Zdislav Šíma

Determination of the Geopotential Scale Factor from TOPEX/POSEIDON Satellite Altimetry

The geopotential scale factor Ro= GM/Wo(the GM geocentric gravitational constant adopted) and/or geoidal potential Wo have been determined on the basis of the first years (Oct 92 – Dec 93) ERS-1/TOPEX/POSEIDON altimeter data and of the POCM 4B sea surface topography model: Ro°=(6 363 672.58°±0.05) m, Wo°=(62 636 855.8°±0.05)m2s−2. The 2°–°3 cm uncertainty in the altimeter calibration limits the actual accuracy of the solution. Monitoring dWo/dt has been projected.

Equatorial flattening and principal moments of inertia of the earth

РезюмеДaюmся резульmamы выво¶rt;a naрaмеmров mрехосносmu Землu nо рaзным мо¶rt;елямгеоnоmенцuaлa u рaзносmuглaвных моменmов uнерцuu Землu, сооmвеmсmвующuе сре¶rt;нuм знaченuям (2), (3).

Determination of the geopotential scale factor from satellite altimetry

SummaryThe geopotential scale factor R0=GM/W0 has been determined on the basis of satellite altimetry as R0=(6 363 672·5±0·3) m and/or the geopotential value on the geoid W0=(62 636 256·5±3) m2s−2. It has been stated that R0 and/or W0 is independent of the tidal distortion of surface W=W0 due to the zero frequency tide.РезюмеПо ¶rt;aнным сnуmнuковоŭ aльmuмеmрuu вычuслен мaсщmaбныŭ фaкmореоnоmенцuaлa R0=GM/W0=(6 363 672,5±0,3) m u/uлu знaченuееоnоmенцuaлa нa nоверхносmuеоu¶rt;a W0=(62 636 256,5±3) m2 s−2. Оmмечено, чmо R0 u/uлu W0 не зaвuсum оm nосmоянноŭ чaсmu зонaльноо членa nрuлuвных ¶rt;еформaцuŭ nоверхносmu W=W0.

Refinement of the geopotential scale factorR 0 on

Altimetric measurements of the GEOSAT satellite were used for the determination of geopotential scale factorR0. The geopotential valueW0 on the geoid surface was then computed (W0 =GM/R0).The GEOSAT Geophysical Data Records (GDRs) covering an initial period of the Exact Repeat Mission (ERM) were filtered and processed. The necessary corrections were made in order to allow a precise detection of the sea surface. Gravitational geopotential, rotation and permanent tides were taken into account and the equipotential surface which is the best approximation of the sea surface was found.The determination of the potential valueW0 on the mean geoid surface in this way is very promising. An associated value withW0 - the geopotential scale factorR0 - seems to be a very good Earth dimension defining quantity. Moreover, there are many possible applications ofW0 (R0) in modern geophysics.The incorporation of one of these parameters - we now recommendR0 - into the set of the Primary Geodetic Parameters (PGP) is discussed and suggested.

Prague sextants of Tycho Brahe

Summary Two sextants constructed for Tycho Brahe are preserved in the National Technical Museum in Prague. One was constructed by Erasmus Habermel, the other by Jost Burgi. Both were made in the year 1600. To overcome the observational errors, several improvements were made in the construction of these instruments, especially in the case of Burgis sextant. It would appear both from these instruments and from his tables of sines that Tycho wanted to reduce the errors to one minute of arc. A replica of Burgis sextant, which is currently under construction, will allow the accuracy of the instrument to be tested.

Dimension of the Earth's General Ellipsoid

The problem of specifying the Earths mean (general)ellipsoid is discussed. This problem has been greatly simplified in the era of satellite altimetry, especially thanks to the adopted geoidal geopotential value, W0 = (62 636 856.0 ± 0.5) m2 s-2.Consequently, the semimajor axis a of the Earths mean ellipsoid can be easily derived. However, an a priori condition must be posed first. Two such a priori conditions have been examined, namely an ellipsoid with the corresponding geopotential that fits best W0 in the least squares sense and an ellipsoid that has the global geopotential average equal to W0. It has been demonstrated that both a priori conditions yield ellipsoids of the same dimension, with a–values that are practically identical to the value corresponding to the Pizzetti theory of the level ellipsoid: a = (6 378 136.68 ± 0.06) m.

The global and local correlation between the Venus gravity field and its topography

The correlation between the undulations of the equipotential and topography surface of Venus have been investigated over 16 meridional sections as well as, in the global scale. The correlation is, in general high. However, the figure parameters of the ellipsoids best fitting the surface in question differ significantly. The global features like figures of the best-fitting ellipsoids are mutually strange.

Possible differences between mean sea-levels from satellite altimetry

SummaryThe first attempt has been made at determining the differences between mean sea-levels, using the recent satellite altimetry data [1].

Two Modes of Gas Streams in Binaries

Two types or “modes” of gas rings around a primary star were described by Smak (1985), that is a hot case - geometrically thick, and a cold case - geometrically thin. Sima and Hadrava (1987) suggested that there are four possible ways to compute gas streams flowing from L 1 towards the ring. Only two of the models are physically meaningful: the adiabatically expanding stream (cool case, geometrically thin, higher density) and the stream in a state of radiative equilibrium (hot case, geometrically large, lower density).

Satellite altimetry determination of differences between mean sea-level heights and testing geopotential models

Abstract The Satellite Altimeter Data has been used for a) Determination of differences between mean ocean levels; b) Testing the accuracy of different geopotential models as regards their internal structure over the oceans.