UAV APPLICATION IN POST – SEISMIC ENVIRONMENT

On April 6, 2009, an earthquake of 6.3 magnitude st ruck central Italy with its epicentre near L'Aquila , at 42.3502° N, 13.3762°E. The earthquake damaged 3,000 to 11,000 buildings in the medieval city of L'Aquila. Several buildings total ly collapsed, 308 people were killed. The post emergency phase till now is just at its beginning step. Conventional surveying techni ques using high precision total stations, GNSS receivers and laser scanners for inv estigations on damaged buildings are always becomin g ore automated, accurate and operative and even much more fast. Even if the se t chniques represent instruments of extreme oper ability there are still many evident limits on their use, especially regarding the survey of both the roofs and the facades of tal l bui dings or dangerous places, typical on post earthquake situations. So using mi cro UAVs for surveying in such particular cases, ma ny of these problems can be easily bypassed. In fact, the present work aims on experimenting using multi-rotor micro UAVs, that wi ll allow high quality image capturing on roofs and facades of structures in the old city center of L' Aquila. To obtain actual ste reoscopic acquisitions of buildings some conditions on the geometry of acquisition have to be observed, for this reason, taking as a guide line classic flight photogrammetric, a flight planning software was dev eloped. Accurate planning for UAVs acquisitions is very important also considering the reduced autonomy of such vehicles. This can be a strategic point if we want to use UAV s for early damage assessment and also for post event reconstruction p lan ing.

To determine the number of the needed waypoints some metric information are necessary.

Flight planning
Then, the geometric characteristics of the camera have to be estimated: the focal length, pixel dimensions and the frame format in order to correctly determine the physical area covered by each acquisition.
According to these parameters, the overlap between two consecutive images can be estimated.The overlap related to the same strip is defined as 'longitudinal overlapping'; in this direction usually each frame covers the previous by a quantity equal to at least 60 to 80% of the image size.Considering instead two adjacent strips, parallel to each other, the frames are acquired so to obtain a 'transverse overlapping', equal to at least 20 to 30% of the size of the image.

University of L'Aquila 'La Sapienza' University of Rome
Why a planning software is necessary?
•Currently planning is performed mainly based on the experience of the operators; •The characteristics of internal orientation and flight modes originate acquisition geometries different from the traditional photogrammetric airplane acquisition; •The optimization of flight plans is of strategic importance considering, the current reduced autonomy of some UAV; •In addition, the planning of the flight plan could allow to: -Execute multitemporal survey, in fact the flight is repeatable with identical parameters at any time.
-Replace immediately not optimal quality images (due to, for example to unexpected intrusion of other subjects or to sudden changes of light or UAV unexpected instability, etc.). ) )

University of L'Aquila 'La Sapienza' University of Rome
The software requires as input data the size, shape and position of the area to be acquired, the optic parameters of the camera installed on the drone and the desired final scale of the acquisitions.
From these first input data the package suggest a flight altitude, which is proposed to the user which is free to edit if it's not suitable for the area to be investigated.
Once estimated the flight height and consequently, the final scale obtainable, the values of longitudinal and across overlap have to be inserted in the software to allow the evaluation of the airbase needed to assure a correct stereoscopic restitution.After this step the software proceed to the calculation of the waypoints and footprint of each acquisition.
In a post seismic environment UAVs can also be used to acquire facade of buildings for near photogrammetry, in this case as input data the size of the area to be acquired, the optic parameters of the camera installed on the drone and the dimension of the pixel in the acquisitions are needed.

Case of study
To validate our approach a comparison with an actual UAV flight executed for near photogrammetry in L'Aquila was performed.In this first test the facade of "The Basilica di Santa Maria di Collemaggio", was acquired; the church is an important place of Catholic worship in the city of L'Aquila.Established in 1287 by Pietro da Morrone, is the most important religious monument in the city in fact it's an University of L'Aquila UNESCO world heritage site.Contains the first Holy Door of the world and is home to a jubilee year unique of its kind.The basilica is the result of a complex blend of Romanesque architecture, the suction Gothic and Baroque style.During the earthquake of 2009, the Basilica was impressed so extremely serious.Part of the vault of the basilica collapsed causing the destruction of the terminal part of the nave.For this reason a complex work of restoration is going to be performed on the church.