Gravity Station

There are four gravity stations in the UK, all around the Cheshire area:

Gravity Stations

T:UK	Station name	Grid Ref	FB	Passive id
TP7192	Prees	SJ 57240 33560	11171	H1SJ5733
TP7237	Hatton Heath	SJ 44690 60510	11172	H1SJ4460
TP7178	North Rode	SJ 89990 66800	11173	H1SJ8966
TP7177	Cat and Fiddle	SK 00100 71910	11174	H1SK0071

The outward appearance of these stations is similar to that of an FBM, except that they have a Flush Bracket on the side and there is no bolt or height tag on the top surface. There is no underground chamber associated with gravity stations . They are classified as FBMs in the OS Passive Station database and in T:UK. Height data has not been published. Gravity stations were purpose-built in the 1960s. All are designated as Passive stations.

The following description appears in "... a Short Calibration Line near Macclesfield. Here a 60 milligal (mgal) difference in gravity between the terminals could be achieved by locating one in Macclefield itself and the other 1200 feet higher up on the Pennine scarp near by. This base was supplemented later by a second between Hatton Heath, near Chester, and Prees in Shropshire, which gave a 55 mgal difference for a much smaller difference in elevation."

Gravity measurements are needed to determine the Geoid Model. The Geoid Model is used to convert ellipsoidal heights (usually on WGS84, ETRS89 or other GPS compliant datum) to so called orthometric heights measured relative to some determination of sea level. The ellipsoid is rarely parallel (never mind coincident!) to the equipotential surface we call sea level.

• 
  Cat and Fiddle
• 
  Hatton Heath
• 
  North Rode
• 
  Prees