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16 octobre 2019

Master thesis (6 month) / Stage de fin d'études (6 mois)

Catégorie : Stagiaire

Imputation of cloudy pixels in Satellite Image Time Series (Stage de fin d'études/Master thesis)


Imputation of cloudy pixels in Satellite Image Time Series

Keywords: Satellite Image Time Series, missing data, Generative Adversarial Networks

On March 7 2017, the European Space Agency (ESA) successfully put its latest high-resolution satellite Sentinel-2B into orbit. The two Sentinel-2 satellites are now capturing pictures of all emerged surfaces every 5 days at high spatial and spectral resolution, which makes it possible to monitor the evolution of the vegetation [1]. Such land surface monitoring is a key input for the prediction of climate trends and the management of territories.

However, satellite image time series (SITS) are contaminated by poor atmospheric conditions, especially the presence of clouds. These aff ect SITS usage in many application including image classi cation, object detection, or image interpretation. Although different reconstruction techniques, known as gapfi lling methods, have been proposed [2], most of the methods focuses on single image or on medium spatial resolution images. As few takes benefi t from the high spatial and temporal resolutions of Sentinel-2 data, new scalable gapfi lling techniques are needed to accurately unveil pixel values below the clouds.

The internship will focus on the proposition of a deep generative model to reconstruct missing values in series of satellite images. Recently, adaptations of the popular Generative Adversarial Network (GAN) [3] have been proposed to impute missing values in images and time series with same distributions than the valid original data. In particular, Generative Adversarial Imputation Network (GAIN) [4] is composed of two networks trained concurrently:
1. a generator, that is in charge to generate the missing values,
2. a discriminator, that should discriminate imputed values from original values.

Hence, the goal of the internship would be to propose and evaluate generator and discriminator networks, that takes into account the spatial and temporal dimensions of SITS, e.g. 3D-CNN or ConvLSTM. Experiments would be carried out on recent Sentinel-2 image
time series.

Required or appreciated skills: strong programming skills, familiar with deep learning techniques, good communication skills, and keen to learn about time series and satellite data analysis.

[1] Inglada, J., Vincent, A., Arias, M., Tardy, B., Morin, D., & Rodes, I. (2017). Operational high resolution land cover map production at the country scale using satellite image time series. Remote Sensing, 9(1), 95.
[2] Shen, H., Li, X., Cheng, Q., Zeng, C., Yang, G., Li, H., & Zhang, L. (2015). Missing information reconstruction of remote sensing data: A technical review. IEEE Geoscience and Remote Sensing Magazine, 3(3), 61-85.
[3] Goodfellow, I., Pouget-Abadie, J., Mirza, M., Xu, B., Warde-Farley, D., Ozair, S., & Bengio, Y. (2014). Generative adversarial nets. In Advances in neural information processing systems (pp. 2672-2680).
[4] Yoon, J., Jordon, J., & Van Der Schaar, M. (2018). GAIN: Missing data imputation using generative adversarial nets. International Conference on Machine Learning (pp. 5675-5684).

Supervisors : Charlotte Pelletier (Univ. Bretagne Sud/IRISA) & Romain Tavenard (Univ. Rennes 2/LETG)
Contact: Charlotte Pelletier: charlotte.pelletier@univ-ubs.fr
Universite Bretagne Sud, UMR IRISA,
Campus Tohannic, 56000 Vannes, France


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