Mikhail Sergeyevich Molodenskii (, sometimes transliterated as M. S. Molodensky, ,

Yepifan Yepifan () is an urban locality (a work settlement) in Kimovsky District of Tula Oblast, Russia, located on the left bank of the Don River about southeast of Kimovsk and southeast of Tula, in the proximity of the Kulikovo Field. Populati ...

or Tula – 12 November 1991,

Moscow Moscow is the Capital city, capital and List of cities and towns in Russia by population, largest city of Russia, standing on the Moskva (river), Moskva River in Central Russia. It has a population estimated at over 13 million residents with ...

) was a

Russian Russian(s) may refer to: *Russians (), an ethnic group of the East Slavic peoples, primarily living in Russia and neighboring countries *A citizen of Russia *Russian language, the most widely spoken of the Slavic languages *''The Russians'', a b ...

physical geodesist. He was once said to be "probably the only geodesist who would have deserved a

Nobel Prize The Nobel Prizes ( ; ; ) are awards administered by the Nobel Foundation and granted in accordance with the principle of "for the greatest benefit to humankind". The prizes were first awarded in 1901, marking the fifth anniversary of Alfred N ...

". He graduated from

Moscow State University Moscow State University (MSU), officially M. V. Lomonosov Moscow State University,. is a public university, public research university in Moscow, Russia. The university includes 15 research institutes, 43 faculties, more than 300 departments, a ...

(1936), since 1946 he worked for the ''Institute of Earth Physics'' (Институт Физики Земли АН СССР). He created an original theory for determining the

figure of the Earth In geodesy, the figure of the Earth is the size and shape used to model planet Earth. The kind of figure depends on application, including the precision needed for the model. A spherical Earth is a well-known historical approximation that is ...

and its gravity field based on measurements done on the topographic surface, built the first Soviet

gravimeter Gravimetry is the measurement of the strength of a gravitational field. Gravimetry may be used when either the magnitude of a gravitational field or the properties of matter responsible for its creation are of interest. The study of gravity c ...

, developed a theory of the nutation of Earth. He won the Stalin Prize (1946 and 1951) and the

Lenin Prize The Lenin Prize (, ) was one of the most prestigious awards of the Soviet Union for accomplishments relating to science, literature, arts, architecture, and technology. It was originally created on June 23, 1925, and awarded until 1934. During ...

(1961). His legacy includes the Molodensky transformations, which are commonly used to transform between

geodetic datums A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame, or terrestrial reference frame) is a global datum reference or reference frame for unambiguously representing the posit ...

. His main work (since 1932) was on the

geoid The geoid ( ) is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is exte ...

and its exterior gravity field or

geopotential Geopotential (symbol ''W'') is the potential of the Earth's gravity field. It has SI units of square metre per square seconds (m2/s2). For convenience it is often defined as the of the potential energy per unit mass, so that the gravity vect ...

. His aim was to develop

hypothesis A hypothesis (: hypotheses) is a proposed explanation for a phenomenon. A scientific hypothesis must be based on observations and make a testable and reproducible prediction about reality, in a process beginning with an educated guess o ...

-free methods for determining both the gravity field and defining

vertical datum In geodesy, surveying, hydrography and navigation, vertical datum or altimetric datum is a reference coordinate surface used for vertical positions, such as the elevations of Earth-bound features (terrain, bathymetry, water level, and built stru ...

s for large areas. As part of this work, he introduced

normal height Normal heights (symbol H^* or H^N; SI unit metre, m) is a type of height above sea level introduced by the Soviet scientist Mikhail Molodenskii. The normal height of a point is defined as the quotient of a point's geopotential number ''C'' (i.e. it ...

s, which can be calculated from geopotential numbers (obtained from precise differential levelling) without needing the uncertain value of gravity along the

plumb line A plumb bob, plumb bob level, or plummet, is a weight, usually with a pointed tip on the bottom, suspended from a string and used as a vertical direction as a reference line, or plumb-line. It is a precursor to the spirit level and used to est ...

of a point, i.e., inside the continental crustal rock under the point.M. S. Molodenskii and V. F. Eremeev and M. I. Yurkina, "Methods for the Study of the External Gravitational Field and Figure of the Earth" (transl. from Russian), Israel Program of Scientific Translations, Jerusalem Corresponding to this new height concept is the concept of the telluroid, the collection of points ''Q'' whose

normal potential Geopotential (symbol ''W'') is the potential of the Earth's gravity field. It has SI units of square metre per square seconds (m2/s2). For convenience it is often defined as the of the potential energy per unit mass, so that the gravity vector i ...

is equal to the true

of a point ''P'' on the terrain, and on the same plumb line. The separation between points ''P'' and ''Q'', i.e., between topographic and telluroid surfaces, is called the ''height anomaly'', and is, contrary to the

geoid undulation The geoid ( ) is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is exten ...

''N'' (with respect to the

reference ellipsoid An Earth ellipsoid or Earth spheroid is a mathematical figure approximating the Earth's form, used as a reference frame for computations in geodesy, astronomy, and the geosciences. Various different ellipsoids have been used as approximation ...

), defined without requiring density information throughout space, not only at sea level. Over time, Molodenskii's theoretical work has found recognition as more and more countries are adopting normal heights for their national height systems. As a compromise to traditional thinking, the concept of '' quasi-geoid'' has been introduced, being a surface separated from the

by precisely an amount equal to the height anomaly evaluated on the topography. Then, the traditional connection between orthometric heights ''H'' and ellipsoidal heights ''h'', :

h = H+N

, is preserved as :

h = H^* + \zeta

, where

\zeta

is the height anomaly (or "quasi-geoid height"), and

H^*

is normal height.

Works

* Molodensky M.S. "Basic issues of geodetic gravimetry", ''Proceedings of the Central Scientific-Industrial Institute of Geodesy, Aerial Photography and Cartography'', 1945, issue 42. * Molodensky M. S., Fedynsky V. V. "Thirty years of Soviet gravimetry (1917-1947)", ''Bulletin of the Academy of Sciences of the Soviet Union, Geographical and Geophysical Series'' 1947. Vol. 11. No. 4. Pp. 395-408. * Molodensky M.S. "Method of joint processing of gravimetric and geodetic materials for studying the gravitational field of the Earth and its shape", ''Bulletin of the Academy of Sciences of the Soviet Union, Geographical and Geophysical Series'', 1951. issue 86. * Molodensky M.S. "Elastic tides, free nutation and some questions of the structure of the Earth", ''Proceedings of the Geophysical Institute of the USSR Academy of Sciences'', 1953, No. 19 (146).

Notes

References

External links

Great Soviet Encyclopedia on Molodensky
1909 births 1991 deaths People from Tula, Russia Corresponding Members of the USSR Academy of Sciences Moscow State University alumni Recipients of the Lenin Prize Recipients of the Order of the Red Banner of Labour Recipients of the Stalin Prize Russian geodesists Russian geophysicists Soviet geodesists {{Geophysics-stub Soviet geophysicists