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→Acquisition and instrumentation
==Acquisition and instrumentation==
==Acquisition and instrumentation==
Gravity can be collected on land, at sea, in the air, and by satellite. On land, sea, and air, most sensors consist of a mass at the end of a spring (see figure below). On land, the instrument is leveled and the mass is set to a null position for reading the spring tension.
[[file:applying-gravity-in-petroleum-exploration_fig15-2.png|thumb|{{figure number|2}}]]
Gravity can be collected on land, at sea, in the air, and by satellite. On land, sea, and air, most sensors consist of a mass at the end of a spring ([[:file:applying-gravity-in-petroleum-exploration_fig15-2.png|Figure 2]]). On land, the instrument is leveled and the mass is set to a null position for reading the spring tension.
In dynamic gravity measurements at sea or in the air, the position of the mass and the spring tension is recorded continuously. The instrument is on a stabilized platform during the measurement to maintain a vertical position. In a dynamic gravity measurement, extra care must be taken to keep track of the platform's position. The resulting gravity is usually not as accurate as land data.
In dynamic gravity measurements at sea or in the air, the position of the mass and the spring tension is recorded continuously. The instrument is on a stabilized platform during the measurement to maintain a vertical position. In a dynamic gravity measurement, extra care must be taken to keep track of the platform's position. The resulting gravity is usually not as accurate as land data.
Satellite gravity is derived from satellite radar altimetry of the sea surface. The sea conforms to the gravity field of the earth; the first derivative of the sea surface height is gravity at the sea surface level. Since the satellite can only measure gravity over water, only the marine areas and large lakes have such data. The data quality is somewhat comparable to surface-acquired data, although the wavelength resolution is usually worse for the satellite data.
Satellite gravity is derived from satellite radar altimetry of the sea surface. The sea conforms to the gravity field of the earth; the first derivative of the sea surface height is gravity at the sea surface level. Since the satellite can only measure gravity over water, only the marine areas and large lakes have such data. The data quality is somewhat comparable to surface-acquired data, although the wavelength resolution is usually worse for the satellite data.
==See also==
==See also==