{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,13]],"date-time":"2025-10-13T15:29:31Z","timestamp":1760369371933,"version":"build-2065373602"},"reference-count":69,"publisher":"MDPI AG","issue":"1","license":[{"start":{"date-parts":[[2017,1,7]],"date-time":"2017-01-07T00:00:00Z","timestamp":1483747200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"CAPES\/MEC - Brazil (Coordena\u00e7\u00e3o de Aperfei\u00e7oamento de Pessoal de N\u00edvel Superior","award":["BEX 1233-13-0"],"award-info":[{"award-number":["BEX 1233-13-0"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Although quantifying the massive exchange of carbon that takes place over the Amazon Basin remains a challenge, progress is being made as the remote sensing community moves from using traditional, reflectance-based vegetation indices, such as the Normalized Difference Vegetation Index (NDVI), to the more functional Photochemical Reflectance Index (PRI). This new index, together with satellite-derived estimates of canopy light interception and Sun-Induced Fluorescence (SIF), provide improved estimates of Gross Primary Production (GPP). This paper traces the development of these new approaches, compares the results of their analyses from multiple years of data acquired across the Amazon Basin and suggests further improvements in instrument design, data acquisition and processing. We demonstrated that our estimates of PRI are in generally good agreement with eddy-flux tower measurements of photosynthetic light use efficiency (\u03b5) at four sites in the Amazon Basin: r2 values ranged from 0.37 to 0.51 for northern flux sites and to 0.78 for southern flux sites. This is a significant advance over previous approaches seeking to establish a link between global-scale photosynthetic activity and remotely-sensed data. When combined with measurements of Sun-Induced Fluorescence (SIF), PRI provides realistic estimates of seasonal variation in photosynthesis over the Amazon that relate well to the wet and dry seasons. We anticipate that our findings will steer the development of improved approaches to estimate photosynthetic activity over the tropics.<\/jats:p>","DOI":"10.3390\/rs9010048","type":"journal-article","created":{"date-parts":[[2017,1,9]],"date-time":"2017-01-09T11:03:23Z","timestamp":1483959803000},"page":"48","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Progress in Remote Sensing of Photosynthetic Activity over the Amazon Basin"],"prefix":"10.3390","volume":"9","author":[{"given":"Celio","family":"De Sousa","sequence":"first","affiliation":[{"name":"Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331, USA"}]},{"given":"Thomas","family":"Hilker","sequence":"additional","affiliation":[{"name":"Department of Forest Engineering, Resources and Management, Oregon State University, Corvallis, OR 97331, USA"}]},{"given":"Richard","family":"Waring","sequence":"additional","affiliation":[{"name":"Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331, USA"}]},{"given":"Yhasmin","family":"De Moura","sequence":"additional","affiliation":[{"name":"Instituto Nacional de Pesquisas Espaciais (INPE), Divis\u00e3o de Sensoriamento Remoto, S\u00e3o Jos\u00e9 dos Campos, SP 12227-010, Brazil"}]},{"given":"Alexei","family":"Lyapustin","sequence":"additional","affiliation":[{"name":"NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA"}]}],"member":"1968","published-online":{"date-parts":[[2017,1,7]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1767","DOI":"10.1098\/rstb.2007.0022","article-title":"Observed change of the standardized precipitation index, its potential cause and implications to future climate change in the Amazon region","volume":"363","author":"Li","year":"2008","journal-title":"Philos. 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