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Beyond 3D: Temporal and Biochemical applica1ons of a Green Terrestrial Laser Scanner Jan U.H. Eitel a,b, Lee A. Vierling a, Troy S. Magney a aGeospa1al Laboratory for Environmental Dynamics, University of Idaho, Moscow, ID 83844-‐1135, USA, e-‐mail: [email protected] (Magney), [email protected] (Eitel), [email protected] (Vierling) bMcCall Outdoor Science School, University of Idaho, McCall, ID 83638, USA
Abstract The three dimensional (3D) datasets provided by terrestrial laser scanners (TLS) play an important role in expanding and improving our understanding of ecological processes. Representa1ve of this progress made possible by TLS data, we present one of our studies that u1lized 3D datasets to obtain new insights into water erosional processes (Eitel et al., 2011a). Besides providing 3D point cloud informa1on, TLS can also provide laser return intensity informa1on that can be u1lized to obtain informa1on about chemical proper1es of natural surfaces. We present findings (Eitel et al., 2010 and 2011b) that illustrate the poten1al of laser return intensity for providing foliar chlorophyll and nitrogen content. We conclude that laser scanning should be seen as a four dimensional (x,y,z, laser return intensity) rather than a three dimensional (x,y,z) measurement process.
A) Water Erosion (Eitel et al., 2011a) We tested the effect of surface roughness effects on erosion processes in rangelands. Local surface roughness (locRMSH) was nega1vely correlated (r2>0.71, RMSE<95.97 g min−1, and r2>0.74, RMSE<90.07 g min−1, respec1vely) with concentrated flow erosion. Our results indicate that TLS is a useful tool to enhance our current understanding of the effect of surface roughness on overland flow erosion processes. The strong rela1onships between locRMSH and concentrated flow erosion suggests further that TLS derived surface roughness allows more rigorous parameteriza1on of soil erosion models and thus ul1mately may lead to model improvements. B) Foliar chlorophyll (Eitel et al., 2010) The objec1ve of this study was to determine the poten1al usefulness of TLS with a green (532 nm) scanning laser to measure chlorophyll a and b content (Chlab). The TLS measurements were obtained from saplings of two tree species (Quercus macrocarpa and Acer saccharum). The green laser return intensity value was strongly correlated with wet-‐ chemically determined Chlab (r2=0.77). Our results show that green scanning terrestrial laser scanners are suitable for measuring foliar Chlab in simple canopies of small broadleaved plants. Literature Cited
Coops, N.C., Hilker, T., Hall, F.G., Nichol, C.J. and Drolet, G.G., 2010. Es1ma1on of light-‐use efficiency of terrestrial ecosystems from space: A status report. BioScience, 60(10). Eitel, J.U.H., Williams, C.J., Vierling, L.A., Al-‐Hamdan, O.Z., Pierson, F.B., 2011a. Suitability of terrestrial laser scanning for studying surface roughness effects on concentrated flow erosion processes in rangelands. Catena, 87, 398-‐407. Eitel, J.U.H., Vierling, L.A., Long, D.S., Hunt, E.R., 2011b. Early season remote sensing of wheat nitrogen status using a green scanning laser. Agricultural and Forest Meteorology 151, 1338-‐1345. Eitel, J.U.H., Vierling, L.A., Long, D.S., 2010. Simultaneous measurements of plant structure and chlorophyll content in broadleaf saplings with a terrestrial laser scanner. Remote Sensing of Environment 114, 2229-‐2237. Gamon, J.A., Penuelas, J. and Field, C.B., 1992. A narrow-‐waveband spectral index that tracks diurnal changes in photosynthe1c efficiency. Remote Sensing of Environment, 41: 35-‐44. Hilker, T. Coops, N.C., Hall, F.G., Black, T.A., Wulder, M.A., Nesic, Z., and P. Krishnan., 2008. Separa1ng physiologically and direc1onally induced changes in PRI using BRDF models. Remote Sensing of Environment, 2777-‐2788.
Acknowledgements This research was supported by USDA-‐NIFA Award No. 2011-‐67003-‐3034, the Research Grant Award No.L08AC14585 by the Bureau of Land Management, a specific coopera1ve agreement between the University of Idaho and the USDA-‐ARS, and the University of Idaho Harold Heady professorship. Funding to acquire the TLS was provided by the University of Idaho, Idaho NSF EPSCoR, and by the Na1onal Science Founda1on under ward number EPS-‐0814387.
C) Foliar nitrogen (Eitel et al., 2011b) We examined the ability to quan1fy foliar nitrogen (N) status of spring wheat (Tri1cum aes1vum L.) using a green (532 nm) terrestrial laser scanner during an early stem extension growth stage (Zadoks growth stage 3.2). Laser data were processed by (1) removing soil background returns based on laser-‐determined height informa1on, (2) standardizing green laser intensity based on white-‐reference panel readings, and (3) filtering noisy laser returns from leaf edges based on a laser return intensity threshold value. The return intensity of the reflected green laser light more accurately (r2 = 0.68, RMSE = 0.30 µg g−1) predicted foliar N concentra1on than conven1onal chlorophyll meter readings (r2 = 0.36, RMSE = 0.41 µg g−1) and spectral indices measured by a ground op1cal on-‐the-‐go sensor (r2 < 0.41, RMSE > 0.39 µg g−1).
D) Current: Remote Mapping of PhotosyntheKc Efficiency / Xanthophyll Cycle Responses
During 1mes when leaves are under some environmental stress (such as that resul1ng from water or heat stress, a situa1on that might increase under global environmental change scenarios), the light that normally would go towards photosynthesis is instead dissipated by the leaf through the xanthophyll cycle. Consequently, the photosynthe1c light use efficiency (and thus plant carbon absorp1on) decreases in order to protect the photosynthe1c apparatus of the leaf. Importantly, with decreasing photosynthe1c efficiency, the rela1ve concentra1on of xanthophyll pigments change, which leads to a decreasing reflectance at 531 nm (Gamon et al., 1992; Hilker et al., 2008; Coops et al., 2010). Since the 532 nm laser coincides closely with the 531 nm detec1on band found to be useful in passive remote sensing studies of vegeta1on physiology, we wish to test whether varia1on in reflected laser intensity in this band can track changes in xanthophyll pigment ac1vity
Conclusion The above studies illustrate the poten1al of TLS datasets for studying ecological processes. Considering the poten1al of laser return intensity to provide chemical proper1es of natural surfaces should encourage the scien1fic community to use laser scanning as a four dimensional (x,y,z, laser return intensity) rather than just a three dimensional (x,y,z) measurement process with myriad applica1ons in a wide variety of different disciplines.
Gamon et al., 1992
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