China
Africa
Explore chapters and articles related to this topic
Geodesy
Published in Basudeb Bhatta, Global Navigation Satellite Systems, 2021
Unlike local geodetic datums, which are essentially defined by parameters associated with a single ‘origin’ terrestrial station, datums used in satellite navigation system are defined by a combination of: (a) physical models such as the adopted model of the earth’s gravity field, gravitational constant of the earth, the rotation rate of the earth, the velocity of light, etc.; and (b) geometric models, such as the adopted coordinates of the satellite tracking stations used in the orbit determination procedure, and the models for precession, nutation, polar motion, and earth rotation, that relate the celestial reference system (in which the satellite’s ephemeris is computed) to the earth-fixed reference system (in which the tracking station coordinates are expressed).
The Geoid and Earth Eotation
Published in Petr Vaníček, Nikolaos T. Christou, GEOID and Its GEOPHYSICAL INTERPRETATIONS, 2020
As far as observations and the associated problems are concerned, the changes in global geoid and Earth rotation differ completely in the state-of-the-art technique and in the precision and noise characteristics as well as the temporal resolution that can be achieved. The monitoring of Earth rotation in terms of ΔLOD and polar motion has a long (astrometric) heritage.10 Modern measurements since about 1980 have almost solely been done by space geodetic techniques of satellite laser ranging and very-long-baseline interferometry-1 The application of the Global Positioning System34 has also proved a latest triumph in obtaining high-resolution Earth rotation data. These techniques, characterized as geometrical, now routinely reach a remarkable precision of a fraction of 1 mas and accuracy to within 1 mas for daily, and often sub-daily, determinations of “Earth orientation”.
Satellite positioning
Published in W. Schofield, M. Breach, Engineering Surveying, 2007
It can be seen from the above statements that constant monitoring of the WGS84 system is necessary to maintain its validity. In 1997, 13 tracking stations situated throughout the globe had their positional accuracies redefined to an accuracy of better than 5 cm, thereby bringing the origin, orientation and scale of the system to within the accuracy of its theoretical specification. Another global datum almost identical to the WGS84 Reference System is the International Terrestrial Reference Frame (ITRF) produced by the International Earth Rotation Service (IERS) in Paris, France. The system was produced from the positional coordinates of over 500 stations throughout the world, fixed by a variety of geodetic space positioning techniques such as Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), Lunar Laser Ranging (LLR), Doppler Ranging Integrated on Satellite (DORIS) and GPS. Combined with the constant monitoring of Earth rotation, crustal plate movement and polar motion, the IERS have established a very precise terrestrial reference frame, the latest version of which is the ITRF2000. This TRF has been established by the civil GPS community, not the US military. It comprises a list of Cartesian coordinates (X, Y, Z), with the change in position (dX, dY, dZ) in metres per year for each station. The ITRF2000 is available as a SINEX format text file from the IERS website. Details are at http://www.iers.org/iers/publications/tn/tn31/. The ITRF is the most accurate global TRF and for all purposes is identical to the WGS84 TRF. A new ITRF2005 is in preparation which will be based on the time series of station positions and earth orientation parameters using observations from at least 1999–2005.
The angular characteristics of Moon-based Earth observations
Published in International Journal of Digital Earth, 2020
Huadong Guo, Yuanzhen Ren, Guang Liu, Hanlin Ye
The Earth’s orientation is defined as the rotation from the Earth’s crust (the terrestrial system) to a geocentric set of axes tied to quasars (a geocentric celestial system, distinguished from the reference celestial system, which has its origin in the barycenter of the solar system). More specifically, it means the rotation between a rotating geocentric set of axes linked to the Earth Gxyz (the terrestrial system determined by the coordinates of observing stations) and a non-rotating geocentric set of axes linked to inertial space GXYZ (the celestial system determined by the coordinates of stars, quasars, and objects in the solar system). The common method of describing the rotation between these two systems is to specify the rotation matrix. Rotation is split into three components; the precession-nutation of the figure axis in space, the diurnal rotation around the celestial intermediate pole (Capitaine et al. 2003), and the polar motion of the celestial intermediate pole with respect to the terrestrial crust. The Earth’s orientation is then obtained by inserting these parameters in the coordinate transformation between the Celestial Reference Frame and the Terrestrial Reference Frame.
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 Earth’s rotational movement characterises the situation of the whole Earth state, as well as the interaction between the various spherical layers forming the Earth’s core, mantle, crust and atmosphere (Zheng and Yu 1996). The Earth Orientation Parameters (EOP) are often used to reflect changes in the Earth’s rotation, including precession-nutation, Polar Motion (PM), Universal Time (UT1-UTC) and Length-of-Day (LOD, the derivative of UT1-UTC). The PM and UT1-UTC/LOD are called Earth Rotation Parameters (ERP). With the rapid development of modern space navigation and deep space exploration, the highest requirements are urged for the accuracy of ERP monitoring and prediction (Kong et al. 2010). Researchers have established a large number of high-precision prediction algorithms based on the existing observations and the characteristics of ERP (Schuh et al. 2002, Niedzielski and Kosek 2008, Kalarus et al. 2010, Kosek 2012, Sun et al. 2015, Lei 2016, Jia et al. 2017, Dill et al. 2019, Modiri et al. 2018). With the improvement of space and geodetic techniques (VLBI, SLR, GNSS and DORIS), the measurement accuracy of the Earth’s rotation has increased by 1–2 orders of magnitude. The ERP product is currently published by the International Earth Rotation Service (IERS), and the formal accuracy of PM x component is 27, PM y component is 25, UT1-UTC is 3.4 and LOD is 10 (Bizouard 2018b).
Error analysis of exterior orientation elements on geolocation for a Moon-based Earth observation optical sensor
Published in International Journal of Digital Earth, 2020
Huadong Guo, Hanlin Ye, Guang Liu, Changyong Dou, Jing Huang
As the description above, the transformation between the geolocation coordinates (pe) and the image coordinates (p) of Earth surface feature can be written as:where [F] and [I] represent the transformation matrices from the sensor body-fixed coordinate system to image coordinate system. It’s worth noticing that the look vector of the sensor can be formed by the azimuth angle and elevation angle, which are comparable to the telescope on Earth. [S] is the transformation matrix between the sensor’s position in the Moon-based platform coordinate system and lunar topocentric coordinate system, [M] stands for the matrix transforming from the Moon-centred Moon-fixed coordinate system to lunar topocentric coordinate system, considering different positions on the lunar surface. Any positions of the Moon-based platform on the lunar surface can be referenced by the latitude and longitude, which are similar to the Earth. [L] and [C] are the relative matrices of the lunar orientation determination. For connecting the Earth coordinate systems and the lunar coordinate systems, an inertial reference system is used, i.e. the International Celestial Reference System (ICRS). The origin of the Geocentric Celestial Reference System (GCRS) is in the barycentre of the Earth while the Selenocentric Celestial Reference System (SCRS) shares the same orientation as GCRS and the origin is at the barycentre of the Moon. The transformation of the SCRS and the GCRS [T] shows up as the origin shift. The [P], [N], [R], [W], and [B] represent the matrices of the precession, nutation, rotation, polar motion and the bias separately. As for the time system, the Barycentric Dynamical Time (TDB) is adopted.