Irene Aicardi

An Image-Based Approach for the Co-Registration of Multi-Temporal UAV Image Datasets

During the past years, UAVs (Unmanned Aerial Vehicles) became very popular as low-cost image acquisition platforms since they allow for high resolution and repetitive flights in a flexible way. One application is to monitor dynamic scenes. However, the fully automatic co-registration of the acquired multi-temporal data still remains an open issue. Most UAVs are not able to provide accurate direct image georeferencing and the co-registration process is mostly performed with the manual introduction of ground control points (GCPs), which is time consuming, costly and sometimes not possible at all. A new technique to automate the co-registration of multi-temporal high resolution image blocks without the use of GCPs is investigated in this paper. The image orientation is initially performed on a reference epoch and the registration of the following datasets is achieved including some anchor images from the reference data. The interior and exterior orientation parameters of the anchor images are then fixed in order to constrain the Bundle Block Adjustment of the slave epoch to be aligned with the reference one. The study involved the use of two different datasets acquired over a construction site and a post-earthquake damaged area. Different tests have been performed to assess the registration procedure using both a manual and an automatic approach for the selection of anchor images. The tests have shown that the procedure provides results comparable to the traditional GCP-based strategy and both the manual and automatic selection of the anchor images can provide reliable results.

Detailed geological mapping in mountain areas using an unmanned aerial vehicle: application to the Rodoretto Valley, NW Italian Alps

ABSTRACT We present a methodology to use a UAV (unmanned aerial vehicle) to perform photogrammetric surveys and detailed geological mapping in mountain areas. This work is specially related to the presented case study with the aim to realize geomorphological maps from UAVs, since they can house different types of sensors and acquire data more rapidly and cheaply than traditional geological surveys directly obtained with field observations. This work explains how UAVs can obtain digital terrain models, orthophotos and 3D models in order to create slope and aspect maps for geological purposes. By integrating data from UAVs with geological surveys made on the field, geological maps can be produced where many of the geological elements are presented. This paper presents the integration of geomatics and geological techniques. Starting from UAV slope map and orthophotos, a new geological map was created in a faster and more detailed way compared to traditional geological survey on the ground. The application of this method regards a sector of the Western Alps (NW Italy), formed by glaciers and deep-seated gravitational slope deformations.

A methodology for acquisition and processing of thermal data acquired by UAVs: a test about subfluvial springs’ investigations

ABSTRACT An accurate description of watercourses helps to easily understand their behaviour both for routine hydrological investigations and in disasters cases. Knowing the position and the dimension of the supply sources of the river is crucial, since they have a direct influence on its behaviour; however, they are not often easily identified, and almost always completely unknown. Aerial thermal data can be critical in order to rapidly reveal and map the river supply source points for extensive areas. Using unmanned aerial vehicles (UAVs) to collect very easily and quickly high-resolution information is thus very interesting. UAVs can house many sensors for performing investigations in different bands of the spectrum, including thermal data. This work explains how UAVs can be used to collect this kind of data (through RGB and thermal devices) and presents a strategy to easily integrate the information from these different sensors. Integration procedures, also applicable in emergency situations, were developed. These methods do not require points on the ground and can be performed using commercial devices.

UAV-based pattern measurement of the SKALA

A novel antenna pattern measurement technique has been recently developed exploiting the capabilities of a micro Unmanned Aerial Vehicle (UAV) as a far-field test-source. This technique is suitable for characterizing VHF antennas such as those for low-frequency radio astronomy. This paper presents some of the measurements recently performed on the Square Kilometer Array Log-periodic Antenna (SKALA), which has been selected as the receiving element for the Low Frequency Aperture Array (LFAA).

UAV-based radiation pattern verification for a small low-frequency array

The Unmanned Aerial Vehicle (UAV) technology has been recently used to develop a pattern measurement system for low-frequency arrays in their real installation conditions. This paper presents the most important results that have been obtained on the Italian Medicina Array Demonstrator (MAD).

Inertial sensors strapdown approach for hybrid cameras and MEMS positioning

In this paper the performances (in terms of accuracy) of an hybrid positioning technique, that brings together an image based recognition approach and MEMS (Micro Electro-Mechanical Systems) technology, will be investigated. The image recognition based (IRB) positioning has already been well investigated in the past and represents a good technology for navigation in GNSS denied environment, like indoor or urban canyon, where GNSS accuracy is poor (tens of meters accuracy). However, for practical exploitation of IRB positioning with smartphones the following main problems must be taken into account. The first one is the optimization of the battery, that implies a proper use of the frame rate. A second main issue is represented by latencies due to image processing algorithms and visual search solutions that may require a cloud architecture to manage the size of the database. To overcome the above problems in IRB, reduction of the frame rate and latencies compensation, inertial platform built with MEMS technology may be exploited. Two different approaches are taken into account for IRB positioning: the first one is represented by a real-time solution obtainable through single images; the second one is achieved from a commercial software that locates all the frames (not suitable for real time applications). The paper presents a methodology that fuses IRB with MEMS measurements. Results have shown that with single IRB fixes fused together with inertial navigation the standard errors with the 95th percentile are about 1.66 m, 2.36 m and 3.16 m if the interval between two IRB localizations are 1, 2 and 5 sec respectively, while these errors decrease up to 0.64 m, 1.79 m and 2.05 m if the commercial hybrid absolute and relative orientation solution is considered. We can affirm that the weakness in single photograms positioning approach resides in poor orientation estimation of photograms that can grow up to some tens of degrees when poor geometry is picked in the camera scene. With this study we have demonstrate that the hybrid IRB positioning technique coupled with an INS instrument is useful for indoor navigation because errors are less than 2 m and 1 m, with intervals of about 2 s and 1 s between two images, respectively.

UAV-based antenna and field measurements

This paper overviews the emerging antenna and EM field measurement strategies based on the modern Unmanned Aerial Vehicle (UAV) technology. UAVs are currently being exploited as source/probe antenna positioners in various applications from HF to microwaves. Several contributions from all-over the world will be discussed in terms of measurement approach, RF setup and positioning strategies. A measurement example at 350 MHz highlights the importance of position and orientation accuracy in the post-processing chain.

Accurate Positioning and Orientation Estimation in Urban Environment Based on 3D Models

This paper describes a positioning algorithm for mobile phones based on image recognition. The use of image recognition based (IRB) positioning in mobile applications is characterized by the availability of a single camera for estimate the camera position and orientation. A prior knowledge of 3D environment is needed in the form of a database of images with associated spatial information that can be built projecting the 3D model on a set of synthetic solid images (range + RGB images). The IRB procedure proposed by the authors can be divided in two steps: the selection from the database of the most similar image to the query image used to locate the camera and the estimation of the position and orientation of the camera based on available 3D data on the reference image. The MPEG standard Compact Descriptors for Visual Search (CDVS) has been used to reduce hugely the processing time. Some practical results of the location methodology in outdoor environment have been described in terms of processing time and accuracy of position and attitude.

Recent results in antenna pattern measurement with UAVs

A novel antenna measurement strategy has been developed to characterize both the embedded-element and the array patterns in the real installation conditions at low frequencies (50 MHz - 650 MHz) [1]. It exploits a micro Unmanned Aerial Vehicle (UAV) as a far-field test source. The system demonstrated good performance on the copolarization radiation pattern of VHF and UHF antennas. Several results with reference antennas have been published [2, 3]. Further experiments have been performed on the Aperture Array Verification System (AAVS0) array and the Medicina Array Demonstrator (MAD), which also focus on the calibration of a small array and the beam forming. This paper presents two recent experiments performed on a log-periodic antenna at 250 MHz and 350 MHz. Significant results have been achieved for both co- and cross-polarization patterns. Moreover, the symmetry of the test-source pattern has also been demonstrated.

The UAV-based test source as an end-to-end verification tool for aperture arrays

A UAV-mounted radio-frequency transmitter is proposed as a known reference field source to perform a set of functional tests on aperture arrays. The experimental results obtained on complete prototypes (end-to-end) and sub-assemblies provide good confidence on both amplitude and timing verification.