Background
From GCOS’s Implementation Plan for the Global Observing System for Climate in Support
of the UNFCCC”, 2003:
Biomass plays two major roles in the climate system: (i) photosynthesis withdraws CO2 from
the atmosphere and stores it as biomass; (ii) the quantity of biomass consumed by fire affects
CO2, other trace gases and aerosol emissions. Only above-ground biomass is measurable with
some accuracy at the broad scale, while below-ground biomass stores a very large part of total
carbon stocks and is rarely measured. Most nations have schemes to estimate woody biomass
through forest inventories (little is recorded on non-forest biomass, except through
agricultural yield statistics); this typically forms the basis for the annual reporting on forest
resources required by the UNFCCC. Experimental airborne sensors have demonstrated
technologies for estimating biomass (low-frequency radar, lidar), and are suitable for satellite
implementation that could provide global above-ground biomass information at subkilometric resolutions. There are limitations to these technologies, some known (for example,
saturation of radar backscatter at higher levels of biomass), some still the subject of research.
National inventories differ greatly in definitions, standards and quality, and the detailed
information available at national level is normally unavailable internationally. Nonetheless,
these form the basis of the country-by-country summary statistics, published by the FAO in
their FRAs. Some regional harmonization efforts, such the European Forest Inventory, lead to
improved input. Nevertheless, biases and uncertainties in these summary values are not
quantified. The only available global gridded biomass data set is that from the World
Resources Institute, based on existing databases supplemented by satellite observations. The
accuracy, resolution and currency of this data set are unknown.
Although a unified standard for biomass inventories will be a long-term aim, the achievable
medium-term aim, with marginal resource implication, is adequate reporting of the methods
employed by countries, together with an accuracy assessment. This information should be
included in the FAO FRAs and then be incorporated into the Forest Resource Information
System.
Progress towards creating global gridded biomass data sets can be achieved by appropriately
designed satellite and aircraft missions, notably active microwave and laser systems. The
Space Agencies should plan for such missions, supported by experimental programmes to
reduce their risks.
Action T31 (TF11)
Action: Develop methodology for forest inventory information and begin acquisition of data.
Who: Parties and FAO.
Time-Frame: By 2009.
Performance Indicator: Availability of consistent statistical information.
Cost Implications: Category II.
6.4. Terrestrial Domain – Scientific and Technological Challenges
Some current and emerging ECVs call for concerted collaborative research efforts to bring
them to the status of operationally-monitored ECVs within the Global Climate Observing
System. Among the key priorities is:
• Development and deployment of airborne and spaceborne microwave and lidar systems for
measurement of above-ground biomass.
From GCOS’s “Systematic Observation Requirements for Satellite-Based Products for
Climate: Supplemental details to the satellite-based component of the ‘Implementation Plan
for the Global Observing System for Climate in Support of the UNFCCC’”, 2006:
Product T.8: Research towards global, above-ground forest biomass and forest-biomass
change
Benefits:
-Biomass change is a direct measurement of carbon sequestration or loss.
-Biomass information can help to validate carbon-cycle models.
-Biomass provides an estimate of carbon stocks for terrestrial ecosystems.
Target requirements:
-Accuracy: 5%
-Spatial and temporal resolution: 10-30m horizontal resolution, 1-year observing cycle.
-Stability: 5%
Requirements for satellite instruments and satellite datasets:
Two approaches are available for estimating biomass from space. The direct approach infers
biomass directly from the signal, while the indirect approach measures forest height, from
which biomass is recovered using regionally-dependent allometric relations:
 Direct approach: The ALOS L-band SAR (launched in January 2006) should provide the
first systematic global observations for generation biomass maps. Longer wavelengths (Pband) should also be considered for future missions. Although historical Japanese Earth
Resources Satellite (JERS) data are available through JAXA and ESA, calibration issues
and lack of systematic coverage prevent their use for global biomass mapping.
 Indirect approach: Two techniques are able to retrieve forest heights from space:
Polarimetric SAR Interferometry (Pol-InSAR) and lidar. For continuous wide-are coverage,
the Pol-InSAR technology seems able to provide the requested accuracy and the ALOS
system will be used to test the viability of this approach.
Calibration, validation, and data archiving needs
 Direct approach: Absolute radiometric calibration to 1dB is needed.
 Indirect approach: Precise control of the interferometric baseline is needed, and polarimetric cross-talk of about 25 dB is required.
 For validation, ground-based biomass and height measurements are needed at a range of
sites.
 Under the Kyoto Protocol and Carbon Initiative of JAXA, systematic global measurements
of backscatter (with a limited amount of polarimetry) will be acquired for the Earth’s forest
biomes, from which biomass could be derived.
Adequacy/inadequacy of current holdings
 Direct approach: Although historical JERS data are available though JAXA and ESA,
calibration issues and lack of systematic coverage prevent their use for global biomass
mapping.
 Indirect approach: Experimental airborne data are available (INDREX-II for tropical
forests, TreeSAR for temperate forests).
Immediate action, partnerships and international coordination
 Actions need to be taken by the space agencies to develop a concept for above-ground
biomass product estimation, for example based on low frequency (L- and P-band) SAR for
both direct and indirect approaches.
 The Kyoto and Carbon Initiative of JAXA needs to be maintained and developed.
Link to GCOS Implementation Plan
Develop methodology for forest inventory information and begin acquisition of data.
Other applications
 Dataset valuable for forest management but only at coarse resolution.
 Consistent input for the FAO Forest Resource Assessment Updates.
From CEOS, “Satellite Observation of the Climate System: The Committee on Earth
Observation Satellites (CEOS) Response to the Global Climate Observing System (GCOS)
Implementation Plan (IP)”:
Biomass and Soil Moisture: ensure the continuity of terrestrial climate monitoring to
meet threshold requirements for biomass and soil moisture ECVs.
CEOS recognizes that current algorithms and planned satellite missions do not
adequately meet the needs for some ECVs required by GCOS. A lidar or P-band
sensor capable of retrieving biomass globally (and avoiding the saturation issue) may
be able to achieve GCOS threshold requirements in the long term.
Action T-5: CEOS agencies will undertake research to support satellite technology
development, such as lidar or P-band sensors, that are capable of retrieving biomass and
LAI globally that meet GCOS requirements. CEOS agencies will also support research
to improve algorithms that do not currently meet CGOS threshold requirements. New
satellite technology and algorithms should be available by 2015. (p.l 5)
Biomass (T.8) Past provisions:
Production of a biomass product from satellite measurements was not possible in the
past. Currently, research data production in being planned. Actions need to be taken
by space agencies to develop a concept for above-ground biomass product estimation,
for example, one based on low frequency (L- and P-band) SAR for both direct and
indirect approaches.
Present/future provisions:
Direct approach: The ALOS L-band SAR (launched in January 2006) should provide
the first systematic global observations for generation biomass maps. Longer
wavelengths (P-band) should also be considered for future missions. Although
historical Japanese Earth Resources Satellite (JERS) data are available through JAXA
and ESA, calibration issues and lack of systematic coverage prevent their use for
global biomass mapping.
Indirect approach: Two techniques are able to retrieve forest heights from space:
Polarimetric SAR Interferometry (Pol-InSAR) and lidar. For continuous wide-are
coverage, the Pol-InSAR technology seems able to provide the requested accuracy and
the ALOS system will be used to test the viability of this approach. Experimental
airborne data are available (Indonesian Airborne Radar Experiment (INDREX II) for
tropical forests and TreeSAR for temperate forests). JAXA is promoting systematic
global observation of the ALOS Phased Array L-band Synthetic Aperture Radar
(PALSAR) through the provision of 1) systematic global observations and consistent
data archives, and 2) derived and verified thematic products. To map or model aboveground biomass, it would be most useful if stratified by vegetation, as defined by
existing satellite land cover maps. Using other vegetation and physiographic
information may be a useful way to frame the biomass information.
Adequacy of provisions:
Past holdings do not exist and future products will be experimental for the foreseeable
future. (p. 44)