Mapping Tropical Forest from Space

The Tropisar airborne campaign is helping to address one of the key objectives of ESA's candidate Earth Explorer mission BIOMASS. The main objective of the BIOMASS mission is to provide consistent global estimates of forest biomass, its distribution and changes over time. In this manner, the mission is expected to greatly improve our knowledge of carbon stored in forests, and better quantify the carbon fluxes to and from the atmosphere from land. To reach this goal, the mission, if selected for implementation, would exploit the longest radar wavelength available to Earth observation - P-Band and its unique sensitivity to forest biomass.

An airborne radar system called Sethi is central to the Tropisar campaign. Built and run by the French Office National d'Ëtudes et de Recherches Aérospatiale (ONERA), it is flown on a Mystere-20 jet. Following each flight over the rain forest, the processing of roughly 500 gigabytes of data into radar images is started on the ground. The first task is to control data quality, which is crucial to the success of the flight, but also to start interpreting what the radar actually 'sees' on the ground.

Sometimes overlooked, but crucial to the success of the activity, are measurements taken on the ground. These are used to interpret the radar images and evaluate methods for generating radar-based maps of forest properties. Biomass measurements are especially difficult in tropical forests due to the huge and sometimes bewildering diversity of tree types and structures. There is also the added difficulty of accessing the dense forests and working in the hot and humid climate.

In total, it is expected that approximately 3.5 million gigabytes of radar data will have been collected during the campaign. The last flight of the Tropisar campaign is planned for 1 September. After this, the data will be processed by experts at ONERA in France and analysed by the Tropisar team. The first results of the campaign will be presented to ESA by the end of the year and used to better guide parallel work being done by European industry on the BIOMASS mission.
 

Radar image of the Tropisar test site (courtesy of ESA).