IGS Analysis Center Workshop - IGS - NASA

@ IGS will develop instructions, analysis standards, formats, recommendations, etc., toNAC’S who will take ensembles of regional cluster solutions and routine globalsolutions to form full global solutions,(k) The. system will have a centralized component (under the supervision of the CentralBureau) that screens andassesses con~ibuted solutions frdm GAC’s, RAC’S, andNAC’S, and provides feedback to them. While any center can act to produce their ownfully combined solution, IGS must also, in cooperation with the IERS, develop astandard solution for purposes expressed in item 2,1 (h).(1)IGS will encourage participation of many RAC’S and NAC’S as part of its research anddevelopment strategy to incrementally improve products and-customer services bybroadening its pool of active participants, IGS will draw up a plan regarding“membership” as a RAC or NAC. The most obvious mechanism is to accept RAC’Sand NAC’s as “Associate Analysis Centers” as defined in the IGS Terms of Reference,(m) (i) GAC’S should use as many globally distributed stations in common (to all GAC’S)as possible. More commonality will result in more robust network combinations anddetection of errors. For purposes of this document, we call these “common stations”.It is recommended that a list of common stations be discussed and agreed upon,keeping in mind the goals set forth in this document.(ii) RAC’S should use at least 3 “common stations” in the reduction of the regionalnetwork data. Although strictly speaking, only 1 common station is necessary for astable origin (the orientation being defined by fixing the GAC orbits), 3 arerecommended for (i) more robust network combinations, and (ii) assessment of errors,by comparing RAC and GAC solutions for the common stations. Apart from qualitycontrol, the assessment of errors will allow for better weighting schemes to bedeveloped for network combinations, and for detection and first-order correction ofanomalous regional network rotations and distortion (possibly due to GAC orbiterrors).(iii) The list of common stations should be sufficiently globally distributed and densesuch that any potential regional survey can be contained within a polygon of at least 3common stations, with at least one common site within 2000 km of the regionalnetwork. If this is not possible with the current global network, then we recommendthat IGS strive to ensure that future global sites be installed to meet this standard. Forpermanent regional arrays, this condition can be easily met by including at least onestation from each of the regional arrays on the list of common stations. The map onthe next page (Figure 3) shows the current status of the global network, where the solidline is the 2000 km contour.68