********************************************************************** ********** Note: new directories on aspen for logs ************ ********************************************************************** RDV08 (Astrometric/Geodetic VLBA-08) 1998 April 15 Notes prepared by Nancy Vandenberg, NVI/GSFC Schedule name: RDV08.skd Pointing files: rdv08crd.br, rdv08crd.fd, rdv08crd.hn, rdv08crd.kp, rdv08crd.la, rdv08crd.mk, rdv08crd.nl, rdv08crd.ov, rdv08crd.pt, rdv08crd.sc on aspen in directory /home/aspen6/astronomy/apr98/rdv08 PCFS files: rdv08.skd on cddisa in directory apr98 Nominal Start: 20:00 U.T. on April 15 (day 105) first observation at 19:30 U.T. on 4C39.25 for Gg-Gc-Wf-Nl- Br-Fd-Sc first observation at 20:05 U.T. on 4C39.25 for Hn-Kp-La-Mc- Gn-Ny-On-Pt first observation at 20:06 U.T. on 0048-097 for Kk-Mk-Ov Duration: 24 hours + 1 hour for Gc-Gg-Wf-Nl-Br-Fd-Sc Nominal Stop: 20:00 U.T. on April 16 (day 106) last observation at 20:00 U.T. on 0014+813 for Kk-Mc-On-Wf last observation at 19:59 U.T. on 0229+131 for Br-Fd-Gc-Hn- Kp-La-Mk-Nl- Gn-Ny-Ov-Pt-Gg last observation at 19:53 U.T. on 0528+134 for Sc Correlator: VLBA at Socorro Summary file for correlator: rdv08.sksum on aspen Stations: 18 Station Codes # of tapes # of obs Occupation Code Brewster B Br 2.2 (TT) 337 76149901 Fort Davis D Fd 2.2 (TT) 361 76139801 Gilcreek A Al 2.2 (TT) 310 40476601 Hancock H Hn 3.1 (TT) 324 76185001 Kokee K Kk 2.1 (TT) 316 72983001 Kitt Peak L Kp 2.2 (TT) 353 76109401 Los Alamos M La 2.2 (TT) 349 76119601 Medicina C Mc 2.1 (TT) 275 72308801 Mauna Kea N Mk 2.2 (TT) 315 76175501 North Liberty O Nl 2.2 (TT) 343 76129701 Green Bank 20m P Gn 2.4 (TT) 317 72484701 Ny Alesund Q Ny 2.1 (TT) 292 73313301 Onsala T On 2.1 (TT) 284 72137701 GGAO (MV3) Z Gg 2.1 (TT) 299 71085301 Owens Valley R Ov 2.2 (TT) 324 76165401 Pie Town S Pt 2.2 (TT) 338 72348601 St. Croix E Sc 2.2 (TT) 323 76159001 Westford F Wf 2.2 (TT) 311 72097301 Special notes on tape usage: - This experiment uses THIN TAPES ONLY at all stations. - VLBA stations record two tapes and then have a tape change for the final few hours of the schedule. The tape change occurs during normal site working hours. - Br, Fd, Nl, and Sc record the MV3 fringe finding scans along with Fairbanks and Westford. - Green Bank records until about 14:00 then breaks away for the 2-hour intensive. Purpose ======= This is the second of six bi-monthly coordinated astrometric/geodetic experiments in 1998 that use the full 10-station VLBA plus the 8 geodetic stations currently capable of recording in VLBA format. This year's series is a continuation of the highly successful series in 1997. These experiments are being coordinated by the geodetic VLBI programs of three agencies: USNO, NASA, and NRAO. The experiments have been designed so that the same data set may be used by each agency for its particular goals. USNO will perform repeated imaging and correction for source structure. These sources will establish a set of core reference sources with known structure and precisely known positions. These data will provide the basis for evaluating the long term stability of the radio reference frame and the ultimate accuracy of wide angle astrometric measurements of extragalactic radio sources using VLBI. NASA will analyze this data to determine a high accuracy terrestrial reference frame. The data will incorporate the VLBA stations into the VLBI reference frame through the inclusion of other geodetic stations for which we have long histories. The data will also produce the most accurate Earth rotation results ever produced. We will use these data to make accurate absolute measurements of UT1. NRAO will use these sessions to provide a service to users who require high quality positions for small numbers of sources. While the quality of these results will be high, the observing and data reduction overhead required will be minimal because such sources can be incorporated into a session of the regular geodetic observations, instead of requiring special observations. Sources for this series of experiments will be selected using the proposed approach. For each experiment we will select a set of 70-80 sources out of the pool of ~400 Northern Hemisphere ICRF sources. About 40-50 of these will remain the same from experiment to experiment and will be chosen to optimize the goals of the three groups. Schedule ======== This is a new schedule generated by Marshall Eubanks using the 9706 version of the NASA sked program which handles continuous tape motion. All stations use thin tapes. "Requested" Sources in RDV08: Paragizs | 1910+052 19 12 54.247 +05 17 59.520 | 100 mJy Greenhill | 0335-364 03 36 54.01 -36 16 07.1 | 500 mJy With this session we continue rotating through the large list of candidate ICRF sources. The method was as follows: - Remove sources from the core list of 80 sources used last year. - Add up to 20 sources from the list of candidates that already have some NEOS or VLBA data available (rotating sources). - Add 3 sources from the list of candidates that have never been observed with the VLBA (new sources). Yearly (Y), ROTATING & NEW (N) SOURCES FOR RDV08: | 0010+405 | 0146+056 | 0305+039 NGC1218 | 0405-385 | 0406+121 | 0422+004 | 0544+273 N| 0821+394 | 1012+232 | 1104+728 N| 1143-245 Y| 1219+044 | 1416+067 N| 1641+399 3C345 Y| 1726+455 | 1920-211 | 1928+738 | 2037+511 3C418 | 2149+056 | 2209+236 | 2337+264 About 10% of the observations in this schedule is an attempt to troubleshoot the "VLBA problem". What we know about the problem: 1. The problem shows up as larger than expected residual scatter and source position scatter. 2. The problem seems to be connected with sources at Southern declination 3. The problem may be related to subnetting. 4. The systematic error is NOT seen in normal VLBA phase connection/ imaging experiments. Point 4 argues for the problem being a systematic error that is smooth in the sky (low spatial wavenumber) (and maybe in slowly varying in time as well) AND/OR a problem with rejoining a priori delays with the fringe phases (since typical AIPS experiments use the residual phase, not the totals). It is also possible that the problem is in forming the group delays. In RDV08 a series of 4 short (~ 1/2 hour) sequencies of differential VLBI observations were inserted into the schedule, using the following "paired" sources: 0402-462 / 0405-385 | 2.43 deg 1145-071 / 1219+044 | 14.47 deg 3C345 / NRAO512 | .48 deg 1908-201 / 1920-211 | 3.05 deg 2145+067 / 2149+056 | 1.40 deg From 210745-214710, observations of the 0402-362/0405-385 pair were made using the FD,KP,LA, MK,GN,SC subarray. The other stations observed normally. This was designed to look for the phase and group stability in the far South. It may be possible to phase connect this sequence. From 050443-052923 observations of the 1145-071 / 1219+044 pair were made using the BR,FD,GC,HN,KK,KP,NL,GN,SC subarray. The other stations observed normally. This pair spans the celestial equator, and is designed to test whether there is some problem associated with it. From 092053-094955, observations of the 3C345 / NRAO512 pair were made using the whole array, except for one scan in the middle where some stations observed another source. These observations should be phase connectable, and the observations were designed to examine the phase group stability for the largest number of stations (in case the problem is connected with array size). It should be possible to phase connect this sequence. From 114551-115656, the 1908-201 / 1920-211 and 2145+067 / 2149+056 pairs were observed separately by different sub-arrays. This was designed to see if information could be "leaking" from one observation to another at the same time. It may be possible to phase connect this sequence. The same criteria were used for generating this schedule as were used during the first year of these sessions. The criteria for sources to be mapped are a minimum of 3 scans and 135 observations. These criteria are relaxed for sources below -25 degrees declination. Most of the sources in this schedule meet the mapping criteria. The schedule was made using a combination of automatic selection plus manual scheduling to improve the coverage of the sources. Automatically scheduled scans were selected first on their improvement of sky coverage in the previous 1 hour, and then the best 60% were evaluated for the minor options: minimize idle time, minimize slewing time, and maximize the number of observations. An individual source was not observed more often than every 90 minutes. An early start of 30 seconds was used for the first scan on a tape pass. The minimum scan length was 40 seconds. Due to its low sensitivity, MV3 was not included directly into the schedule because the necessarily longer scan lengths would have compromised the experiment results. Instead, after the schedule was made, MV3 was tagged along to the schedule. In the tagalong mode, MV3 observes with the longest scan duration of all the stations participating in each scan, to maximize SNR. MV3 will make fringes on about 2/3 of the observations in which it participates. This amount of data will allow a good determination of MV3's position in the reference frame. Recording Mode and Frequencies: same as previous experiments ============================================================ The data will be recorded using 8 channels in VLBA format, 1:4 fan-out, 16 MHz sample rate, 1-bit sampling. This mode is designated 128-8-1. The correlator gets a speed-up factor of 2. The frequency sequence covers 490 MHz in 8 channels. This span fits in one VLBA receiver passband but it uses both the high and low parts of the geodetic receivers. Because only 8 channels are available when observing with the VLBA stations, a wider spanned bandwidth is not advisable. With the 1:4 fanout at 16 MHz sample rate, all 32 tracks are recorded in one pass, so there will be 14 passes on a tape. These tables list the setup for the VLBA stations, the geodetic stations with VLBA back ends, and the geodetic stations with Mark IV back ends. These are the SAME frequencies used in the first two RDV0x sessions. Geodetic stations: please read the special procedures in the next section! VLBA | Fairbanks | Kokee, GB Chan Sky Tracks LO IF BBC | LO IF BBC | LO IF BBC 1 X 8405.99 2, 4, 6, 8 7900 B 505.99| 7600.1 B 805.89| 7600 B 805.99 2 X 8475.99 10,12,14,16 7900 B 575.99| 7600.1 B 875.89| 7600 B 875.99 3 X 8790.99 18,20,22,24 7900 B 890.99| 8080.0 C 710.99| 8100 C 690.99 4 X 8895.99 26,28,30,32 7900 B 995.99| 8080.0 C 815.99| 8100 C 795.99 5 S 2220.99 3, 5, 7, 9 2900 A 679.01| 1540.1 A 680.89| 1500 A 720.99 6 S 2240.99 11,13,15,17 2900 A 659.01| 1540.1 A 700.89| 1500 A 740.99 7 S 2330.99 19,21,23,25 2900 A 569.01| 1540.1 A 790.89| 1500 A 830.99 8 S 2360.99 27,29,31,33 2900 A 539.01| 1540.1 A 820.89| 1500 A 860.99 Onsala, Medicina, VLBA | Westford, MV3, Ny Alesund Chan Sky Tracks LO IF BBC | LO IF VC VC# Patch 1 X 8405.99 2, 4, 6, 8 7900 B 505.99| 8080.0 1 325.99 3 H 2 X 8475.99 10,12,14,16 7900 B 575.99| 8080.0 1 395.99 4 H 3 X 8790.99 18,20,22,24 7900 B 890.99| 8580.1 3 210.89 5 L 4 X 8895.99 26,28,30,32 7900 B 995.99| 8580.1 3 315.89 6 H 5 S 2220.99 3, 5, 7, 9 2900 A 679.01| 2020.0 2 200.99 9 L 6 S 2240.99 11,13,15,17 2900 A 659.01| 2020.0 2 220.99 10 L 7 S 2330.99 19,21,23,25 2900 A 569.01| 2020.0 2 310.99 13 H 8 S 2360.99 27,29,31,33 2900 A 539.01| 2020.0 2 340.99 14 H Procedures ========== With continuous tape motion, the tape starts moving and recording at the beginning of the first scan of a pass. The tape runs and records continuously thereafter to the end of the tape (EOT or BOT). A parity check is done after the tape reaches this point. The tape starts moving in the opposite direction at the early start time (30 seconds) before the next scan. There will be a variable length of time between tape passes. For the VLBA stations, there will normally be a long enough time gap between passes for playback. Special procedures for non-VLBA stations ======================================== The tape motion in this experiment will be different from normal start&stop schedules. Please read this section carefully so that you know what to expect. At the time the antenna gets on source, you should see the "Data start" comment from the SNAP schedule. This is the signal that the VLBA correlator will use to determine when to start correlating this scan. Please make notes in the log if your antenna is consistently late or early for the "Data start". We may need to adjust some antenna slewing parameters to correct the models in sked for the next schedule. At the time the antenna begins slewing to the next source, you will see the "Data stop" comment from the schedule. This is the signal the correlator will use to stop correlating that scan. There will be no "et" command at the end of a scan. The DRUDG listing has an extra column that lists the time that the tape will stop. Note the "Start Tape" and "Stop Tape" columns list times only when the tape will start or stop, otherwise the time is blanked out because the tape is moving. For each scan, the "Start Data" column will be the time when the antenna is expected to be on source. The "Stop Data" column is the time when the antenna starts slewing to the next source. After the setup procedure, the tape is started at the beginning of each pass and will continue to move, at record speed, until it reaches the end of the pass. There are no fast tape motions in this schedule. The tape is continuously recording from the initial "st" command at the start of the pass. There are no other "st" commands during a pass and there are no other setup procedures called. If you have to re-start the schedule for a problem or emergency, you will be able to do it either 1) at the beginning of a pass or 2) in the middle of a pass by entering the setup and start tape commands manually. The problem is that the heads cannot be positioned reliably when the tape is moving if there is recorded data on the tape. If the tape is moving the reproduce power level can cause cross-talk with the head positioner and give false indications of position. At the end of each pass a parity check is done. You will need procedures named "check2m1, check2m2" or "check2v1, check2v2". If you have not already done so for the first two sessions, please create these procedures as a copy of "check2c1, check2c2" and change the tracks to be "v0,v1,v2,v3". Check and adjust the timing of this procedure and then make sure it can complete in the 70 seconds that the schedule allows. If it cannot be completed, you could check the odd tracks in one direction and the even tracks in the other. If you have any questions or problems with these parity procedures, please contact Nancy Vandenberg as soon as possible. There could be some times when the tape reaches the end of a pass and you should still be observing. This should not happen, but since this is the first time we are trying continuous recording, it might. Please note in the log when this occurs, if your station is manned at that time. Special procedures for Onsala, Medicina, Westford, MV3, Ny Alesund ================================================================== Onsala, Medicina, Westford, MV3, and Ny Alesund have Mark IV formatters. You can use the same procedures as for the previous RDV0x sessions. You can also have DRUDG generate the procedures. Please verify your procedures against this writeup. Remember this is a non-standard setup. There are 8 video converters used: 3, 4, 5, 6, 9, 10, 13, and 14. These were selected so that you will NOT have to change the standard geodetic IF patching. The 6 unused VCs 1, 2, 7, 8, 11, and 12 should be set to frequencies which do not occur in any of the passbands. Any value in the 100-200 MHz range is OK. The Mark IV formatters currently have no barrel roll capability, so please verify that your FORM command has no specification for barrel roll. The IF3 command in the procedure IFDSX assumes that VC3 will be patched to High. Please verify that the switches for your IF3 module are wired this way, and if they are not please edit the IF3 command to change the switches. If you have questions about the wiring, please contact Brian Corey at Haystack. Special procedures for Fairbanks, Kokee, Green Bank =================================================== Fairbanks, Kokee, and Green Bank have VLBA back ends. You can use the same procedures generated for the previous sessions. You can also have DRUDG generate them for you. You must swap your IF inputs so that BBCs 1-8 have the inputs shown in the table above. The unused BBCs 9-14 should be set to frequencies which do not occur in any of the passbands. Any value in the range 500-600 MHz is OK. The formatter should be set up to use barrel roll. Please verify that you are using the same barrel roll as you used in previous sessions correlated at the VLBA. CHECKLIST for non-VLBA stations =============================== Please follow the checklist below to ensure you have done all the necessary steps for this experiment: 1. Make .prc file with DRUDG and check them out, or use the procedures from last session. Make and check out parity check procedures. 2. Make .snp file and listings using DRUDG options 3 or 31 and 5. 3. Set up your system to monitor the clocks with the "gps-fmout" or "fmout-gps" commands, per Ed Himwich's messages. If you have questions or problems, please contact Ed as soon as possible. 4. Send a "ready" message an hour or so before the experiment to the ops mail list. Copy Peggy Perley at the VLBA (pperley@nrao.edu) on the message. 5. Send a "start" message soon after you have started recording. Copy Peggy Perley on the message. 6. During the experiment, please continue noting any times when the antenna is not on source at the "Data start" times. Also note any times that the tape stops before the "et" command is issued at BOT or EOT. This information will be useful in checking out the antenna slewing models. 7. At the end of the experiment, send a "finish" message summarizing how the experiment was conducted. 8. *IMPORTANT* Transfer your log files BOTH to aspen.nrao.edu and to cddisa. Remember that you have to use different naming conventions! on cddisa: rdv08xx.log in directory apr98 on aspen: rdv08log.xx in directory /home/aspen6/astronomy/apr98/rdv08 Correlation =========== This experiment will be correlated at the VLBA Correlator. Tapes should be shipped to Socorro as soon after the experiment as practical. Summary ======= The following listing is a summary of the observations in this schedule.