Monthly Archives: May 2015

GUEST POST: Forest AGB Estimation and Mapping through Hi-Res Satellite Imagery (<5m resolution) – A Global Review

There is no remote sensing method that can give direct measurement of Above Ground Biomass (AGB). In most studies of AGB utilizing remote sensing, field-measured biomass values are used to train methods in predicting AGB values, linking biophysical parameters extracted from remote sensing data. Design (sample extrapolation) or model (empirical and mechanistic) based remote sensing approaches are being commonly adopted for biomass assessment and mapping. Although coarse and medium spatial resolution data, such as MODIS or Landsat TM, provide the potential for AGB estimation at a sub-national to national to regional level, mixed pixels and data saturation are major problems in AGB estimation in sites with complex biophysical environments.

Figure 1: Geographical coverage of peer-reviewed published studies on forest AGB estimation using high-resolution satellite imagery (in the time span 2004-2015).

Figure 1: Geographical coverage of peer-reviewed published studies on forest AGB estimation using high-resolution satellite imagery (in the time span 2004-2015). The legend shows the satellite datasets used for different studies.

In terms of assessment and mapping of deforestation (area, location, type of change), forest degradation (reduction in production capacity i.e. timber volume / biomass) and proxies of forest degradation (canopy closure, canopy morphology, number of mature trees, number of preferred trees, density, species composition, wild fire, and soil surface erosion), high resolution images are capable of predicting accurate results. Apart from other tree parameters, high resolution satellite data are being used for the estimation and mapping of AGB.

For site specific or sub-national level AGB estimation, high resolution satellite data could provide better results. However, due to diversity of data sources, study locations, number of samples, statistical methods and modelling standards, it is difficult to compare studies, and there is still no agreement on best practices to estimate biomass. In research communities, high resolution satellite data is gaining increasing popularity, so this post gives a quick glance of 28 peer reviewed published studies of the last 11 years (2004 – 2015) in this field of study.

Out of 28 peer reviewed published articles, 12 have been on study sites in Asia, 8 in North America, 5 in Africa, 2 in Latin America and only 1 in Europe (Table-1). QuickBird and IKONOS satellite have mostly been used for estimation and mapping forest biomass. Even in some cases, either two different sensors are jointly used (e.g. GeoEye-1 & QuickBird and QuickBird & WorldView-1) or integrated with active and passive medium resolution optical data (e.g. Landsat, ASTER and LiDAR) or microwave remotely sensed data (e.g. SAR / InSAR). Figure-1 provides the geolocations of studied conducted in different parts of world.

Table 1: Continent-level specification of high-resolution imagery used for forest AGB estimation and mapping in the time span 2004-2015.

High resolution satellite sensor* Africa Asia Europe Latin America North America Grand Total
GeoEye-1 4 4
GeoEye-1 & QuickBird 1 1
IKONOS 2 2 1 1 6
QuickBird 1 3 1 5 10
QuickBird & WorldView-1 1 1
SPOT-5 2 1 1 4
WorldView-2 1 1 1
Grand Total 5 12 1 2 8 28

Conflicts of Interest: The findings reported stand as scientific study and observations of the author and do not necessarily reflect as the views of author’s organizations.


Cheaper Centimeter-Grade Positioning Accuracy via Software-Defined Receivers

A recent report by UT-Austin researchers explains how researchers have developed a software-defiend GPS receiver which can bring centimeter-grade GPS accuracy, which will be soon available right on the smartphone. Centimeter-grade accuracy is currently available in surveying through elaborate and sophisticated setups of differential GPS, satellite-based augmentation systems, or Real Time Kinematic (RTK) systems. With this new software-defiend review based out of a cellphone, it will become increasingly possible to utilize centimeter-level position accuracy in applications such as virtual reality (VR). Check out the news report here: