Abstract
Abstract. Precision agriculture has always been the research hotspot around the world. And the optimization of nitrogen fertilization for crops is the core concerns. It is not only to improve the productivity of crops but also to avoid the environmental risks caused by over-fertilization. Therefore, accurate estimation of nitrogen status is crucial for determining an nitrogen recommendation. Remote sensing techniques have been widely used to monitor crops for years, and they could offer estimations for stress status diagnosis through obtaining vertical structure parameters and spectral reflectance properties of crops. As an active remote sensing technology, lidar is particularly attractive for 3-dimensional information at a high point density. It has unique edges in obtaining vertical structure parameters of crops. However, capability of spectral reflectance properties is what the current lidar technology lacks because of single wavelength detection. To solve this problem, the concept of novel hyperspectral lidar (HSL), which combines the advantages of hyperspectal reflectance with high 3-dimensional capability of lidar, was proposed in our study. The design of instrument was described in detail. A broadband laser pulse was emitted and reflectance spectrum with 32 channels could be detected. Furthermore, the experiment was carried out by the novel HSL system to testify the potential application for monitoring nitrogen stress. Rice under different levels of nitrogen fertilization in central China were selected as the object of study, and four levels of nitrogen fertilization (N1-N4) were divided. With the detection of novel lidar system, high precision structure parameters of crops could be provided. Meanwhile, spectral reflectance properties in 32 wavebands were also obtained. The high precision structure parameters could be used to evaluate the stress status of crops. And abundant spectral information in 32 wavebands could improve the capacity of lidar system significantly. The results demonstrate that it is more effective for HSL system to distinguish different levels of nitrogen fertilization. Overall, HSL allows for probing not only high precision structure parameters but also spectral reflectance properties of crops. Compared with other approaches, the novel HSL has the potential to provide more comprehensive information of crops which can be assessed remotely in the application of precision agriculture.
Highlights
The photosynthesis plays a significant role in the yields of crops production, which is the key procedure of energy and carbon balance in the ecosystem (Zheng Niu et al, 2015)
Since N is a key element in chlorophyll of crops, N shortage will result in non-optimal photosynthesis, which makes the monitoring of N content and management of N fertilizer important for the precision agriculture
Reflectance spectra collected by hyperspectral lidar (HSL) can be used to represent the different status of rice because they are related to properties of chlorophyll absorption to the incident laser
Summary
The photosynthesis plays a significant role in the yields of crops production, which is the key procedure of energy and carbon balance in the ecosystem (Zheng Niu et al, 2015). As for the traditional management technologies in agriculture, soil and plant testing methods have been successfully applied in monitoring N content and the N fertilizer effectivity (Liu et al, 2003; Chen et al, 2004, 2006). LiDAR with just single wavelength is lack of spectral properties of the crops, which makes it difficult to assess precisely nitrogen contents than passive hyperspectral remote sensing. There are some limitation to this technology in practical application, such as the laser sources and sensors selection according to the detection goals, the integration of different types of instruments (Nevalainen et al, 2013) These problems have not been solved until a supercontinuum laser source with a spectrum range from about 600 nm to 2000 nm was put forward (Kaasalainen et al 2007). In this paper, (1) a novel HSL system with supercontinuum laser source and 32-channel photosensitive detector array was introduced. (2) Rice under different nitrogen fertilization levels was employed by HSL to demonstrate the potential of this novel system in monitoring nitrogen stress of rice
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