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 − S)Δh (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) |