Forests cover 30 per cent of all land on Earth and play an important role in carbon sequestration and global climate control, alongside with human well-being, sustainable development. Forests have also a hydrological value and offer the additional climate benefit of increasing cloud cover, leading to localised cooling and engendering rainfall. (https://www.nature.com/articles/s41467-021-24551-5)
Moreover, the living of over 25 per cent of the world’s population directly depends on forest ecosystems. Forests are home of approximately 80 per cent of all terrestrial species and are essential in climate change mitigation and adaptation, as well as in the conservation of biodiversity.
When sustainably managed, all types of forests are healthy, productive, resilient, and renewable ecosystems, providing essential goods and services to people worldwide. Example of such goods and services include timber, food, fuel, fodder, non-wood products and shelter, as well as contribute to soil and water conservation and clean air.
Deforestation can be monitored from space using optical and synthetic aperture radar (SAR) satellite data, in order to identify the current state of forests, the extent and density of forest cover, and its changes over time. Satellite Earth observation for deforestation monitoring offers large coverage and short revisit-time. Monitoring deforestation and stopping the loss of forests play an important role in climate change mitigation. (https://ukcop26.org/glasgow-leaders-declaration-on-forests-and-land-use/)
Deforestation can be monitored and quantified by spaceborne optical sensors by detecting change in the land classification and mapping the extent of deforestation, however this technology is highly dependent on the cloud cover over the forest.
While optical sensors depend on radiation from the sun, SAR satellites emit and detect their own wave pulses, in certain wavelengths that have the ability to penetrate clouds. SAR sensors can also capture images through darkness, unlike optical sensors, making it a very effective way to monitor forests changes all year round and in any weather condition. SAR change detection, meaning the comparison of images from different moments, is very useful to detect deforestation. An example of deforestation using SAR can be found here (https://digital-geography.com/observing-deforestation-sentinel-1/)
Fire monitoring and burnt area mapping
Several variables, related to forest fires can be measured by satellite sensors. The heat generated by fires can be detected by the thermal and mid infrared bands of spaceborne sensors, enabling the detection of fire hotspots. The visible and the near-infrared bands of optical sensors are used to identify burnt areas, and to monitor vegetation regeneration post fire. For instance, one method used for mapping burnt areas is combining the red, near infrared and green bands of the spaceborne sensor.
More information on the capacities of satellites for forest fire can be found on the UN-SPIDER Knowledge Portal (https://www.un-spider.org/links-and-resources/data-sources/daotm-fire )
The near real-time active fire global map developed by NASA based on satellite data can be found here: https://firms.modaps.eosdis.nasa.gov/map/#d:24hrs;@0.0,0.0,3z
Fire is an ECV defined by GCOS. https://gcos.wmo.int/en/essential-climate-variables/fire/
Forest biomass estimation
Above ground biomass (https://www.un-redd.org/glossary/aboveground-biomass) plays a n important role in the carbon cycle as it stores carbon dioxide, therefore estimating the forest biomass quantity is crucial to monitor the impact it can have on climate.
The above ground forest biomass can be measured with spaceborne LiDAR, an active optical sensor using laser pulses. This technology is based on the time it takes for a pulse to return to the sensor after reflexion on the target (in this case the tree canopy), allowing to calculate the distance between the sensor and the target as the speed of the laser pulse is known, and therefore estimate the forest canopy height.
The knowledge of the forest biomass is crucial for effective climate mitigation and resilience policies
Above ground biomass ECV https://gcos.wmo.int/en/essential-climate-variables/biomass/