April/24 Report
DEFORESTATION MONITORING TECHNICAL REPORT
Last updated
DEFORESTATION MONITORING TECHNICAL REPORT
Last updated
The study area comprises the "Fazenda Floresta Amazônica" located in the municipality of Apuí-AM (Figure 1). According to the IBGE vegetation classification (2021), the area of the farm falls into two types of vegetation: Open Ombrophilous Forest (FOA) and Dense Ombrophilous Forest (FOD).
Área de estudo = Study area
Brasil = Brazil
This technical report employs vegetation cover monitoring using NDVI to track potential changes in vegetation within the area known as "Fazenda Floresta Amazônica," as well as to detect possible degraded and deforested areas. Additionally, using deforestation alert images from INPE and Imazon databases, deforestation alerts were monitored from April 1 to April 30, 2024, both within the farm area and its surroundings.
In remote sensing, monitoring changes in vegetation cover at regional and global scales commonly employs the Normalized Difference Vegetation Index (NDVI) (Shi et al., 2021; Wu et al., 2020). NDVI is an important indicator that reflects the state of vegetation, which is influenced by precipitation, anthropogenic activities, temperature, and soil moisture.
For the creation of the NDVI map for the periods from April 1 to April 15 and from April 16 to April 30, Sentinel L2A satellite images were used. On April 1, satisfactory conditions for the NDVI map were observed, with 35% cloud cover. Additionally, the image from April 26 was utilized, showing 30% cloud cover.
Following the usual procedure, NDVI was obtained through the application of the algorithm based on the difference between near-infrared reflectance and red reflectance divided by the sum of these spectral bands (1), where NIR is the near-infrared electromagnetic spectrum and R is the red electromagnetic spectrum, varying between -1 and 1 (ROUSE et al., 1974), according to the equation:
Landsat 9
04/01/24
2024
B8-B4
Landsat 9
04/26/24
2024
B8-B4
Table 1. Specifications of the satellite image used for NDVI calculation
Additionally, a Soil Adjusted Vegetation Index (SAVI) map was developed to assess and confirm that there is no deforestation occurring within the study area. The Soil Adjusted Vegetation Index (SAVI) is a variation of the Normalized Difference Vegetation Index (NDVI) that takes into account the influence of soil on the spectral response of plants. It is used to estimate vegetation density and vigor by correcting soil effects present in satellite images.
The same images from NDVI captured on April 26th were used. The formula for SAVI is as follows:
Where: NIR is the reflectance value in the near-infrared band; RED is the reflectance value in the red band; and L is the soil adjustment factor, which ranges from -1 to 1 (typically set to 0.5).
The inclusion of the soil adjustment factor (L) in the formula allows compensating the influence of soil reflectance, especially in areas with sparse vegetation or exposed soil. The value of L is typically set to 0.5, but it can vary depending on the characteristics of the vegetation and soil in the study area.
To provide a more comprehensive understanding of the indexes used in the study area, a Normalized Burn Ratio (NBR) map was also created in QGIS. This index is widely used to detect areas affected by fires (Key and Benson, 1999), deforestation, or damaged vegetation. It utilizes the near-infrared (NIR) and mid-infrared (MIR) bands from satellite images to map the extent and severity of burns. Landsat 9 satellite images, specifically bands 5 and 7 dated from April 29th, 2024, were used (available at https://earthexplorer.usgs.gov/).
The formula for NBR is as follows:
Where: NIR is the reflectance value in the near-infrared band, and MIR is the reflectance value in the midinfrared band.
The Normalized Burn Ratio (NBR) varies on a scale of values depending on the methodology and scale used. However, a common convention is for NBR to range from -1 to 1. Negative values of NBR (-1 to 0) typically indicate areas affected by recent fires, deforestation, or damaged vegetation. Values closer to -1 indicate higher severity of the burn or vegetation damage. Positive values of NBR (0 to 1) are often associated with areas of healthy vegetation. Values closer to 1 indicate greater vegetation vigor.
To assess deforestation expansion around the farm "Fazenda Floresta Amazônica" area, a radius of 50 km was determined. Databases from deforestation alerts provided by INPE and Imazon were utilized. The data obtained for February were in shapefile format, and all processing and filtering of alert points within the radius were conducted using QGIS software.
The Imazon Deforestation Alert System (SAD) currently employs NASA's Landsat 7 and 8 satellites, as well as ESA's Sentinel 1A, 1B, 2A, and 2B satellites. SAD detects forest degradation or deforestation events that occur in areas larger than 1 hectare.
INPE utilizes imagery from the WFI sensor on the CBERS-4 satellite and the AWiFS sensor on the Indian Remote Sensing Satellite (IRS), which have spatial resolutions of 64 and 56 meters, respectively.
The data is sent daily to the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA) without a minimum mapped area restriction. However, for the general public, polygons are made available with a minimum size of 6.25 hectares, allowing for comparison with data generated by the PRODES project.
The identification of forest cover change patterns is conducted through visual interpretation based on five main elements (color, tone, texture, shape, and context), using the Spectral Mixture Analysis (SMA) technique along with multispectral imagery in color composition to map the following classes:
Deforestation with exposed soil and deforestation with vegetation and mining;
Degradation, forest fire scar;
Selective Logging Type 1 (Disordered)
Selective Logging Type 2 (Geometric).
The analysis of the spatial-temporal distribution of the Normalized Difference Vegetation Index (NDVI), obtained from Sentinel-L2A images dated April 1, revealed a wide range of values, spanning from -0.49 to 0.89. These data provide significant insight into the vegetation cover in the studied region. Lower NDVI values, ranging from -0.03 to 0.2, generally correspond to water bodies, such as rivers, and small areas devoid of vegetation along the banks of these water bodies. This distinction occurs due to the presence of water, which lowers NDVI values, as well as the openness of the forest canopy in these areas. On the other hand, values ranging from 0.3 to 0.89 are associated with dense and healthy forest areas. This higher range of NDVI indicates robust vegetation, reflecting the density and health of the forest canopy in these specific areas.
Upon examining the NDVI images dated April 26 (as illustrated in Figure 3), it was found that the values were consistent with those recorded on March 7, ranging from -0.86 to 0.92. The consistency of these patterns over time strengthens the understanding of the stability and vitality of the vegetation cover in the analyzed region.
When examining the Soil-Adjusted Vegetation Index (SAVI), a variation in values from -0.16 to 0.68 was identified. These results reinforce the conclusion that there is no evidence of deforestation or significant human activities in the study area. Values in the range of -0.16 to 0.3 can be associated with water bodies, such as rivers, and exposed areas along the riverbanks. Conversely, values above 0.35 indicate areas covered by dense forests in good preservation condition.
Regarding the normalized burn ratio index, variability was observed in the mapped values, ranging from 0.02 to 0.55. It is important to note that no negative values were identified, suggesting the absence of deforestation or burning in the area in question. This finding reinforces the indication of environmental stability in the region, pointing to the preservation of natural conditions.
Values of the index above 0.3 indicate the presence of dense vegetation. This consistency suggests the absence of evidence of deforestation or significant burning events within the study area during this period.
During the month of April, a deforestation alert point was identified within a 50 km radius of the farm. This alert was detected approximately 42 km from the farm, as indicated in Figure 6. The point is precisely located at UTM coordinates 774861.46 m E, 9161636.34 m S, and covers a deforested area of 38.5 hectares. It is observed that this deforestation point is close to other deforested locations from previous months.
There is no indication of deforestation and/or forest degradation within the farm based on the NDVI, SAVI, and NBR maps for the month of April.
The deforestation alert for April indicates a decrease compared to the previous month (10 points).
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Botucatu (SP), May 13th, 2024.
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