| 1. |
- Mahoney, Craig, et al.
(författare)
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Slope Estimation from ICESat/GLAS
- 2014
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 6:10, s. 10051-10069
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel technique to infer ground slope angle from waveform LiDAR, known as the independent slope method (ISM). The technique is applied to large footprint waveforms (similar to 60 m mean diameter) from the Ice, Cloud and Land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS) to produce a slope dataset of near-global coverage at 0.5 degrees x 0.5 degrees resolution. ISM slope estimates are compared against high resolution airborne LiDAR slope measurements for nine sites across three continents. ISM slope estimates compare better with the aircraft data (R-2 = 0.87 and RMSE = 5.16 degrees) than the Shuttle Radar Topography Mission Digital Elevation Model (SRTM DEM) inferred slopes (R-2 = 0.71 and RMSE = 8.69 degrees). ISM slope estimates are concurrent with GLAS waveforms and can be used to correct biophysical parameters, such as tree height and biomass. They can also be fused with other DEMs, such as SRTM, to improve slope estimates.
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| 2. |
- Shakesby, Richard A., et al.
(författare)
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The Schmidt hammer as a Holocene calibrated-age dating technique : Testing the form of the R-value-age relationship and defining the predicted-age errors
- 2011
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 21:4, s. 615-628
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Tidskriftsartikel (refereegranskat)abstract
- Most recent developments of Schmidt-hammer exposure-age dating (SHD) as a calibrated-age dating tool have been limited by the use of locations at two age control points. This has necessitated: (1) making assumptions about a linear R-value-age relationship; and (2) basing predictions of age errors only on R-value variance at the two age control points. This paper analyses 9900 R-values obtained from multiple-age control points on a sequence of glacio-isostatically raised shorelines with well constrained ages (Skuleskogen High Coast World Heritage Site and environs, Gulf of Bothnia, northern Sweden) ranging from modern to 10.5 ka in age. The sampling design involved 30 measurements on granite beach boulders from 30 sites at 11 age control points. The R-value-age relationship is best described by a linear function (ordinary least squares, OLS) with an R-2 of 0.89 (p < 0.0001). Predicted-age errors are calculated using two approaches: (1) OLS regression, which takes account of the uncertainties associated with the regression line and the age control points; and (2) weighted total least squares (WTLS) regression which, in addition, takes account of possible shoreline age errors and the heteroscedasticity of R-value residuals with increasing age. With both approaches, 95% predicted-age errors are relatively modest: +/- 355-455 years and +/- 300-515 years, respectively, with larger R-value variance and hence uncertainty for older surfaces, and the possibility of further improvement from a more selective field sampling scheme that differentiates between age-related and non-age-related rock-surface variability. Our results also indicate that for certain lithologies and weathering environments, it is possible to construct reliable calibrated-age curves from relatively few age control points.
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