The Derwent Estuary habitat project 1:25000 depicts marine habitats from Piersons Point [147 02, -43 03] to New Norfolk [147 02 , -42 42 ] from the coastline to the 40metre depth contour. The habitat types depicted in the dataset include reef, sand, seagrass, silt, silty sand and aquatic macrophytes. The data was collected through intensive field sampling from June to December 2000 by marine researchers at the Tasmanian Aquaculture and Fisheries Institute. The use of underwater camera equipment, echo sounder data and a Differential GPS unit allowed for the extensive area to be surveyed. The dataset is intended to be used to fulfil coastal management objectives according to The Living Marine Resources Act 1995.

Depth and positional point data was captured using a Garmin 135 GPS unit coupled with a RACAL differential correction unit. A FURUNO 600L colour sounder was used to discriminate habitat type. Employing a specially designed program, Seabed Mapping Tool Version 1.3, point data was attributed with one of six habitat classifications. The point dataset was checked for extraneous data, cleaned and converted to a point coverage using ESRI ARCVIEW Version 3.2. The point data was used to interpret boundaries and formed the basis of a polygon coverage that was generated from the data. Selected aerial photographs were scanned at 600dpi and stored as 24bit colour TIFF images. Each was georeferenced using ESRI ARCINFO Version 7.2.1 to the Tasmanian Coastline coverage in AGD66. The point data was overlayed on the aerial photographs to check for continuity especially in generating the reef habitat polygons. The generated polygon coverage was edge matched to the 1:25000 coastline shape. The 1:25000 coastline was supplied by the Land Information Services Division of the Department of Primary Industry, Water and Environment Tasmania.

Position Accuracy: The accuracy of the GPS was assessed by recording at fixed points over extended time periods. It was found to vary by no more than 12meters over a three-hour period. Aerial photographs were rectified using a minimum of 15 ground control points for each image. The average root mean square error for the photographs was X8.157 and Y10.246. Attribute Accuracy: The attributes assigned to the 1:25000 Derwent Habitat Mapping Series were based on the interpretation of the readings given from the FURUNO colour sounder. These attributes were cross-referenced with underwater video information used to ground truth the sounder interpretations. Logical Consistency: All data has been checked for duplicate features, extraneous points, unclipped polygons and unattributed polygons by both visual and automated means. Completeness: The 1:25000 Habitat Mapping Series has been completed for the south eastern section of Tasmanian waters from the coastline to the 40metre depth contour. (see South East Tasmania Marine Habitat Map 1:25000 Digital Series) Additional: South East Tasmania Marine Habitat Map 1:25000 South East Tasmania Contour Series - 1:25000