Integrating surveying methodologies to provide specific solutions

Donatella Dominici Professor of Cartography and Geomatics, Department of Civil, Environmental Engineering and Architecture, University of L’Aquila, Italy. Laboratory of Geomatics – Via Gronchi, L’Aquila, Italy

Elisa Rosciano Environmental Engineer and PhD Student in Geomatics, Department of Civil, Environmental Engineering and Architecture, University of L’Aquila, Italy. Laboratory of Geomatics – Via Gronchi, L’Aquila, Italy

Michail Elaiopoulos Civil Engineer and Master student in Civil Engineering, Department of Civil, Environmental Engineering and Architecture, University of L’Aquila, Italy. Laboratory of Geomatics – Via Gronchi, L’Aquila, Italy

Modern geomatic techniques have provided interesting advantages in a wide range of research areas. However, the traditional surveying methodologies continue remaining essential in order to ensure reliable and precise results of any kind. This paper aims to illustrate how the simultaneous use of various instruments can guarantee satisfying results even in apparently complex situations. The presented experiment regards the study of two antenna prototypes, developed to identify the presence of bodies buried under collapses in a post-earthquake scenario and/or other calamities. Numerous geomatic techniques and instruments have been integrated among them in order to determinate the position, dimension, orientation, precision and reliability of the two prototypes. The test area has been chosen near Onna, a small village unfortunately destroyed by the earthquake of April 6, 2009.

Introduction

Modern instruments as well as newborn software are able to acquire and process huge amount of data. In addition, the synergy with the traditional surveying permits achieving outstanding precision and accuracy of the final result; this was the reason that led us combining the advantages of both. The development of this radio prototype was born from the idea that the immediate and automatic identification of victims buried under collapses could decidedly reduce the number of deaths in such situations. Certainly, this would be possible through the recognition of signals produced by suitable devices.

A radio antenna uses a continuous wave system (CW) able to estimate the inbound direction of any kind of signal (Direction of Arrival principle – DoA). The reliability of this estimation directly depends on the so-called “path loss” of the antenna; the path loss represents the reduction, in terms of power density (attenuation), of the electromagnetic wave during the path from the object to the receiver. This phenomenon is naturally amplified in presence of flat surfaces (such as buildings), that can reflect the signal (creating the also called multipath error). The evaluation process for the DoA’s evaluation for each prototype was divided into three parts:

• the reproduction of the test scenario using the laser scanning (described later);

• the materialization of a control surveying network using a total station in order to georeference the scenario reconstructed ;

• and finally, the observation with the same orientation of the surveying instruments of the two prototypes in order to estimate their position during the experiment. Figure 1 illustrates the test area and one of the two prototypes.

Surveying methodology and test area

For this experiment, in order to simulate the emission of a signal coming from a collapsed building a radio emitter has been placed through a plastic pipe at the bottom of a pile of debris representing the collapsed structure. The position of the emitter was then measured by the total station using a prism placed on the heap. Thus the first prototype was placed in the vicinities of the rubbles; as it was gradually being rotated, a characteristic sound reproduced by an onboard speaker was indicating the reception of the signal. The positioning and orientation of the prototype was made in these phases: firstly, the normal direction to the antenna has been calculated by observing with a total station the antenna’s two extremities materialized with a couple of surveying prisms. Then the direction between the prototype and the signal’s emitter was calculated. The deviation error was then estimated by the difference
among them. This deviation represents the error with which each prototype failed to locate the signal’s origin. Using this geomatic procedure, the systematic errors in the receiving system of both prototypes has been identified. About 50 placements of both prototypes were made in the same way calculating position, orientation and errors for each one.

Surveying execution

A 3D surveying network has been materialized using a total station (Leica TS30) in order to curry the described operations, thus five control points have been chosen to be used by the needed instruments. Figure three illustrates the control points in red; in green the baselines of this local network are also presented. The TS30 total station has been chosen for its elevated angle and distance precisions (0.5cc and 0.5mm+6ppm respectively). A terrestrial laser scanner campaign has also been curried in order to create an accurate overview of the whole area using a Leica HDS 3200 Laser scanner. Overall, five point clouds have been obtained by making station on each control point and thus covering, with the desired resolution, the whole test area.

The final product of this surveying campaign is a georeferenced point cloud of 7.5 millionpoints with the precision of 4.5 mm. the resulting point cloud is geo-referenced to the local reference system created by the total station ensuring the consistency between the corresponding points in the two reference systems. Figure 4 illustrates an orthophoto depicting the test area.
Having a three-dimensional representation was crucial in order to identify and quantify any obstacle in the path of propagation of the received signal. In this way, overlapping all the information extracted from all survey operations, the detection of any abnormal behavior was possible. Currying a detailed observation of the interested area about 40 elements of possible reflections (facades, metal elements like doors or windows and garages) were identified and localized using the topographic network in order to be used in the post processing. (Figure 5)
During the data elaboration, and, having measured both the angle between the total station and antenna’s prism and the total station and the antenna during the signal’s reception, the deviation error was expressed as the difference between them. As a further result, the probability of a correct identification of the signal’s DoA and therefore, the antenna’s success percentage, was also calculated. In figure 6 the error eclipse around the signal’s origin is shown. The ellipse shows that in the 99.5% of cases the antenna has been able to locate the right direction of the signal within 1.2 meters of error.

Conclusions and discussion

The presented research illustrates a synergy among different techniques and instruments. The motivation of the paper is to highlight that there is no need of searching particular methods neither advanced technologies to overcome with apparently complex situations. The integration and the smart use of well-established techniques can meet the requirements of any situation, especially in problematic cases such as post-calamity emergencies. In future, the same methodologies could be ulteriorely enhanced by integrating GNSS receivers in RTK mode in order to continually track the position of the antenna’s both extremities over time. The equations needed to elaborate these coordinates will be loaded in a model’s routine able both to track these data and to calculate all results in real time. In this way both the testing, the evaluation and the application of similar prototypes will be possible.