GET TO KNOW MAPBIOMAS ALERTA METHOD

MapBiomas Alerta is a system that compiles alerts from different deforestation detection systems in Brazil, all based on remote sensing. The processing of this set of alerts involves the aggregation, validation, and refinement of spatial boundaries based on the use of high-resolution satellite imagery (Planet Scope with 3.7 m spatial resolution), generating reports, and publishing the final results on a single, open-access platform (https://plataforma.bolivia.alerta.mapbiomas.org/).

This section provides a simplified explanation of the MapBiomas Alerta processing methodology. It also highlights some limitations of the method and differences compared to official annual deforestation data.

DESCRIPTION OF THE STEPS

The MapBiomas Alerta process encompasses the following steps: compilation, validation, refinement, cross-referencing with public data, auditing, and publication of deforestation alerts and reports (Figure 1).

Figure 1. MapBiomas Alerta's methodological process for compiling, validating, refining, cross-referencing data, auditing, and publishing deforestation alerts in Brazil.

Step 1: Compilation of alerts from existing systems for all Brazilian biomes.

MapBiomas Alerta gathers, organizes, and consolidates deforestation information from various official and independent monitoring systems in Brazil. These systems utilize satellite imagery with resolutions ranging from 10 meters to 60 meters to generate deforestation alerts (Table 1). In 2023, MapBiomas Alerta consulted alerts provided by the following sources and systems on a monthly basis:

Table 1: Deforestation Detection Systems and Sources Used in Brazilian Biomes by MapBiomas Alerta

Name	Fountain	Biomas	Link
GLAD-RADD	Maryland University	Amazon, Chiquitano, Chaco, Pantanal, Bolivian Tucumano, Valleys, and Andes	https://glad.umd.edu/
FAN	Friends of Nature Foundation	Amazon, Chiquitano, Chaco, Pantanal, Bolivian Tucumano, Valleys, and Andes	https://www.fan-bo.org/

Step 2: Validation and selection of before and after images

The validation process occurs in two stages. The first stage is automated, eliminating all deforestation alerts that have already been validated, refined, and published in previous surveys. The second stage is carried out through visual inspection by trained analysts organized into teams by biome, supported by monthly mosaics of high-resolution images from the Planet satellite constellation (with 3.7-meter resolution). At this stage, alerts that correspond to false positives may also be discarded, with the reason for rejection duly recorded (e.g., forestry, agriculture, seasonality). Only when the visual inspection confirms the deforestation event is the alert considered valid. From that point, two satellite images are selected and acquired with project resources: one image showing the native vegetation before deforestation and another showing the area after it has been cleared. Image acquisition considers a minimum area of 700 by 700 meters, covering both the deforested area and its surroundings to help contextualize the deforestation event.

Step 3: Validation and refinement in high-resolution images

After confirming the deforestation associated with each alert and selecting the pair of high-resolution images, it is necessary to refine the spatial boundaries of the effectively deforested area. This refinement is done through an automated classification process that ensures greater precision in defining the contours of the area where native vegetation has been cleared. The generation of the refined polygon is done using a supervised classification algorithm (Random Forest), which is processed in the Google Earth Engine platform through the Workspace, an application developed by MapBiomas for processing. The classification is performed by collecting training samples from the high-resolution images, both to represent the deforested area and the adjacent non-deforested areas. The final classification results in a refined polygon that undergoes a simplification process to remove excess vertices (Figure 2). Based on the before and after images of deforestation, the interpreter also identifies and records the pressure vector that may have caused the deforestation event (mining, prospecting, urban expansion, agriculture, natural causes, or others).

Figure 2. Example of Planet images before and after deforestation, along with the refined alert polygon (ID 1232983 from 2024).

Step 4: Cross-referencing with public territorial databases

The refined polygons are spatially overlaid with spatial land and surveillance information, including boundaries of Indigenous Lands (ITs), Conservation Units (UCs), quilombola territories, rural settlements, areas registered in the Rural Environmental Registry (CAR) - including declared Areas of Permanent Preservation (APPs) and Legal Reserve (RL) - in addition to areas embargoed by the environmental agency, suppression authorizations and forest management plans from IBAMA's Sinaflor. The alerts are also linked to geographical boundaries such as municipalities, states, biomes, and watersheds. Crossings with special territories are also considered, such as Legal Amazon, area of application of the Atlantic Forest Law, MATOPIBA, AMACRO, Biosphere Reserves, and others. These crossings qualify the alerts and allow the generation of technical reports based on information that is relevant to the user institutions.

Step 5: Auditing

Each refined polygon goes through an audit process done by the technical supervisor of each biome. At this stage, the eventual need to redo some adjustments is evaluated before the final publication of the confirmed deforestation.

Step 6: Publication

All confirmed deforestation polygons are published on the MapBiomas Alert Platform, with weekly updates. Reports are available for each confirmed deforestation and for each intersection of an alert with a property registered in the CAR, SIGEF and SNCI (with an area larger than 0.1 ha). The reports contain the following information:

• Deforestation alert code;
• Deforestation area;
• Original source of the alert (detection system);
• Department, Municipality, and Ecoregion;
• Image and date from before the deforestation;
• Image and date from after the deforestation;
• Overlay of deforestation with: departments, municipalities, biomes, ecoregions, national protected areas, subnational protected areas, indigenous territories, Ramsar sites, land-clearing plans, and forestry concessions;
• MapBiomas Bolivia Land Cover and Land Use History for the evaluated area.
• Landsat imagery history for the evaluated area.
• Data sources used in the spatial overlay.

Post-Publication Alert Cancellation and Correction

Under certain circumstances, alerts published on the MapBiomas Alerta Platform may be corrected or even canceled. Whenever there is a formal indication or a well-founded request pointing to possible errors associated with the alerts, whether from environmental agencies or platform users, the technical team carries out a new thorough analysis of these alerts.

This analysis is carried out by reviewing Planet images and, when necessary, various complementary sources such as images from other satellites (Sentinel, Landsat, etc.), high-resolution satellite imagery available on Google Earth, and the MapBiomas Land Use and Land Cover Mapping. In cases where it is confirmed that the published alert does not correspond to an actual deforestation event or native vegetation conversion (regardless of timber extraction, legality, or responsibility), the alert is canceled. This means it is removed from the map and from the platform's statistics but remains in the database for individual consultation through its unique identifier code.

In some cases, spatial delimitation rectifications of the alert may be carried out, always with the aim of better representing the deforestation event in question (Figure 3). Similarly, if any error or problem is related to the images linked to the alert polygon, new images can be selected and updated on the platform. All rectifications are recorded in the system and the information is made available publicly on the platform, including the date on which the alert was rectified.

Figure 3. Example of rectification of spatial boundaries of the alert after publication for alert Code 564078, detected in the year 2022.

The MapBiomas Alerta platform does not analyze or determine the legality or regularity of the deforestation alerts it presents. The platform's primary function is to detect and confirm the loss of native vegetation, regardless of legal or regulatory considerations.

LIMITATIONS OF THE METHOD

As every method, MapBiomas Alerta has some limitations that must be considered when applying its data:

1. Processing time - the importation of alerts from their sources (detection systems) occurs monthly, with the exception of DETER alerts, which occur every 15 days. As part of the alerts processing is done individually and visually by trained analysts, the validation and processing time depends on the biome and the time of year. It can vary from 30 to 90 days from the date of detection by the source system to publication on the MapBiomas Alerta platform. The purpose of MapBiomas Alerta is to increase certainty about confirmed deforestation data and provide ready reports for remote surveillance. Rapid field surveillance operations aimed at flagrant deforestation can be planned directly with the pre-existing detection systems.
2. Alert Omissions – deforestation are validated and refined based on the existence of an alert previously captured by a third-party deforestation detection system. The possible omissions of these systems in detecting deforestation also affect the alerts evaluated by MapBiomas Alerta.

To avoid omissions, MapBiomas supported the development of Deforestation Alert Systems (SAD) tailored to each Brazilian biome by various universities, research institutions, and civil society organizations. Based on the "SAD" methodology, the system was replicated in Bolivia and adapted to the context of our forests and biomes; subsequently, the alerts were renamed FAN.

It is also worth noting that deforestation monitoring systems have minimum detection thresholds and may therefore miss some instances of deforestation. For example, alerts covering less than 0.3 hectares are not detected by both sources (GLAD/RADD, FAN). Using multiple data sources for the same region aims to reduce omissions in deforestation detection.

3. Deforestation Speed Underestimated – when validating and refining an alert, a search is performed for a pair of good quality Planet satellite images of before and after deforestation. The "before" image is the most recent available in the period up to 12 months before detection, and the "after" image is the one closest to the end of deforestation. The presence of clouds can increase the period between before and after images by days, weeks, and even months. This does not change the statement that deforestation occurred in the period between the two images, but it does affect the calculation of the average speed at which deforestation actually occurred.
4. Automatic Polygon Delimitation – polygons delimiting the refined alerts are established by a process of automatic classification of the area of change between the two images, i.e., the place where the native vegetation was suppressed. In delimiting the deforestation polygon, areas with signs of previous change or with small clusters of trees that were maintained in the midst of deforestation are removed. In 2020, a procedure was developed to minimize the small islands within the polygons in the refinement step, as well as the excess of vertices *which correspond to the points that form the polygons).