| Date: | 1997-04-08 19:00:00 | |
| Sender: | Van Husson, Andrew Sinclair <[Mailed Andy Sinclair <ats@ast.cam.ac.uk>]> | |
| Subject: | [SLR-Mail] No. 48: SLR SYSTEM LOG FILES | |
| Author: | Van Husson, Andrew Sinclair | |
| Content: | ******************************************************************************** SLR Electronic Mail 1997-04-08 19:00:00 UTC Message No. 48 ******************************************************************************** Author: Van Husson, Andrew Sinclair Subject: SLR SYSTEM LOG FILES SLR SYSTEM CONFIGURATIONS AND SYSTEM CHANGES Description of content and layout of log files. Van S. Husson, Andrew T. Sinclair 1997 March During the CSTG Laser Ranging Subcommission meeting in Shanghai in November 1996 a proposal to maintain better records of SLR system configuration descriptions and changes was presented by Van Husson and Andrew Sinclair. John Degnan, Mike Pearlman and Philip Gibbs contributed valuable suggestions in discussions leading to the formulation of this proposal. The proposal was accepted by the Subcommission. The intention is that there will be two log files, one giving information on changes to hardware and software made at SLR stations, and the other defining alternative modes of operation, for cases where stations perhaps use alternative configurations for different satellites. The purpose of this note is to define the standard layout of these log files that will be used to maintain this information, and to give guidelines on the information that should be placed in the files. Files for all the stations will be maintained at the data centers, and in addition each station should maintain its own file. The idea is that flags in the SLR normal point data record will indicate that a significant change has been made at a station, or that one of several alternative operational configurations is in use for a particular pass, and that these log files will give supplementary descriptive information of the system changes and configurations. Each time a significant change is made at a station, or a new operational configuration is introduced, then a line of text in a standard format should be added to the station´s file and sent to the data centers. No changes will be made to previous lines of data, and there is no provision for subsequently adding an end date to an earlier line of data. Instead, if a change involves the replacement of one piece of equipment by another, then the description should state that the old piece of equipment has been replaced, and thus will give an end date for its use. If an operational configuration is discontinued, then it can be cancelled by inserting a line of text with the same System Configuration Indicator, stating that this configuration will not be used again. SYSTEM CHANGE LOG FILE. ´SCH´ Each line of text in the system change log file should contain: In cols 1-8: The system Site Occupancy Designator (SOD) - 8 digits. This will be repeated in every line of data, but has the advantage that it will permit automatic sorting of e-mail messages. In col 11: The System CHange indicator (SCH), which is contained in character 46 of the normal point header record (in the 1997 revised version of the data format). This flag is incremented for every major change of the system (hardware or software). When the value ´9´ is exceeded, the value rolls back to ´0´. In cols 13-19: The start date of this system change in YYYYDDD format (7 digits), where YYYY is the four digit year and DDD the 3 digit day of the year. In cols 22-79: A brief description of this particular system change (use more than one line if necessary). The first line in the file should give a baseline list of the principal items of equipment of the station. It is up to the judgement of the station what should be included in this baseline description of the system, and what constitutes a significant change to the system. Some suggestions are given at the end of this note. SYSTEM CONFIGURATION LOG FILE. ´SCI´ Each line of text in the system configuration log file should contain: In cols 1-8: The system Site Occupancy Designator (SOD) - 8 digits, In col 11: The System Configuration Indicator (SCI), which is contained in character 47 of the normal point header record. This is used for systems which have alternative operational configurations, e.g., use of a different detector for very high satellites. If a system has only one mode of operation, then this indicator should be set to the value ´1´. In cols 13-19: The start date of this system configuration in YYYYDDD format (7 digits), where YYY is the four digit year and DDD the 3 digit day of the year. In cols 22-79: A brief description of the configuration. It need only describe the ways in which it differs from the baseline configuration. If the system has only one mode of operation then this description should simply say ´Baseline´. IMPLEMENTATION The log file system will be implemented sometime in 1997. Stations should endeavour to backtrack, and construct accurate descriptions and dates for system configurations and changes over the last few years, if their records permit. There will be no attempt to modify previous SLR data to include the flags assigned to these log file histories, but at the date of implementation of the system the latest flag values in the logs will be adopted for the then current SLR normal point data. EXAMPLES OF LOG FILES Example 1. The RGO system is used as an example of a system which has alternative modes of operation. (Normally a SPAD is used, but a PMT may be used if a very wide range gate is required for GFZ-1, or for a low signal-to-noise ratio from the GPS satellites). The descriptions and dates are accurate, but the flag values are ficticious, as these configurations and changes were introduced before the implementaion of these log files. At the date of implementation of this system, the latest flag values in these files will be those that will be adopted in the normal point data records. RGO system change file. SOD Byte Start Description 46 date -------- -- ------- -------------------------------------------------------- 78403501 1 1993295 Baseline system configuration: SPAD-2 Detector , HP5370A Timer , 120ps laser, Rb-1 controlled system clock with epoch and frequency checked by GPS-2 time receiver, clock board 1, Nimbus Sensors for presssure,temperature & humidity 78403501 2 1994013 SR620-2 timer introduced as alternative to HP5370A 78403501 3 1994041 SPAD-3 replaced SPAD-2 78403501 4 1994062 SPAD-2 replaced SPAD-3 78403501 5 1994146 Different Etalon fitted to laser to shorten pulse 78403501 6 1994158 SPAD-3a replaced SPAD-2 78403501 7 1994172 PMT-3 detector introduce as alternative to SPADs 78403501 8 1994188 SPAD-2 replaced SPAD-3a 78403501 9 1994245 SPAD-3a replaced SPAD-2 78403501 0 1994250 SPAD-2 replaced SPAD-3a 78403501 1 1994284 SR620-1 timer replaced SR620-2 78403501 2 1994347 Clock board 2 now epoch timing device 78403501 3 1995004 SPAD-3b replaced SPAD-2 78403501 4 1995054 Rb-1a controlling system 78403501 5 1995090 Semi-train introduced for laser, but only 1st pulse used 78403501 6 1995227 New start diode 78403501 7 1995286 Etalon removed from laser to shorten pulse further 78403501 8 1995304 All pulses of semi-train now being used for issued data 78403501 9 1995344 Humidity: Nimbus replaced by Voltage device 78403501 0 1996135 Rb-1a replaced by Rb-2 - but still compared to GPS-2 78403501 1 1996136 SPAD-2 replaced SPAD-3b 78403501 2 1996169 Rb-2 replaced by DFS. DFS has GPS-3 as primary source and Rb-2 as secondary source. System still checked against GPS-2 78403501 3 1996171 Humidity: Voltage device replaced by Vaisala device. 78403501 4 1996253 Etalon put back into laser - pulse length 80ps ish *************************************** RGO system configuration file. SOD Byte Start Description 47 date -------- -- -------- ---------------------------------------------------------- 78403501 1 1993295 Baseline configuration (i.e., SPAD + HP5370A timer) 78403501 1 1994013 Configuration 1 discontinued 78403501 2 1994013 SPAD + SR620 timer 78403501 3 1994172 PMT + HP5370A timer 78403501 3 1994347 Configuration 3 discontinued 78403501 4 1994347 PMT + SR620 timer *************************************** Example 2. MOBLAS-7 is used as an example of a system which had only a single mode of operation from 1988 day 207 up to 1996 day 30, which is referred to as the baseline configuration, and in 1996 an alternative configuration for very high satellites was introduced, for which the items that differ from the baseline system are described. MOBLAS-7 system change file. SOD Byte Start Description 46 date -------- -- ------- -------------------------------------------------------- 71050712 1 1988207 Baseline system configuration: MCP-PMT, cascaded constant fraction discriminator, 200 ps laser, HP5370B timer, Paroscientific barometer, cesium beam freqency standard, GPS time receiver, Az-El mount, ND: YAG laser, wavelength 532.1 nm, 200 meter calibration target with anti-parallax 71050714 2 1989166 Final anti-parallax modification 71050715 3 1989215 Original anti-parallax modification reinstalled 71050718 4 1990244 ETALON tracking hardware and software modification 71050719 5 1990344 Anti-parallax modification installed 71050720 6 1991191 Anti-parallax/translator, optical attenuation mechanism (OAM), and CDD camera modifications installed 71050721 7 1991204 OAM and CCD camera modifications removed; original receive package re-installed 71050722 8 1991291 OAM and CCD camera modifications installed 71050723 9 1991343 MODCOMP version 6.2 and HP version 2 software installed 71050724 0 1992190 Mount replacement completed 71050724 1 1994356 Installation of processor ”M” (HPDLP V9.1 and GNP V1.2) 71050724 2 1996030 New controller computer and new software 71050724 3 1996120 High sensivity receiver modification installed *************************************** MOBLAS-7 system configuration file. SOD Byte Start Description 47 date -------- -- -------- ---------------------------------------------------------- 71050712 1 1988207 Baseline configuration 71050724 2 1996030 High sensivity single channel receiver installed for high satellite tracking operations SUGGESTED ITEMS FOR BASELINE DESCRIPTIONS AND SIGNIFICANT CHANGES Suggested items to be included in the baseline description and in subsequent descriptions of changes are the laser pulse width, type of detector, type of timer, method of synchronisation of epoch with UTC, source of reference frequency, type of barometer, type of mount. However the main guideline is that it should be the sort of information that would be useful for the station if it was, for example, tracing back to try to explain a subsequently detected change of range or time bias. Changes to system software should also be considered for inclusion. These are a frequent source of data problems. The station should also be wary of non-obvious possible sources of bias. For example, it is now recognised that SR620 timers are affected by temperature variation. So a change of location of a SR620, or a change to an air conditioning system, could be a source of bias variation. However also avoid listing too many items. If more than about 10 items per year are listed then the file will become too large to be useful, and it probably means that the station is going into too much detail, or that it is fiddling with its system too much. However all of this is just a starting point, to try to get something going. The system should be allowed to evolve, according to what analysts and stations find to be useful, and so these initial recommendations are all subject to revision in the light of experience. ----------------------------------------------------------- TRANSMISSION OF LOG FILE MESSAGES TO THE DATA CENTERS Transmission of log file update messages will be from the stations to EDC, from where a copy will be sent to CDDIS, and the accumulated log files for each station will be available from both data centers. The file names will be of the form: SCH_7840.LOG for the system change file SCI_7840.LOG for the system configuration file (with of course the appropriate station number in place of 7840). The system change file is likely to be the most frequently used, and the label SCH can be remembered from ´CH´ for ´CHange´. The initial e-mail message for each file may consist of many lines, if the station is able to trace its history of changes and configurations back over a few years. Subsequent e-mail messages will consist of one or more update lines to be added to the end of the file. ------------------------------------------------------ The initial files for each station should be sent to the usual e-mail address of the EDC, edc@dgfi.badw-muenchen.de . These will be handled manually. Subsequent update messages will be handled automatically, and so they should be sent to a special address, with the subject line and message of a precise form : e-mail update messages should be sent to SLREPORT@dgfi.badw-muenchen.de (note: SLREPORT, not SLRREPORT) The subject line should be, for example, SCH_7840.LOG The message should contain ONLY the lines of data, with no blank lines. ------------------------------------------------------ The proposed starting date is 1997 May 1. Stations should construct their log files, and send the initial files to EDC at any time before this date. >From 1st May the data generated by the station should implement the small changes described in the note ´CSTG SLR NORMAL POINT FORMAT CHANGES´. Specifically, in the header record: col 45: Should be modified to describe both the calibration method and calibration shift type. col 46: this index should be the same as the final index in the station´s SCH log file. col 47: this index should be one of the current configuration indicators in the station´s SCI file. col 55: should contain the value ´1´ to indicate that this format revision has been implemented. The other minor changes described in the format note should also be implemented. [Mailed From: Andy Sinclair ******************************************************************************** |