urn:nasa:pds:context:investigation:other_investigation.geodesy 1.0 1.13.0.0 Product_Context 2020-05-03 1.0 Context product for geodesy -- the science of accurately measuring and understanding the Earth's geometric shape, orientation in space, and gravity field. https://en.wikipedia.org/wiki/Geodesy A brief overview of geodesy and its principal sub-disciplines. Updated at irregular intervals. Hofmann-Wellenhof, B, and Helmut Moritz, Physical Geodesy, Springer-Verlag Wien, ISBN 978-3-211-33544-4, 2006. An updated edition of the 1967 original by W.A. Heiskanen and H. Moritz. The 2006 version incorporates a global integration of geometry and gravity, making extensive use of GPS methods. Altamimi, Zuheir, Xavier Collilieux, and Laurent Métivier, ITRF 2008: An Improved Solution of the International Terrestrial Reference Frame, Journal of Geodesy, 85, 457-473, 2011. doi 10.1007/s00190-011-0444-4 A description of the 2008 revised solution for the International Terrestrial Reference Frame. ITRF2008 is based on reprocessed solutions of the four space geodetic techniques: VLBI, SLR, GPS and DORIS, spanning 29, 26, 12.5 and 16 years of observations, respectively. The input data were time series (weekly from satellite techniques and 24-h sessions from VLBI) of station positions and daily Earth Orientation Parameters (EOPs). Considering the level of scale consistency between VLBI and SLR, the ITRF2008 scale accuracy is evaluated to be at the level of 1.2 ppb (8 mm at the equator) over the common time-span of the observations of both techniques. Although the performance of the ITRF2008 is demonstrated to be higher than ITRF2005, future ITRF improvement resides in improving the consistency between local ties in co-location sites and space geodesy estimates. Geodesy Other Investigation -0580-01-01 2099-12-31 Geodesy is the science of accurately measuring and understanding the Earth's geometric shape, orientation in space, and gravity field. Pythagoras (580-490 BC) is credited with postulating that the Earth was spherical, and Eratosthenes (276-194 BC) estimated Earth's circumference at 25000 miles. Today the Earth's shape is known to result from the competition of gravity, rotation, tides, plate tectonics, volcanism, fluid motion (ocean and atmosphere), and other forces. Rotation and gravity are themselves also variable. All factors are measured repeatedly and modeled for both historical correlation and prediction.