years 11.9 3.9 3.3 2.6 2.6 Tbeg−Tend 1979.6–1991.5 1991.5–1995.5 1995.5–1998.7 1998.7–2001.4 2001.4–2004.0 # of sessions 3425 1873 1234 1002 976 # of 24h sessions 1628 901 444 348 432 Here are some extreme statistics with examples: Maximum number of stations: 20 (991220XA) Maximum number of baselines: 188 (991220XA) Maximum number of sources: 263 (950715XV) Maximum number of observations: 34221 (991220XA) Maximum number of good observations: 30372 (991220XA) Maximum number of bad observations: 4092 (940812XV) Maximum percentage of good observations: 100.0 (860223X ) Maximum percentage of bad observations: 90.8 (911205MV) The longest sessions, h: 99.2 (830520D ) Table 3 shows most active stations during the whole period of observations, and Ta- bles 4–5 present statistics for sources and baselines. The longest attempted baselines is SESHAN25–TIGOCONC (12660 km), but no successful observations (zero quality code in NGS files) was obtained. The longest baseline with successful observations is DSS65– HOBART26 (12520 km). The shortest baselines was KAUAI–KOKEE (39 m) Figures 2 and 3 show the evolution of some observational data and EOP uncertainty (IAA EOP series) with time. 2 0 1 2 3 4 5 6 1980 1985 1990 1995 2000 2005 Number of observations, millions 0 0.1 0.2 0.3 0.4 0.5 1980 1985 1990 1995 2000 2005 Number of observations per year, millions 0 2000 4000 6000 8000 10000 1980 1985 1990 1995 2000 2005 Number of sessions 0 200 400 600 1980 1985 1990 1995 2000 2005 Number of sessions per year 0 1000 2000 3000 4000 1980 1985 1990 1995 2000 2005 Number of 24h sessions 0 100 200 300 1980 1985 1990 1995 2000 2005 Number of 24h sessions per year 0 1000 2000 3000 4000 1980 1985 1990 1995 2000 2005 Cumulative session durartion, days 0 100 200 300 1980 1985 1990 1995 2000 2005 Cumulative session durartion per year, days 0 50 100 150 200 1980 1985 1990 1995 2000 2005 Number of stations 0 20 40 60 1980 1985 1990 1995 2000 2005 Number of stations per year 0 500 1000 1500 2000 2500 1980 1985 1990 1995 2000

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