On November 9, the Brazilian government released data eagerly awaited by the Brazilian public and the international community: the 36th official annual deforestation rate in the Legal Amazon, an area of approximately 5 million square kilometers (km²) that corresponds to 58.9% of the country’s national territory. The figures were encouraging.
According to an estimate from the Brazilian Amazon Deforestation Satellite Monitoring Program (PRODES), run by the Brazilian National Institute for Space Research (INPE), the area deforested between August 2022 and July this year was 9,001 km², 22.3% lower than in the previous year. The rate had remained above 10,000 km² per year between 2019 and 2022.
Created in 1988, PRODES is the first and oldest initiative to use satellite imaging to monitor deforestation in the Brazilian Amazon, home to the largest tropical forest on the planet. The data collected by the program, recognized in international agreements and cited in almost 1,600 scientific articles, indicate that around a fifth of the rainforest has been deforested in recent decades.
In 2004, INPE’s Real-Time Deforestation Detection System (DETER) began operating alongside PRODES, issuing daily alerts about parts of the rainforest where vegetation is being lost. These daily notices are intended for environmental agencies, which use the information to counter deforestation.
“Brazil is renowned for its remote sensing, an area in which we do First World work,” says engineer and geoprocessing specialist Gilberto Câmara, who was general director of INPE between 2006 and 2013 and now works as a consultant in the sector. “In the 1970s, Brazil was the third country in the world to use images from the Landsat satellites, after the USA and Canada.”
After PRODES and DETER, projects led by public scientific organizations, such as MapBiomas and the Institute for Humans and the Environment in the Amazon (Imazon), began monitoring the dynamics and progress of deforestation in the Brazilian Amazon via satellite image analysis.
Although they share points in common with INPE’s pioneering initiatives, each pursues slightly different objectives and uses specific methodologies to produce data. They may use different satellites, for example, with different spatial resolutions and revisit times for each point in the Amazon. They may also analyze images automatically, using software alone, or together with the trained eye of a specialist. They all, however, publish some calculation of monthly or annual deforestation in the Amazon (see graph below).
Due to these specificities, the results often do not coincide 100% with the information provided by PRODES and DETER. Experts do not consider these divergences a concern, as long as the general overview portrayed by each initiative points to similar trends, such as an increase or reduction in deforestation.
“The public system for monitoring deforestation in the Amazon is good and reasonably robust,” says physicist Ricardo Galvão, president of the Brazilian National Council for Scientific and Technological Development (CNPq). “Initiatives by civil society are welcome and do very important complementary work.” The country has made an international commitment to eliminate deforestation in the Amazon by 2030.
In August 2019, Galvão was dismissed from his position as INPE director after having publicly defended the accuracy and fairness of the institute’s data on deforestation in the Amazon against unfounded criticism made by then-president Jair Bolsonaro and his ministers.
At the time, the annual deforestation rate calculated by PRODES had exceeded 10,000 km, something that had not occurred since 2008. The federal government questioned the veracity of the number and threatened to hire a private company to do INPE’s work. The incident received international news coverage and the idea of outsourcing the monitoring process did not go ahead.
Having several systems dedicated to observing and calculating the suppression of native vegetation in the Amazon allows official data to be confirmed, refined, or even refuted by the public. If PRODES and DETER ever fail to operate for some reason, there are alternatives available. “These alternative systems can also function as a backup of INPE’s services,” says Imazon remote sensing specialist Carlos Souza Jr.
To help understand the similarities and differences between the systems, Pesquisa FAPESP summarized the main characteristics of five initiatives that monitor deforestation in the Amazon—four Brazilian and one from abroad.
PRODES
Remote sensing specialist Cláudio Almeida, head of INPE’s Monitoring Program for the Amazon and other Biomes, tells an interesting story about the projects that preceded and fostered the expertise needed to set up PRODES. In the 1970s, when official public policies aimed to encourage occupation of the Amazon and the implementation of large agricultural projects, one of the federal government’s concerns was how to ensure the financial incentives were being used appropriately.
“It was then that monitoring the Amazon using satellite images was conceived of as a way of ensuring the projects were being correctly implemented, to verify that areas of the forest were being deforested to make room for agriculture and livestock,” says Almeida.
This notion of progress began to be heavily questioned as the environmental movement grew in strength in the 1980s. As home to the largest tropical forest on the planet, Brazil became internationally responsible for the Amazon, which plays an important role in regulating the global climate, in addition to its rich biodiversity. Against this backdrop, contrary to the prevailing philosophy of the previous decade, PRODES was created in 1988 with a simple objective: to estimate the annual deforestation rate of native forest in the Legal Amazon. The Legal Amazon—a designation established in 1953 with the aim of stimulating economic development in a region that stretches across nine Brazilian states—covers the entire Amazon biome in Brazil, as well as 37% of the Cerrado (a wooded savanna), and 40% of the Pantanal.
The Amazon biome in Brazil, where the tropical forest is located, extends over an area of almost 4.2 million km², equivalent to 49% of the country’s national territory. The difference between the Legal Amazon and the Amazon biome is around 800,000 km², more than 9% of Brazil’s land. “It is important not to compare deforestation data from the Legal Amazon with data for the Amazon biome,” emphasizes Almeida.
One unique aspect of PRODES is that it follows the so-called deforestation calendar, based around the fact that deforestation tends to occur most intensely during the driest time of the year. The PRODES year thus begins in August, at the beginning of the dry season, and ends in July of the following year. The data for 2023 covers the period from August 2022 to July 2023.
The type of deforestation recorded by PRODES is clearcutting, which is the complete removal of forest cover from one year to the next. It is generally done to open space for agricultural activities or to establish urban areas or hydroelectric dams.
In 2022, PRODES began to also measure deforestation that occurs through the progressive clearing of vegetation. This process is slower, more difficult to detect by satellite, and can take place over a number of years. It is associated with selective logging and the use of fires.
Only deforested areas that reach a minimum of 6.25 hectares (ha) in size, equivalent to 62,500 square meters (m2) or just over six soccer fields, are included in the calculation of the annual deforestation rate. Critics have claimed that the minimum size is too large, resulting in much deforestation being missed.
“In the Amazon, deforestation is carried out to establish large properties, areas of soybean monoculture, or cattle farms. It is not worth clearing small areas, which is very costly and laborious,” explains Câmara, who does not consider the size of the area monitored by PRODES to be a significant limitation. “The 6.25 ha area is enough to take most deforestation into account.” The PRODES system already monitors deforestation in areas as small as 1 ha (10,000 m2), but it does not include them in the calculation of its annual rate. It is likely that it will begin to do so soon.
The system uses images from five satellites: Landsat 8 and 9, launched by the North American Space Agency (NASA) and the United States Geological Survey (USGS); Sentinel, from the European Space Agency (ESA); and CBERS 4 and 4A, a joint project by Brazil and China.
The Landsat images form the system’s main database. To monitor the entire Legal Amazon, 229 satellite images from the Landsat family are needed. Each image, also known as a scene, covers an immense area of 32,400 km², just over four times the size of the São Paulo Metropolitan Area.
If areas of the rainforest are covered by clouds when the Landsat satellites pass overhead, CBERS and Sentinel images are used to fill in the missing data points. On average, any given area is observed by a satellite used by PRODES every 16 days. In practice, the interval between two images can range from 5 to 26 days.
The smallest information point within a Landsat image is the equivalent to a square measuring 30 by 30 meters (0.09 ha or 900 m2), slightly larger than two basketball courts. Remote sensing experts thus describe the spatial resolution (one pixel) of a Landsat image as 30 meters (m). The minimum area of deforestation taken into account by PRODES, at 6.25 ha, is therefore composed of 69.4 pixels. A CBERS or Sentinel pixel is even smaller. The images produced by the Chinese-Brazilian satellites have a spatial resolution of 20 m. The European hardware offers 10 m.
To calculate the annual deforestation rate, around 25 technicians at INPE headquarters in São José dos Campos manually compare the best available images of what an area looked like at the beginning and end of the current PRODES year.
These experts delimit the newly deforestated areas directly on a computer screen, identifying changes in forest cover based on elements visible in the images, such as tone, shape, texture, and context of deforested areas. “Our workforce is made up of many CNPq grant recipients. We need more staff hired on a stable basis,” says Almeida.
NASA / Landsat
Deforestation in an area of the Brazilian Amazon over almost 20 years
NASA / LandsatDETER
Launched 16 years after PRODES, when deforestation rates in the Legal Amazon were on the rise, DETER was conceived as a tool to help combat the problem in near-real time. It issues daily deforestation notices that are automatically sent to goverment bodies and state environmental departments responsible for stopping deforestation.
These notices are also shared publicly online, usually on a Friday, with a one-week delay. The system also publishes monthly and annual deforestation totals, following the PRODES calendar year. Although the DETER numbers differ to PRODES’s due to methodological differences, they typically show the same deforestation trends.
Its methodology has been improved and refined over time. From 2004 to 2015, it used data from NASA’s Terra satellites and Brazil and China’s CBERS-2b, with a spatial resolution of 250 m. With these images, it was possible to issue deforestation alerts for areas larger than 25 ha. However, they did not allow DETER to differentiate between areas that were completely deforested and others that suffered progressive degradation.
From 2015 onwards, it started to use images from CBERS-4 and CBERS-4A and the Amazonia-1 satellite, designed and operated by INPE, with a spatial resolution of between 56 and 64 meters. “Today, DETER only uses images from satellites developed with Brazilian technology,” highlights Almeida. The change made it possible to reduce the minimum warning area to 3 ha and to separate the alerts into two classes: deforestation and degradation. One of the three satellites passes over any given part of the Amazon at least every two days. The high frequency allows for continuous monitoring of the region, meaning deforestation alerts can be issued in near-real time.
The total or partial removal of native vegetation in an area with no previous record of clearing is classified as new deforestation. Although it is not possible to define the exact day that an area of the forest was cut down, DETER associates the event with the date on which the satellite image was taken.
New areas are identified on a daily basis and manually, like PRODES, but by a different team of specialists. Ten technicians at INPE’s Belém unit analyze the images on computers. Deforestation alerts are separated into the categories of clearcutting, deforestation with vegetation, and deforestation due to mining. The degradation warnings are broken down as geometric selective logging, disordered selective logging, and wildfire scarring.
With this approach, the system can differentiate a natural disturbance from one caused by human activity. The former mostly present irregular, nonlinear shapes, while the former generally exhibit geometric and linear clearing.
SAD
Based in Belém, Imazon created the Deforestation Alert System (SAD) in 2008. Its objective is to monitor forest degradation and the clearing of native vegetation in the Legal Amazon on a monthly basis, to shed light on dynamics and trends. “Having alternatives to PRODES and DETER gives civil society security and autonomy in the event that the INPE initiatives fail or are discontinued,” says Carlos Souza Jr., from Imazon.
The SAD system records clearcutting and degradation in areas from as small as 1 ha. It uses images from the American Landsat 8 and 9 satellites and the European Sentinel 1A and 1B (both 20 m pixels) and Sentinel 2A and 2B (10 m pixel) satellites. Any given point in the Amazon is scanned by one of the satellites every five to eight days.
The images are initially analyzed automatically using Google Earth Engine, but they are all validated by experts before the data is finalized. The SAD publishes deforestation statistics monthly for the entire Amazon and the states it is located in, as well as an annual deforestation rate. “Normally, our data shows 70% to 80% of the value recorded by PRODES, which we see as a strong performance given the methodological differences,” explains Souza Jr.
MapBiomas
In 2015, the MapBiomas network began producing maps and data on changes in land use in Brazil (existence of vegetation, agricultural activities, and urban structures) based on remote sensing images automatically analyzed using Google Earth Engine. It is thus able to calculate an annual deforestation rate for all the biomes in the country, including the Amazon.
Four years ago, the network—run by Observatório do Clima, a nongovernmental organization (NGO) that brings together universities, technology companies, and civil organizations—launched a project specifically to monitor the clearing of native vegetation across the nation. Known as MapBiomas Alerta, it verifies and refines deforestation warnings issued by other systems, such as DETER and SAD, and produces a public report for each area suffering deforestation.
This data is published weekly by MapBiomas Alerta and consolidated every year in an annual deforestation report (RAD). “Despite its name, MapBiomas Alerta does not provide warning about ongoing deforestation,” explains geographer Marcos Rosa, technical coordinator at MapBiomas. “It uses high-resolution images to confirm whether deforestation has occurred in an area and cross-references this information with public data to classify the type of deforestation and produce a report.”
When it has sufficient evidence that vegetation has been removed, MapBiomas uses satellite imaging from a private satellite network called Planet. According to the American company, every point on Earth is recorded daily by one of its 200 satellites, at a spatial resolution of just 3.7 m. What that means is that the smallest visible area within a Planet image covers approximately 14 m2, the size of a room in a house.
Every verified and refined alert produced by SAD includes a report with high-resolution images of before and after deforestation. The MapBiomas system can also be used to cross-reference the geographic information of the deforested area with data from various public databases, such as the Rural Environmental Registry (CAR) and the Land Management System (SIGEF). “We are thus able to include information about the deforested area in the report and infer signs of illegality,” explains Rosa.
NASA / Landsat
Satellite image from 2018 shows the region around the Amazon River covered by clouds, a feature that makes forest mapping by remote sensing more difficult
NASA / LandsatGFW
There are also international initiatives that publish regular data on deforestation in the Brazilian Amazon. Global Forest Watch (GFW) is possibly the most impactful. Run by scientists from the University of Maryland, USA, and funded by the World Resources Institute (WRI), a nongovernmental organization based in Washington DC, GFW has been monitoring land use and deforestation since 1997, especially in tropical forests, such as the Amazon.
The initiative uses satellite images from Landsat and has adopted the minimum spatial resolution of these satellites as the smallest area of deforestation it monitors: 1 pixel of a Landsat image, measuring 0.09 ha. The information is processed automatically.
“The system focuses on the tree canopy above 5 m. It records the cutting of trees and the removal of vegetation by fire,” says geographer Jefferson Ferreira, head of the WRI’s program in Brazil. “It shows the loss of forest cover, whether due to deforestation or not.” The GFW publishes an annual deforestation rate for the Amazon every year, calculated from January to December.
System limitations
No deforestation monitoring system is perfect. Remote sensing satellites, which generally capture images in infrared and visible light frequencies, face a common problem: if there are clouds between their cameras and the Earth, the resulting images are often of little or no value. Data redundancy and the use of images from more than one satellite are therefore particularly important strategies.
Microwave-frequency radars on the satellites can also be used to overcome this obstacle. Their observations are not blocked by clouds and can be made during the day and at night. “The CBERS-6 satellite will feature radar technology,” says Galvão.
Although faster and cheaper, fully automated analysis of deforestation may miss some forms of clearing that a trained human eye would spot, and it can even lead to erroneous alerts. It is important to know the historical and geographical context of the location of the apparent deforestation,” stresses Câmara. “Sometimes, automatic systems can interpret an image of an Amazonian floodplain obtained during flood season as a sign of vegetation having been removed. But this conclusion is wrong.” The image of a flooded floodplain resembles that of a clearcut area of forest. But a technician need only look at an image of the same area taken in the dry season to verify whether the vegetation is still there.
Despite criticism, Câmara is an advocate of machine learning for assisting remote monitoring of the Amazon. In 2014, he obtained funding from FAPESP’s eScience program for a study on the use of big data from satellites to classify land use and cover with the aid of machine learning.
Based on this research, the remote sensing specialist obtained funding from other sources to develop free software dubbed SITS (satellite image time series analysis), currently in the final testing phase to potentially replace PRODES. According to Câmara, the use of state-of-the-art deep learning methods makes it possible to achieve a 95% consensus between the visual interpretation of images by humans and the analysis performed by algorithms.
There has never been so much information available about the dynamics of deforestation in the Amazon, which is so necessary for the implementation of public policies designed to improve forest management and maintenance. “Every monitoring system makes the manager and society look at the problem differently. Today we know the extent of deforestation, where it is occurring, and how fast. Sometimes, we can even identify who is doing the deforesting,” points out Ane Alencar, director of science at the Amazon Environmental Research Institute (IPAM). “The big challenge is to understand the level of illegality in the deforestation and implement more efficient enforcement actions, embargoes, and even restrictions on access to credit [for those who remove native vegetation].”
