Sara Freitas

Ms. Sara Freitas


Research Focus & Metrics

Academic Career Length

11Years (2016-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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29 June 2021 in Remote Sensing
Verified
Journal Article
Open access
PDF file
SFSara Freitas
Sara Freitas
HSHugo Silva
Hugo Silva
ESEduardo Silva
Eduardo Silva
This paper addresses the development of a remote hyperspectral imaging system for detection and characterization of marine litter concentrations in an oceanic environment. The work performed in this paper is the following: (i) an in-situ characterization was conducted in an outdoor laboratory environment with the hyperspectral imaging system to obtain the spatial and spectral response of a batch of marine litter samples; (ii) a real dataset hyperspectral image acquisition was performed using manned and unmanned aerial platforms, of artificial targets composed of the material analyzed in the laboratory; (iii) comparison of the results (spatial and spectral response) obtained in laboratory conditions with the remote observation data acquired during the dataset flights; (iv) implementation of two different supervised machine learning methods, namely Random Forest (RF) and Support Vector Machines (SVM), for marine litter artificial target detection based on previous training. Obtained results show a marine litter automated detection capability with a 70–80% precision rate of detection in all three targets, compared to ground-truth pixels, as well as recall rates over 50%.

2 November 2022 in Remote Sensing
Verified
Journal Article
Open access
PDF file
SFSara Freitas
Sara Freitas
HSHugo Silva
Hugo Silva
ESEduardo Silva
Eduardo Silva
This paper addresses the development of a novel zero-shot learning method for remote marine litter hyperspectral imaging data classification. The work consisted of using an airborne acquired marine litter hyperspectral imaging dataset that contains data about different plastic targets and other materials and assessing the viability of detecting and classifying plastic materials without knowing their exact spectral response in an unsupervised manner. The classification of the marine litter samples was divided into known and unknown classes, i.e., classes that were hidden from the dataset during the training phase. The obtained results show a marine litter automated detection for all the classes, including (in the worst case of an unknown class) a precision rate over 56% and an overall accuracy of 98.71%.

1 May 2019 in International Journal of Advanced Robotic Systems
Verified
Journal Article
Open access
PDF file
SFSara Freitas
Sara Freitas
HSHugo Silva
Hugo Silva
JAJosé Miguel Almeida
José Miguel Almeida
ESEduardo Silva
Eduardo Silva
This work addresses a hyperspectral imaging system for maritime surveillance using unmanned aerial vehicles. The objective was to detect the presence of vessels using purely spatial and spectral hyperspectral information. To accomplish this objective, we implemented a novel 3-D convolutional neural network approach and compared against two implementations of other state-of-the-art methods: spectral angle mapper and hyperspectral derivative anomaly detection. The hyperspectral imaging system was developed during the SUNNY project, and the methods were tested using data collected during the project final demonstration, in São Jacinto Air Force Base, Aveiro (Portugal). The obtained results show that a 3-D CNN is able to improve the recall value, depending on the class, by an interval between 27% minimum, to a maximum of over 40%, when compared to spectral angle mapper and hyperspectral derivative anomaly detection approaches. Proving that 3-D CNN deep learning techniques that combine spectral and spatial information can be used to improve the detection of targets classification accuracy in hyperspectral imaging unmanned aerial vehicles maritime surveillance applications.

16 October 2017 in Journal of Intelligent & Robotic Systems
Verified
Journal Article
Open access
PDF file
SFSara Freitas
Sara Freitas
HSHugo Silva
Hugo Silva
JAJosé Almeida
José Almeida
ESEduardo Silva
Eduardo Silva
This work address hyperspectral imaging systems use for maritime target detection using unmanned aerial vehicles. Specifically, by working in the creation of a hyperspectral real-time data processing system pipeline. We develop a boresight calibration method that allows to calibrate the position of the navigation sensor related to the camera imaging sensor, and improve substantially the accuracy of the target geo-reference. We also develop an unsupervised method for segmenting targets (boats) from their dominant background in real-time. We evaluated the performance of our proposed system for target detection in real-time with UAV flight data and present detection results comparing favorably our approach against other state-of- the-art method.

1 June 2017
Verified
Conference Paper
Closed access
GAGuilherme Amaral
Guilherme Amaral
HSHugo Silva
Hugo Silva
FLFlavio Lopes
Flavio Lopes
JRJoao Pedro Ribeiro
Joao Pedro Ribeiro
SFSara Freitas
Sara Freitas
ESEduardo Silva
Eduardo Silva
This paper addresses the topic of target detection and tracking using a team of UAVs for maritime border surveillance. We present a novel method on how to integrate the perception into the control loop using two distinct teams of UAVs that are cooperatively tracking the same target. We demonstrate and evaluate the effectiveness of our approach in a simulation environment.

1 December 2016
Verified
Conference Paper
Open access
HSHugo Silva
Hugo Silva
JAJosé Almeida
José Almeida
FLFlavio Lopes
Flavio Lopes
JRJ.P. Ribeiro
J.P. Ribeiro
SFSara Freitas
Sara Freitas
ESEduardo Silva
Eduardo Silva
This paper addresses the use of heterogeneous sensors for target detection and recognition in maritime environment. An Unmanned Aerial Vehicle payload was assembled using hyperspectral, infrared, electro-optical, AIS and INS information to collect synchronized sensor data with vessel ground-truth position for conducting air and sea trials. The data collected is used to develop automated robust methods for detect and recognize vessels based on their exogenous physical characteristics and their behaviour across time. Data Processing preliminary results are also presented.