Quantifying illegal deforestation in French Guiana: TropiSCO's invaluable help

This article is an adaptation of the report "Satellite remote sensing: a major asset in the fight against illegal gold panning in French Guiana", produced by Caroline Debris, a student at Ponts ParisTech, during her internship at the SCO France from January to August 2024. We would like to thank her for her great involvement and especially for this remarkable study.

Overview of the situation in French Guiana

To explore this issue in greater depth, which resonates with the current context of over-exploitation of resources, Caroline Debris contacted local players involved in this fight. The SCO would like to thank Lise Layotte and Clément Villien from WWF France, Mathilde André from the ONF (National Forestry Office), and Sébastien Linares from EMOPI (State staff to combat illegal gold washing and fishing) for their invaluable collaboration.

What contribution can satellite data make in this context?

Faced with the growing threat of illegal gold panning in French Guiana, Mathilde André (ONF/OAM) describes satellite remote sensing as "indispensable". This technology is of vital importance in the fight against this activity, given the extent and inaccessibility of the areas concerned. Dense forests and remote regions make traditional surveillance from the ground or from the air not only difficult, but often impossible. Now, thanks to the Copernicus constellation, every point in the territory can be revisited every 3 to 6 days, with free data, so without being dependent on private suppliers.

How is this data processed?

1. Using an optical image, such as those from Sentinel-2, the general principle of this method is based on the use of contrasts between the object observed and its environment. Here, the object observed is the gold panning site and the environment is the tropical forest. The contrast is therefore strong: the bare ground (yellow, brown) stands out clearly from the surrounding vegetation (green). This makes it possible to detect deforestation.

2. This is followed by a characterization of the deforestation detected. Various contextual data are used (gold potential of the area, mining cadaster, location of production units, presence of parks and mining plots) to determine the legal activity of the area and thus highlight deforestation carried out outside this legal framework.

3. We then look at the shape of the clearings to identify the type of exploitation. For example, abattis, a traditional method of slash-and-burn agriculture, is characterized by small circular plots, fruit cultivation adopts a slightly larger square shape, and logging has linear detections due to the roads created for the purpose. Gold panning, on the other hand, often takes a sinuous form following the course of rivers and, unlike abattis, which generally reaches a stable stage after 6 to 12 days, is constantly evolving geographically. 

4. The distinction between legal and illegal activities is a little more complex. Generally speaking, deforestation in a non-mining area listed in the mining register is probably illegal. These illegal sites are often isolated, tucked away from main access routes, close to borders and along watercourses. The use of mercury, often associated with illegal gold panning, is clearly identifiable on satellite images: the rivers appear almost white, reflecting increased turbidity due to the stirring and scraping caused by this practice. This observation makes it possible to trace the course of the rivers back to the exploitation site, facilitating efforts to combat these illegal activities. It is also possible to examine the date of deforestation: legal gold panning sites are more frequent in the dry season, while illegal sites are more common in the wet season.

This is how the ONF uses the data. Once the detections have been made, the data is transmitted via a collaborative cloud to the relevant authorities, including the army and the gendarmerie. This information is used to plan targeted field missions, particularly in isolated areas, facilitating precise location prior to checks by plane, drone or helicopter. This ensures faster, more effective intervention, enabling these detections to be validated and adding to a database of "exploited areas" that contains more than 30 years of monitoring. Historical satellite images, which have been available for several years now, can also be used to retrace the chronology of gold panning sites, identifying mines that are still active and those that have been abandoned or restored. This provides crucial information to the authorities before any intervention in the field, helping them to anticipate the possible presence of people on the sites and to plan operations accordingly.

An example of use: decision support for regional regulations

In 2013, a "fast-track procedure for setting up mining companies" was implemented, co-piloted by the State services, the territorial authority of French Guiana, the ONF and representatives from the mining sector. The aim was to facilitate the rapid establishment of legal mining operators in place of illegal gold panners. The challenge was to determine the deterrent effect of this measure on the garimpeiros. To do this, satellite images were analyzed to measure the distance between legal mines and illegal workings between 2013 and 2022.

Heading for TropiSCO

In order to assess the platform's operability, Caroline Debris tried to verify facts reported in the press using TropiSCO. Here are the results obtained:

• The cross-border dimension of the problem and the difference in treatment between Guyana and Suriname  

Although the use of barges (for alluvial gold panning) is banned in French Guiana, it remains legal in Suriname. On the Maroni River, the border between the two countries, Surinamese barges continue to destroy the riverbanks, causing erosion and deforestation. The Surinamese banks are cleared, and the top layer of soil is levelled with mechanical shovels, then the barges come into action, digging up the earth from the banks in search of gold. In addition to the large quantities of sludge discharged into the river, which stifle or drive away all marine biodiversity, this practice leads to deforestation and subsidence of the banks, making them vulnerable to erosion in a region with very high rainfall. In some places, the riverbed itself has been significantly altered. In 2019, 36.7 hectares of forest disappeared along just 25 km of the river between Maripasoula and Papaïchton as a result of these illegal practices. [Source : Orpaillage sur le fleuve frontalier entre la Guyane et le Suriname : télédétection des dommages causés par les barges aux rives du Maroni – Marie Ballère, CESBIO, September 9, 2020]

This procedure can be monitored in near-real time throughout the year using the deforestation maps produced by TropiSCO.

▲ These images from 2017 (left) and 2023 (right) show the creation of a barge on the Maroni River, demonstrating that this practice still exists in Suriname and is extremely destructive. © TropiSCO

These practices, regularly denounced by the French authorities and local organizations, should eventually disappear. In August 2020, the new Surinamese government made a commitment, in a cooperation agreement with France, not to issue new operating licenses for these floating factories and not to renew those that were due to expire. Respecting this agreement would be a step forward for the Maroni River and its inhabitants. The precise monitoring that Sentinel-1 will enable us to carry out will enable us to check whether these announcements are actually followed up by action.

• Support for operations: The case of Bagot creek

Satellite images have revealed areas of deforestation and water pollution, helping to plan targeted crackdowns. This is the case of the Bagot creek, whose waters are regularly polluted by illegal gold mining activities, which can be found on TropiSCO.

▲ The chronology of this operation illustrates the effectiveness of satellite data for rapid and targeted intervention. It all began on 15 May 2019 with a satellite image captured by Sentinel-2A. On 20 May 2019, the ONF detected suspicious activity thanks to this image. A week later, on 27 May 2019, a joint operation led by the ONF and the Gendarmerie was launched. This operation resulted in the destruction of a camp comprising twelve cabins and two worksites equipped with motor-driven pumps and lifting tables. Twelve individuals were arrested, and the police seized 300 liters of fuel, 300 kg of food and 100 kg of other equipment. © TropiSCO

Epilogue

The experience of the ONF and other local players shows that satellite imagery is not only a detection tool but also a central element in the strategy to combat gold washing. It maximizes the effectiveness of interventions on the ground, reduces the environmental impact and strengthens international cooperation.

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