{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,21]],"date-time":"2026-04-21T15:18:12Z","timestamp":1776784692088,"version":"3.51.2"},"reference-count":38,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2022,5,4]],"date-time":"2022-05-04T00:00:00Z","timestamp":1651622400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Natural Science Foundation of China","award":["42171378"],"award-info":[{"award-number":["42171378"]}]},{"name":"National Natural Science Foundation of China","award":["2017YFE0122500"],"award-info":[{"award-number":["2017YFE0122500"]}]},{"name":"National Natural Science Foundation of China","award":["2018CXGC0209"],"award-info":[{"award-number":["2018CXGC0209"]}]},{"name":"National Key Research and Development Program of China","award":["42171378"],"award-info":[{"award-number":["42171378"]}]},{"name":"National Key Research and Development Program of China","award":["2017YFE0122500"],"award-info":[{"award-number":["2017YFE0122500"]}]},{"name":"National Key Research and Development Program of China","award":["2018CXGC0209"],"award-info":[{"award-number":["2018CXGC0209"]}]},{"name":"Major Science and Technology Innovation Project of Shandong Province","award":["42171378"],"award-info":[{"award-number":["42171378"]}]},{"name":"Major Science and Technology Innovation Project of Shandong Province","award":["2017YFE0122500"],"award-info":[{"award-number":["2017YFE0122500"]}]},{"name":"Major Science and Technology Innovation Project of Shandong Province","award":["2018CXGC0209"],"award-info":[{"award-number":["2018CXGC0209"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>As the major nutrient affecting crop growth, accurate assessing of nitrogen (N) is crucial to precise agricultural management. Although improvements based on ground and satellite data nitrogen in monitoring crops have been made, the application of these technologies is limited by expensive costs, covering small spatial scales and low spatiotemporal resolution. This study strived to explore an effective approach for inversing and mapping the distributions of the canopy nitrogen concentration (CNC) based on Unmanned Aerial Vehicle (UAV) hyperspectral image data in a typical apple orchard area of China. A Cubert UHD185 imaging spectrometer mounted on a UAV was used to obtain the hyperspectral images of the apple canopy. The range of the apple canopy was determined by the threshold method to eliminate the effect of the background spectrum from bare soil and shadow. We analyzed and screened out the spectral parameters sensitive to CNC, including vegetation indices (VIs), random two-band spectral indices, and red-edge parameters. The partial least squares regression (PLSR) and backpropagation neural network (BPNN) were constructed to inverse CNC based on a single spectral parameter or a combination of multiple spectral parameters. The results show that when the thresholds of normalized difference vegetation index (NDVI) and normalized difference canopy shadow index (NDCSI) were set to 0.65 and 0.45, respectively, the canopy\u2019s CNC range could be effectively identified and extracted, which was more refined than random forest classifier (RFC); the correlation between random two-band spectral indices and nitrogen concentration was stronger than that of other spectral parameters; and the BPNN model based on the combination of random two-band spectral indices and red-edge parameters was the optimal model for accurately retrieving CNC. Its modeling determination coefficient (R2) and root mean square error (RMSE) were 0.77 and 0.16, respectively; and the validation R2 and residual predictive deviation (RPD) were 0.75 and 1.92. The findings of this study can provide a theoretical basis and technical support for the large-scale, rapid, and non-destructive monitoring of apple nutritional status.<\/jats:p>","DOI":"10.3390\/s22093503","type":"journal-article","created":{"date-parts":[[2022,5,4]],"date-time":"2022-05-04T10:49:30Z","timestamp":1651661370000},"page":"3503","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":27,"title":["Inversion of Nitrogen Concentration in Apple Canopy Based on UAV Hyperspectral Images"],"prefix":"10.3390","volume":"22","author":[{"given":"Wei","family":"Li","sequence":"first","affiliation":[{"name":"College of Resources and Environment, Shandong Agricultural University, Tai\u2019an 271018, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xicun","family":"Zhu","sequence":"additional","affiliation":[{"name":"College of Resources and Environment, Shandong Agricultural University, Tai\u2019an 271018, China"},{"name":"National Engineering Research Center for Efficient Utilization of Soil and Fertilizer Resources, Tai\u2019an 271018, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xinyang","family":"Yu","sequence":"additional","affiliation":[{"name":"College of Resources and Environment, Shandong Agricultural University, Tai\u2019an 271018, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Meixuan","family":"Li","sequence":"additional","affiliation":[{"name":"College of Resources and Environment, Shandong Agricultural University, Tai\u2019an 271018, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xiaoying","family":"Tang","sequence":"additional","affiliation":[{"name":"College of Resources and Environment, Shandong Agricultural University, Tai\u2019an 271018, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jie","family":"Zhang","sequence":"additional","affiliation":[{"name":"College of Resources and Environment, Shandong Agricultural University, Tai\u2019an 271018, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yuliang","family":"Xue","sequence":"additional","affiliation":[{"name":"College of Resources and Environment, Shandong Agricultural University, Tai\u2019an 271018, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Canting","family":"Zhang","sequence":"additional","affiliation":[{"name":"College of Resources and Environment, Shandong Agricultural University, Tai\u2019an 271018, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yuanmao","family":"Jiang","sequence":"additional","affiliation":[{"name":"National Apple Engineering and Technology Research Center, College of Horticulture Science and Engineering, Shandong Agricultural University, Tai\u2019an 271018, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2022,5,4]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1714","DOI":"10.1016\/S2095-3119(18)62098-2","article-title":"Correlation of production constraints with the yield gap of apple cropping systems in Luochuan County, China","volume":"18","author":"Zhang","year":"2019","journal-title":"J. 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