Q$5.$ A $1$D linear reflection survey is undertaken where, due various factors, a variable fold was achieved across the survey line.

a$)$ Why might this be the case $($include sketches$)$: $[5$ marks$]$

i$)$ at the edges of the survey line?

ii$)$ elsewhere $($away from the edges$)?$

b$)$ Before stacking we require the equivalent zero$-$offset records. How do we account for the non$-$zero offset and variable path lengths in a CMP gather? $[5$ marks$]$

c$)$ What limitations do the low$-$fold survey points have? You should include concepts of noise reduction, and note in what case might increasing the fold of the CMP be detrimental. $[5$ marks$]$