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LiDAR-Derived DEM and Raw Height Comparisons along Profile Corridor Gradients within a Forest  [PDF]
Michael G. Wing, Michael Craven, John Sessions, Jeff Wimer
Journal of Geographic Information System (JGIS) , 2013, DOI: 10.4236/jgis.2013.52011
Abstract:

We compared field based and airborne LiDAR-derived profile corridor measurements across forest canopy types and terrain ranging from 37% to 49% slope. Both LiDAR-derived DEM and raw LiDAR point elevations were compared to field data. Primary objectives included examining whether canopy type or terrain slope influenced LiDAR-derived profile measurements. A secondary objective included comparing cable logging payloads based on field measured profile elevations to payloads based on LiDAR-derived elevations. Average RMSE elevation errors were slightly lower for profile point to LiDAR DEM values (0.43 m) than profile point to nearest LiDAR elevation point (0.49 m) with differences being larger when sites within forest clearings were removed from analysis. No statistically significant relationship existed between field measured ground slopes and associated profile point and LiDAR DEM elevation differences but a mild correlation existed when LiDAR raw point elevation differences were compared. Our payload analysis determined the limiting payload distance and had consistent results across study sites. The DEM-based profile outperformed the nearest point profile by 5% on average. Results suggest that forest analysts should consider using the nearest LiDAR DEM value rather than the nearest LiDAR point elevation for terrain heights at discrete locations, particularly when forest canopy occludes locations of interest.

Return Signal Intensity Ratio Modulates the Impact of Background Signal on Ozone DIAL Night Time Measurement in the Troposphere  [PDF]
Nianwen Cao, Tetsuo Fuckuchi, Takashi Fujii, Zhengrong Chen, Jiansong Huang
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2010, DOI: 10.4236/jemaa.2010.27059
Abstract: This paper discusses the uncertainty of ozone differential absorption lidar (DIAL) measurements due to the impact of background signal. The impact of background signal on ozone concentration profiles is proportional to the background intensity and the ratio of return signal intensities at “on” and “off” wavelength ( ) (hereinafter we call it the return signal intensity ratio). Analysis suggests that an appropriate return signal intensity ratio can make the impact of background signal very small, negligible. The simulations based on the analysis coincide with the experimental results. The experimental results show that the impact of background signal is negligible at an appropriate return signal intensity ratio of 0.96 at wavelength pair (280,285 nm). In case of unknown background intensity, we can adjust the laser pulse energy levels at the two wavelengths to obtain an appropriate return signal intensity ratio on the oscilloscope to suppress the impact of background signal and ensure the accuracy of night time ozone measurements.
Cirrus Clouds and Multiple Tropopause Events over Buenos Aires  [PDF]
Susan Gabriela Lakkis, Mario Lavorato, Pablo Osvaldo Canziani, Héctor Lacomi
Atmospheric and Climate Sciences (ACS) , 2011, DOI: 10.4236/acs.2011.13013
Abstract: Lidar measurements of midlatitude cirrus clouds over Buenos Aires, collected between 2002 and 2003 are compared with multiple tropopauses (MT) retrieved from rawinsonde temperature retrievals. Results derived from the rawinsondes display MT events with an annual cycle which are fewest in March. Comparison with lidar observations shows that cirrus clouds are mostly located closely below the first tro-popause, but when cloud top is above the first tropopause, in 25% of cases, the cloud base is not above it, resulting in a cirrus cloud crossing the inter-tropopause region. Compared with the distribution of the whole population of midlatitude cirrus clouds, cross-tropopause cirrus clouds display a similar geometrical thick-ness as inter-tropopause cirrus clouds.
Effect of Elevation Data Accuracy on Storm Drainage Schemes, Lagos, Nigeria  [PDF]
Ashraf M. Elmoustafa, Hesham N. Farres, Mohamed M. ElFawy
Natural Resources (NR) , 2015, DOI: 10.4236/nr.2015.67041
Abstract: The check of elevation data is an essential step prior the start of any drainage study. An investigation for this concept was done in Lagos, Nigeria using two types of survey sources; a Digital Elevation Model (DEM) with a 15 m resolution produced from Russian Stereo Satellite images (RSS) and a LiDAR survey with a 5 m DEM resolution. A comparison between the RSS model survey and the LiDAR survey showed that LiDAR survey was more accurate than RSS survey and given high reliability. The study also showed that RSS survey could sometimes become misleading and could not assure reliability. A watershed modeling tool was used to analyze both surveys to produce the expected drainage streams. It was found that some locations using RSS had a false drainage direction when compared with higher accurate LiDAR surveys.
Remote sensing of volcanic terrains by terrestrial laser scanner: preliminary reflectance and RGB implications for studying Vesuvius crater (Italy)
A. Pesci,G. Teza,G. Ventura
Annals of Geophysics , 2008, DOI: 10.4401/ag-4455
Abstract: This work focuses on the use of terrestrial laser scanner (TLS) in the characterization of volcanic environments. A TLS survey of the Vesuvius crater (Somma-Vesuvius volcano, Italy) allows the construction of an accurate, georeferenced digital model of different sectors of the crater. In each sector, the intensity is computed for each point as the ratio between the emitted amplitude and the received one, normalized to the maximum signal, providing the radiometric information. Moreover, the RGB colours of the observed surfaces can be captured by means of a calibrated camera mounted on the TLS instrument. In this way, multi-band information is given, since a long range TLS operates in the near infrared band. The reflectance and RGB data are compared in order to verify if they are independent enough to be complementary for model analysis and inspection. Results show that the integration of RGB and intensity data can fully characterize this volcanic environment. The collected data are able to discriminate different volcanic deposits and to detect their stratigraphic features. In addition, our results shed light on the spatial extension of landslides and on the dimensions of rock fall/flow deposits affecting the inner walls of the crater. The remotely acquired TLS information from the Vesuvius crater is compared with that from a sedimentary terrain (coal-shale quarry) to detect possible similarities/differences between these two geological environments.
Ghost Imaging Lidar via Sparsity Constraints in Real Atmosphere  [PDF]
Mingliang Chen, Enrong Li, Wenlin Gong, Zunwang Bo, Xuyang Xu, Chengqiang Zhao, Xia Shen, Wendong Xu, Shensheng Han
Optics and Photonics Journal (OPJ) , 2013, DOI: 10.4236/opj.2013.32B021
Abstract:

We present a series of results acquired at a 2-kilometer distance using our lidar system under several weather conditions, clear, cloudy, light rain, moderately foggy, and night. The experimental results show that ghost imaging lidar via spar-sity constraints can realize imaging in all these weather conditions.

Urban Vegetation Mapping from Fused Hyperspectral Image and LiDAR Data with Application to Monitor Urban Tree Heights  [PDF]
Fatwa Ramdani
Journal of Geographic Information System (JGIS) , 2013, DOI: 10.4236/jgis.2013.54038
Abstract:

Urban vegetations have infinite proven benefits for urban inhabitants including providing shade, improving air quality, and enhancing the look and feel of communities. But creating a complete inventory is a time consuming and resource intensive process. The extraction of urban vegetation is a challenging task, especially to monitor the urban tree heights. In this study we present an efficient extraction method for mapping and monitoring urban tree heights using fused hyperspectral image and LiDAR data. Endmember distribution mapping using the spectral angle mapper technique is employed in this study. High convenience results achieved using fused hyperspectral and LiDAR data from this semiautomatics technique. This method could enable urban community organizations or local governments to map and monitor urbans tree height and its spatial distribution.

Compression of LiDAR Data Using Spatial Clustering and Optimal Plane-Fitting  [PDF]
Tarig A. Ali
Advances in Remote Sensing (ARS) , 2013, DOI: 10.4236/ars.2013.22008
Abstract:

With the advancement in geospatial data acquisition technology, large sizes of digital data are being collected for our world. These include air- and space-borne imagery, LiDAR data, sonar data, terrestrial laser-scanning data, etc. LiDAR sensors generate huge datasets of point of multiple returns. Because of its large size, LiDAR data has costly storage and computational requirements. In this article, a LiDAR compression method based on spatial clustering and optimal filtering is presented. The method consists of classification and spatial clustering of the study area image and creation of the optimal planes in the LiDAR dataset through first-order plane-fitting. First-order plane-fitting is equivalent to the Eigen value problem of the covariance matrix. The Eigen value of the covariance matrix represents the spatial variation along the direction of the corresponding eigenvector. The eigenvector of the minimum Eigen value is the estimated normal vector of the surface formed by the LiDAR point and its neighbors. The ratio of the minimum Eigen value and the sum of the Eigen values approximates the change of local curvature, which determines the deviation of the surface formed by a LiDAR point and its neighbors from the tangential plane formed at that neighborhood. If the minimum Eigen value is close to zero for example, then the surface consisting of the point and its neighbors is a plane. The objective of this ongoing research work is basically to develop a LiDAR compression method that can be used in the future at the data acquisition phase to help remove fake returns and redundant points.

Validation of High-Density Airborne LiDAR-Based Feature Extraction Using Very High Resolution Optical Remote Sensing Data  [PDF]
Shridhar D. Jawak, Satej N. Panditrao, Alvarinho J. Luis
Advances in Remote Sensing (ARS) , 2013, DOI: 10.4236/ars.2013.24033
Abstract:

This work uses the canopy height model (CHM) based workflow for individual tree crown delineation from LiDAR point cloud data in an urban environment and evaluates its accuracy by using very high-resolution PAN (spatial) and 8-band WorldView-2 imagery. LiDAR point cloud data were used to detect tree features by classifying point elevation values. The workflow includes resampling of LiDAR point cloud to generate a raster surface or digital terrain model, generation of hill-shade image and intensity image, extraction of digital surface model, generation of bare earth digital elevation model and extraction of tree features. Scene dependent extraction criteria were employed to improve the tree feature extraction. LiDAR-based refining/filtering techniques used for bare earth layer extraction were crucial for improving the subsequent tree feature extraction. The PAN-sharpened WV-2 image (with 0.5 m spatial resolution) used to assess the accuracy of LiDAR-based tree features provided an accuracy of 98%. Based on these inferences, we conclude that the LiDAR-based tree feature extraction is a potential application which can be used for understanding vegetation characterization in urban setup.

Wind Motions around the Tropical Cirrus Using Simultaneous Radar and Lidar Observations over Gadanki (13.45°N, 79.18°E), India  [PDF]
C. Dhananjaya Rao, M. Arunachalam Srinivasan, M. Krishnaiah, Y. Bhavani Kumar, S. V. B. Rao
International Journal of Geosciences (IJG) , 2014, DOI: 10.4236/ijg.2014.511103
Abstract: The present study describes variation of peak linear depolarization ratio (LDR) with wind around the cloud altitude using simultaneous observation of winds and cirrus cloud for the first time using Indian MST radar and polarization lidar co-located over a low latitude station Gadanki (13.7°N and 79.2°E). Three different cases of passage of the cirrus at different altitudes are noticed, one during a North-East monsoon day and other two during South-West monsoon days. The zonal wind below the cloud height has shown similar variation with LDR during 02 November 2006 and the meridional wind within the cloud height during 25 July 2007 and 08 June 2006 has shown opposite variation with LDR. Even though there is a significant increase in zonal wind due to the existence of tropical easterly jet (TEJ) above cloud height during 25 July 2007 and 08 June 2006, also, the vertical wind is found to be continuously varying during 25 July 2007 and it is upward dominant in the initial stage and is mostly downward in the later stage of observation on 08 June 2006, there is a slight descent in cloud altitude only during 25 July 2007. Thus, the wind above the cloud height alone may not affect the ascent/descent of the cloud top altitude. The potential temperature gradient is high within the cloud heights when the cirrus present near the cold point tropopause indicates the maximum air-mass mixing near the tropopause.
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