1. Recent Data Campaigns and Results from the Laser Vegetation Imaging Sensor (LVIS): An Airborne, Medium-Footprint, Full-Waveform, Swath Mapping Laser Altimeter System
    Blair, J. B.; Hofton, M. A. R. D. L. L. S. B. G. H.  AGU  December 2005

    The Laser Vegetation Imaging Sensor (LVIS) is an airborne, medium-sized footprint laser altimeter system. By digitally recording the shape of the returning laser pulse (waveform), LVIS provides a precise and accurate view of the vertical structure within each footprint/pixel including both the sub-canopy and canopy-top topography. Applications of LVIS data include biomass estimation for a wide variety of forest types, ground surface change detection for tectonic studies, mapping sea surface topography to assist in coastal hazard assessment, and hydrology studies utilizing sub-canopy topography in densely forested regions. Since 1998, LVIS data have been collected in various areas of New Hampshire, Maine, Massachusetts, California, Maryland, Panama and Costa Rica. The data calibration and geolocation processing system utilizes a formal Bayesian least-squares-estimation of pointing, ranging and timing parameters based on a batch reduction of altimeter range residuals. Data are released publicly on the LVIS website at http://lvis.gsfc.nasa.gov. Results show data precisions of <50 cm are routinely achieved in all forest types and <5 cm in bare ground conditions. Because of its unique capability to simultaneously map vegetation and sub-canopy ground topography, LVIS data can be used to assess the accuracy of other remote sensing systems. For example, ground and canopy top elevations generated by LVIS were used to assess the accuracy of Shuttle Radar Topography Mission (SRTM) elevations at study sites with different levels of relief and land cover type. Results showed that the mean vertical offset between the SRTM elevations and LVIS ground elevations varied with landcover type and study site location. Comparisons between LVIS and ICESat will also be presented.



  2. Mapping Recent Lava and Pyroclastic Flows at Arenal Volcano, Costa Rica, Using Medium-Footprint, Waveform-Recording Airborne Lidar
    Hofton, M. A.; Blair, J. B. R. D. L. G. H.  AGU  December 2005

    Arenal volcano is a small (1.1 km in height), young stratovolcano in Costa Rica. Since 1968, when a lateral explosion occurred causing 78 deaths, the volcano has remained continuously active, with Strombolian eruptions, blocky lava flows, pyroclastic flows, and a permanent lava lake since 1974. In 1998 and 2005, NASA's Laser Vegetation Imaging Sensor (LVIS) was used to collect wide-swath 3-dimensional topographic images of the volcano. The LVIS is a full-waveform, scanning, medium-sized footprint airborne laser altimeter (also referred to as lidar) system. By digitally recording the shape of the returning laser pulse (waveform), the LVIS provides a precise and accurate view of both the sub-canopy and canopy-top topographies as well as the vertical and horizontal structure of vegetation at a horizontal resolution of 25 m. By comparing georeferenced waveform data collected in 1998 and 2005, as well as products derived from the laser waveform such as sub-canopy topography and canopy top topography, we map lava and pyroclastic flows deposited from 1998 to 2005. The thickness of the lava flows is estimated as well as the magnitude of any corresponding surface elevation and canopy change. As in situ measurements of lava height at flow edges are not representative of the total flow thickness, precise elevation data such as those provided by the LVIS are essential to calculate eruption volume and to study magma-supply dynamics. This study is an example of how air- and space-borne lidar can play a significant role in studying volcanoes in remote areas.



  3. Estimating Changes in Forest Height and Structure in Hubbard Brook Experimental Forest Using LIDAR Remote Sensing
    Odell, K.; Dubayah, R. H. M. B. J. B. H. G.  AGU  December 2005

    Understanding forest successional state and dynamics is important from the perspective of ecological modeling and management but presents challenges for remote sensing. In this paper we explore the efficacy of medium footprint waveform recording lidar remote sensing in detecting forest growth and successional status in a northeastern temperate mixed deciduous forest. Using data from the Laser Vegetation Imaging Sensor (LVIS) over Hubbard Brook Experimental Forest in northern New Hampshire, USA, we evaluated the changes in forest height and vertical structure that occurred between 1999 and 2003. LVIS is an airborne, medium-footprint (20- to 25-meter diameter), full waveform-recording lidar that has flown several missions since 1998 over various ecosystems. The system is unique amongst airborne sensors in that it digitally records the shape of the returning laser echo, or waveform, after its interaction with the various reflecting surfaces of the earth (leaves, branches, ground, etc.), providing a true 3-dimensional record of the surface structure. The Hubbard Brook Experimental Forest (HBEF) is a 3,160-hectare reserve located in the White Mountain National Forest of New Hampshire. It was established by the U.S. Forest Service in 1955 for hydrological research, and is now part of the NSF Long Term Ecological Research (LTER) network. In order to determine how the forest has changed, we examined medium-footprint lidar return waveform data from both years and compared changes in LVIS-derived canopy height and structural metrics (i.e. the height above the ground where 50% of waveform energy occurred). Additionally, footprints that had larger than expected height changes were examined to discover if observed differences were related to true disturbance, such as tree fall, or were the result of system and processing errors.



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