RTM calculation from a high resolution DSM
20/09/2016 | 17:00 | Session 3: Local/regional geoid determination methods and models
Author(s): Roosevelt De Lara Jr and Sergio F. De Souza
Roosevelt De Lara Jr and Sergio F. De Souza
The effect of residual terrain model (RTM) is usually calculated from digital surface models (DSM), altimetric and or bathymetric. In this study was used the DSM generated from LiDAR data (Light Detection and Ranging) derived from a survey by airborne laser scanning in an area of about 900 km² in the region of the municipality of Porto Alegre, Rio Grande do Sul, Brazil. The original LiDAR data distribution had an average density of 3 points/m². From the LiDAR data subsequently generated a DSM with a resolution of 10x10m² covering the whole area of interest. Using geological maps of the same region was compiled a density map with a resolution of 10x10m². The gravimetric survey covered 58 stations in the urban area of Porto Alegre with an area of about 528 km². The gravimetric stations were positioned on points whose planimetric coordinates were determined by GNSS (Global Navigation Satellite Systems) and orthometric heights determined by geometric leveling (the orthometric height range 0-270 m). The discrepancy between the altimetry and DSM is approximately ± 10 cm. The RTM was calculated for each of stations from a square base prisms (10x10m²) and height equal to its orthometric height. Each prism regards the density in the respective point in the DSM. The effect of the RTM was calculated from cylinder with a radius of 5 km, composed of the individual prisms within the circular area centered on a gravimetric station. The results indicate that the effects of high frequencies modeled by local RTM are the order of ± 1 mGal, which justifies its consideration in terms of gravimetric reductions.