agronomy Article Assessment of the SASI Spectral Shape Index Time Series for Mapping Rice Ecosystems in the Mediterranean Region Lucía Tornos 1 , José Antonio Domínguez 2 , Maria C. Moyano 3 , Laura Recuero 3,4 ,Víctor Cicuéndez 3 , María Jesús García-García 1 and Alicia Palacios-Orueta 1,4, *   Citation: Tornos, L.; Domínguez, J.A.; Moyano, M.C.; Recuero, L.; Cicuéndez, V.; García-García, M.J.; Palacios-Orueta, A. Assessment of the SASI Spectral Shape Index Time Series for Mapping Rice Ecosystems in the Mediterranean Region. Agronomy 2021, 11, 1365. https:// doi.org/10.3390/agronomy11071365 Academic Editors: Jitka Kumhálová, Jan Lukáš, Pavel Hamouz and Jose Antonio Dominguez-Gómez Received: 18 May 2021 Accepted: 30 June 2021 Published: 5 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Forestal y del Medio Natural, E.T.S.I. Montes, Universidad Politécnica de Madrid, C/Jose Antonio Novais, n ◦ 10, 28040 Madrid, Spain; luciatornos@gmail.com (L.T.); mariajesus.garcia.garcia@upm.es (M.J.G.-G.) 2 GIS and Remote Sensing Lab, Institute of Agri-Food Research and Development (IMIDA), C/Mayor s/n, La Alberca, 30150 Murcia, Spain; josea.dominguez@carm.es 3 Alimentaria y de Biosistemas, E.T.S.I. Agronómica, Universidad Politécnica de Madrid, Av. Puerta de Hierro, n ◦ 2, 28040 Madrid, Spain; mcarmen.moyano@gmail.com (M.C.M.); laura.recuero@upm.es (L.R.); victorcicuendezlopocana@gmail.com (V.C.) 4 Centro de Estudios e Investigación para la Gestión de Riesgos Agrarios y Medioambientales (CEIGRAM), Universidad Politécnica de Madrid, Paseo de la Senda del Rey, n ◦ 13, 28040 Madrid, Spain * Correspondence: alicia.palacios@upm.es Abstract: There is a growing need to map rice ecosystems and to develop methods for monitoring rice distribution in order to account for rapid land use changes worldwide. In this study, we evaluated a methodology based on Vegetation Indices time series derived from an 8-day MODIS composite to identify rice fields and develop rice maps that can be timely updated in the long term. We have assessed the potential of the Spectral Shape Index time series and compared its performance with the Normalized Difference Vegetation Index in two coastal locations and in an inland location in the Mediterranean Region for 2012. A profile similarity comparison method, the Spectral Angle Mapper, was accomplished between the reference rice annual profile and the annual profiles of both indices in a pixel basis in order to determine rice pixels. The resultant maps were validated with rice masks, where available, or ortophotos and crop surface statistics where not. The results obtained demonstrated the potential of both indices to provide accurate rice maps when applied together with spectral matching techniques. The overall accuracy was 92.8%, 98.1% and 90.1% for the Spectral Shape Index and 92.4%, 77.24% and 82.8% for the Normalized Difference Vegetation Index in each location. The excellent performance of the Spectral Shape Index in the three locations highlighted the importance of exploring angular indices to improve the identification of land cover dynamics. Keywords: spectral index; rice mapping; time series; NDVI; SASI; wetland; land cover dynam- ics; MODIS 1. Introduction On the light of recent international developments, such as the Sustainable Develop- ment Goals (SDGs) of the 2030 Agenda and the Paris Agreement, there is a need to monitor and report accurately any spatial variable with strong implications in food security, water usage and climate change. Rice fields are key for food security, providing staple food for almost half of the world’s population [1]. They also have strong implications for natural resource management due to the large quantities of water needed in rice cultivation, having important effects in water demand and quality [2]. In addition, the maintenance of flooded soils constitutes an important source of methane emissions [3]. Thus, counting on reliable information on rice field distribution is crucial to assess the status of food security and environmental sustainability [4] at a regional and global scale. Recently, there have been dramatic changes in rice field distribution as a consequence of agricultural expansion [5–7], urban development and shortage of resources due to Agronomy 2021, 11, 1365. https://doi.org/10.3390/agronomy11071365 https://www.mdpi.com/journal/agronomy