Seismic data acquisition is the first of the three distinct stages of seismic exploration, the other two being seismic data processing and seismic interpretation. Seismic acquisition requires the use of a seismic source at specified locations for a seismic survey, and the energy that travels within the subsurface as seismic waves generated by the source gets recorded at specified locations on the surface by what is known as receivers (geophones or hydrophones). Before seismic data can be acquired, a seismic survey needs to be planned, a process which is commonly referred to as the survey design. This process involves the planning regarding the various survey parameters used, e.g. source type, receiver type, source spacing, receiver spacing, number of source shots, number of receivers in a receiver array (i.e. group of receivers), number of receiver channels in a receiver spread, sampling rate, record length (the specified time for which the receiver actively records the seismic signal) etc. With the designed survey, seismic data can be recorded in the form of seismic traces, also known as seismograms, which directly represent the "response of the elastic wavefield to velocity and density contrasts across interfaces of layers of rock or sediments as energy travels from a source through the subsurface to a receiver or receiver array." Survey parameters Source types for land acquisition For land acquisition, different types of sources may be used depending on the acquisition settings. Explosive sources such as dynamite are the preferred seismic sources in rough terrains, in areas with high topographic variability or in environmentally sensitive areas e.g. marshes, farming fields, mountainous regions etc. Such type of sources needs to be buried (coupled) into the ground in order to maximize the amount of seismic energy transferred into the subsurface as well as to minimize safety hazards during its detonation. An advantage of explosive sources is that the seismic signal (known as the seismic wavelet) is minimum phase i.e. most of the wavelet's energy is focused at its onset and therefore during seismic processing, the wavelet has an inverse that is stable and causal and hence can be used in attempts to remove (deconvolve) the original wavelet. A significant disadvantage of using explosive sources is that the source/seismic wavelet is not exactly known and reproducible and therefore the vertical stacking of seismograms or traces from these individual shots can lead to sub-optimal results (i.e. the signal-to-noise ratio is not as