Dynamic satellite geodesy

The term dynamic satellite geodesy was coined in the early 1960s in order to classify the rapidly developing satellite geodesy . The department investigates the effect of various forces on the movement of artificial earth satellites and was initially also called physical satellite geodesy . Its counterpart is geometric satellite geodesy (the construction of purely geometric networks from directional and distance measurements without analyzing the satellite orbits), while the combined methods combine the advantages of both groups of methods.

Methods

Dynamic geodetic methods with satellites are understood to mean in particular:

• The orbital movement of satellites in the earth's gravitational field
  • based on Kepler's laws and the perturbation calculation ,
  • The non-gravitational forces (which are generally far less than one per thousand) were initially only treated as disturbing influences and were eliminated in the orbit calculations where possible.
• The determination of important parameters of the earth's gravity field through harmonic analysis of the gravity potential ( spherical surface functions ):
  • above all the flattening of the earth and the zonal mass functions of low order (J2, J4, J6 ...), which only work depending on the width , and the so-called "pear shape" J3
  • since about 1970 also of the tesseral mass functions C (n, m) and S (n, m), in which width and length-dependent effects are superimposed and which today can be determined up to degree or order 70 of the spherical surface functions ;
  • Since around 1975, harmonic coefficients of a higher degree due to the combination of the terms C (n, m) determined from satellite orbits with terrestrial gravitational field parameters, which today is possible up to about degree / order 720 (n = 2, 3 ... 720, m = 0 , 1, 2… n) and contains some 10,000 parameters;
• Density determination of the high atmosphere from the braking of satellite orbits
• Gravity field analysis with other methods of potential theory (e.g. with surface coverage ), with multipoint methods , or by numerical integration ;
• Analysis of resonance effects and the effects of the earth's tides on satellite orbits
• Satellite-to-satellite tracking and gradiometry (new satellite projects such as GRACE and GOCE ) for large-scale geoid determination (resolution about 200 km) and for temporal changes in the earth's gravity field
• Satellite dynamics (reaction of the satellite and its rotation to the braking effects of the high atmosphere, the radiation pressure of the sun or tidal effects, as well as to orbit maneuvers )

historical development

While a distinction had to be made between geometric and physically dynamic satellite processes up to around 1975, it has been possible to solve very complex calculation models with tens of thousands of parameters for several decades. In addition to the orbital elements and their changes, these include the coefficients of the gravitational field and the earth models used , the exact coordinates of all observation stations and other parameters such as the slow movements of continental plates .

The first significant combination of geometric and dynamic models was the NNSS system of satellite navigation . With precise measurements of the Doppler effect on its 5–6 Doppler satellites , online accuracies of around 30 meters were possible from 1970, while large-scale surveying networks already achieved decimeter accuracies offline. Since the beginning of the 1990s, the combination methods have gained significantly in importance due to the development of GPS and GLONASS , so that today there is hardly any distinction between geometric and physical-dynamic satellite geodesy.

literature

• Rudolf Sigl , E. Groten: Dynamic Satellite Geodesy - An Overview. DGK . Series A, Volume 49. Munich 1966.
• Manfred Schneider : Celestial Mechanics. In 4 volumes. Volume I and III. Munich 1995 and 1999.
• Kurt Arnold : Satellite Geodesy. around 1965.
• Karl Ledersteger : ÖZV article, around 1961.
• Günter Seeber : Satellite Geodesy. around 1975 and 2000.
• R. Rummel, Jürgen Müller : Reports from the GRACE and GOCE project groups. Munich, Vienna around 2003.
• Manfred Schneider, Chunfang Cui: Theorems about motion integrals and their application in railway theories. DGK. Issue A / 121. Munich 2005, ISBN 3-7696-8201-7 ( online , PDF file; 1.3 MB, 132 pages).

Web links

• University of Bonn: Satellite Geodesy a. Gravity field earth ( Memento from January 6, 2013 in the web archive archive.today )