Biomass rocks and rolls
Biomass orbits our planet in a Sun-synchronous dawn-dusk orbit at altitude of 666 km. The satellite’s left-looking synthetic aperture radar covers a single fifty- to sixty-kilometre-wide swath at a time.
After 44 orbits in a three-day period, the Biomass satellite repeatedly observes the same area, but with a small longitudinal displacement to produce the stack of images needed for forest data products. Each stack comprises seven images for tomographic coverage and comprises three images for interferometric coverage.
Following the completion of an image stack with the single swath, the Biomass satellite carries out a ‘mechanical roll’ manoeuvre close to the North Pole. This ensures the next observations are adjacent to the area previously measured. Upon completion of the third swath, one major cycle is completed.
Over the following 9–12 days, Biomass then performs a repositioning manoeuvre so that its instrument can start measuring the adjacent strip. This repositioning manoeuvre is achieved by raising the satellite’s orbit, drifting for a certain period, and then returning to its normal 666 km orbital height. At this point, the acquisition pattern described earlier is repeated until a total of seven of these major cycles have been completed and a global coverage has been reached.
While the animation shows how global coverage builds up in a generic sense, the Biomass mission actually commences with a single tomographic global coverage phase to reveal the structure of the forest which takes about 18 months. This is then followed by multiple nine-month interferometric global coverages for the remainder of the mission’s life to understand how forests change over time.
