What is EcoSAR and how does it help?
EcoSAR was a new instrument concept developed by some of our team members to help measure forest structure (i.e. forest canopy height, density, ), a metric that is useful for the quantification of carbon biomass stored in the woody mas per unit area of trees. This instrument has the capacity to produce 2 and 3-dimensional fine scale sensor measurements using Synthetic Aperture Radar. As you may recall from our introduction about remote sensing, there are two main types of remote sensing instruments; active and passive. This SAR instrument is an active sensor in that it can provide it’s own source of energy (microwave in this instance) to illuminate entire vegetation and ground volumes, densities, or biomass (Fatoyinbo, et al., 2012).
Synthetic Aperture Radar
SAR’s ability to actively produce P-Band SAR (0.3 – 1 GHz or 30 – 100 cm wavelengths)energy to sense vegetation structures is ideal because it is able to measure large amounts of mass in excess of up to 2009 mega grams per hectare or Mg/ha due to the longer wavelengths and deeper penetration of the microwaves in canopies. In contrast the shorter wavelengths like the L-band saturate at a maximum of 140 Mg/ha (Mougin, 1999). The biomass in forests can sometimes reach masses that are far to large for some sensors to handle, this is why SAR is relevant and useful.
“Many tropical and temperate forests’ biomasses can reach up to 600 Mg/ha, which cannot be measured with current SAR capabilities. To measure tree height using radar data, a technique known as interferometric Synthetic Aperture Radar (InSAR) is used (Graham, 1974).”-Fatoyinbo et al., 2012
The main goal is to use this instrument to estimate forest biomass and canopy height. Some of the estimate that it can provide for canopy height at 1 meter accuracy and estimates of above-ground woody biomass up to a 20% accuracy. It is important to note that there are gaps in sciences measurements which are very much needed for environmental management frameworks like REDD (Reducing Emissions from Deforestation and Degradation) which develops incentives for countries to implement forest conservation policies.
Case Study – AfriSAR Campain, Gabon (PI: Lola Fatoyinbo)
The project objective was to utilize multi-baseline L- and P-band radar data for the derivation of canopy height and vertical structure from polarimetric-interferometric SAR data collected for the AfriSAR campaign. This ambitious campaign is in collaboration with the European Space Agency (ESA) in preparation for the BIOMASS Earth Explorer Core Mission which addresses the need for research on forest carbon sinks and sources world wide.
Gabon, a Central African country is an area of interest due to it’s globally recognized pristine rainforests. Over a two-week-long period, researchers were able to collect measurements of vegetation structure, extent, distributions, etc., for the country’s wetlands, mangroves, and savannas. ESA launched the field campaign July 2015, lead by the French National Aerospace Research Center and was later joined by NASA and the German Aerospace Center (DLR) in the second phase.