Added value:
Permanent survey markers were established to provide a fixed reference framework and datum for regular low level (1500 feet) aerial photography. Furthermore, they were used as reference points for surveys of the beach, seaward fringes and other investigative works.
Markers have been established at approximately 300m centres adjacent to the backshore above the mean high water mark. Purpose built monuments were constructed or locations selected at well defined permanent structures such as coastal defence walls. The custom built markers take the form of grey polymer concrete plates with black markings approximately 250mm x 250mm. The plates were fixed as surface features to existing permanent structures or attached to the purpose built monuments. Each survey marker was sited to allow terrestrial or GPS observations.
Innovation:
Each survey marker was witnessed, photographed and the details combined with the Ordnance Survey digital mapping and set in a proforma which was published as an AutoCAD file. Following installation, each of the 92 permanent markers was related to the Ordnance Survey national mapping framework OSGB 36.
This was achieved by undertaking simultaneous GPS observations from a minimum of three Ordnance Survey triangulation stations between Selsey Bill and South Lancing. Line vectors between adjacent OS triangulation stations were measured adopting both Static and Short Static methods, thus enabling GPS derived WGS 84 co-ordinates to be transformed to National Grid OSGB 36 co-ordinates.
Individual survey markers were heightened above Ordnance Datum Newlyn adopting traditional survey techniques. This enabled GPS derived WGS 84 ellipsoidal heights to be transformed to orthometric heights.
Team work:
Halcrow Geomatics was responsible for the initial project feasibility and client liaison. Recommendations were made on the marker specifications and appropriate locations. The commission also included the preparation of the technical specification, conditions of contract and associated tender documents. On completion of the award process, field observations were supervised with verification of computational processes.
