We examined the acquisition accuracy of high-resolution airborne LiDAR for capturing the external forms of individual trees in an urban district. The accuracy of the voxel-based reconstruction of the crown form was verified in anticipation of estimating the leaf area density (LAD) distribution. We calculated the decrease in the number of airborne laser beams incident on a crown in each height bin for 20 Japanese zelkova trees, and then, determined the target tree. Terrestrial LiDAR data of the target tree was used for the verification. We examined the spatial accuracy of the airborne LiDAR points on the crown surface before verifying the accuracy of the voxel-based reconstruction. The results confirmed that airborne LiDAR captured the crown periphery with the spatial accuracy of 0.5 m and 1 m in the upper and lower parts of the crown, respectively. Next, voxels including one or more points were extracted as the areas in which the foliage is distributed. We then verified the distribution accuracy of the extracted voxels, and we found that 60 % of the external voxels derived by the terrestrial LiDAR can be extracted. We also investigated the reasons for voxels not being extracted by the airborne LiDAR, using the LAD in voxels derived from the terrestrial LiDAR data. We observed that 96 % of the external voxels derived by the terrestrial LiDAR was comprised of voxels extracted by airborne LiDAR (the adjacent voxels of which can be extracted) and voxels that had insufficient foliage to trigger a return pulse. Our results quantitatively indicate that high-resolution airborne LiDAR is applicable to the voxel-based reconstruction of external forms of individual trees in urban spaces.
We performed Raman lidar observation to obtain water vapor measurements in order to improve the performance of numerical weather prediction models. The obtained water vapor mixing ratio profiles were assimilated into the Weather Research and Forecasting (WRF) model. The results from the simulation showed that the lidar-based water vapor mixing ratio was able to improve the performance of numerical weather prediction models.
We developed an algorithm to estimate the vertical profiles of extinction coefficients at 355 nm for three aerosol components (black carbon, dust, and air pollution particles other than black carbon), using the extinction coefficient, backscatter coefficient, and depolarization ratio at 355 nm for total aerosols derived from data measured with a high spectral resolution lidar (HSRL) with a depolarization measurement function installed on EarthCARE. We also developed a similar algorithm to analyze 532 nm polarization HSRL data from ground-based and airborne measurements. The mode radii, standard deviations, and refractive indexes for each aerosol component were prescribed; the optical properties of each aerosol component were computed and modeled on the assumption that dust was spheroidal and the other components were spherical. We performed sensitivity studies on retrieval errors due to measurement uncertainty or due to assumptions of the algorithms, and characterized the algorithm performance. We demonstrated the ability of the algorithm by applying it to the 532 nm HSRL data measured at Tsukuba, Japan from retrieved plumes consisting of black carbon, dust, air pollution aerosols or some mixture thereof, with results that were consistent with previous studies. We further compared the distributions of the aerosol components retrieved in this study with those retrieved by the aerosol classification retrieval algorithm using the 532 nm HSRL data and the lidar signal at 1064 nm developed in the previous study. We found that the estimates probably agreed in lower layers below 3 km but the dust and air pollution aerosol extinction coefficients in the upper layers differed. The simulation of 1064 nm lidar signals suggests that the mode radius of dust differs in the lower and upper layers.
Reef-building corals are threatened by global climate change and other problems, and thus the monitoring of regional coral distributions is becoming increasingly important. We developed a glass-bottom-boat-based coral observation system that uses lidar (light detection and ranging) techniques for large-area coral monitoring. The lidar system consisting of an ultraviolet (UV) pulsed laser with a wavelength of 355 nm and a gated ICCD camera has been designed and tested. Most reef-building corals have fluorescent proteins that emit blue-green fluorescence on UV excitation. Seabed images were recorded by emitting UV pulsed laser and receiving fluorescence by the gated ICCD camera synchronized with the laser. Because the exposure time is very short, the sunlight background effect for the lidar image is suppressed, and this makes it possible to detect weak UV excited fluorescence even in the daytime. Live corals can be distinguished from dead coral skeletons based on the fluorescence images by verifying the coral image pattern and fluorescence intensity. We evaluated the system in a testing basin to 30-m depth, and we used the system to observe corals using a glass-bottom boat at Taketomi Island, Okinawa, Japan. Information about the live coral distribution along the boat track was obtained successfully around the island at depths from 2 to 12 m.
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