Digitala höjdmodeller och höjdsystem : insamling av höjddata med fokus på flygburen laserskanning

Sammanfattning: Elevation data of high quality is important. In Sweden a governmental climate and vulnerability study (Klimat och sårbarhetsutredningen) states that some analyses of vulnerability due to future climate changes, like hydrological analyses to estimate the risk of flooding, do require elevation models of high quality. The present national elevation model does not reach the accuracy requirements. Since these analyses are of national interest it has been decided that Lantmäteriet (the Swedish mapping, cadastral and land registration authority) shall produce a new digital elevation model. A digital elevation model is a digital representation of the bare ground. The most common structures for storing an elevation model are grid and TIN (Triangular Irregular Network). The new national elevation model will be stored as a TIN, but delivered as grid. Each time data is ordered a grid is created from the TIN. The advantage of this is that data delivered will always be updated. Data for the new model will be collected using airborne laser scanning, lidar. Two other remote sensing techniques used to collect elevation data are photogrammetry and radar. Of the three techniques, lidar gives the highest accuracy, with photogrammetry only slightly lower. Radar data is of lower quality. Maybe the most important advantage of lidar is that the pulses can penetrate vegetation, giving more accurate bare ground elevation in dense vegetation. Another advantage compared to photogrammetry is that lidar is an active sensor allowing it to collect data in the dark, or under cloudy skies. Lidar also makes it possible to collect data over large areas in short time. Direct digital capture of data makes data available fast. A disadvantage is that large amount of data is collected. This sometimes means dataprocessing is time consuming. Another disadvantage is that if the quality of GPS- and inertial data, collected during the scanning to enable georeferencing, is low, the lidar data can not be used, and has to be re-collected.