Technical Details: Accuracy of the Height Data

In order to predict how high the water level will reach for a tide height measured at Dock Head we need to have land heights accurate to around 10cm or less error. All heights will be referred to “Chart Datum” defined to be ([Ordnance Datum Newlyn] + 2.74m) as used in the current ABP Tide Tables unless stated otherwise.

Comparison of Lidar and Topographic Survey Data

The LIDAR data are obtained from an aerial survey so are available for the whole area of interest, however normally they would only be expected to be accurate to around 20cm due to the need to determine the height of the aircraft. In order to check the Lidar data a topographic survey was performed along Priory Road. The heights would be expected to be accurate to better than 1cm but only for the exact spots that the data were taken. In Figures 1 and 2 the LIDAR data (red dots) are shown to give larger values compared to the topographic data (blue squares) for those regions where both data types are available. The average difference is 17cm. The green diamonds show the LIDAR data corrected by subtracting 17cm. There is now better agreement with the survey data.