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 Gravity field component

Satellite Gravity

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gravitasi satelit

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    Gravity field component

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    Satellite gravimetry (gravimetric methods)

    Earths Gravity measurement from satelite:

    1. CHAMP (Gravity And Magnetic Field Mission)

    2. GRACE (Gravity Recovery and Climate Experiment)

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    Present models for the mean gravity field of the Earth are

    derived from combinations of various space and ground

    based data which have been gathered over the past several

    decades. These data include terrestrial and space basedsatellite tracking (like SLR, Doris, GPS), conventional

    gravimetry over land and satellite altimetry over the

    oceans. The accuracy of the mean gravity models is

    currently limited by the heterogeneity of the data qualityand origin and the lack of global coverage with uniform

    accuracy.

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    Sistem Dinamika bumi

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    CHAMP (CHAllenging Minisatellite Payload)

    Gravity And Magnetic Field Mission

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    Low altitude orbit satellite

    Launch by GFZ and DLR, July 2000

    Objectives of the mission:

    1. Highly precise global long-wavelength features of the static

    Earth gravity field and the temporal variation of this field.

    2. Unprecedented accuracy global estimates of the main and

    crustal magnetic field of the Earth and the space/time

    variablity of these field.

    3. good global distribution a large number of GPS signal

    refraction data caused by the atmosphere and ionosphere,

    which can be converted into temperature, water vapor and

    electron content

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    measurement :

    1. Gravity: GPS receiver accurately and continuously monitoring of

    the orbit perturbations and a high precision accelerometer

    measuring the surfaces forces accelerations.

    2. Magnetics: a high performance magnetometer set measuring the

    components of magnetic field.3. Atmosphere/ionosphere: GPS dan magnetometer also observe

    parameter2 static and dynamic atmosphere and ionosphere. Ex. GPS

    measurements can be used for the derivation of temperatur and water

    vapor profiles

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    Contribution to the Earth system:

    1. Geosphere: investigation of the structure anddynamics of the solid Earth from the core along themantle to the crust, and investigation of interactionswith the ocean and atmosphere2. Hydrosphere: more accurate monitoring of ocean

    circulation, global sea level changes and short-termchanges in the global water balance as well asinteractions with weather and climate.3. Atmosphere: global sounding of the vertical layersof the neutral and ionized gas shell of the Earth andrelationship with weather on Earth and space weather

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    GRACE (Gravity Recovery and Climate Experiment)

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    Launched March 2002, joint project CSR, NASA, DLR

    and GFZ Main objective : unprecedented accuracy estimates of the

    global high-resolution models of the Earth's gravity field

    for a period of up to five years.

    Orbit altitude : 458500km:1. Guarantee 5 years lifetime

    2. Good compromise between gravity and atmosphere

    salution.

    Two identical satellites fly in same orbit with distance 220km.

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    Gravity measurement system by GRACE

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    Measurement system : The orbits of the two satellites,which are dependent on the integrated effect of themass distributions and movements in the Earth system,are influenced by these effects at slightly differentphases and will therefore be perturbed slightlydifferentially. This perturbation difference will causechanges in the inter-satellite range, which is measuredvery precisely (< 1 m/s) by the K-Band ranging

    equipment. By monitoring this distance, GRACE will beable to detect fluctuations in the gravitational fieldand, therefore, differences in the density of theEarth's surface beneath the satellites.The data will becombined with GPS data to produce a map of the gravityfield approximately once a month.

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    Application:

    1. Deep ocean current changes,

    2. Large-scale evapotranspiration,3. Soil moisture changes,

    4. Mass balance of ice sheets and glaciers,

    5. Changes in the storage of water and snow of the

    continents,6. Mantle and lithospheric density variations,

    7. Postglacial rebound

    8. Solid Earth's isostatic response.

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    Geometrics methods

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    s

    t

    H

    Orbit satelit

    Permukaan laut

    Elipsoid

    H = s - t

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    Topografi

    (sea surface)

    Geoid

    Elipsoid

    N

    H

    h

    N=H-h