2] [2] [7] 2B (a) State two application areas of gravimetry. What is the typical magnitude of signals that need to be me

[answerhappygod]

2 2 7 2b A State Two Application Areas Of Gravimetry What Is The Typical Magnitude Of Signals That Need To Be Me 1 (107.21 KiB) Viewed 43 times

2] [2] [7] 2B (a) State two application areas of gravimetry. What is the typical magnitude of signals that need to be measured (in Gal)? (b) Two types of instrument used for gravity surveys are relative gravimeters and absolute gravimeters. What are potential advantages and disadvantages of using gravity as a mea- surement tool for underground mass anomalies? Describe how a relative gravimeter and absolute gravimeter operate. State one advantage and one disadvantage for each of the relative gravimeter and absolute gravimeter. (c) A relative gravimeter has a resonant frequency of 2 Hz and a displacement noise of 1 nm/V/Hz. Estimate the signal-to-noise ratio of the gravimeter if it is left to monitor the Earth tides in Glasgow, with a measurement bandwidth of 100 s. (d) An absolute gravimeter is constructed using a 20cm drop and an inter- ferometer having a wavelength = 633 nm. The local force of gravity is g = 9.98 ms-2. By considering the range of velocities achieved by the mass over the course of the measurement and hence the range of frequencies pro- duced by the output of the interferometer, show that the required bandwidth over which the signal needs to be measured is 6.313 MHz. (e) The interferometer output is detected using a photodiode which is shot- noise limited. If the silicon photodiode produces a current of 0.5 mA for a 1 mW input optical power, what is the signal-to-noise ratio of the interferometer output with a 1 mW laser? The shot-noise current spectral density of a current with full shot noise is given by isha = 21 ppe where ipd is the photodiode current in amps, and e is the charge of an electron, 1.602 x 10-19 C.) [3] [3] [3] 3 (f) What distance error in the interferometer output does this noise corre spond to? (g) What error in the measurement of g does this correspond to? (h) Given the variation of the force of gravity over the Earth's surface is from 9.7639 ms –2 to 9.8337ms-, how many bits of precision should be used to store the results of the gravimeter? [2] [2] [2]