Measuring biomass in depth

ESA’s Biomass is the first satellite to carry a P-band synthetic aperture radar. Thanks to the long wavelength of P-band, around 70 cm, this novel radar is able to penetrate through the forest canopy, allowing it to collect information on different parts of the forest, such tree trunks, branches and stems – which is where trees store most of their carbon.

The radar is fully polarimetric, which means it is capable of transmitting and receiving in two orthogonal linear polarisations, horizontal and vertical. The different signals in each polarisation channel are needed to yield different information about the forest. However to achieve information on forest height and the structure of the forest beneath the canopy, multiple satellite passes over the exact same area are needed – a technique called synthetic aperture radar interferometry. Biomass is also the first synthetic aperture radar in space to have a dedicated tomographic phase as part of its mission plan.

The animation shows Biomass’ measuring technique starting from a single pass to retrieve the polarimetric radar signature of the forest, which provides an initial view of the forest canopy and forest density. The mission’s Interferometric Phase includes a second and third pass over the same area which is crucial to measuring forest height and gaining more accurate measurements of above-ground biomass. During the mission’s Tomographic Phase, the area is revisited up to seven times to reveal the inner structure of the forest.

While the animation shows the build-up of the measuring technique as a function of increasing complexity, the Biomass mission will actually commence with a single tomographic global coverage phase, which takes about 18 months, followed by multiple nine-month interferometric global coverages for the remainder of the mission life. This will be used for understanding how forests change over time.