{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,26]],"date-time":"2025-10-26T14:25:41Z","timestamp":1761488741538,"version":"build-2065373602"},"reference-count":55,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2011,8,4]],"date-time":"2011-08-04T00:00:00Z","timestamp":1312416000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>We present a network of sites across Fennoscandia for optical sampling of vegetation properties relevant for phenology monitoring and satellite data calibration. The network currently consists of five sites, distributed along an N-S gradient through Sweden and Finland. Two sites are located in coniferous forests, one in a deciduous forest, and two on peatland. The instrumentation consists of dual-beam sensors measuring incoming and reflected red, green, NIR, and PAR fluxes at 10-min intervals, year-round. The sensors are mounted on separate masts or in flux towers in order to capture radiation reflected from within the flux footprint of current eddy covariance measurements. Our computations and model simulations demonstrate the validity of using off-nadir sampling, and we show the results from the first year of measurement. NDVI is computed and compared to that of the MODIS instrument on-board Aqua and Terra satellite platforms. PAR fluxes are partitioned into reflected and absorbed components for the ground and canopy. The measurements demonstrate that the instrumentation provides detailed information about the vegetation phenology and variations in reflectance due to snow cover variations and vegetation development. Valuable information about PAR absorption of ground and canopy is obtained that may be linked to vegetation productivity.<\/jats:p>","DOI":"10.3390\/s110807678","type":"journal-article","created":{"date-parts":[[2011,8,5]],"date-time":"2011-08-05T08:19:22Z","timestamp":1312532362000},"page":"7678-7709","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":64,"title":["An Optical Sensor Network for Vegetation Phenology Monitoring and Satellite Data Calibration"],"prefix":"10.3390","volume":"11","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7644-6517","authenticated-orcid":false,"given":"Lars","family":"Eklundh","sequence":"first","affiliation":[{"name":"Department of Earth and Ecosystem Sciences, Lund University, S\u00f6lvegatan 12, Lund, SE-223 62, Sweden"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3100-7814","authenticated-orcid":false,"given":"Hongxiao","family":"Jin","sequence":"additional","affiliation":[{"name":"Department of Earth and Ecosystem Sciences, Lund University, S\u00f6lvegatan 12, Lund, SE-223 62, Sweden"}]},{"given":"Per","family":"Schubert","sequence":"additional","affiliation":[{"name":"Department of Earth and Ecosystem Sciences, Lund University, S\u00f6lvegatan 12, Lund, SE-223 62, Sweden"}]},{"given":"Radoslaw","family":"Guzinski","sequence":"additional","affiliation":[{"name":"Department of Geography and Geology, University of Copenhagen, \u00d8ster Voldgade 10, Copenhagen K, DK-1350, Denmark"}]},{"given":"Michal","family":"Heliasz","sequence":"additional","affiliation":[{"name":"Department of Earth and Ecosystem Sciences, Lund University, S\u00f6lvegatan 12, Lund, SE-223 62, Sweden"}]}],"member":"1968","published-online":{"date-parts":[[2011,8,4]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"479","DOI":"10.1046\/j.1365-2486.2003.00629.x","article-title":"Assessing the eddy covariance technique for evaluating carbon dioxide exchange rates of ecosystems: past, present and future","volume":"9","author":"Baldocchi","year":"2003","journal-title":"Glob. Chang. Biol"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"653","DOI":"10.1016\/j.envpol.2007.06.070","article-title":"Flux and concentration footprint modelling: State of the art","volume":"152","author":"Vesala","year":"2008","journal-title":"Environ. Pollut"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"165","DOI":"10.1016\/0273-1177(87)90308-5","article-title":"Evaluating North American net primary productivity with satellite observations","volume":"7","author":"Goward","year":"1987","journal-title":"Adv. Space Res"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1313","DOI":"10.1080\/01431169108929728","article-title":"A model of regional primary production for use with coarse resolution satellite data","volume":"12","author":"Prince","year":"1991","journal-title":"Int. J. Remote Sens"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"5263","DOI":"10.1029\/93JD03221","article-title":"Methodology for the estimation of terrestrial net primary production from remotely sensed data","volume":"99","author":"Ruimy","year":"1994","journal-title":"J. Geophys. Res"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"149","DOI":"10.1016\/0168-1923(95)02268-6","article-title":"Remote sensing of net primary production in boreal forest stands","volume":"78","author":"Goetz","year":"1996","journal-title":"Agr. Forst. Meteorol"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"20069","DOI":"10.1029\/2000JD000115","article-title":"Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981 to 1999","volume":"106","author":"Zhou","year":"2001","journal-title":"J. Geophys. Res"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"131","DOI":"10.1016\/S0304-3800(03)00267-9","article-title":"A remote sensing-based primary production model for grassland biomes","volume":"169","author":"Seaquist","year":"2003","journal-title":"Ecol. Model"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"519","DOI":"10.1016\/j.rse.2003.11.008","article-title":"Satellite-based modeling of gross primary production in an evergreen needleleaf forest","volume":"89","author":"Xiao","year":"2004","journal-title":"Remote Sens. Environ"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"G04014","DOI":"10.1029\/2006JG000162","article-title":"On the use of MODIS EVI to assess gross primary productivity of North American ecosystems","volume":"111","author":"Sims","year":"2006","journal-title":"J. Geophys. Res"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"576","DOI":"10.1016\/j.rse.2009.10.013","article-title":"A continuous measure of gross primary production for the conterminous United States derived from MODIS and AmeriFlux data","volume":"114","author":"Xiao","year":"2010","journal-title":"Remote Sens. Environ"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"817","DOI":"10.5194\/bg-5-817-2008","article-title":"Towards operational remote sensing of forest carbon balance across northern Europe","volume":"5","author":"Olofsson","year":"2008","journal-title":"Biogeosciences"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1178","DOI":"10.1016\/j.rse.2010.01.005","article-title":"Estimating northern peatland CO2 exchange from MODIS time series data","volume":"114","author":"Schubert","year":"2010","journal-title":"Remote Sens. Environ"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"379","DOI":"10.1023\/A:1016125215496","article-title":"Phenology: Its importance to the global change community","volume":"54","author":"Menzel","year":"2002","journal-title":"Climate Change"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1969","DOI":"10.1111\/j.1365-2486.2006.01193.x","article-title":"European phenological response to climate change matches the warming pattern","volume":"12","author":"Menzel","year":"2006","journal-title":"Glob. Chang. Biol"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"698","DOI":"10.1038\/386698a0","article-title":"Increased plant growth in the northern high latitudes from 1981 to 1991","volume":"386","author":"Myneni","year":"1997","journal-title":"Nature"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"3303","DOI":"10.1080\/01431160310001618149","article-title":"European plant phenology and climate as seen in a 20-year AVHRR land-surface parameter dataset","volume":"25","author":"Vidale","year":"2004","journal-title":"Int. J. Remote Sens"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"155","DOI":"10.1007\/s00484-006-0042-y","article-title":"Growing seasons of Nordic mountain birch in northernmost Europe as indicated by long-term field studies and analyses of satellite images","volume":"51","author":"Shutova","year":"2006","journal-title":"Int. J. Biometeorol"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"513","DOI":"10.1007\/s00484-007-0091-x","article-title":"Variability of the start of the growing season in Fennoscandia, 1982\u20132002","volume":"51","author":"Karlsen","year":"2007","journal-title":"Int. J. Biometeorol"},{"key":"ref_20","first-page":"253","article-title":"MODIS-NDVI-based mapping of the length of the growing season in northern Fennoscandia","volume":"10","author":"Karlsen","year":"2008","journal-title":"Int. J. Appl. Earth Obs"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"26","DOI":"10.1016\/j.rse.2005.03.011","article-title":"Determination of phenological dates in boreal regions using normalized difference water index","volume":"97","author":"Delbart","year":"2005","journal-title":"Remote Sens. Environ"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"385","DOI":"10.1016\/j.rse.2006.11.025","article-title":"AVHRR Derived Phenological Change in the Sahel and Soudan, Africa, 1982\u20132005","volume":"108","author":"Heumann","year":"2007","journal-title":"Remote Sens. Environ"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"2335","DOI":"10.1111\/j.1365-2486.2009.01910.x","article-title":"Intercomparison, interpretation, and assessment of spring phenology in North America estimated from remote sensing for 1982\u20132006","volume":"15","author":"White","year":"2009","journal-title":"Glob. Chang. Biol"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"178","DOI":"10.1007\/s004840100103","article-title":"Temperature data for phenological models","volume":"45","author":"Snyder","year":"2001","journal-title":"Int. J. Biometeorol"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2719","DOI":"10.1016\/j.rse.2010.06.005","article-title":"Annual changes in MODIS vegetation indices of Swedish coniferous forests in relation to snow dynamics and tree phenology","volume":"114","author":"Eklundh","year":"2010","journal-title":"Remote Sens. Environ"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"13521","DOI":"10.1073\/pnas.0506179102","article-title":"Satellite-observed photosynthetic trends across boreal North America associated with climate and fire disturbance","volume":"102","author":"Goetz","year":"2005","journal-title":"Proc. Nat. Acad. Sci. USA"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"323","DOI":"10.1007\/s00442-006-0657-z","article-title":"Use of digital webcam images to track spring green-up in a deciduous broadleaf forest","volume":"152","author":"Richardson","year":"2007","journal-title":"Oecologia"},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Balzarolo, M, Anderson, K, Nichol, C, Rossini, M, Vescovo, L, Arriga, N, Calvet, J-C, Carrara, A, Cerasoli Salvatori, S, and Cogliati, S (2011). Ground-based optical measurements at European flux sites: A review of methods, instruments and current controversies. Sensors, in review.","DOI":"10.3390\/s11087954"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"227","DOI":"10.1016\/j.rse.2006.04.003","article-title":"Spectral Network (SpecNet): What is it and why do we need it?","volume":"103","author":"Gamon","year":"2006","journal-title":"Remote Sens. Environ"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"411","DOI":"10.1016\/j.scitotenv.2007.11.007","article-title":"The use of remote sensing in light use efficiency based models of gross primary production: A review of current status and future requirements","volume":"404","author":"Hilker","year":"2008","journal-title":"Sci. Total Environ"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"1049","DOI":"10.1080\/01431168708954747","article-title":"Oblique view reflectance for assessing nitrogen status of incomplete canopies","volume":"8","author":"Court","year":"1987","journal-title":"Int. J. Remote Sens"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1131","DOI":"10.1080\/0143116031000116967","article-title":"Effect of sensor view angle on the assessment of agronomic traits by ground level hyper-spectral reflectance measurements in durum wheat under contrasting Mediterranean conditions","volume":"25","author":"Aparicio","year":"2004","journal-title":"Int. J. Remote Sens"},{"key":"ref_33","first-page":"961","article-title":"Comparison of nadir and off-nadir multispectral response patterns for six tallgrass prairie treatments in Eastern Kansas","volume":"62","author":"Dunham","year":"1996","journal-title":"Photogramm. Eng. Rem. Sens"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"139","DOI":"10.1016\/S0034-4257(99)00086-3","article-title":"View zenith angle effects on the forest information content of three spectral indices","volume":"72","author":"Gemmel","year":"2000","journal-title":"Remote Sens. Environ"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"3797","DOI":"10.1080\/09500340500106931","article-title":"View angle effects on the discrimination of selected Amazonian land cover types from a principal-component analysis of MISR spectra","volume":"26","author":"Xavier","year":"2005","journal-title":"Int. J. Remote Sens"},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Nicodemus, FE, Richmond, JC, Hsia, JJ, Ginsberg, IW, and Limperis, T (1977). Geometrical Considerations and Nomenclature for Reflectance, U.S. Department of Commerce, National Bureau of Standards.","DOI":"10.6028\/NBS.MONO.160"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"27","DOI":"10.1016\/j.rse.2006.03.002","article-title":"Reflectance quantities in optical remote sensing\u2014Definitions and case studies","volume":"103","author":"Schaepman","year":"2006","journal-title":"Remote Sens. Environ"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"127","DOI":"10.1016\/0034-4257(79)90013-0","article-title":"Red and photographic infrared linear combinations for monitoring vegetation","volume":"8","author":"Tucker","year":"1979","journal-title":"Remote Sens. Environ"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"244","DOI":"10.1016\/S0034-4257(99)00111-X","article-title":"A directional multispectral forest reflectance model","volume":"72","author":"Kuusk","year":"2000","journal-title":"Remote Sens. Environ"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"75","DOI":"10.1016\/0034-4257(90)90100-Z","article-title":"PROSPECT: A model of leaf optical properties spectra","volume":"34","author":"Jacquemoud","year":"1990","journal-title":"Remote Sens. Environ"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"675","DOI":"10.1109\/36.581987","article-title":"Second simulation of the satellite signal in the solar spectrum, 6S\u2014An overview","volume":"35","author":"Vermote","year":"1997","journal-title":"IEEE Trans. Geosci. Remote Sens"},{"key":"ref_42","unstructured":"Walck, C (2007). Handbook on Statistical Distributions for Experimentalists, University of Stockholm. International Report SUF-PFY\/96-01;."},{"key":"ref_43","unstructured":"Kuusk, A Personal communication: E-mail message, 09 May 2011."},{"key":"ref_44","doi-asserted-by":"crossref","unstructured":"Liang, S (2004). Quantitative Remote Sensing of Land Surfaces, John Wiley & Sons, Inc.","DOI":"10.1002\/047172372X"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"752","DOI":"10.2134\/agronj1986.00021962007800040039x","article-title":"Techniques for measuring intercepted and absorbed photo-synthetically active radiation in corn canopies","volume":"78","author":"Gallo","year":"1986","journal-title":"Agron. J"},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"490","DOI":"10.1016\/j.rse.2004.04.009","article-title":"Evaluation of MODIS LAI, fAPAR and the relation between fAPAR and NDVI in a semi-arid environment using in situ measurements","volume":"91","author":"Fensholt","year":"2004","journal-title":"Remote Sens. Environ"},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"240","DOI":"10.1016\/j.rse.2007.02.020","article-title":"Estimation of absorbed PAR across Scandinavia from satellite measurements. Part II: modeling and evaluating the fractional absorption","volume":"110","author":"Olofsson","year":"2007","journal-title":"Remote Sens. Environ"},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"3833","DOI":"10.1016\/j.rse.2008.06.006","article-title":"Development of a two-band enhanced vegetation index without a blue band","volume":"112","author":"Jiang","year":"2008","journal-title":"Remote Sens. Environ"},{"key":"ref_49","unstructured":"Bass, M, Mahajan, VN, and Stryland, EV (2010). Handbok of Optics, McGraw-Hill."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"1424","DOI":"10.1111\/j.1365-2486.2005.001002.x","article-title":"On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm","volume":"11","author":"Reichstein","year":"2005","journal-title":"Glob Chang Biol"},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"1597","DOI":"10.1016\/j.agrformet.2010.08.009","article-title":"Testing the performance of a novel spectral reflectance sensor, built with light emitting diodes (LEDs), to monitor ecosystem metabolism, structure and function","volume":"150","author":"Ryu","year":"2010","journal-title":"Agr. Forerst Meteorol"},{"key":"ref_52","unstructured":"Cohen, M, and Wallace, JR (1993). Radiosity and Realistic Image Synthesis, Morgan Kaufmann publishers."},{"key":"ref_53","unstructured":"Bass, M, Mahajan, VN, and Stryland, EV (2010). Handbook of Optics, McGraw-Hill."},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"1501","DOI":"10.1016\/j.agrformet.2010.07.011","article-title":"On the bias of instantaneous FAPAR estimates in open-canopy forests","volume":"150","author":"Widlowski","year":"2010","journal-title":"Agr. Forerst Meteorol"},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"980","DOI":"10.1364\/JOSA.38.000980","article-title":"Notes on the cos4 law of illumination","volume":"38","author":"Reiss","year":"1948","journal-title":"J. Opt. Soc. Am. A-Opt. Image Sci"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/11\/8\/7678\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T21:56:58Z","timestamp":1760219818000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/11\/8\/7678"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2011,8,4]]},"references-count":55,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2011,8]]}},"alternative-id":["s110807678"],"URL":"https:\/\/doi.org\/10.3390\/s110807678","relation":{},"ISSN":["1424-8220"],"issn-type":[{"type":"electronic","value":"1424-8220"}],"subject":[],"published":{"date-parts":[[2011,8,4]]}}}