**1. Introduction**

Gravity method is one of the geophysical methods widely used in environmental, engineering, archeological, and other subsurface investigations. The gravity method measures the difference in earth's gravitational field at different locations by tools known as gravimeters. Recent developments in observation, processing, and data analysis due to technological improvement added the efficiency and sensitivity of the gravity method, which made it more applicable to a wider range of problems. Airborne gravimeters have the potential to recover a precise gravity field at any place. Recent advancements in detailed aircraft positioning with global positioning system (GPS) carrier phase data have stretched the use of airborne measurement practice to land as well as overwater surveys. To date, large areas of the earth remain unmapped because of the limitations of land and marine surveys. BGI contributes to the recognition of derived gravity products with the aim of providing significant information about the Earth's gravity field at worldwide or provincial scales. Their products used mostly by scientists are the World Gravity Maps and Grids (WGM), which signify the first gravity anomalies computed in spherical geometry considering a realistic Earth model. With long-range aircraft, nearly all the Earth is accessible to airborne surveying. Improvements in hardware, software, and survey methodology continue to lower the overall error budget for airborne gravity. Even though there is no method universally agreed for evaluating data

accuracy and anomaly resolution being a function of the speed of aircraft, reported RMS error and resolution indicates the technique's accuracy [1]. The gravitational field strength is directly proportional to the density of subsurface materials. This gives gravity anomalies that correlate with source body density variations. Positive gravity anomalies are connected to shallow high-density bodies and negative anomalies are connected to low-density bodies. Potential field anomaly maps present the effects of shallow (residual) and deeper (regional) geological sources. Therefore, the main issue in potential field data interpretation is the separation of anomalies into two components [2]. Consequently, in order to produce meaningful results, potential field datasets generally need many processing techniques that are in accordance with the nature of the geology of the study area. Numerous commercial software packages (e.g. Geosoft Oasis Montaj, GeosystemWinGlink, MagPick, and IGMAS) are commonly used for the analysis of potential field datasets by employing some of the methods stated above.

Quite a lot of graphical and empirical methods have been established for the interpretation of gravity anomalies that are caused by simple bodies [3]. The derivatives have a tendency to expand near-surface structures by increasing the power of the linear dimension in the denominator. This is because the gravity effect differs inversely as the square of the distance, and the first and second derivatives vary as the inverse of the third and the fourth power, respectively, for three-dimensional structures.

The second vertical derivative is frequently employed in gravity interpretation for isolating anomalies and for upward and downward continuation. This chapter aims to emphasize the advantage of using the second vertical derivative on gravity data for subsurface delineation. The second derivative is very important for gravity interpretation due to the fact that the double differentiation with respect to depth tends to emphasize the smaller, shallower geologic anomalies at the expense of larger, regional features [4]. Micro-gravimetric and gravity gradient surveying methods can be applied for the detection and delineation of shallow subsurface cavities and tunnels [5]. The second vertical derivative method is very important in edge location and edges are thought to contain most of the two mineralized ore deposits [6].
