Intra-Annual Map of the State of Vegetation

The Intra-Annual Maps of the State of Vegetation (MIAEV) are a set of products of the Soil Occupation Monitoring System (SMOS), an innovative initiative, designed and developed by the Directorate-General of the Territory, with the objective of continuously producing cartographic information on land use and occupation. SMOS uses the latest developments in space technologies and Artificial Intelligence to create products with more detail, quality, speed and made available with open data policy. All products can be viewed in vismos. (https://smos.dgterritorio.gov.pt/vi-smos). The MIAEVs are the result of DGT’s research and development activities, and users are encouraged to report to [email protected] a critical analysis of the use of maps. MIAEV are raster products with 10 meters pixels and a monthly production frequency that characterise the vegetative vigor of vegetation through quantitative indicators calculated based on Sentinel-2 satellite images. These indicators are based on the standardised vegetation index (NDVI) that is associated with vegetation greenness. NDVI is the difference between the reflectance of light in the near-infrared (IVP) and red (V) regions, normalised by the sum of the same reflectances. In other words, the NDVI formula is as follows: (IVP-V)/(IVP+V). In Sentinel-2 satellites these reflectances are recorded in bands 8 and 4. The NDVI formula results in an index ranging from -1 to 1. The higher the NDVI, the higher the vigor of the vegetation. MIAEVs are made available in the following month to which they relate and DGT started production in May 2022. The MIAEV limits coincide with the COSC limits, and within these limits a mask is applied that removes less vegetation-relevant zones. The mask applied is produced with some thematic classes of the Land Use and Occupation Charter (COS) of 2018. These classes, in level 1 of the COS nomenclature, are: Artificialised territories, Spaces discovered or with little vegetation (except sparse plantation class of level 4), Wetlands, and Masses of surface water. Masks are applied to all MIAEVs except Vegetation Verse (VV). Each MIAEV uses NDVI for the production of quantitative indicators of the state of vegetation in absolute terms or compared to a reference period beginning in October 2016. The aim of the MIAEV is to periodically characterise the vegetative vigor of vegetation in the territory of mainland Portugal, namely vegetation in agricultural, forestry and bush areas. Updated monthly, the MIAEV aim to monitor the evolution of vegetation over time, allowing to monitor the phenological cycle of vegetation, including crop development states and agricultural practices, detect vegetation loss events due to fires or shallow cuts, monitor the recovery of vegetation post-disturbation, and compare inter-annual variations in the state of vegetation that may result from weather and climatic factors. The MIAEVs are as follows: Vegetable Vegetation (VV) — Characterises the current (monthly) vigor of the vegetation. NDVI is calculated from a mosaic composed of Sentinel-2 images with 10 m pixels, which is created from the median of several images from different dates of the same month. NDVI, which ranges from -1 to 1, is multiplied by 100 and all negative values are reclassified to zero. Thus, VV varies between 0 and 100. VV homologous percentile (PHVV) — Compares the current (monthly) vigor of vegetation with the same historical period. The current NDVI is calculated from the same mosaic used in Vegetation Vegetation (VV). The same historical period corresponds to the monthly Sentinel-2 mosaics obtained in the same month as previous years since October 2016. For example, PHVV from May 2022 uses the months from May 2017 to 2021 as a historical period. Comparing the current NDVI with historical values allows you to determine the percentile of the new value. Being a percentile, this MIAEV ranges from 0 to 100 and its interpretation is made like any percentile. For example, if the current NDVI is at the 75th percentile, it means that 75 % of historical values are lower than the current value, and only 25 % are higher. Monthly VV Difference (DMVV) — Difference between the vigor of the current vegetation (most recent) and the previous month (most recent value of that month). Unlike previous MIAEVs, NDVI is not calculated from the mosaics composed of Sentinel-2 images. In this MIAEV, the NDVI is calculated with the most recent date within the months (current and previous). If during the current month there is no Sentinel-2 observation (due to clouds), this MIAEV leaves the pixels empty (no data). If during the previous month there is no Sentinel-2 observation (due to clouds), the most recent NDVI of older months is used. For example, the DMVV of May 2022 uses the most recent NDVI value of that month and April to calculate the difference. If there are no NDVI values in April (due to clouds), the most recent NDVI of the previous month (March) is used and so on. Before calculating the difference, NDVI is multiplied by 100 and all negative values are reclassified to zero. Thus, the DMVV values range from -100 to 100. If you are not familiar with the provision of spatial data through visualisation services (e.g., WMS) and download can be found in the Support Guides on the open data page of DGT (https://www.dgterritorio.gov.pt/dados-abertos).