CDDIS Bulletin - April 1991
Volume 6 No. 4

In this issue:

• Cover:
  • CDP Footprint Sites
• Articles:
  • IERS Submissions to the CDDIS
  • Analyzed Results in CDDIS -- U. of Texas/CSR SLR Results
  • Changes in SLR Data Processing
• Data Bits and Bytes:
  • Test Sets of SLR Normal Points
  • NAVNET VLBI Experiments
  • New GPS Data Submissions -- Simeiz Survey and Pinyon Flats Footprint
  • CSTG Recommendations for SLR Releases"

On the cover: CDP Footprint Sites

IERS Submissions in the CDDIS

Several IERS analysis centers have submitted their annual solutions to the CDDIS. These groups include both the SLR and VLBI analysis groups at GSFC and the SLR analysis group at the Center for Space Research (CSR), University of Texas.

The GSFC SLR submission consists of both earth rotation and station position determinations. These data sets span May 1976 through June 1990 are stored in the following CDDIS data base tables:

ROTAROTATIONIERS_SLRGSFC  Earth orientation parameters
POSITIONSIERS_SLRGSFC     Station position solution

ROTATIONIERS_VLBIGSFC       Earth orientation parameters
CORRELATIONSIERS_VLBIGSFC   Earth orientation parameter correlations
POSITIONSIERS_VLBIGSFC      Station position solutions
VELOCITIESIERS_VLBIGSFC     Station velocities and positions with correlations
SOURCESIERS_VLBIGSFC        Source coordinates

The four solutions are combined in the above tables and are identified by number (716, 718, 720, and 722). More details about the four solutions can be obtained from the CDDIS help library (DIS Main Menu Item 1).

The CSR SLR submission to the IERS is composed of two solutions (L 02 and L 03). These data span May 1976 through February 1991 and are stored in the following CDDIS data base tables:

ROTATIONIERS_SLRCSR    Earth orientation parameters
POSITIONSIERS_SLRCSR   Station position results

The two CSR solutions are also described in the CDDIS help library (DIS Main Menu Item 1).

Analyzed Results in CDDIS

The Center for Space Research at the University of Texas has recently submitted their latest station position and baseline solutions derived from SLR data. These solutions are stored in the DIS data base tables POSITIONS_SLRCSR and BASELINE_SLRCSR and can be accessed through the DIS SQL Query Menu (Main Menu Item 4). The data sets were computed in sixty-day intervals and span the years 1976 through 1988. Both geodetic and cartesian computations were performed.

Changes in SLR Data Processing

With all data taken since March 1, 1991, several changes will be introduced into the processing of SLR data. The changes are:

1. The center of mass is computed by not applied to the time of flight.
2. The tropospheric refraction correction is computed but not applied to the time of flight.
3. The time tags refer to the time of laser fire, not the satellite transmit time.
4. The LAGEOS center of mass is computed using the new value but is not applied to the data. The revised value is 251 mm; the old value was 240 mm.

These changes are fully documented in the data itself in that all flags will be set properly to reflect these changes. Therefore, analysts are strongly encouraged to check all flags to ensure proper use of the data. Data from the following stations will affected: Bar Giyorra, MOBLAS-4 through 8, TLRS-1 through 4, HOLLAS, MLRS, Arequipa, Matera, and Orroral. Orroral data taken since November 12, 1990 and Arequipa data taken since November 22, 1990 (as opposed to March 1, 1991) will have the above data standards applied. The March 1991 Version A data set will be released from the CDDIS in May 1991.

DATA BITS AND BYTES

This section is designed to give brief notices of special events, new data sets, or problems encountered in recent months.

Test Sets of SLR Normal Points

In addition to other SLR data processing changes, as of the March 1991 A release, test sets of normal points for STARLETTE, AJISAI, and ETALON-I and -II will be produced and distributed to interested parties. Users should contact the CDDIS staff if they wish to receive these test sets of normal points.

NAVNET VLBI Experiments

The CDDIS has recently received the USNO's NAVNET data bases from September 1988 through January 1991. These data sets are in VLBI data base handler (DBH) format but can be converted to NGS card-image format upon request. Users interested in receiving copies of any of these data sets should contact the CDDIS staff.

New GPS Data Submissions

Data taken in support of the GIG Ô91 campaign at Simeiz, USSR have been archived in the CDDIS. The data are in raw Minimac format only at this time and span January 23 through February 12, 1991.

NGS has contributed their Pinyon Flat footprint survey conducted in June 1986 to the CDDIS. The survey was performed during four days at eleven sites in the Pinyon Flat, CA area using six TI 4100 receivers.

CSTG Recommendations for SLR Releases

At a recent CSTG SLR meeting held at GSFC on October 23, 1990, the group recommended that future SLR data releases contain operational and engineering data in a single merged data set. Prior to this decision, engineering data was released to the CDDIS on a monthly basis on a separate release tape. In the merged form, data classified as engineering can be identified by a release flag set to Z; operational data has a release flag of A, B, C, etc. When/if engineering data is considered operational, the release flag will be updated from Z to the current value for the release flag (e.g., B, C, etc.). This policy will become effective with all CDDIS releases after February 1, 1991.