{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,23]],"date-time":"2026-01-23T19:12:29Z","timestamp":1769195549282,"version":"3.49.0"},"reference-count":46,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2015,12,19]],"date-time":"2015-12-19T00:00:00Z","timestamp":1450483200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000038","name":"Natural Sciences and Engineering Research Council of Canada","doi-asserted-by":"publisher","award":["RGPAS 446036-13"],"award-info":[{"award-number":["RGPAS 446036-13"]}],"id":[{"id":"10.13039\/501100000038","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Understanding plant photosynthesis, or Gross Primary Production (GPP), is a crucial aspect of quantifying the terrestrial carbon cycle. Remote sensing approaches, in particular multi-angular spectroscopy, have proven successful for studying relationships between canopy-reflectance and plant-physiology processes, thus providing a mechanism to scale up. However, many different instrumentation designs exist and few cross-comparisons have been undertaken. This paper discusses the design evolution of the Automated Multiangular SPectro-radiometer for Estimation of Canopy reflectance (AMSPEC) series of instruments. Specifically, we assess the performance of the PP-Systems Unispec-DC and Ocean Optics JAZ-COMBO spectro-radiometers installed on an updated, tower-based AMSPEC-III system. We demonstrate the interoperability of these spectro-radiometers, and the results obtained suggest that JAZ-COMBO can successfully be used to substitute more expensive measurement units for detecting and investigating photosynthesis and canopy spectra. We demonstrate close correlations between JAZ-COMBO and Unispec-DC measured canopy radiance (0.75 \u2264 R2 \u2264 0.85) and solar irradiance (0.95 \u2264 R2 \u2264 0.96) over a three month time span. We also demonstrate close agreement between the bi-directional distribution functions obtained from each instrument. We conclude that cost effective alternatives may allow a network of AMSPEC-III systems to simultaneously monitor various vegetation types in different ecosystems. This will allow to scale and improve our understanding of the interactions between vegetation physiology and spectral characteristics, calibrate broad-scale observations to stand-level measurements, and ultimately lead to improved understanding of changing vegetation spectral features from satellite.<\/jats:p>","DOI":"10.3390\/s151229906","type":"journal-article","created":{"date-parts":[[2015,12,21]],"date-time":"2015-12-21T10:43:59Z","timestamp":1450694639000},"page":"32020-32030","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":11,"title":["Technological Advancement in Tower-Based Canopy Reflectance Monitoring: The AMSPEC-III System"],"prefix":"10.3390","volume":"15","author":[{"given":"Riccardo","family":"Tortini","sequence":"first","affiliation":[{"name":"Integrated Remote Sensing Studio, Department of Forest Resources Management, University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Thomas","family":"Hilker","sequence":"additional","affiliation":[{"name":"College of Forestry, Oregon State University, 231 Peavy Hall, Corvallis, OR 97333, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0151-9037","authenticated-orcid":false,"given":"Nicholas","family":"Coops","sequence":"additional","affiliation":[{"name":"Integrated Remote Sensing Studio, Department of Forest Resources Management, University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Zoran","family":"Nesic","sequence":"additional","affiliation":[{"name":"Faculty of Land and Food Systems, Univeristy of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2015,12,19]]},"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":"1908","DOI":"10.1109\/TGRS.2005.853936","article-title":"Evaluation of remote sensing based terrestrial productivity from Modis using regional tower eddy flux network observations","volume":"44","author":"Heinsch","year":"2006","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"383","DOI":"10.1046\/j.1365-2486.2003.00573.x","article-title":"A cross-biome comparison of daily light use efficiency for gross primary production","volume":"9","author":"Turner","year":"2003","journal-title":"Glob. Chang. Biol."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"108","DOI":"10.1016\/S0034-4257(99)00061-9","article-title":"A global terrestrial monitoring network integrating tower fluxes, flask sampling, ecosystem modeling and Eos satellite data","volume":"70","author":"Running","year":"1999","journal-title":"Remote Sens. Environ."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1029\/2006JD007366","article-title":"ISLSCP Initiative II global data sets: Surface boundary conditions and atmospheric forcings for land-atmosphere studies","volume":"111","author":"Hall","year":"2006","journal-title":"J. Geophys. Res. Atmos."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"246","DOI":"10.1016\/j.rse.2006.04.006","article-title":"A mobile tram system for systematic sampling of ecosystem optical properties","volume":"103","author":"Gamon","year":"2006","journal-title":"Remote Sens. Environ."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"72","DOI":"10.1016\/j.compag.2007.01.003","article-title":"Instrumentation and approach for unattended year round tower based measurements of spectral reflectance","volume":"56","author":"Hilker","year":"2007","journal-title":"Comput. Electron. Agric."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"319","DOI":"10.1080\/10739149.2010.508357","article-title":"A new, automated, multiangular radiometer instrument for tower-based observations of canopy reflectance (Amspec II)","volume":"38","author":"Hilker","year":"2010","journal-title":"Instrum. Sci. Technol."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"4154","DOI":"10.3390\/s150204154","article-title":"Characterization of a field spectroradiometer for unattended vegetation monitoring. Key sensor models and impacts on reflectance","volume":"15","year":"2015","journal-title":"Sensors"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"255","DOI":"10.1016\/j.rse.2005.01.021","article-title":"The short wave aerostat-mounted imager (SWAMI): A novel platform for acquiring remotely sensed data from a tethered balloon","volume":"103","author":"Vierling","year":"2006","journal-title":"Remote Sens. Environ."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Rahman, A.F., Sims, D.A., and Cordova, V.D. (2005). Potential of MODIS EVI and surface temperature for directly estimating per-pixel ecosystem C fluxes. Geophys. Res. Lett., 32.","DOI":"10.1029\/2005GL024127"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"212","DOI":"10.1016\/j.rse.2005.07.006","article-title":"A MODIS-derived photochemical reflectance index to detect inter-annual variations in the photosynthetic light-use efficiency of a boreal deciduous forest","volume":"98","author":"Drolet","year":"2005","journal-title":"Remote Sens. Environ."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2136","DOI":"10.3390\/s8042136","article-title":"Relationship between remotely-sensed vegetation indices, canopy attributes and plant physiological processes: What vegetation indices can and cannot tell us about the landscape","volume":"8","author":"Glenn","year":"2008","journal-title":"Sensors"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"271","DOI":"10.1016\/0034-4257(89)90069-2","article-title":"Remote-sensing of foliar chemistry","volume":"30","author":"Curran","year":"1989","journal-title":"Remote Sens. Environ."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"138","DOI":"10.1016\/0034-4257(94)00071-T","article-title":"Status of remote-sensing algorithms for estimation of land-surface state parameters","volume":"51","author":"Hall","year":"1995","journal-title":"Remote Sens. Environ."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1918","DOI":"10.1016\/j.rse.2011.03.014","article-title":"Photosynsat, photosynthesis from space: Theoretical foundations of a satellite concept and validation from tower and spaceborne data","volume":"115","author":"Hall","year":"2011","journal-title":"Remote Sens. Environ."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"301","DOI":"10.1016\/j.rse.2012.02.007","article-title":"Data assimilation of photosyntetic light-use efficiency using multi-angular satellite data: I. Model formulation","volume":"121","author":"Hall","year":"2012","journal-title":"Remote Sens. Environ."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"421","DOI":"10.1016\/j.rse.2008.10.003","article-title":"Detection of foliage conditions and disturbance from multi-angular high spectral resolution remote sensing","volume":"113","author":"Hilker","year":"2009","journal-title":"Remote Sens. Environ."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"287","DOI":"10.1016\/j.rse.2012.02.008","article-title":"Data assimilation of photosynthetic light-use efficiency using multi-angular satellite data: II. Model implementation and validation","volume":"121","author":"Hilker","year":"2012","journal-title":"Remote Sens. Environ."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"31","DOI":"10.1016\/j.rse.2013.05.023","article-title":"Remote sensing of transpiration and heat fluxes using multi-angle observations","volume":"137","author":"Hilker","year":"2013","journal-title":"Remote Sens. Environ."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"227","DOI":"10.1016\/j.rse.2006.04.003","article-title":"Spectral Network (Specnet)\u2014What is it and why do we need it?","volume":"103","author":"Gamon","year":"2006","journal-title":"Remote Sens. Environ."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"291","DOI":"10.1111\/j.1469-8137.1995.tb03064.x","article-title":"Assessment of photosynthetic radiation-use efficiency with spectral reflectance","volume":"131","author":"Filella","year":"1995","journal-title":"New Phytol."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"492","DOI":"10.1007\/s004420050337","article-title":"The photochemical reflectance index: An optical indicator of photosynthetic radiation use efficiency across species, functional types, and nutrient levels","volume":"112","author":"Gamon","year":"1997","journal-title":"Oecologia"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"264","DOI":"10.1016\/S0034-4257(01)00224-3","article-title":"Remote sensing of canopy light use efficiency using the photochemical reflectance index-model and sensitivity analysis","volume":"78","author":"Barton","year":"2001","journal-title":"Remote Sens. Environ."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"33579","DOI":"10.1029\/2001JD900157","article-title":"Modeling spatially distributed ecosystem flux of boreal forest using hyperspectral indices from AVIRIS imagery","volume":"106","author":"Rahman","year":"2001","journal-title":"J. Geophys. Res."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"3201","DOI":"10.1016\/j.rse.2008.03.015","article-title":"Multi-angle remote sensing of forest light use efficiency by observing PRI variation with canopy shadow fraction","volume":"112","author":"Hall","year":"2008","journal-title":"Remote Sens. Environ."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Hilker, T., Coops, N.C., Hall, F.G., Black, T.A., Chen, B., Krishnan, P., Wulder, M.A., Sellers, P.J., Middleton, E.M., and Huemmrich, K.F. (2008). A modeling approach for upscaling gross ecosystem production to the landscape scale using remote sensing data. J. Geophys. Res., 113.","DOI":"10.1029\/2007JG000666"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"189","DOI":"10.1016\/j.foreco.2004.12.001","article-title":"Estimating stand structure using discrete-return lidar: An example from low density, fire prone ponderosa pine forets","volume":"208","author":"Hall","year":"2005","journal-title":"For. Ecol. Manage."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"400","DOI":"10.1016\/j.rse.2005.08.017","article-title":"A method to convert AVHRR normalized difference vegetation index time series to a standard viewing and illumination geometry","volume":"99","author":"Los","year":"2005","journal-title":"Remote Sens. Environ."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"4381","DOI":"10.1080\/01431160500113393","article-title":"Time-series validation of MODIS Land biophysical products in a Kalahari woodland, Africa","volume":"26","author":"Huermmrich","year":"2005","journal-title":"Int. J. Remote Sens."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.agrformet.2005.04.006","article-title":"Midday values of gross CO2 flux and light use efficiency during satellite overpasses can be used to directly estimate eight-day mean flux","volume":"131","author":"Sims","year":"2005","journal-title":"Agric. For. Meteorol."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"321","DOI":"10.1093\/treephys\/tpn040","article-title":"Influence of spring phenology on seasonal and annual carbon balance in two contrasting New England forests","volume":"29","author":"Richardson","year":"2009","journal-title":"Tree Physiol."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"447","DOI":"10.1016\/j.rse.2005.05.003","article-title":"Global mapping of foliage clumping index using multi-angular satellite data","volume":"97","author":"Chen","year":"2005","journal-title":"Remote Sens. Environ."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"237","DOI":"10.1016\/j.agrformet.2004.11.012","article-title":"Carbon, energy and water fluxes at mature and disturbed forest sites, Saskatchewan, Canada","volume":"136","author":"Amiro","year":"2006","journal-title":"Agric. For. Meteorol."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"29029","DOI":"10.1029\/97JD02317","article-title":"Carbon distribution and aboveground net primary production in aspen, jack pine, and black spruce stands in Saskatchewan and Manitoba, Canada","volume":"102","author":"Gower","year":"1997","journal-title":"J. Geophys. Res."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"89","DOI":"10.1111\/j.1365-2486.2006.01281.x","article-title":"Comparison of carbon dioxide fluxes over three boreal black spruce forests in Canada","volume":"13","author":"Bergeron","year":"2007","journal-title":"Glob. Chang. Biol."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"747","DOI":"10.2307\/2401901","article-title":"Solar radiation and productivity in tropical exosystems","volume":"9","author":"Monteith","year":"1972","journal-title":"J. Appl. Ecol."},{"key":"ref_38","unstructured":"Spectralon\u00ae Diffuse Reflectance Targets Specifications. Available online: http:\/\/www.webcitation.org\/6ds9dOh0w."},{"key":"ref_39","unstructured":"Ocean Optics Glossary. Available online: http:\/\/www.webcitation.org\/6ds9jzIxC."},{"key":"ref_40","first-page":"277","article-title":"Climate and the efficiency of crop production in Britain","volume":"281","author":"Monteith","year":"1977","journal-title":"Philos. Trans. R. Soc. B"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"20455","DOI":"10.1029\/92JD01411","article-title":"A bidirectional reflectance model of the Earth's surface for the correction of remote sensing data","volume":"97","author":"Roujean","year":"1992","journal-title":"J. Geophys. Res."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"21077","DOI":"10.1029\/95JD02371","article-title":"On the derivation of kernels for kernel-driven models of bidirectional reflectance","volume":"100","author":"Wanner","year":"1995","journal-title":"J. Geophys. Res. Atmos."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"2863","DOI":"10.1016\/j.rse.2010.07.004","article-title":"Remote sensing of photosynthetic light-use efficiency across two forested biomes: Spatial scaling","volume":"114","author":"Hilker","year":"2010","journal-title":"Remote Sens. Environ."},{"key":"ref_44","doi-asserted-by":"crossref","unstructured":"Hilker, T., Coops, N.C., Hall, F.G., Nichol, C.J., Lyapustin, A., Black, T.A., Wulder, M.A., Leuning, R., Barr, A., and Hollinger, D.Y. (2011). Inferring terrestrial photosynthetic light use efficiency of temperate ecosystems from space. J. Geophys. Res., 116.","DOI":"10.1029\/2011JG001692"},{"key":"ref_45","doi-asserted-by":"crossref","unstructured":"Mather, P., and Koch, M. (2011). Computer Processing of Remotely-Sensed Images: An Introduction, John Wiley & Sons. [4th ed.].","DOI":"10.1002\/9780470666517"},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"489","DOI":"10.1016\/j.agrformet.2010.01.004","article-title":"A simple filtered photodiode instrument for continuous measurement of narrowband NDVI and PRI over vegetated canopies","volume":"150","author":"Garrity","year":"2010","journal-title":"Agric. For. Meteorol."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/15\/12\/29906\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T20:54:25Z","timestamp":1760216065000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/15\/12\/29906"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2015,12,19]]},"references-count":46,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2015,12]]}},"alternative-id":["s151229906"],"URL":"https:\/\/doi.org\/10.3390\/s151229906","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2015,12,19]]}}}