module 6 Flashcards
Simple Convolution Model
S(t) = Rc * w(t)
Types of Noise
Random Coherent (ground roll, direct, refractions, multiples, diffractions
CDP stacking benefits
reduce S/N multiple suppression average velocities increase normal move out decreases w depth primaries are stacked "in-phase" multiples are stacked "out of phase"
Land sources
Dynamite mechanical wave generator vibroseis (upsweep, downsweep) dinoseis thumper air guns mini-sosie
conventional field record
eg dynamite where you can see data
why do multiple vibe trucks sweep simultaneously in source arrays
attenuate surface noise
improve S/N ratio
marine sources
bubble pulse maxipulse flexotir vaporchoc starjet airgun water gun sparkler
what are the 3 source groups (Marine)
tuned —- set to cancel out bubble oscillations
single source units - recorded signature eliminates bubble pulse
single or multiple source arrays - deigned to NOT generate or to ATTENUATE bubble pulse oscillations
Forerunner
a wavelet before a spike is FORERUNNER
Oscillations
wavelet that trickles off at the end is OSCILLATIONS
Preferred signature
spike
How do geophones work ?
GEOPHONE
arrival of a p-wave
geophone case has a coil and it’s coupled to the ground
magnet is stationary and is suspended on springs
The coil moves within the magnetic field. It induces an electrical voltage
Voltage is recovered on tape in binary format
particle motion gephones record vertically vibrating P or P/Sv waves
Special geophones are used to record Sh
What are the geophone components ?
output
coil
magnet
spoke
How do hydrophones work ?
There is a piezoelectric transducer within the hydrophone. It measures pressure changes in the water. These are changes from seismic pressure waves from bubbles
What is strumming?
vibration of the cable and sudden acceleration
how do you reduce cable “strumming” ?
ship motion is decoupled using an elastic non=active lead-in
ensure streamers are at a constant depth
What is telemetry?
automatic transmission and measurement of data by wire or radio.
Shear wave generation
dynamiHorizontal S waves are generated by a source which is polarized in the X-axis and detected by a receiver in the same axis
what are the 3 main types of shear-wave source?
dynamite laid out in rows
anchored horizontal vibrator
directionally alternating horizontal hammer blows against the base plate
problems to overcome in data and acquisition of shear wave data?
time scale adjustment
frenquency spectra of s waves are lower and more narrow band than p-waves
what are the recording equipment?
analog -> digital -> analog reconstruction
recording amplifier
logic unit
tape transport
camera unit
what are the components of recording amplifier
pre-amplifier - amplify input signal
analog filters - 3
multiplexer - sample in sequence
what are the components of logic unit
formatter
digital to analog converter
demultiplexer
tell me about the camera unit ?
wiggle trace records
