Search

As a result of the catastrophic hydrogeological events which occurred in May 1998 in Campania, in the south of Italy, the distinctive features of airborne laser scanning mounted on a helicopter were used to survey the landslides at Sarno and Quindici. In order to survey the entire zone of interest, approximately 21 km2, it was necessary to scan 12 laser strips. Many problems arose during the survey: difficulties in receiving the GPS signal, complex terrain features and unfavorable atmospheric conditions. These problems were investigated and it emerged that one of the most influential factors is the quality of GPS signals. By analysing the origi¬nal GPS data, the traces obtained by fixing phase ambiguity with an On The Fly (OTF) algorithm were iso¬lated from those with smoothed differential GPS solution (DGPS). Processing and analysis of laser data showed that not all the overlapping laser strips were congruent with each other. Since an external survey to verify the laser data accuracy was necessary, it was decided to utilize the Kinematic GPS technique. The laser strips were subsequently adjusted, using the Kinematic GPS data as reference points. Bearing in mind that in mountainous areas like the one studied here it is not possible to obtain nominal precision and accu¬racy, a good result was nevertheless obtained with a Digital Terrain Model (DTM) of all the zones of inter¬est.

Academia, Industry and Government are investigating the reliability to use the real time kinematic (RTK) Global Navigation Satellite System (GNSS) techniques for centimetre level positioning of many existing and emerging applications. These include for instance mobile mapping and airborne laser scanning systems. The classical RTK methodology allows for an operational distance between the reference station and the user, within a range of 10-15 kilometres, due to the effect of correlation of some GNSS errors which tend to increase with distance. The adoption of a network-based RTK (NRTK) allow to extend centimetric level positioning within continuously operating reference station network (CORS) with separation distance up to 70 kilometres. One of the research aim was to evaluate the positional accuracy of the GNSS NRTK for mobile mapping applications. In order to understand the potentiality and the limitations of this methodology a testing procedure was designed using the BO-POS Network, established in 2003 in an area within Emila-Romagna, Marche e Toscana. From an operational point of view, a double antenna system was mounted on board of a vehicle also equipped with three dual frequency receivers capable of NRTK positioning. In order to investigate the GNSS NRTK positional accuracy for mobile mapping system applications a least square-based algorithm was developed to determine a reference trajectory. This paper describes the Bologna CORS network, the testing procedure adopted and details the algorithm based on a constrained least square adjustment of the phase centres’ coordinates of the 2 antennae. The positional accuracy of the NRTK path will be finally assessed by comparing the results of the NRTK trajectory with post processed adjusted one.