A standard radiometric calibration was applied to convert the amplitude and the echo width to a physically well-defined radiometric quantity, namely the backscatter coefficient. However, the backscatter coefficient is strongly affected by the incidence angle between the laser beam and the leaf normal. In order to compensate for incidence angle effects, reference reflectors (Spectralon from Labsphere, Inc.) were used to build a look-up table to calibrated the backscatter coefficient. Our results showed that the backscatter coefficient had a strong correlation (R2 = 0.66) with LWC after correcting for the incidence angle effect. Good agreements were achieved between the predicted vertical profile of LWC and the measured vertical profile of LWC with a mean RMSE (root mean square error) value of 0.001 g/cm2 and a mean MAPE (mean absolute percent error) value of 4.46 %. Our study successfully demonstrated the feasibility of retrieving LWC vertical distribution within plant canopy from a terrestrial full-waveform LiDAR.
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Xi Zhu, Andrew K. Skidmore, Roshanak Darvishzadeh, Tiejun Wang, "Retrieval of vertical leaf water content using terrestrial full-waveform lidar," Proc. SPIE 9998, Remote Sensing for Agriculture, Ecosystems, and Hydrology XVIII, 99981U (25 October 2016);