Geostatistical estimation in spatial projection of geophysical parameters in aquifer mapping using heliborne geophysics
Student name: Ms Jagriti Dabas
Guide: Dr P K Joshi
Year of completion: 2015
Host Organisation: CSIR- National Geophysical Research Institute, Hyderabad
Supervisor (Host Organisation): Dr Shakeel Ahmed
Abstract: Present study attempts the spatial modeling and projection of the aquifer system in the
region of Patna (Bihar) using Heliborne Geophysical Transient Electromagnetic (HTEM)
data and the ground TEM data using geostatistical estimation techniques.
Flying permissions are often denied due to administrative and safety reasons and data
acquisition cannot be completed for all the study areas. Thus a very precise estimation
technique such as Geostatistics could serve the purpose. In an area of the aquifer
mapping project in Bihar only 18% of the area was allowed to fly and thus a large
portion could not be covered by the heli-borne TEM survey. A few ground TEM; VES
were conducted at a possibly greater spacing.
Thus it was proposed to use the TEM data (mainly on aquifer layers and their
resistivities) obtained from two sources of measurements with their 3D spatial position
and construct variogram in a number of directions. The directional variogram will in
addition to the spatial variability, provide the vertical as well as horizontal anisotropy.
Thus four main variable on the geometry of the aquifers viz., top of the first unconfined
aquifer, top of the clay layer, top of the 2nd confined aquifer and bottom of the 2nd
confined aquifer were considered for geostatistical estimation along with their
respective resistivity values. These being non-stationary variables, variograms were
calculated after detrending them using suitable trends. After the variographic analyses,
estimation at an interval of 250m were made to generate the estimated values of the
variables in the non flying part of the study area. And thereafter, 3D modeling of
geometry of the aquifer system in the area was carried out to have better picture.
Thus this exercise provided a complete mapping of the aquifer in the entire area as the
entire area has really been flown. The work has not only provided the dense data as
estimated values but has proved to be cost effective.
Keywords- HTEM, Geostatistics, Directional Variograms, Detrending, 3D modeling
