Recently, the demand of forest resources monitoring technology on a large scale is growing, and spaceborne LiDAR is expected to provide a means for accurate monitoring. This study aims to clarify the potential of ICESat/GLAS spaceborne LiDAR for forest resources monitoring on a regional scale. The study areas were Hokkaido Island in Japan (cool-temperate forest), Borneo Island (tropical forest), and Siberia (boreal forest). Firstly, we conducted field measurements in Hokkaido and Borneo, and calculated the average canopy height (Lorey’s height) and the above-ground biomass (AGB) for each GLAS-footprint. Then, we developed some models to estimate canopy height and AGB from the GLAS waveform parameters based on the field measurement data. Next, we applied the developed models to the GLAS data in Hokkaido and Borneo. The average canopy height and AGB were 17.8 m and 119.4 Mg ha-1, respectively, in Hokkaido, and 16.2 m and 190.2 Mg ha-1, respectively, in Borneo. These results suggest that the tropical forest in Borneo has a higher biomass than the cool-temperate forest in Hokkaido. Furthermore, we applied the estimation model to the GLAS data acquired in Siberia. The average AGB was 86.2 Mg ha-1, and it has decreased especially in Southern area of Western Siberia. This study showed that spaceborne LiDAR had an ability of forest resources monitoring on a regional scale, for each of boreal, cool-temperate, and tropical forests.
High-accuracy three-dimensional (3D) information of global area is useful in various fields, such as global observations of canopy height, elevation and ice sheet. Especially, there are pressing needs to advance understanding of how changes in the 3D structure of terrestrial vegetation are affecting the global carbon dynamics and their implications for climate change. Thus new space based observations are needed to measure global maps of the 3D structure of vegetation. Japan Aerospace Exploration Agency has started a conceptual study of the spaceborne vegetation LiDAR called MOLI (Multi- Footprint Observation LiDAR and Imager) which will enable us to obtain high-accuracy 3D information of vegetation areas from the globe. To investigate waveforms and analysis procedure, the waveform-simulator for MOLI was developed. Comparing with previous studies about the canopy height estimation from GLAS waveforms, waveform analysis procedure in which waveforms were fitted with a sum of Gaussian functions was studied. The maximum canopy height error was divided into two components; the basic error (EB) which was not depending on terrain index (TI), which was the vertical difference between the highest and lowest elevation within a footprint, and the error depending on TI (ETI). The total error (ETotal) could be RMS of the two. We propose ETotal in which EB is 1 m and ETI is 1/3*TI as a target observation accuracy of MOLI. According to this error estimation, the observation accuracy of MOLI is 1m at a plane area (TI ≈ 0) and 3 m at slope area up to about 20 degree.
It is very important to watch the spatial distribution of vegetation biomass and changes in biomass over time,
representing invaluable information to improve present assessments and future projections of the terrestrial carbon cycle.
A space lidar is well known as a powerful remote sensing technology for measuring the canopy height accurately. This
paper describes the ISS(International Space Station)-JEM(Japanese Experimental Module)-EF(Exposed Facility) borne
vegetation lidar using a two dimensional array detector in order to reduce the root mean square error (RMSE) of tree
height due to sloped surface.
We developed a methodology to estimate the canopy height from the ICESat/GLAS waveform for the purpose of
contributing to the design of the Japanese spaceborne LiDAR mission; iss-jem LiDAR for Observation of Vegetation
Environment (i-LOVE). We adopted an estimation method using a terrain index, which indicates the steepness of ground
surface, to accurately estimate the canopy height in sloped areas. The study area is Hokkaido Island. We conducted a
ground survey and collected airborne LiDAR data to use as the ground truth for the canopy height. We then developed
some models to estimate the canopy height from a GLAS waveform. As a result, the estimation accuracy decreased in
steep sloped areas where the terrain index exceeded 15 m. To reduce the influence of this effect, the estimation equation
was separated for a gentle slope (terrain index ≤ 15 m) and a steep slope (terrain index < 15 m). In this case, RMSE was
3 to 5 m. These findings indicated that an accurate estimation method would be ensured by using a footprint of less than
15 m of terrain index for the i-LOVE mission. On the assumption of a forested area located primarily at less than a 30°
surface slope on a global scale, it is recommended that the diameter of the i-LOVE footprint should be less than 25 m. i-
LOVE is planned to transmit four laser pulses arranged at 2×2 simultaneously. This characteristic of i-LOVE, which
does not require DEM, makes it possible to calculate the terrain index accurately and has a large advantage for accurately
estimating the canopy height on a global scale.