No abstract

Since 1982. the Crustal Dynamics Data Information System (CDDTS) has supported the archive and distrihution of geodetic data products acquired by the National Aeronautics and Space Administration (NASA) as well as national and international programs. The CDDIS provides easy, timely, and reliable access to a variety of data sets, products, and information about these data. These measurements. obtained from a global network of nearly 650 instruments at more than 400 distinct sites, include DORIS (Doppler Orbitog~ raphy and Radiopositioning Integrated by Satellite), GNSS (Global Navigation Satellite System), SLR and LLR (Satellite and Lunar Laser Ranging), and VLm (Very Long Baseline Interferometry). The CDDIS data system and its archive have become increasingly important to many national and international science communities, particularly several of the operational services within the International Association of Geodesy (lAG) and its observing system the Global Geoddic Observing System (GGOS), induding the International DORIS Service (IDS), the International GNSS Service (lGS). the International Laser Ranging Service (lLRS), the International VLBI Service for Geodesy and Astrometry (lVS). and the International Earth rotation and Reference frame Service (IERS), Investigations resulting from the data and products available through the CDDIS support research in many aspects of Earth system science and global change. Each month, the CDDTS archives more than one million data and derived product files totaling over 90 Gbytes in volume. In turn. the global user community downloads nearly 1.2 Thytes (over 10.5 million files) of data and products from the CDDTS each month. The requirements of analysts have evolved since the start of the CDDIS; the specialized nature of the system accommodates the enhancements required to support diverse data sets and user needs. This paper discusses the CDDTS. including background information about the system and its. user communities. archive contents. available meradata, and future plans. Published by Elsevier Ltd. on hehalf of COSPAR.

This article discusses the attitude modes employed by present Global (and Regional) Navigation Satellite Systems (GNSSs) and the models used to describe them along with definitions of the constellation-specific spacecraft body frames. A uniform convention for the labeling of the principal spacecraft axes is proposed by the International GNSS Service (IGS), which results in a common formulation of the nominal attitude of all GNSS satellites in yaw-steering mode irrespective of their specific orbit and constellation. The conventions defined within this document provide the basis for the specification of antenna phase center offsets and variations in a multi-GNSS version of the IGS absolute phase center model in the ANTEX (antenna exchange) format. To facilitate the joint analysis of GNSS observations and satellite laser ranging measurements, laser retroreflector array coordinates consistent with the IGS-specific spacecraft frame conventions are provided in addition to representative antenna offset values for all GNSS constellations.

No abstract

No abstract