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REDEFINITION OF INDIAN VERTICAL DATUM -
DENSIFICATION
GTS
Levelling
was
carried
out
between 1850 to 1905.
Indian Vertical Datum was first time
defined in 1905.
Then no Invar staves were used.
No Fore – Back Levelling was done.
Most of the BMs established then do
not exist on the ground now due to
developmental activities and vagaries
of the weather.
Without Gravity Values.
It was assumed that water level of
Arabian Sea and Bay of Bengal is
same, which is infact different due to
different
salinity
and
consequent
different density.
Levelling was not adjusted in single
all India Level Network.
Hence necessary to Redefine Vertical
Datum.
With
the
requirement
of
height
accuracy within few centimetres and
to achieve water flow criterion, we
needed to redefine vertical datum.