## 3 Advancement of Gravity and Aeromagnetic Exploration in Offshore Sarawak, Malaysia  
Gravity and magnetic surveys have been used in the exploration of natural resources in Malaysia since the 1930s [32] as tools to map sedimentary basins and develop a structural framework around them. The gravity methods have evolved with a variety of acquisitions and processing approaches to produce good quality and high-resolution subsurface images based on anomalies originating from rock density contrasts. The advent of public-domain global marine gravity database (free-air satellite gravity) with uniform coverage and measurement quality [33; 34; 35] allowed for the consistent mapping of regional-scale structural features over a large spatial extent [36]. Circumspection is required when interpreting gravity data from both free-air satellite and airborne gravity because both data are less reliable in water depths shallower than 20 m, mainly due to a higher variability of the sea surface, poor near-shore tidal models, and a loss of altimeter tracking caused by the interference with the onshore reflectors [37].  
The government of Malaysia, under partnership between the Department of Survey and Mapping Malaysia (DSMM) and Kort & Matrikelstyrensen (KMS) from Denmark under the MyGeoid Project has carried out airborne gravity surveys over land areas of Peninsula and East Malaysia in 2002-2003 [38]. The survey was repeated in 2014-2017 for the offshore Sabah and Sarawak [39] (Figure 1B). The aim of the 2014-2017 survey was to develop a new-geoid-based vertical datum from airborne gravity data for area of out-coast of East Malaysia region. This survey marks a remarkable first attempt for the Malaysian government in attaining a systematic high-accuracy wide geoid model at nationwide scale. Through this program, the accuracy of the gravimeter geoid is estimated to be better than 5 cm across most of East Malaysia land and marine areas [40]. Although the airborne gravity database from the MyGeoid Project remains confidential, Free-air and Bouguer anomalies maps were extracted from the airborne data as final plots. The downward continuation data was part of the geoid determination output, processed from filtered airborne gravity data (Figure 1B). Collaboration project between DSMM and KMS produced an airborne gravity field that revealed many interesting regional geological features on land as well as in the marine area of Malaysia-Borneo [40].  
In 2014, the Airborne Full Tensor Gradiometry (FTG) Gravity or Air-FTG(r) approach was successfully acquired in the vicinity of Central Luconia-Tatau Province (Figure 1C) in Sarawak by Bell Geospace Limited (BGL) with a terrain elevation covering 174 m below sea level to 24 m above sea level [41]. The penetration of airborne gravity and aeromagnetic in the subsurface is limited within shallow water depth (<2000 m), thus, the coverage of Air-FTG(r) in offshore Sarawak is restricted to the Central Luconia Province. The survey area (Figure 1C) covers a total of 14,330 line-kilometers with 2000 m and 1000 m inline-spacing and 10,000 m and 5000 m tie-lines spacing. The usage of airborne Air- FTG(r) within this limestone province is highly suitable because of the density contrasts between carbonates, siliciclastic (shale, claystone, and sandstone) and the crystalline basement underlying the basin. Therefore, the utilization of free-air satellite gravity and magnetic data along with advanced Air-FTG(r) gravity and aeromagnetic data is crucial in analyzing the basement structures' geometries and relate them to the regional framework.