Airborne laser scan data: a valuable tool to infer partial beam-blockage in urban environment
Abstract. High spatial resolution weather radar observations are of primary relevance for hydrological applications in urban areas. However, when weather radars are located within metropolitan areas, partial beam blockages and clutter by buildings can seriously affect the observations. Standard simulations with simple beam propagation models and digital elevation models (DEMs) are usually not able to evaluate the buildings contribution to partial beam blockages. In the recent years airborne laser scanners (ALS) evolved to the state-of-the-art technique for topographic data acquisition. ALS data, providing small footprint diameters (10–30 cm), allow accurate reconstruction of buildings and forest canopy heights. Analysing the three weather C-band radars located in the metropolitan area of Helsinki, Finland, the present study investigates the benefits of using ALS data for quantitative estimations of partial beam blockings. The results obtained applying beam standard propagation model are compared with stratiform 24-hour rainfall accumulation to evaluate the effect of partial beam blocking due to the constructions and trees. To provide the physical interpretation of the results, the detailed analysis of beam occultations is achieved by open spatial data sets and interface services with open source Geographic Information Systems.