Passive station names

Introduction

Each passive station has a name composed of the following elements:

A single letter prefix denoting the station's historical significance

A single digit to distinguish multiple stations in the same 1km grid square

A 10km grid reference

So for example, Kelso FBM is H1NT7531

Prefix

The following is adapted from an Ordnance Survey FAQ, published a number of years ago. The corresponding web page, if it still exists, has not been traced.

What are the B, C, H and T prefixes in the Passive Station Number?

The letter prefix in the Passive Station numbering system is largely a historical one indicating the origins of the station.

Stations prefixed with the letter 'B' are stations originally included in the SciNet (EUREF GB92) network of stations. Before the Active GPS Network these were of a higher order, however there is no longer any difference in quality between any of the designated Passive Layer stations.

Stations prefixed with the letter 'C' are stations which originally met the criteria for a National Network GPS (Passive Layer) station. Namely: have good aspect of the sky for GPS occupation; be accessible 24 hours a day to a two-wheel drive vehicle in all weather conditions; and permission for access, if required, easy to obtain. Most of these monuments were constructed specifically for GPS use, though where suitable, existing Fundamental Bench Mark or Triangulation monuments were adopted.

Stations prefixed with the letter 'H' or 'T' are Fundamental Bench mark or Triangulation monuments included in the Passive Network for transformation computation purposes, but do not generally meet the access requirements for a 'C' designated station.

The number immediately following these prefixes differentiates between stations when more than one exists within the same km square.

Station numbering

The Fundamental Bench Mark Aux stations were initially numbered to match the corresponding FBM .

For example, the passive station name for Skipton FBM at SD 99600 52520 is H1SD9952 whilst the name for Skipton FBM Aux 1 at SE 00001 52952 was originally H2SD9952. In this instance, the Aux station name does not give the true grid reference.

Later, FBM Aux stations were renumbered according to their actual grid square. So Skipton FBM Aux 1 was changed from H2SD9952 to H1SE0052.

Station database

The passive station database can be searched. Where available, the station page links to the corresponding photo (in JPG format) at https://www.ordnancesurvey.co.uk/gps/Stationpics/jpg/ and to the sketch (in GIF format) at https://www.ordnancesurvey.co.uk/gps/Stationpics/gif/. The OS considered the coordinate data for FBMs to have commercial value and so, for these stations, the main record may not be available although the sketch and photo can sometimes be accessed.

Thus, for Skipton, the station record for the FBM is not available but the Aux may be viewed. There is a station photo provided for the FBM only; the photo for the Aux is missing. Sketches are available for FBM and Aux. Note that, for the Aux, the station record uses the renumbered name whilst the sketch uses the original name.

Although they were not passive stations, details of some Active stations were originally included the database. For example, Newcastle Active Station was named A1NZ2465