| Date: | 1997-06-02 20:00:00 | |
| Sender: | John J. Degnan <###FROM###> | |
| Subject: | [SLR-Mail] No. 66: Proposed International Laser Ranging Service | |
| Author: | John J. Degnan | |
| Content: | ******************************************************************************** SLR Electronic Mail 1997-06-02 20:00:00 UTC Message No. 66 ******************************************************************************** Author: John J. Degnan Subject: Proposed International Laser Ranging Service Over the past several months, the CSTG SLR/LLR Subcommission has been drafting the Terms of Reference and Working Group Charters for an International Laser Ranging Service (ILRS) modelled after the highly successful International GPS Service (IGS). These documents will be presented and discussed at the next General Subcommission Meeting to be held at the Grand Hotel Pianeta Maratea in Maratea, Italy from 9:00 am to 12:30 pm on June 13, 1997 following the Eighth WEGENER Symposium. The goal is to finalize the documents for submission to Professor Gerhard Beutler, President of the CSTG Commission. It is anticipated that Requests for Proposals (RFP´s) will be initiated to select the ILRS Central Bureau in a manner analagous to that which was initiated for the IGS. The document is attached below. The document will be available shortly from the What´s New line on the CSTG SLR/LLR Subcommission WWW Home Page at http://cddis.gsfc.nasa.gov/cstg/slr_cstg.html Please submit any comments by email to the SLR/LLR Subcommission Chairman, John Degnan, at jjd@ltpmail.gsfc.nasa.gov DRAFT (5/28/1997) INTERNATIONAL LASER RANGING SERVICE (ILRS) TERMS OF REFERENCE and WORKING GROUP CHARTERS INTERNATIONAL LASER RANGING SERVICE (ILRS) TERMS OF REFERENCE The primary objective of the ILRS is to provide a service to support, through Satellite and Lunar Laser tracking data and related products, geodetic and geophysical research activities. The service also develops the necessary standards/specifications and encourages international adherence to its conventions. The ILRS collects, merges, archives and distributes SLR/LLR observation data sets of sufficient accuracy to satisfy the objectives of a wide range of applications and experimentation. These data sets are used by the ILRS to generate, at a minimum, the following data products: - earth rotation parameters - coordinates and velocities of the ILRS tracking stations - geocenter coordinates - parameters of the Earth´s gravity field - high accuracy satellite ephemerides - the determination of fundamental physical constants The accuracies of these products are sufficient to support current scientific objectives including: - realization of global accessibility to and the improvement of the International Terrestrial Reference Frame (ITRF) - monitoring three dimensional deformations of the solid earth - monitoring earth rotation and polar motion - support the monitoring of variations in the topography and volume of the liquid earth (ocean circulation, mean sea level, ice sheet thickness, wave heights, etc.) - scientific satellite orbit determinations - climatological research - calibration of microwave tracking techniques Lunar ranging data has additional application in the following research areas: Gravitational Physics - Einstein´s Strong Principle of Equivalence - Relativistic Precession of the Lunar Orbit - Changes with Time of the Gravitational Constant Lunar Science from Librational Studies - Dissipation of Rotational Energy (is there a liquid core?) - Shape of the Lunar Core-Mantle Boundary (Love number k2) - Lunar Free Librations (stimulating mechanisms?) Solar System Dynamics - Intersection of Earth´s Equatorial Plane with Moon´s Orbit Plane - Angle Between these Planes - Dynamical Equinox - Tying the Solar System to the ICRF Earth sciences - Variations in the Earth Rotation - Nutations and precession - Long period torque on the mantle due to the core The ILRS accomplishes its mission through the following components: - Networks of Tracking Stations - Operational Centers - Data Centers and Archives - Analysis Centers - Associate Analysis Centers - Analysis Coordinator - Lunar Coordinator - Central Bureau - Governing Board - Working Groups 1 TRACKING STATIONS ILRS Tracking Stations provide ranging data to a constellation of approved satellites (including the Moon), contained in a list of satellites compiled and approved by the ILRS Governing Board, through the use of state of the art laser tracking equipment and data transmission facilities allowing for a rapid (at least daily) data transmission to one or more Operational and/or Data Centers (see below). The stations must meet requirements which are specified in separate documents. The tracking data produced by the ILRS stations are regularly and continuously analysed by at least one ILRS Analysis Center or one mission-specific Associate Analysis Center. The Tracking Stations may be organized in regional or institutional subnetworks. 2 OPERATIONAL CENTERS The Operational Centers are in direct contact with tracking sites organized in a subnetwork. Their tasks include the collection and merging of data from the subnetwork, data quality checks, data reformatting into a uniform format, compression of data files if requested, maintenance of a local archive of the tracking data, and the electronic transmission of data to a designated ILRS Data Center. Operational Centers also provide the tracking sites with sustaining engineering, communications links, and other technical support. In addition, Operational Centers can perform limited services for the entire network. Individual tracking Stations can also perform part or all of the tasks of an Operational Center themselves. 3 DATA CENTERS The Regional Data Centers reduce traffic on electronic networks. They collect reformatted tracking data from Operational Data Centers and/or individual tracking stations, maintain a local archive of the data received and transmit these data to the Global Data Centers. Regional Data Centers may also meet the requirements for Operational Centers and Global Data Centers (as defined in the previous and following paragraphs) of strictly regional network operations and duplicate activities of Global Data Centers to facilitate easy access to the information and products. The Global Data Centers are the main interfaces to the Analysis Centers and the outside user community. Their primary tasks include the following: - receive/retrieve, archive and provide on line access to tracking data received from the Operational/Regional Data Centers - provide on-line access to ancillary information, such as site information, occupation histories, meteorological data, site specific engineering data, etc., - receive/retrieve, archive and provide on-line access to ILRS scientific data products received from the Analysis Centers - backup and secure ILRS data and products. 4 ANALYSIS CENTERS The analysis centers fall into two categories: Analysis Centers and Associate Analysis Centers. The Analysis Centers receive and process tracking data from one or more data centers for the purpose of producing ILRS products. The Analysis Centers are committed to produce the products, without interruption, at an interval and with a time lag specified by the Governing Board to meet ILRS requirements. The products are delivered to the Global Data Centers, to the IERS (as per bilateral agreements), and to other bodies, using designated standards. The Analysis Centers provide, as a minimum, earth orientation parameters on a weekly or subweekly basis, as well as other products, such as station coordinates, on a monthly or quarterly basis. The Analysis Centers also provide a second level of quality assurance on the global data set by monitoring individual station range and time biases via the fitted orbits (primarily the LAGEOS 1 and 2 satellites) used in generating the quick-look science results. Associate Analysis Centers are organizations that produce special products, such as satellite predictions, time bias information, precise orbits for special-purpose satellites, station coordinates and velocities within a certain geographic region, or scientific data products of a mission-specific nature. Organizations with the desire of eventually becoming Analysis Centers may also be designated as Associate Analysis Centers by the Governing Board until they are ready for full scale operation. 5 ANALYSIS AND LUNAR COORDINATORS The laser ranging technique is a broad based one. As an observational technique, the division between lunar laser ranging and artificial satellite laser ranging has become largely a historical one. Due to many instrumental changes already taking place, and others soon to take place, ranging to the Moon is rapidly becoming no different from ranging to artificial satellites, and vice-versa. Indeed, the Moon itself is a satellite of the Earth. However, present differences in many areas related to observations (e.g., predictions and data formats) are still being reconciled. It must also be recognized that the major data analysis packages that are used for artificial satellite analysis (e.g., GEODYNE, UTOPIA, etc.) are not yet equipped to deal with lunar laser ranging observations and most of the LLR analysis packages are equally not yet compatible with SLR observations. Thus, it is prudent to maintain separate LLR and SLR coordinators for an, as yet, undefined time into the future. For the time being, both the SLR and LLR coordinators must work within their own disciplines to maintain observational and data integrities. However, they must also work together in an efort to unify both techniques, bringing together the best of both, and, when possible, learning from the other. The Analysis and Lunar Coordinators serve as the respective technique Coordinators to the IERS. They are voting members of the ILRS Governing Board and elected by the Governing Board as the ILRS representatives on the IERS Directing Board. The Analysis Coordinator chairs the Analysis Working Group which includes, at a minimum, one representative from each of the Global Analysis Centers and may contain representatives of Associate Analysis Centers as well. The responsibility of the Analysis Coordinator is to monitor the Analysis Centers´ activities to ensure that the ILRS objectives are carried out. Specific expectations include global data quality control, station performance evaluation and reporting, and continued development of appropriate analysis standards and formats for the final science products. The Analysis Coordinator is also responsible for the appropriate combination of designated Analysis Centers products into a single and coherent set of products. The Analysis Coordinator ensures that the ILRS products produced by the ILRS Analysis and Associate Analysis Centers conform with IERS requirements and standards. 6 CENTRAL BUREAU The Central Bureau (CB) is responsible for the general management of the ILRS consistent with the directives and policies set by the Governing Board. The primary functions of the CB are to facilitate communications between the ILRS and the external scientific community, coordinate ILRS activities, maintain a list of satellites approved for tracking support, establish and promote compliance to ILRS network standards, monitor network operations and quality assurance of data, maintain ILRS documentation, produce reports as required, and organize meetings and workshops. Although the Chairperson of the Governing Board is the official representative of the ILRS at external organizations, the CB, consonant with the directives established by the Governing Board, is responsible for the day-to-day liaison with such organizations. The CB coordinates and publishes all documents required for the satisfactory planning and operation of the Service, including standards/specifications regarding the performance, functionality and configuration requirements of all elements of the Service including user interface functions. The CB operates the communication center for the ILRS. It maintains a hierarchy of documents and reports, both hard copy and electronic, including network information, standards, newsletters, electronic bulletin board, directories, summaries of ILRS performance and products, and an Annual Report. The Central Bureau proposes to the Governing Board names of individuals to be elected as members at large to help ensure the proper representation of important contributing organizations. The activities of the Central Bureau may be distributed between different groups and organizations according to written agreements and charters. In summary, the Central Bureau performs primarily a long term coordination and communication role to ensure that ILRS participants contribute to the Service in a consistent and continuous manner and adheres to ILRS standards. The Central Bureau is headed by a Central Bureau Director, who is an ex-officio member of the ILRS Governing Board. The Secretary of the GB is also provided by the Central Bureau. 7 GOVERNING BOARD The Governing Board is responsible for the general directions in which the ILRS is providing its services. It defines the official ILRS products, decides upon the satellites to be included into the ILRS tracking list, accepts standards and procedures prepared and proposed by the individual bodies of the ILRS and ensures, through its chairperson, the contact to other services and organizations. The Governing Board consists of both appointed and elected members. The appointed members include: Director of the Central Bureau 1 Secretary of the Central Bureau 1 President of IAG Sect. II or Com.VIII (CSTG) 1 Members elected by their peers within the ILRS Associates include: NASA SLR Network representatives 3 EUROLAS Network representatives 3 WPLTN Network representatives 3 Analysis and Associate Analysis Centers´ representatives 2 Data centers´ representative 1 LLR Representative 1 At-Large Members 2 Total 16 The appointed members are considered ex officio and are not subject to institutional restrictions. The elected board positions are nominated by the ILRS components they represent or by the Central Bureau for a two year term. The At-Large members are intended to compensate for under-representation among the various components of the ILRS or to provide additional skills or knowledge of use to the Board in carrying out its duties. The total GB membership should be properly balanced in all respects with regard to supporting organizations, skill mix, geography, etc. ILRS Associate Members, together with the GB, may nominate and vote for elected members of the GB at the General Election Meeting held approximately every two years in conjunction with the International Workshop on Laser Ranging. With the exception of At-Large members, nominees must be associated with the relevant ILRS component (e.g. Analysis, Data Centers, Lunar, etc.), and the GB will be final arbiter on an individual´s qualifications for a particular elected post on the Board. Nominations for the GB will be accepted by the Central Bureau at any time prior to the General Election Meeting. Election is by a simple majority of votes received. In the unlikely event of a tie vote, the GB will make the final selection in Executive Session. The GB Chairperson is elected by the Board from among their number for a term of two years, renewable for three terms. Nomination and selection of the Chairperson is carried out in GB Executive Session following the biannual General Election Meeting. The Chairperson does not vote, except in case of a tie. He/she is the official representative of ILRS to external organizations. The GB exercises general control over the activities of the Service including modifications to the organization that would be appropriate to maintain efficiency and reliability, while taking full advantage of the advances in technology and theory. Most GB decisions are to be made by consensus or by a simple majority vote of the members present, provided that there is a quorum consisting of at least ten members of the GB. In case of lack of a quorum the voting is by mail. Changes in Terms of References and the Chairperson of the GB can be made by a 2/3 majority of the members of the GB, i.e., by twelve or more votes. The Board shall endeavor to meet semiannually and at such other times as shall be considered appropriate or opportune by the Chairperson or at the request of at least eight members. Members of the GB shall become IAG Fellows with the appropriate rights and privileges following two years of recognized service. 8 WORKING GROUPS The Governing Board, at its discretion, can create or disband Working Groups. A Working Group (WG) may be either permanent (Standing) or temporary (Ad-Hoc) in nature. Standing Working Groups are created by the GB to carry out continuously evolving business of the ILRS. Ad-Hoc Working Groups are appointed to carry out special investigations or tasks of a temporary nature. The Coordinator of each WG is selected by the GB from amongst its members to ensure close coupling of the WG with the GB and its goals. The WG Coordinator can independently appoint additional members to the WG from among the other GB members, ILRS Associate Members or ILRS Correspondents (see below). The WG Coordinator may also designate a Deputy to act on his/her behalf in his or her absence. Currently, the Standing Working Groups are: Missions Data Standards and Processing Networks and Engineering Analysis The charters for these working groups are attached as Appendices. 9 ILRS ASSOCIATE MEMBERS Persons representing organizations which participate in any of the ILRS activities (missions, tracking, operations, data analysis, or archiving) and who are not members of the Governing Board are considered ILRS Associate Members. They may attend open (non-executive) ILRS meetings which are announced to the general community by the CB, place nominations for elected GB posts, and vote in ILRS elections. A directory, electronic and/or hard copy, of ILRS Associate Members is maintained by the CB. ILRS Associate Members are considered IAG Affiliates with the corresponding rights and privileges. 10 ILRS CORRESPONDENTS ILRS Correspondents are persons on a mailing list maintained by the Central Bureau, who do not actively participate in the ILRS but express interest in receiving ILRS publications, wish to participate in workshops or scientific meetings organized by the ILRS, or generally are interested in ILRS activities. Ex officio ILRS Correspondents are the following persons: - IAG General Secretary - President of IAG Section V MISSIONS WORKING GROUP CHARTER 1 Introduction The primary task of the ILRS is the timely collection, merging, archiving, and distribution of laser ranging data to various approved spacecraft properly equipped with retroreflectors. Currently, artificial satellites tracked by the global tracking network fall into four major categories: Geodetic (e.g., LAGEOS 1&2, Etalon 1&2, Starlette, Stella, Ajisai, GFZ-1) Altimetric (e.g. ERS 1&2, TOPEX/POSEIDON) Space Navigation and Positioning (e.g. GPS, GLONASS, METEOR-2/PRARE) Special (e.g. TiPS, METEOR/Fizeau, RESURS-3, ADEOS/RIS) Geodetic satellites are dedicated passive satellites used in defining the Terrestrial Reference Frame and gravity field and in scientific studies of tectonic plate motion, regional crustal deformation, Earth rotation and polar motion, postglacial uplift, etc. Such satellites generally require frequent and long term tracking (decades) to achieve their scientific goals. Altimetric satellites are usually limited life missions lasting approximately three to ten years. Typical scientific goals include dynamic sea surface topography, mean sea level and wave height determination, global ocean circulation, ice sheet thickness and topography, and, with future laser altimeters, land surface topography including biomass estimation. The frequency and duration of laser tracking required is usually dependent on the desired radial accuracy for the orbit, the presence or absence of complementary microwave tracking devices such as GPS, DORIS, or PRARE, and the periodic need for inflight calibrations of these techniques and/or the altimetric sensors themselves. Space Navigation and Positioning satellites provide an alternate means (usually based on microwaves) of obtaining precise geodetic positioning on the Earth or precise navigation in space. Laser tracking provides an independent means of calibrating the performance of these systems, further defining satellite force models, and/or directly tieing their orbits into the SLR reference frame with its well-defined geocenter and vertical scale height. Tracking can be of long term interest (e.g. GPS) or relatively short term (e.g. METEOR 3/PRARE). Special satellites usually have a unique, short-term scientific or engineering goal such as the study of tether dynamics in Earth orbit (TiPS), testing the performance of new retroreflector designs (METEOR 2/Fizeau, RESURS-3), the evaluation and optimization of two color SLR systems (ADEOS/RIS), or intercontinental time transfer experiments (METEOSAT P2/LASSO). In one case (ADEOS/RIS), lasers provide the precise orbit predictions which permit ground-based lidars to rapidly acquire the onboard reflector for atmospheric experiments. 2.Responsibilities of the Spacecraft or Mission Sponsor The Point of Contact for every organization requesting tracking support of new satellites or modification of the adopted tracking priorities is the ILRS Central Bureau. It is the responsibility of the Spacecraft or Mission sponsor requesting laser tracking support to file a Laser Tracking Support Plan with the ILRS Central Bureau. In the past, NASA has generated the Laser Tracking Support Plans for most new missions, including many non-NASA experiments. These plans are required to obtain tracking approval at NASA and many non-NASA sites. In the future, it will be the responsibility of the spacecraft or mission sponsor to generate the plan and submit it in a timely manner to the Central Bureau. Pertinent information on the Mission will be extracted from the Plan and posted on the CSTG SLR/LLR Subcommission Web Page for easy access by individual stations. The Laser Tracking Support Plan must provide, to the best of the sponsor´s ability, the following information: -Scientific and Technical Points of Contact for the Mission -the scientific or engineering goals of the mission -the proposed launch scenario and approximate dates -expected duration of the mission -special tracking requirements or restrictions (if any) during the pre-launch, launch, and post-launch phases of the mission -the tracking sites requested to participate in the operational phase of the Mission and the frequency and duration of tracking required from those sites (required orbital accuracy may be substituted for this) -the acquisition, tracking, and/or data services to be provided by the sponsoring organization for the Mission -those acquisition and data services of a special or non-routine nature requested from the ILRS - required timelines for data processing and delivery -repository for scientific or engineering results resulting from the mission and a statement of availability of raw and/or analyzed data to the general SLR community 3. Roles and Responsibilities of the Missions Working Group A laser station can only track one satellite at a time. The rapidly growing constellation of satellites tracked by lasers, combined with a vastly different tracking requirement for each satellite and limited tracking resources, necessitates the formation of a Missions Working Group to review all requests for laser tracking and to make a recommendation to the Governing Board regarding tracking and its relative priority with respect to other approved satellites. 3.1 Review of the Laser Tracking Support Plan The Central Bureau will refer the Laser Tracking Support Plan to the Missions Working Group which will in turn review it for: -adequate scientific or engineering relevance and sufficient justification for laser tracking (to justify the additional workload of the tracking sites to site sponsors and obtain their concurrence) -concurrence on the stated laser tracking requirements and recommended assignment of tracking priority to the Mission -adequacy of the prediction service (generating institution, format, method and frequency of distribution) -special requirements (e.g. time biases, drag functions, librating functions, calibration passes, accelerated data submissions) -organization of the data flow from the data centers to the mission analysis centers 3.2 Generation of new procedures for special requirements Whenever the normal procedures and formats are inadequate for proper support of a new mission, the Mission Working Group must work out possible solutions in cooperation with the Mission sponsor and the other Working Groups. 3.3 Propose acceptance of new missions The Missions Working Group proposes to the ILRS Governing Board the acceptance or refusal of a new or modified mission, based on the documents submitted by the mission sponsor, and taking into account the currently adopted mission plan. Prior to making a recommendation to the Board, the Missions Working Group consults with the Network and Engineering, Data Format, and Analysis Working Groups as necessary. 3.4 Recommends New Tracking Priorities The Missions Working Group proposes to the ILRS Governing Board any changes in the current priority list due to new missions or changes in the requirements of currently supported missions. DATA FORMATS AND PROCEDURES WORKING GROUP CHARTER 1. Introduction The function of the ITLN is to generate accurate and precise laser tracking data, and to merge, archive and distribute these data. In doing so a variety of data handling and processing procedures are involved, and it is essential that standardised and efficient procedures should be utilized throughout the network. This Working Group is concerned with procedures affecting the data up to and including the generation of full-rate or normal point data. The subsequent procedures concerning the generation of higher level data products (such as Earth rotation parameters, station coordinates, etc.) are the concern of the Analysis Working Group. There are two main aims of this Working Group: i) to maximise the efficiency of the process of generating the laser data, by ensuring that accurate predictions are available and that standardised software procedures are available to produce a uniform quality data product, ii) to ensure that the data product contains all the information needed by the analyst, and that the data and related information are available for the analyst in a convenient form. 2. Role of the Data Formats and Procedures Working Group 2.1 Predictions: It will be the responsibility of the Working Group to document and maintain standards for: Force model and reference frame of IRV integrator. Format of IRV state vectors. Standard methods to correct IRVs for unmodelled forces. Standard format for time bias functions. Standard software packages for generating predictions from IRVs. The Working Group will endeavour to ensure that there are several groups within the network with the capability of generating IRVs and time bias corrections, and that there are efficient and rapid means of distribution. The Working Group will endeavour to ensure that a standard software package is maintained for generating pass predictions from IRVs. 2.2 Data processing The Working Group will document and maintain the standard algorithm for formation of normal points, and will endeavour to maintain standard software packages for fitting a trend function to pass residuals, for analysing the distribution of pass residuals, and calculating various reference points (mean, peak, etc) 2.3 Station information The Working Group will document and maintain formats for recording station information, such as: eccentricity vectors details of occupancy of sites changes to systems alternative operational configurations of stations. 2.4 Data format The Working Group will maintain the documentation of the format for the final data products, full-rate data and site-formed normal points, and will coordinate the continuing activity to review and if necessary revise the format. Many of the actions discussed above are already carried out by various organisations, groups and individuals within the laser ranging community. The function of the Working Group is not to change any of these arrangements, but to consolidate and build on them, and ensure that developments take place in a coordinated way. NETWORKS AND ENGINEERING WG CHARTER 1.Introduction SLR systems constituting the ILRS provide ranging data to satellites (artificial or otherwise) to meet the requirements of the scientific community. SLR must consistently produce high quality data if it is to fulfill its potential role as a ”geodetic calibrator”. The diversity in hardware, software and technologies in the ground based SLR/LLR systems which make up the global network creates a unique set of monitoring problems for SLR as compared to other space based geodetic techniques. This diversity makes it necessary to establish an international entity dedicated to monitoring overall network performance and ensuring the quality and timeliness of the data it produces. An increasing number of satellites are being launched with an expectation of SLR support. Adequate coordination between the analysis community and the network is essential to ensuring that mission needs and scientific/engineering goals are being met. Feedback from the data analysts on faulty or inconsistent station performance must be documented and corrective actions initiated as rapidly as possible. The need often exists to review network performance versus mission requirements on a periodic basis to ensure adequacy of the global SLR dataset for the full complement of approved missions. Individual station capabilities often dictate data quality and quantity and the number of spacecraft that it can support. At present, data quality (i.e. precision, accuracy and stability) can vary by as much as an order of magnitude from one station to the next. Such a large disparity compromises the full potential of the SLR technique and requires a coordinated approach to achieve greater uniformity and versatility. A globally coordinated WG, which understands both the user needs and station constraints, can provide a broad perspective in arriving at an optimal approach. 2. Role of the Networks and Engineering Working Group The Networks and Engineering WG will seek to improve and optimize the input-output functions and products of the SLR network by working closely with the data analysis community and the individual SLR stations through appropriate interactions and feedback. The primary responsibility of the Networks and Engineering WG is to facilitate the generation, collection and distribution of data in a timely and efficient manner to the user community while meeting the data quality and quantity requirements of the approved missions and to serve as a catalyst in improving the overall performance of the global network. To this end, the WG: 2.1 Provides a communications link between the analysis community and the global network Feedback from the analysis community on network performance will be routinely sought by the Networks and Engineering WG and communicated to individual stations or subnetworks. 2.2 Facilitates ranging data problem and/or anomaly resolution The Networks and Engineering WG will serve as a technical resource to individual stations or subnetworks in the resolution of data problems or engineering anomalies as reported by the Analysis community. The Networks and Engineering Working Group will routinely provide engineering feedback as well as technical information and advise and will coordinate corrective actions as necessary. 2.3 Reviews and maintains the system configuration data base The Networks and Engineering group will collect and maintain a comprehensive and up-to-date SLR system configuration database for each SLR station. These databases will reside, at a minimum, at the global Data Centers. Such a database is extremely useful in mission planning and network scheduling. Analysts often consult the engineering database to explain data anomalies in both short term and long term solutions so it is important that configuration histories of inactive stations be retained in the database as well. The WG will periodically query the global community of active stations to ensure that the engineering information in the database remains current. 2.4 Maintains a ”knowledge base” of SLR technology, algorithms, processes, problems and resolutions The Networks and Engineering WG will seek to share the accumulated wisdom and knowledge of the global SLR community by establishing and maintaining, at the Data Centers, an online technology database of publications and reports describing all aspects of SLR technology including transmitters, detectors, range receivers, epoch timers, satellite array designs and performance, tracking mounts, past problems and resolutions, etc. 2.5 Performs engineering analyses in support of new missions and network scheduling The WG will assist the Mission and Analysis Working Groups in defining the minimum and optimum network configurations necessary to support new and existing missions. Examples of engineering analysis performed by the WG will include spacecraft link calculations, projected data quality and quantity, etc. 2.6 Coordinate and catalyze engineering improvements within the global SLR network Continued technology enhancement within the SLR community to improve the data quality and productivity is extremely important to the long-term relevance of the technique. The Networks and Engineering WG will play a pro-active role for improved performance of the network by championing new technology and engineering improvements. ANALYSIS WORKING GROUP CHARTER 1.Introduction SLR Analysis Centers provide geodetic solutions of various types to the International Earth Rotation Service (IERS) where applicable and/or to the Global Data Centers for use by the scientific community. Solutions provided to the IERS are related to the Terrestrial Reference Frame (TRF) and include station positions and velocities in a geocentric reference frame as well as those components of the Earth Orientation Parameters observable via the SLR technique. Other data products of a more specialized nature include static and time-varying gravity field coefficients, precise satellite orbits, etc. A major goal of the space geodetic community is to freely use space geodetic data of all types in establishing and maintaining the TRF and in performing other scientific analyses. This is most easily accomplished if the presentation format of the scientific data product is largely independent of the technique. In recent years, the GPS community has adopted the SINEX format, and, since the overwhelming volume of data will flow from the GPS network, it seems appropriate for the SLR and other space geodetic analysis communities to either adopt the SINEX format or to work together toward some other mutually agreeable format. This will ensure that SLR data, with its unique strengths and capabilities, will continue to be attractive to researchers anxious to use all the space geodetic tools at their disposal to achieve their demanding scientific goals. SLR Analysis Centers provide independent solutions, but have sometimes adopted reference frames and/or models for gravity, plate motion, tides, nonconservative forces, etc. which were either non-standard or poorly defined. These force model differences can produce apparent disparities and inconsistencies between solutions from centers employing different analysis techniques. Inadequate description of the reference frame can also create confusion among outside scientists attempting to use the archived results in their own analyses. It is therefore important that certain standards be uniformly applied to all formal solutions submitted by the Analysis Centers to the IERS and that those force or other models for which no standards have been adopted be clearly stated. It is the function of the Analysis WG to ensure that all IERS standards be adopted in formal SLR submissions to that body, to lobby on behalf of the ILRS to change IERS standards when warranted, to establish and maintain a knowledge base of analysis and data presentation standards which are easily accessible to the SLR Analysis community, to assist the analysis community in adopting and adhering to ILRS standards and practices in a pro-active manner, and to advise the Missions WG when necessary in the evaluation and/or improvement of global SLR network support to existing and future missions. 2.Roles and responsibilities of the Analysis Working Group 2.1 Support the SLR Analysis Coordinator The Analysis Coordinator is a voting member of the IERS Directing Board and chairs the Analysis WG. The Analysis WG supports the Analysis Coordinator in carrying out his IERS duties. 2.2. Provide quality control on IERS submissions The Analysis WG works in a pro-active fashion to ensure that all SLR Analysis Centers which submit geodetic solutions to the IERS adhere to approved IERS models for gravity field, non-conservative forces, plate motion, atmospheric propagation, relativistic effects, etc, and that those models for which no standards have been adopted are clearly defined. The WG also maintains standards for methods of analysis. 2.3. Ensure data compatibility with other techniques To the maximum extent possible, the Analysis WG ensures that all SLR Analysis Centers present their science products in a format compatible with, and interchangeable with, that of other space geodetic techniques (e.g. SINEX). 2.4 Provide feedback to the Networks and Engineering WG on station/network performance Through its analysis of geodetic satellite orbits (and particularly LAGEOS 1 and 2) as determined by the global SLR network, the analysis community is the final arbiter on the data quality from a particular SLR station. The Analysis WG advises the Networks and Engineering WG when a particular SLR station is performing outside minimum or normal specifications or when overall network data quality or quantity is not meeting mission requirements. 2.5 Support the Missions WG in their analyses The Analysis WG assists the Missions WG in projecting the tracking needs of new satellites and, when necessary, suggests means of readjusting tracking priorities to satisfy the data needs of the full complement of SLR satellites. 2.6 Establish and maintain a knowledge base for the analysis community The Analysis WG maintains a knowledge database (reports, web sites) which are easily accessible to the global SLR analysis community. Besides the approved models discussed previously, the database would include summaries of publications and reports which describe new forces or models suggested for inclusion in satellite orbit analysis, ”optimum” techniques for data reduction and analysis, etc. ******************************************************************************** |