University of Twente Student Theses


Evaluating the Potential of ICESat/GLAS data to Estimate Canopy Height in the New Forest National Park, UK

Iqbal, Irfan Akhtar (2010) Evaluating the Potential of ICESat/GLAS data to Estimate Canopy Height in the New Forest National Park, UK.

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Abstract:Geoscience Laser Altimeter System (GLAS) aboard Ice, Cloud and land Elevation Satellite (ICESat) is a new generation of spaceborne LiDAR which was launched in January, 2003. It is the first spaceborne instrument which can digitize the backscattered waveform and offer global coverage. Among others, scientific objectives of the mission include precise measurement of land topography and vegetation canopy heights. GLAS waveforms are affected by within-footprint topographic variations. This leads to uncertainty in accurate ground detection from the waveform which, in turn, is reflected in canopy heights. Existing approach of waveform processing suggests Gaussian decomposition of the waveform to a maximum of six modes. Peak of the last, out of six, mode is considered to be representing the ground return. Six modes, however, are not always sufficient to fit the waveform, resulting in discrepant information. This emphasizes the need of efficient waveform processing for accurate estimation of vegetation height. This study investigated GLAS elevation products, insights from which were inputs in canopy heights estimation from ‘raw’ waveforms. Further, canopy height estimates from GLAS were compared with those of airborne LiDAR heights acquired under similar environmental and topographic conditions. Digital elevation models were created from GLAS point elevations and compared with Ordnance Survey elevations. Possible reasons of uncertainties were analysed, on the basis of which a new method of waveform processing was developed. An automated method, applying Fourier Transformation technique, was used for the efficient detection of ground peak from ‘raw’ waveform. Canopy heights retrieved from GLAS waveforms were validated with field measured heights. The new method was able to explain 79% of variation in canopy heights with an RMSE of 3.18 meters, in the study area. In the premises of the study area, a non-coincident airborne LiDAR explained 80% of variation in canopy heights with an RMSE of 2.76 meters. The unexplained variation in canopy heights retrieved from GLAS data can be due to the possible sources errors; such as, footprint eccentricity, decay of energy between emitted and received energy, clinometric measurements in the field and limited number of sampled footprints. Results achieved with the new method were encouraging and demonstrated the potential of full-waveform large footprint spaceborne LiDAR in estimating canopy height. Keywords: GLAS/ICESat, Canopy height, Waveform processing, Full waveform, LiDAR
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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