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Table 1 Correction and calculation of RGM method at KGF.

From: Mass variation in outcome to high production activity in Kamojang Geothermal Field, Indonesia: A reservoir monitoring with relative and absolute gravimetry

Correction factors

Difference

Correction types

At the KGF

Variation with position

– The difference height above sea level (about 300 μGal/m)

Height and tide correction

calculated

 

– The difference latitude position (about 0.8 μGal/m)

  
 

– The difference longitude position (<0.01 μGal/m)

  

Variation with time

The difference position of the sun and moon

Tide correction

calculated

Drift

The difference condition of gravimeter (It can be caused by the movement of the instrument)

Drift correction

calculated

Topographic change/Ground subsidence

The difference elevation of the station

Free air correction (Telford et al., 1976)

calculated

Variation in shallow groundwater level

The difference of the shallow groundwater volume (the rainfall rate changes) (about 5–10 μGal (Goodkind, 1986))

Δg w = 2πGρφ(1 − Sh (Hunt, 2000)

Negligible (The RGM in the similar season)

Variation in soil moisture

The difference in the saturation (The rainfall rate changes)

Δg a = 2π GρφΔSd (Hunt, 2000)

Negligible (The RGM in the similar season)

Atmospheric pressure variation

The changes of air pressure (<5 hPa or about 2 μGal)

Air pressure correction

Negligible (It is too small)

Active volcanism

The emplacement of the magma at shallow depths

Volcanism correction

Negligible (No relation to location of the KGF)

Mining operation

The removal of mineral ore, rock and other mining from underground

Mass change correction

Negligible (No relation to location of the KGF)

Variation of the surrounding area

The difference surface topography of the terrain (such as construction of canal, road, etc.)

Terrain correction

Negligible (It is too small in the KGF)