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Co-ordinates of heaven and Earth
Published in Martin Vermeer, Antti Rasila, Map of the World, 2019
In describing the movements of the planets, we use a so-called inertial reference system, in which Newton's laws of motion apply in their simplest form. The official system, the International Celestial Reference System or Frame1 (ICRS/ICRF), uses as its origin the common centre of mass of the whole solar system2. In many practical applications one rather uses, however, a variant of the reference system in which the origin has been shifted to the centre of mass of the Earth. In this way, one obtains a so-called geocentric, quasi-inertial system. The system is called quasi-inertial because the centre of mass of the Earth is in a permanent state of free fall toward the Sun.
Other Techniques
Published in C. R. Kitchin, Astrophysical Techniques, 2020
The current1 absolute reference frame is called the International Celestial Reference Frame (ICRF3) and contains 4,536 extragalactic sources; 303 of these sources (called the ‘defining sources’) form the primary basis of the system, with their positions determined by radio interferometry to an accuracy (at best) of about ±30 microarcseconds. Until 1998, the ICRF1 was based upon optical astrometric measurements and, when space-based interferometric systems produce their results, the definition may well revert to being based upon optical measurements.
Analysis on the differences between EOP 08C04 and EOP 14C04 related to the Earth rotation characteristics
Published in Journal of Spatial Science, 2022
Zhangzhen Sun, Tianhe Xu, Shi'e Zhou, Nan Jiang, Chunhua Jiang, Yuguo Yang
The IERS provides three types of products: International Celestial Reference Frame (ICRF), International Terrestrial Reference Frame (ITRF) and Earth Orientation Parameters (EOP). ITRF is the foundation for positioning services, satellite orbit determination and Earth science application. Since 1988, the IERS has released 13 versions of ITRF, among which ITRF2008 and ITRF2014 are commonly used. EOP 08C04 and EOP 14C04 were also released together with ITRF2008 and ITRF2014, respectively. Compared to previous ITRF versions, ITRF2014 is more stable and accurate (Altamimi et al. 2016).
On-orbit geometric calibration of satellite laser altimeters using infrared detectors and corner-cube retroreflectors
Published in International Journal of Digital Earth, 2023
Junfeng Xie, Ren Liu, Xiaomeng Yang, Fan Mo, Fangxu Zhang, Lirong Liu
A satellite laser accurately measures the distance between the satellite and a ground target, considers the laser pointing angle and satellite orbit/attitude data, and corrects for atmospheric and tidal errors, thereby deriving a satellite laser geometric positioning model according to the geometric relationship between the satellite laser and the ground footprint, as shown in formula (5). where refers to the coordinates of the center of the laser footprint and represents the coordinates of the center of mass of the satellite, which is obtained by interpolating postprocessed orbit determination data. Its accuracy is approximately 5 cm (Zhao and Tang 2013), which can be ignored. represents the offset from the center of the GNSS antenna to the center of mass of the satellite; is the rotation matrix from the International Celestial Reference Frame (ICRF) to the International Terrestrial Reference Frame (ITRF); is the rotation matrix from the satellite body frame (SBF) to the ICRF; denotes the offset of the laser relative to the center of mass of the satellite; is the actual ranging value of the laser after correcting the atmospheric delay and laser ranging errors; is the tidal error; and , , and are the three components of the satellite laser pointing angle, that is, the angle between the optical axis and the X, Y, and Z axes of the satellite coordinate system, respectively.