{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,10]],"date-time":"2026-04-10T06:04:18Z","timestamp":1775801058958,"version":"3.50.1"},"reference-count":43,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2022,2,10]],"date-time":"2022-02-10T00:00:00Z","timestamp":1644451200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["31500392"],"award-info":[{"award-number":["31500392"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["41876093"],"award-info":[{"award-number":["41876093"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100003995","name":"Anhui Provincial Natural Science Foundation","doi-asserted-by":"publisher","award":["2008085QD166"],"award-info":[{"award-number":["2008085QD166"]}],"id":[{"id":"10.13039\/501100003995","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Science and Technology Innovation Action Plan of Shanghai Science and Technology Commission","award":["19DZ1201505"],"award-info":[{"award-number":["19DZ1201505"]}]},{"name":"Key Project of Philosophy and Social Science Research of the Ministry of Education","award":["19JZD023"],"award-info":[{"award-number":["19JZD023"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The chlorophyll content of leaves is an important indicator of plant environmental stress, photosynthetic capacity, and is widely used to diagnose the growth and health status of vegetation. Traditional chlorophyll content inversion is based on the vegetation index under pure species, which rarely considers the impact of interspecific competition and species mixture on the inversion accuracy. To solve these limitations, the harmonic analysis (HA) and the Hilbert\u2013Huang transform (HHT) were introduced to obtain the frequency index, which were combined with spectral index as the input parameters to estimate chlorophyll content based on the unmanned aerial vehicle (UAV) image. The research results indicated that: (1) Based on a comparison of the model accuracy for three different types of indices in the same period, the estimation accuracy of the pure spectral index was the lowest, followed by that of the frequency index, whereas the mixed index estimation effect was the best. (2) The estimation accuracy in November was lower than that in other months; the pure spectral index coefficient of determination (R2) was only 0.5208, and the root\u2013mean\u2013square error (RMSE) was 4.2144. The estimation effect in September was the best. The model R2 under the mixed index reached 0.8283, and the RMSE was 2.0907. (3) The canopy chlorophyll content (CCC) estimation under the frequency domain index was generally better than that of the pure spectral index, indicating that the frequency information was more sensitive to subtle differences in the spectrum of mixed vegetation. These research results show that the combination of spectral and frequency information can effectively improve the mapping accuracy of the chlorophyll content, and provid a theoretical basis and technology for monitoring the chlorophyll content of mixed vegetation in wetlands.<\/jats:p>","DOI":"10.3390\/rs14040827","type":"journal-article","created":{"date-parts":[[2022,2,11]],"date-time":"2022-02-11T02:40:17Z","timestamp":1644547217000},"page":"827","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":16,"title":["UAV Mapping of the Chlorophyll Content in a Tidal Flat Wetland Using a Combination of Spectral and Frequency Indices"],"prefix":"10.3390","volume":"14","author":[{"given":"Wei","family":"Zhuo","sequence":"first","affiliation":[{"name":"School of Geography and Tourism, Anhui Normal University, Wuhu 241000, China"},{"name":"Resources, Environment and Geographic Information Engineering Anhui Engineering Technology Research Center, Anhui Normal University, Wuhu 241000, China"}]},{"given":"Nan","family":"Wu","sequence":"additional","affiliation":[{"name":"School of Geographic Sciences, East China Normal University, Shanghai 200241, China"},{"name":"Key Laboratory of Geographic Information Science, Ministry of Education, East China Normal University, Shanghai 200241, China"}]},{"given":"Runhe","family":"Shi","sequence":"additional","affiliation":[{"name":"School of Geographic Sciences, East China Normal University, Shanghai 200241, China"},{"name":"Key Laboratory of Geographic Information Science, Ministry of Education, East China Normal University, Shanghai 200241, China"},{"name":"Joint Research Institute of Resources and Environment, East China Normal University, Shanghai 200241, China"},{"name":"Institute of Eco-Chongming, East China Normal University, Shanghai 202162, China"}]},{"given":"Zuo","family":"Wang","sequence":"additional","affiliation":[{"name":"School of Geography and Tourism, Anhui Normal University, Wuhu 241000, China"},{"name":"Resources, Environment and Geographic Information Engineering Anhui Engineering Technology Research Center, Anhui Normal University, Wuhu 241000, China"}]}],"member":"1968","published-online":{"date-parts":[[2022,2,10]]},"reference":[{"key":"ref_1","first-page":"3701","article-title":"Assessing and Modeling the Impacts of Wetland Land Cover Changes on Water Provision and Habitat Quality Ecosystem Services","volume":"29","author":"Rahimi","year":"2020","journal-title":"Nonrenewable Resour."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Wu, N., Shi, R., Zhuo, W., Zhang, C., Zhou, B., Xia, Z., Tao, Z., Gao, W., and Tian, B. 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