|AGREST – AGRiculture at ESTarreja region: a satellite screening over the past four decades|
Observatoire Hommes-Millieux International (OHMI)
2019-11-01 - 2020-10-30 (12)
CNRS/INEE - Centre National de la Recherche Scientifique/Institut Ecologie et Environnement - through the OHMI - International Observatory Hommes-Milieux
Universidade de Aveiro
Agriculture has a major role in the ecosystem dynamics and is still a key sector for the local economy in many regions of Portugal. The ecosystems and consequently agriculture at Estarreja region have been suffering several pressures over the past decades. The impacts from a strong heritage related with released untreated effluents from industrial activity before the nineties may still be recorded and potentiated by weather conditions. This area is also under the permanent threat of increasing flooding and saline intrusion, due to high sea levels induced by changes in the Ria de Aveiro hydrodynamics. These pressures influenced negatively the agricultural activities leading to the abandonment of agricultural fields. Under a climate change scenario, with mean sea level rise and intensification of extreme weather events that can change fluvial discharges, significant impacts on crops can occur, affecting the local agriculture-based economy. Therefore, it is important to study how the use of soil for agriculture has evolved over the past decades and how agriculture fields are being affected either by pollution, droughts, river floods and saltwater intrusion induced by sea level rise in order to predict future scenarios.
Earth Observation (EO) based on satellite imagery is an important source of information for monitoring land cover dynamics allowing to obtain long-term observations in extensive areas. Multispectral sensors aboard satellites, such as Landsat, have delivered the longest temporal record (over 35 years) for land observation of moderate spatial resolution, providing valuable data to monitor land surface dynamics over time and space. Multiple products with different objectives can be derived from remote sensing imagery, especially from multispectral sensors. Vegetation indices (VIs) are one of the most popular and extensively products used to monitor land surface dynamics by using transformations of spectral bands that are measured as reflectance from the Earth's surface. Most of the VIs use the inverse relationship between red and near-infrared land reflectance associated with healthy green vegetation allowing to monitor fluctuation in vegetation at the Earth’s surface. Measurements of vegetation attributes can contribute, for example, to examine climate trends, monitor drought, schedule crop irrigation and management, monitor evaporation and plant transpiration, assess changes in biodiversity and classify vegetation. On the other hand, it is advisable to use the green and NIR spectral bands in order to study and map water level changes (e.g. flooding).