Kinematic GPS survey as validation of LIDAR strips accuracy

M Barbarella M Barbarella,C Gordini C Gordini

doi:10.4401/ag-3145

Abstract

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 original GPS data, the traces obtained by fixing phase ambiguity with an On The Fly (OTF) algorithm were isolated 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 accuracy, a good result was nevertheless obtained with a Digital Terrain Model (DTM) of all the zones of interest.

Highlights

In 1998 a hydrogeological disaster caused landslides in the Campania territory, in the south of Italy
LIDAR data make possible to obtain a cloud of points with considerable density and acceptable precision to permit many engineering applications and studies
The analyses performed on overlapping zones and the comparisons with the kinematic field survey made it possible to determine some averages of altimetric differences to apply as constants to each strip

Summary

Introduction

In 1998 a hydrogeological disaster caused landslides in the Campania territory, in the south of Italy. This event represented an environmental emergency, requiring a DTM to be provided as quickly as possible of part of the territory, such as for instance of the landslide slopes. Characteristics of the area of interest and dynamics of the landslides. Two particular conditions can be identified as the cause of the 1998 event: lithologic characteristics (loose rocks between stratum of limestone with the same inclination as the slope side) and the steep slopes of the sides. The urban development of the area without good planning contributed to the disaster. A heavy shower aggravated the situation a few day before the catastrophic event

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Conclusion