Firstly, I checked simple results as below by using matlab

reference: http://mathforum.org/library/drmath/view/63767.html

lon=[0:360]

lat=[-90:90]

R=6371

for ix=1:360

for iy=1:180

      A(ix,iy)=(pi/180)*R^2*abs(sind(lat(iy))-sind(lat(iy+1)))*abs(lon(ix)-lon(ix+1));

end

end

But It looks too small and having some errors.

I checked the different method from https://badc.nerc.ac.uk/help/coordinates/cell-surf-area.html

So, I did as below and get the same results

lon=[0:360];

lat=[-90:90];

R=6371;

lonrad=degtorad(lon);

latrad=degtorad(lat);

for ix=1:360

for iy=1:180

% A(ix,iy)=((pi/180)*R^2)*abs(sind(lat(iy))-sind(lat(iy+1)))*abs(lon(ix)-lon(ix+1));

A(ix,iy)=R^2*(lonrad(ix+1)-lonrad(ix))*(sin(latrad(iy+1))-sin(latrad(iy)));

end

end

It looks correct method above two.

In grads, gint function can calculate the area of grid box.

It will be better method.

On shot gathers one can see direct seismic evidence - amplitude decay and   time delays in first breaks, and strong reflection phase from top and bottom of LVL.  But these are not always possible.  Depends on relative thickness of HVL and LVL.  We should know the geology of the area while analyzing shot gathers.  Whether we see time delays or not in the first breaks, we see reflection phases if S/N is good.   

Hi,

You can use the SAGA-GIS program to solve the problem. It is possible to do many spatial analysis and grid operations with this program

http://www.saga-gis.org/en/index.html