Yoshito Sawada

Waveform simulator and analytical procedure for JAXA's future spaceborne lidar to measure canopy height

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.

Simulation and visualization of echo signals from forest for iLOVE

This paper describes the method and process of developing a forest echo signal simulator to be applied in “iLOVE” : Issjem LiDAR Observation of Vegetation Environment. The goal of this study was to develop an echo signal simulation model and to visualize the generation process of echo signals. The simulator consists of four components: 1) terrain and features, 2) sensor configuration, 3) echo signal generation and 4) visualization. Terrain and feature data were defined to be full polygon object in 3D space. A laser beam refers to numerous sub laser beams, with each sub laser beam featuring specific intensity based on TEM00. The time-series intensity change of sub laser beams was based on Gaussian distribution. At the start of the echo signal generating process, intersections between sub laser beams and target objects were calculated. Then, echo signal of sub laser beams was calculated from the position of intersections, pulse width and specific reflectance of target objects. Finally, an echo signal suitable for footprint size was calculated by synthesizing echo signals of sub laser beams. Meanwhile, intersections were drawn in 3D on the surface of target objects. The results indicated that the simulator was highly useful for understanding the relationship between the echo signal and the structure of target objects, and also for developing algorism for forest applications.