International Laser Ranging Service

Data Correction Free Format

The purpose of this page is to list discovered anomalies in SLR and LLR data. To date, the following problems have been uncovered by the community:

 

Station 7109 (MOBLAS 8) Barometer Error

Van Husson/ATSC in 12/95

All MOBLAS 8 (Station 7109) data taken between October 11, 1995 at 0:00 hours GMT and October 14, 1995 at 18:15 GMT has a barometric error of 50 millibars. The barometric readings in the data were low by exactly 50 millibars. The data can be corrected by adding 50 millibars to the barometric pressure during this time interval. NASA and ATSC regret any inconvenience that this error may have caused.

 

Station 7110 (MOBLAS 4) Barometer Error

Van Husson/ATSC in 02/96

Data taken by the MOBLAS-4 (Station 7110) between April 15 through December 19, 1995, inclusive, have a potential uncertainty in the barometric measurements. This problem was corrected on December 20, 1995. The maximum uncertainty of the barometric measurement is +/- 5 millibars based on historical barometric information from this location. Due to the nature of the problem, the barometric uncertainty is a random error over this entire period (i.e., no systematic fixed offset). For most of the affected data, the error is believed to be less than 1-2 millibars. NASA and ATSC regret any inconvenience that this error may have caused.

 

Station 7840 (RGO) Humidity Error

Philip Gibbs/RGO in 02/96

An error in the humidity values in the SLR normal points generated by the RGO system (station number 7840) has been discovered. A summary of the corrections which should be added to the humidity values for the given time periods is given in Table 3 below.

Corrections for Humidity Values
Start Date	End Date	Value
24-Dec-95	24-Dec-95	20%
25-Dec-95	27-Dec-95 15:00	10%
27-Dec-95 15:00	29-Dec-95 16:00	20%
29-Dec-95 16:00	17-Jan-96	30%
17-Jan-96	17-Jan-96 11:00	0%
17-Jan-96 11:00	22-Jan-96	15%
22-Jan-96	12-Feb-96 15:00	30%

 

Sation 7080 (MLRS) Barometer Error

Randy Ricklefs in 06/96

Randy Ricklefs of the McDonald Laser Ranging System (MLRS, station number 7080) staff reports that due to improper application of the barometric pressure sensor offsets, the pressure readings recorded in the MLRS full-rate and field-generated normal point (FGNP) data for parts of 1995 and 1996 are in error. The correct pressure can be recovered by adding the following corrections to the values recorded in the data files:

MLRS Barometer Correction Values
Start Date	End Date	Correction
March 6, 1995	January 25, 1996	2.1 mB
January 26, 1996	April 24, 1996	10.3 mB
April 25, 1996	May 8, 1996, 20 hours	9.7 mB

After May 8, 1996, 20 hours UTC, the recorded pressure should be correct.

 

Station 7090 (MOBLAS-5) Epoch Time Error

Van Husson in 08/96

The Data Services Group at ATSC reports that in July MOBLAS-5 at Yarragadee, Austraila (station number 7090) started to experience problems with their Cesium clock, e.g., excessive drift rates, which has affected the timetags in data from the system. The data is totally recoverable by applying the epoch corrections given in the table below. In order to correct MOBLAS-5 timetags these epoch corrections must be subtracted from the normal point timetags using the equation:

corrected timetag = normal point timetag - epoch correction

MOBLAS-5 Epoch Timetag Corrections
Date	Epoch Corrections (microseconds)
18-Jul-96	-1.0
19-Jul-96	-1.2
20-Jul-96	-1.3
21-Jul-96	-1.5
22-Jul-96	-1.6
23-Jul-96	-1.8
24-Jul-96	-2.0
25-Jul-96	-2.1
26-Jul-96	-2.3
27-Jul-96	-2.3
28-Jul-96	-2.4
29-Jul-96	-2.4
30-Jul-96	-2.5
31-Jul-96	-2.5
01-Aug-96	-2.5
02-Aug-96	-2.5 (before 21:57 GMT)
02-Aug-96	+0.5 (after 21:57 GMT)

The problem was resolved on August 02, 1996 at 21:57 GMT, when the drift rate returned to nominal levels and the station clock was resychronized to the Cesium.

 

Station 7110 (MOBLAS-4) Fixed Range Bias

Van Husson in 10/96

AlliedSignal Technical Services Corporation (ATSC) reports that all MOBLAS-4 (station 7110 at Monument Peak, CA) data from August 27 through October 02, at 2:50 GMT, 1996 is biased by +16.36cm. To correct for this bias, users should subtract 16.36 cm from the range. ATSC regrets any inconvience this has caused.

 

Recall of NASA SLR Data from GPS Satellites

Van Husson in 12/96

Van Husson of AlliedSignal Technical Services (ATSC) reports that a number of SLR normal point pass segments from the NASA SLR network for the GPS satellites potentially contain no useful data (i.e., all noise) and are being recalled from the CDDIS to avoid the future use of these known problem data. The data in all of these recalled passes, listed in Table 2 below, are currently under evaluation for the possibility of useful data. If any data are found in these pass segments, normal points will be reissued at a later date. Furthermore, as of December 06, 1996, new procedures have been implemented at ATSC to prevent SLR data with known problems from being distributed to the user community. The ATSC and CDDIS staff regret any inconvenience these data problems may have caused the user community.

GPS-35 and -36 SLR Data Recalled

Satellite	Date	Time	Station	Num. of Npts.	CDDIS File Name*
GPS-35	24-Oct-96	02:34	7090	3	NEW_QL961024.GPS35
GPS-35	24-Oct-96	04:08	7090	6	NEW_QL961024.GPS35
GPS-35	24-Oct-96	10:52	7918	5	NEW_QL961025.GPS35
GPS-35	25-Oct-96	02:09	7090	8	NEW_QL961025.GPS35
GPS-35	26-Oct-96	03:52	7090	2	NEW_QL961026.GPS35
GPS-35	26-Oct-96	04:42	7090	5	NEW_QL961026.GPS35
GPS-35	29-Oct-96	09:07	7105	3	NEW_QL961029.GPS35
GPS-35	29-Oct-96	09:49	7918	6	NEW_QL961030.GPS35
GPS-35	29-Oct-96	10:08	7105	7	NEW_QL961030.GPS35
GPS-35	29-Oct-96	10:43	7918	9	NEW_QL961030.GPS35
GPS-35	30-Oct-96	19:13	7105	3	NEW_QL961031.GPS35
GPS-35	31-Oct-96	09:18	7105	9	NEW_QL961101.GPS35
GPS-35	31-Oct-96	09:18	7918	12	NEW_QL961101.GPS35
GPS-35	31-Oct-96	10:42	7105	6	NEW_QL961101.GPS35
GPS-35	31-Oct-96	10:47	7918	6	NEW_QL961101.GPS35
GPS-35	01-Nov-96	08:18	7110	3	NEW_QL961101.GPS35
GPS-35	02-Nov-96	03:48	7090	4	NEW_QL961102.GPS35
GPS-35	04-Nov-96	10:31	7918	7	NEW_QL961105.GPS35
GPS-35	05-Nov-96	11:34	7110	8	NEW_QL961105.GPS35
GPS-35	07-Nov-96	12:03	7110	4	NEW_QL961108.GPS35
GPS-35	08-Nov-96	07:42	7110	3	NEW_QL961108.GPS35
GPS-35	11-Nov-96	11:27	7110	6	NEW_QL961112.GPS35
GPS-35	12-Nov-96	07:22	7110	8	NEW_QL961112.GPS35
GPS-35	12-Nov-96	08:36	7918	4	NEW_QL961112.GPS35
GPS-35	12-Nov-96	10:15	7918	2	NEW_QL961113.GPS35
GPS-35	16-Nov-96	18:18	7105	1	NEW_QL961117.GPS35
GPS-35	17-Nov-96	08:19	7105	16	NEW_QL961117.GPS35
GPS-35	21-Nov-96	08:40	7105	4	NEW_QL961121.GPS35
GPS-35	23-Nov-96	08:44	7105	5	NEW_QL961123.GPS35
GPS-35	23-Nov-96	09:37	7105	4	NEW_QL961124.GPS35
GPS-35	24-Nov-96	07:44	7105	10	NEW_QL961124.GPS35
GPS-35	25-Nov-96	08:02	7105	7	NEW_QL961126.GPS35
GPS-35	25-Nov-96	09:14	7105	4	NEW_QL961126.GPS35
GPS-36	11-Oct-96	15:06	7105	4	NEW_QL961012.GPS36
GPS-36	11-Oct-96	15:29	7105	3	NEW_QL961012.GPS36
GPS-36	11-Oct-96	15:58	7105	2	NEW_QL961012.GPS36
GPS-36	14-Oct-96	13:19	7105	7	NEW_QL961015.GPS36
GPS-36	14-Oct-96	14:19	7105	12	NEW_QL961015.GPS36
GPS-36	15-Oct-96	14:28	7105	8	NEW_QL961016.GPS36
GPS-36	16-Oct-96	14:59	7105	6	NEW_QL961017.GPS36
GPS-36	16-Oct-96	15:49	7105	5	NEW_QL961017.GPS36
GPS-36	17-Oct-96	14:03	7105	7	NEW_QL961018.GPS36
GPS-36	17-Oct-96	14:59	7105	8	NEW_QL961018.GPS36
GPS-36	17-Oct-96	15:53	7105	4	NEW_QL961018.GPS36
GPS-36	23-Oct-96	13:23	7105	3	NEW_QL961024.GPS36
GPS-36	29-Oct-96	12:48	7918	7	NEW_QL961030.GPS36
GPS-36	31-Oct-96	14:33	7105	6	NEW_QL961101.GPS36
GPS-36	03-Nov-96	13:08	7105	6	NEW_QL961104.GPS36
GPS-36	04-Nov-96	11:49	7918	14	NEW_QL961105.GPS36
GPS-36	04-Nov-96	13:13	7918	13	NEW_QL961105.GPS36
GPS-36	11-Nov-96	11:22	7918	7	NEW_QL961112.GPS36
GPS-36	12-Nov-96	11:31	7918	2	NEW_QL961113.GPS36
GPS-36	15-Nov-96	11:10	7918	12	NEW_QL961116.GPS36
GPS-36	17-Nov-96	11:34	7105	8	NEW_QL961118.GPS36
GPS-36	23-Nov-96	11:34	7105	5	NEW_QL961124.GPS36
GPS-36	25-Nov-96	11:32	7105	4	NEW_QL961126.GPS36
GPS-36	25-Nov-96	11:42	7918	3	NEW_QL961126.GPS36
GPS-36	27-Nov-96	11:04	7918	5	NEW_QL961128.GPS36
GPS-36	27-Nov-96	11:41	7918	16	NEW_QL961128.GPS36
GPS-36	27-Nov-96	11:44	7105	8	NEW_QL961128.GPS36
GPS-36	27-Nov-96	12:44	7105	8	NEW_QL961128.GPS36
GPS-36	02-Dec-96	11:18	7918	11	NEW_QL961203.GPS36
GPS-36	02-Dec-96	13:34	7110	3	NEW_QL961203.GPS36

Note: * The SLR data files for GPS-35 are stored in the on-line CDDIS data archive in the directory SLR_DATA:[SLRQL.GPS35.1996]; the GPS-36 SLR data files are stored in the directory SLR_DATA:[SLRQL.GPS36.1996].

In addition, since they contain no useful data, the following daily GPS-36 files have been deleted from the CDDIS on-line data archive (directory SLR_DATA:[SLRQL.GPS36.1996]).

 

Station 7109 (MOBLAS-8) Fixed Range Bias

Van Husson/ATSC in 01/97

AlliedSignal Technical Services Corporation (ATSC) reports that all MOBLAS-8 (Quincy, CA, station number 7109) normal points between January 9, 1997 and January 17, 1997 inclusive (six passes in all, shown in the table below) have a fixed +16.49 cm range bias. To correct this error, 16.49 cm needs to be subtracted from the one-way satellite range. ATSC regrets the error and apologize for any inconvience this may have caused.

MOBLAS-8 Passes Affected by Range Bias
Date	Time	Satellite
09-Jan-97	22:02	TOPEX
10-Jan-97	20:24	TOPEX
13-Jan-97	18:03	STELLA
13-Jan-97	19:04	ERS-2
13-Jan-97	19:35	TOPEX
17-Jan-97	23:11	LAGEOS-1

 

Station 7308 (CRL) Epoch Time Bias

Toshimichi Otsubo/CRL in 03/97

Toshimichi Otsubo (Communications Research Laboratory, CRL) reports that all on-site normal points from the CRL station in Tokyo (station number 7308) from February 11 through 27, 1997 have an unrecoverable time bias, up to hundreds of microseconds, because of a clock problem. CRL regrets any inconvienience this error has caused.

 

Station 7403 (TLRS-3) Epoch Time Bias

Van Husson/ATSC in 03/97

TLRS-3 (Station 7403) in Arequipa, Peru experienced an excessive drift rate with their station clock. This high drift rate affected all TLRS-3 taken between January 24, 1997 through March 10, 1997, inclusive. The drift rate was corrected by replacing the station clock on March 10, 1997 at 21:20 GMT. The data during this period are recoverable by applying the epoch corrections given in the table below. In order to correct TLRS-3 timetags these epoch corrections must be subtracted from the normal point timetags using the equation:

Time Corrections for TLRS-3
Date	Epoch correction (microseconds)
01/24/97	1.1
01/25/97	1.5
01/26/97	2.0
01/27/97	2.4
01/28/97	2.8
01/29/97	3.3
01/30/97	3.7
01/31/97	4.1
02/01/97	4.6
02/02/97	5.0
02/03/97	5.4
02/04/97	5.8
02/05/97	5.5
02/06/97	5.1
02/07/97	4.6
02/08/97	4.2
02/09/97	3.8
02/10/97	3.4
02/11/97	2.9
02/12/97	2.5
02/13/97	2.1
02/14/97	1.6
02/15/97	1.2
02/16/97	0.8
02/17/97	0.3
02/18/97	-0.1
02/19/97	-0.5
02/20/97	-1.0
02/21/97	-1.4
02/22/97	-1.8
02/23/97	-2.2
02/24/97	-2.7
02/25/97	0.0
02/26/97	-0.4
02/27/97	-0.9
02/28/97	-1.3
03/01/97	-1.8
03/02/97	-2.2
03/03/97	-2.6
03/04/97	-3.1
03/05/97	-3.5
03/06/97	-4.0
03/07/97	-4.4
03/08/97	-4.8
03/09/97	-5.3
03/10/97	-5.7 (before 21:20)
03/10/97	0.0 (after 21:20)

 

Station 7109 (MOBLAS 8) Epoch Time Bias

Van Husson/ATSC in 03/97

MOBLAS-8 (Station 7109) in Quincy, California experienced problems with their station clock affecting all their data taken between December 03, 1996 through December 16, 1996, inclusive, and January 09, 1997 and January 17, 1997, inclusive. The data during these two periods are recoverable by applying the epoch corrections given in the table below. In order to correct MOBLAS-8 timetags these epoch corrections must be subtracted from the normal point timetags using the equation:

Time Corrections for MOBLAS-8
Date	Epoch correction (microseconds)
12/03/96	-1.1
12/04/96	-1.1
12/05/96	-1.2
12/06/96	-1.2
12/07/96	-1.2
12/08/96	-1.3
12/09/96	-1.3
12/10/96	-1.3
12/11/96	-1.4
12/12/96	-1.4
12/13/96	-1.5
12/14/96	-1.5
12/15/96	-1.5
12/16/96	-1.6
01/09/97	-2.4
01/10/97	-2.4
01/11/97	-2.4
01/12/97	-2.5
01/13/97	-2.5
01/14/97	-2.5
01/15/97	-2.6
01/16/97	-2.6
01/17/97	-2.6

 

Station 7210 (HOLLAS) Epoch Time Bias

Van Husson/ATSC in 03/97

HOLLAS (Station 7210) in Haleakala, Hawaii experienced an excessive drift rate in their station clock. This high drift rate affected all HOLLAS taken between December 13, 1994 through June 14, 1995, inclusive. The drift rate was corrected by a combination of replacing the station clock and performing Cesium adjustments. The data during this period are recoverable by applying the epoch corrections given in the table below. In order to correct HOLLAS timetags these epoch corrections must be subtracted from the normal point timetags using the equation:

Time Corrections for HOLLAS

Date	Epoch correction (microseconds)	Date	Epoch correction (microseconds)
12/13/94	1.5	03/15/95	3.3
12/14/94	1.6	03/16/95	3.5
12/15/94	1.6	03/17/95	3.7
12/16/94	1.7	03/18/95	3.9
12/17/94	1.8	03/19/95	4.1
12/18/94	1.9	03/20/95	4.4
12/19/94	2.0	03/21/95	4.6
12/20/94	2.1	03/22/95	4.8
12/21/94	2.2	03/23/95	5.0
12/22/94	2.2 (before 2:55)	03/24/95	5.2
12/22/94	0.2 (after 2:55)	03/25/95	5.5
12/23/94	0.3	03/26/95	5.7
12/24/94	0.5	03/27/95	5.9
12/25/94	0.6	03/28/95	5.8
12/26/94	0.8	03/29/95	6.0
12/27/94	0.9	03/30/95	6.1
12/28/94	1.1	03/31/95	6.3
12/29/94	1.2	04/01/95	6.4
12/30/94	1.4	04/02/95	6.6
12/31/94	1.5	04/03/95	6.7
01/01/95	1.7	04/04/95	6.9
01/02/95	1.8	04/05/95	7.1
01/03/95	2.0	04/06/95	7.2
01/04/95	2.1	04/07/95	7.4
01/05/95	2.3	04/08/95	7.5
01/06/95	2.4	04/09/95	7.7
01/07/95	2.6	04/10/95	7.9
01/08/95	2.7	04/11/95	8.0
01/09/95	2.9 (before 18:20)	04/12/95	8.2
01/09/95	0.0 (after 18:20)	04/13/95	8.3
01/10/95	0.1	04/14/95	8.5
01/11/95	0.2	04/15/95	8.5
01/12/95	0.4	04/16/95	8.6
01/13/95	0.5	04/17/95	8.4
01/14/95	0.6	04/18/95	8.2
01/15/95	0.8	04/19/95	8.0
01/16/95	0.9	04/20/95	7.8
01/17/95	1.0	04/21/95	7.7
01/18/95	1.2	04/22/95	7.8
01/19/95	1.3	04/23/95	7.9
01/20/95	1.4	04/24/95	8.1
01/21/95	1.6	04/25/95	8.2
01/22/95	1.7	04/26/95	8.3
01/23/95	1.8	04/27/95	8.3
01/24/95	1.9	04/28/95	8.3
01/25/95	2.1	04/29/95	8.2
01/26/95	2.2	04/30/95	8.2
01/27/95	2.3	05/01/95	8.1
01/28/95	2.5	05/02/95	8.1
01/29/95	2.6	05/03/95	8.0
01/30/95	2.7	05/04/95	8.1
01/31/95	2.9	05/05/95	8.2
02/01/95	3.0	05/06/95	8.3
02/02/95	3.1	05/07/95	8.4
02/03/95	3.3	05/08/95	8.5
02/04/95	3.4	05/09/95	8.7
02/05/95	3.5	05/10/95	8.8
02/06/95	3.7	05/11/95	8.9
02/07/95	3.8	05/12/95	8.8
02/08/95	3.9	05/13/95	8.7
02/09/95	4.1	05/14/95	8.5
02/10/95	4.2	05/15/95	8.4
02/11/95	4.3	05/16/95	8.3
02/12/95	4.5	05/17/95	8.2
02/13/95	4.6	05/18/95	8.3
02/14/95	4.7	05/19/95	8.4
02/15/95	4.9	05/20/95	8.5
02/16/95	5.0 (before 9:00)	05/21/95	8.6
02/16/95	0.0 (after 9:00)	05/22/95	8.7 (before 16:16)
02/17/95	-0.3	05/22/95	19536.9 (after 16:16)
02/18/95	-0.6	05/23/95	19536.9
02/19/95	-0.8	05/24/95	19536.9 (before 5:27)
02/20/95	-1.1	05/24/95	-0.2 (after 5:27)
02/21/95	-1.3 (before 13:30)	05/25/95	-0.1
02/21/95	-0.1 (after 13:30)	05/26/95	0.0
02/22/95	0.2	05/27/95	0.1
02/23/95	0.4	05/28/95	0.2
02/24/95	0.7	05/29/95	0.3
02/25/95	0.9	05/30/95	0.4
02/26/95	1.2	05/31/95	0.5
02/27/95	1.4	06/01/95	0.6
02/28/95	1.7	06/02/95	0.7
03/01/95	1.9	06/03/95	0.8
03/02/95	2.2	06/04/95	0.9
03/03/95	2.1	06/05/95	1.0
03/04/95	1.9	06/06/95	1.1
03/05/95	1.8	06/07/95	1.2
03/06/95	1.7	06/08/95	1.3
03/07/95	1.6	06/09/95	1.3
03/08/95	1.7	06/10/95	1.3
03/09/95	1.9	06/11/95	1.4
03/10/95	2.2	06/12/95	1.4
03/11/95	2.4	06/13/95	1.4
03/12/95	2.6	06/14/95	1.4 (before 14:33)
03/13/95	2.8	06/15/95	0.0 (after 14:33)
03/14/95	3.0

 

Station 7210 (HOLLAS) Epoch Time Bias

Van Husson/ATSC in 07/97

The HOLLAS SLR system (station number 7210) had an -54.1 microsecond epoch time bias between January 12, 1988 and December 02, 1988, inclusive. This problem will affect all HOLLAS data products (i.e., full-rate data, full-rate normal points, quick-look data, etc.) recorded during this period of time. ATSC regrets any inconvienience this problem has caused. The user should correct for the time bias as follows:

 

Station 7832 (SALRO) Epoch Time Bias

Peter Bargewell/SALRO in 07/97

All data obtained by the SALRO system (station number 7832) between May 29,1997 and June 25, 1997, inclusive, have a time bias of approximately -41 microseconds caused by an unexplained jump in the station cesium.

 

Station 7810 (Zimmerwald) Fixed Range Bias

Werner Gurtner/AIUB in 08/97

The SLR observations collected between July 9 and July 17, 1997 by the new ZIMLAT telescope at the Zimmerwald station (station number 7810) have been affected by a range bias of +0.45 ns = 6.75 cm. The ranges have been reported too long. The bias has been generated by an inappropriate rounding of a correction term to the nearest nanosecond.

 

Sation 7810 (Zimmerwald) Fixed Range Bias and Epoch Time Bias

Werner Gurtner/AIUB in 08/97

The SLR station located in Zimmerwald, Switzerland (ZIMLAT, station number 7810) has again suffered from a range bias, this time by -0.43 ns which is equal to -6.45 cm. All ranges collected between July 30 and September 3, 1997 (included) were reported too short. In addition, the following passes were affected by a time bias due to a sporadically malfunctioning interface:

Passes Affected by ZIMLAT Time Bias

Satellite	Date	Start Time	End Time	Time Bias (microsec)
GLONASS-67	97-07-10	03:15:07	03:23:28	50.6
STARLETTE	97-08-15	23:17:44	23:18:27	68.1
LAGEOS	97-08-15	23:18:57	23:24:47	68.0
RESURS-3	97-08-18	20:36:37	20:39:09	62.5
STELLA	97-08-18	20:54:25	20:55:05	62.5
STARLETTE	97-08-18	22:17:57	22:27:37	62.4
STARLETTE	97-09-01	00:42:57	00:48:50	66.6
DIADEME-1	97-09-03	20:11:21	20:15:14	65.3
STARLETTE	97-09-03	20:13:17	20:20:46	65.3

These bias values must be subtracted from the reported epochs. Werner regrets the inconveniences these problems may have caused the SLR user community.

 

Station 1884 (Riga) Fixed Range Bias

Kazimirs Lapushka/University of Latvia in 12/97

Dr. Lapushka reports that after many years, the bias in the Riga (station number 1884) laser ranging system has been solved. The problem was in the data reduction software; the light pass interval was added twice. As result, 7.5 +/-0.1 cm must be added to all single-way distances from January 01, 1994, to September 1, 1997. Dr. Lapushka regrets any inconvenience this problem has caused the user community.

 

Station 7090 (MOBLAS 5) Frequency Error

Van Husson/ATSC in 02/98

ATSC reports that data from station 7090, MOBLAS-5 in Yarragadee, Australia, exhibited a frequency error for the following periods of time:

Data taken after January 27, 1998 at 11:20 are not affected along with data taken between January 26, 1998 at 21:40 GMT and January 27, 1998 at 9:00 GMT. ATSC recommends that the data with the frequency error not be used for scientific purposes since the exact error cannot be verified by engineering measurements. ATSC regrets any inconvenience this error may have caused the user community.

 

Replacement SLR Data Issued for Russian MCC Stations

Vladimir Glotov, Russian Mission Control Center in 04/98

The Russian Mission Control Center (MCC) has detected problems in some SLR on-site normal point data passes that were generated for the stations 1864 (Maidanak), 1868 (Komsomolsk), and 1870 (Mendeleevo) from September 1996 to December 1997. At times the on-site normal points generated on the some bins were incorrect and thus the RMS of these passes was increased (for the LAGEOS satellites the RMS was increased by 20-50%). The source of the error was a misprint in the formula of orthogonal polynomials. That algorithm and software was used mainly for geodetic satellites but some passes of other satellites are affected also. MCC reports they identified and analyzed the problem in December 1997 and since January 1998, all on-site normal point data from these stations are free from the specified error. The data (for satellites LAGEOS-1 and -2, GLONASS-67 and -71, STARLETTE, STELLA, AJISAI, TOPEX) have been resupplied to the CDDIS and the EDC; on CDDIS, these data can be found in files dated 28-Feb-1998. MCC recommends using these new data, especially for the scientific and precise purposes; MCC also regrets any inconvenience these errors have caused the user community.

 

Station 7837 (Shanghai) Epoch Time Bias

Yang Fu-Min,Shanghai Observatory in 06/98

Yang Fu-Min of the Shanghai Observatory reports that three passes of data from the Shanghai SLR system (monument number 7837) on May 22, 1998 had a large time bias. The passes where from LAGEOS-1, TOPEX, and GFO-1. Users should disregard these data. The staff at Shanghai regret any problems these data may have cause analysts.

 

Station 7210 (HOLLAS) Barometer Error

Dan O'Gara/University of Hawaii

As was reported in the CDDIS Bulletin for October 1997, the HOLLAS (station 7210) barometer was giving false readings for the period June 18, 1996 through November 24, 1996. All data in this period were taken during the time the barometer was giving false readings. In this previous issue, not all passes were listed that were affected by this problem. A complete pass-by-pass listings of the bad and correct readings can be found on the CDDIS at ftp://cddis.gsfc.nasa.gov/misc/hollas_barometer.tab. The last column (Mees*1.33322 - 3.2) contains the correct pressure that should be used with the corresponding pass. The final value is converted from mmHg and is adjusted by a -3.2 mbars. This -3.2mb corrects for the +1.5mb difference in the Mees data caused by the lower elevation, and a +1.6mb error in the Mees barometer that was detected with the calibration barometer. The average offset was 2.5 mb, measuring high. The HOLLAS staff regrets any inconvenience this problem may cause the user community.

 

Station 7090 (MOBLAS 5) Epoch Time Bias

Van Husson/NASA SLR

The MOBLAS 5 system (station number 7090) had a +387.5 microsecond epoch time bias on December 21, 1998. The problem was corrected by re-synchronization of the timing equipment. The station regrets any inconvenience caused by this problem. The user should correct for the time bias as follows:

 

Station 7110 (MOBLAS 4) Epoch Time Bias

Van Husson/NASA SLR

The MOBLAS 4 system (station number 7110) had a drifting epoch time bias between 25 November 1998 at 12:00 GMT and 26 November 1998 at 15:00 GMT, inclusive. The problem was corrected by replacing the cesium. The station regrets any inconvenience caused by this problem. The time bias correction = -0.4 microseconds -12 microseconds*(fraction of day past 12:00 GMT on November 25).

For example, the time bias correction at 12:00 GMT on November 25  is -0.4 microseconds = -0.4 -0
The time bias correction for 10:00 GMT on November 26 is -11.4 microseconds = -0.4 - 12 *(22/24).

The user should correct for the time bias as follows:

 

Station 7105 (MOBLAS 7) Epoch Time Bias

Van Husson/NASA SLR

The MOBLAS 7 system (station number 7105) had a fixed epoch time bias between 4 March 1999 at 20:15 GMT and 10 March 1999 at 19:15 GMT, inclusive. The station regrets any inconvenience caused by this problem. The time bias correction is +201.5 microseconds.

The user should correct for the time bias as follows:

 

Station 7105 (MOBLAS 7) Unrecoverable Epoch Time Bias

Van Husson/NASA SLR

The MOBLAS 7 system (station number 7105) had an unknown epoch time bias between 29 April 1999 at 5:00 GMT through 3 May at 14:37 GMT, inclusive. Since the epoch time bias is unknown please edit this data from any orbital solutions. The station regrets any inconvenience caused by this problem.

 

Station 7210 (HOLLAS) Epoch Time Bias

Van Husson/NASA SLR

The HOLLAS system (station number 7210) had varying epoch time biases between 2 June 1999 and 4 August 1999, inclusive. The station regrets any inconvenience caused by this problem. The time bias corrections appear below:

Date	Time bias correction
02-Jun-1999	-0.6 microseconds
03-Jun-1999	-0.5 microseconds
04-Jun-1999	0.7 microseconds
08-Jun-1999	0.6 microseconds
17-Jun-1999	5.8 microseconds
18-Jun-1999	7.3 microseconds
29-Jun-1999	3.2 microseconds
30-Jun-1999	4.1 microseconds
01-Jul-1999	4.9 microseconds
02-Jul-1999	5.6 microseconds
07-Jul-1999	9.1 microseconds
08-Jul-1999	9.8 microseconds
09-Jul-1999	1.1 microseconds
14-Jul-1999	5.6 microseconds
15-Jul-1999	6.6 microseconds
16-Jul-1999	7.5 microseconds
21-Jul-1999	12.2 microseconds
22-Jul-1999	13.6 microseconds
23-Jul-1999	14.6 microseconds
29-Jul-1999	12.4 microseconds
30-Jul-1999	15.4 microseconds
03-Aug-1999	26.9 microseconds
04-Aug-1999	30.8 microseconds

The user should correct for the time bias as follows:

 

Station 7124 (MOBLAS-8) Range Bias

Dennis McCollums/NASA SLR

The MOBLAS-8 system (station number 7105) had a bias because the translator was not used for calibrations since May 2004; the bias was corrected on July 1, 2004 at 17:34Z. These calibrations induced an error equal to the translator offset of 0.16319m. The translator offset values are resolved to a tenth of a millimeter.

 

Station 7119 Barometer Error (30 Jan to 31 Jan 2012)

Nikki Desch/NASA SLR

Haleakala (7119) informed the NASA SLR Operations Center that 10 satellite passes were delivered to the CDDIS and EDC with invalid pressure readings. The readings were not high enough to fail the ILRS QC however the readings are still invalid. The data centers are currently removing all problem passes from their respective centers. The errors apply to all Haleakala data submitted between 30 January 2012 19:40 UTC to 31 January 2012 00:15 UTC. The original released data was removed from the data centers and has been replaced with corrected data, with an incremented release flag.

 

Station 7110 Range Error (23 Feb 23 to 09 Mar 2012)

Tom Varghese/NASA SLR

• Moblas 4 has shown an extra ordinarily large Range Bias (RB) since Feb 23, 2012, due to a hardware change occurred that day. The problem is potentially due to a time interval counter issue or the frequency feed going to the counter.
• We consider it prudent to quarantine the "problematic" data since Feb 23, due to the magnitude of the observed error (>7cm for Lageos). Those who want to still access the data can have it from CDDIS or EDC.
• The above RB problem is in addition to the multi-year monotonically increasing RB (~2cm in 2011) observed at the station.
• As some of you may know, M4 has been under increased engineering scrutiny for a while. As a consequence of the larger RB problem, Engineering needs to conduct systematic study and make necessary hardware changes at the station before station can resume its routine SLR operations. During this time, we will collect data in the old and new configurations. This is estimated to take approx. 10 days (weather co-operating). Any changes to configuration will have associated flags.
• The quarantined data flow to CDDIS will be as per the standard protocol. There are no changes to LRO operations or its data flow.
• During the quarantine period, the operations of the station will not follow the ILRS priority of tracking. Rather, it will cover: (1) 20 degrees to 20 degrees Lageos 1&2 passes, (2) longer duration (30 minutes) Etalon passes, and (3) Ajisai passes at the highest priority and order. During the remaining time, other available satellites will be tracked at ILRS priority.
• We are exploring ways to correct the data since Feb 23 at the 1 cm level; there is NO guarantee at this time whether this is possible or not.
• We will give you an operational status update upon completion of the due process.

More information is available.

 

Station 7824 Interval counter frequency reference failure (17 June to 18 June)

Antonio Pazos García

Data from 21h UTC 17/06/2015 to 04h UTC 18/06/2015 are not valid. A no constant offset has been detected due to a failure of the frequency reference in the interval counter.