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Article: Multi-scale integration of satellite remote sensing improves characterization of dry-season green-up in an Amazon tropical evergreen forest

TitleMulti-scale integration of satellite remote sensing improves characterization of dry-season green-up in an Amazon tropical evergreen forest
Authors
KeywordsMulti-scale satellite observations
PlanetScope
MODIS
BRDF correction
Reflectance cross-calibration
Issue Date2020
PublisherElsevier Inc. The Journal's web site is located at http://www.elsevier.com/locate/rse
Citation
Remote Sensing of Environment, 2020, v. 246, p. article no. 111865 How to Cite?
AbstractIn tropical forests, leaf phenology—particularly the pronounced dry-season green-up—strongly regulates biogeochemical cycles of carbon and water fluxes. However, uncertainties remain in the understanding of tropical forest leaf phenology at different spatial scales. Phenocams accurately characterize leaf phenology at the crown and ecosystem scales but are limited to a few sites and time spans of a few years. Time-series satellite observations might fill this gap, but the commonly used satellites (e.g. MODIS, Landsat and Sentinel-2) have resolutions too coarse to characterize single crowns. To resolve this observational challenge, we used the PlanetScope constellation with a 3 m resolution and near daily nadir-view coverage. We first developed a rigorous method to cross-calibrate PlanetScope surface reflectance using daily BRDF-adjusted MODIS as the reference. We then used linear spectral unmixing of calibrated PlanetScope to obtain dry-season change in the fractional cover of green vegetation (GV) and non-photosynthetic vegetation (NPV) at the PlanetScope pixel level. We used the Central Amazon Tapajos National Forest k67 site, as all necessary data (from field to phenocam and satellite observations) was available. For this proof of concept, we chose a set of 22 dates of PlanetScope measurements in 2018 and 16 in 2019, all from the six drier months of the year to provide the highest possible cloud-free temporal resolution. Our results show that MODIS-calibrated dry-season PlanetScope data (1) accurately assessed seasonal changes in ecosystem-scale and crown-scale spectral reflectance; (2) detected an increase in ecosystem-scale GV fraction (and a decrease in NPV fraction) from June to November of both years, consistent with local phenocam observations with R2 around 0.8; and (3) monitored large seasonal trend variability in crown-scale NPV fraction. Our results highlight the potential of integrating multi-scale satellite observations to extend fine-scale leaf phenology monitoring beyond the spatial limits of phenocams.
Persistent Identifierhttp://hdl.handle.net/10722/283324
ISSN
2019 Impact Factor: 9.085
2015 SCImago Journal Rankings: 3.369

 

DC FieldValueLanguage
dc.contributor.authorWang, J-
dc.contributor.authorYang, D-
dc.contributor.authorDetto, M-
dc.contributor.authorNelson, BW-
dc.contributor.authorChen, M-
dc.contributor.authorGuan, K-
dc.contributor.authorWu, S-
dc.contributor.authorYan, Z-
dc.contributor.authorWu, J-
dc.date.accessioned2020-06-22T02:55:02Z-
dc.date.available2020-06-22T02:55:02Z-
dc.date.issued2020-
dc.identifier.citationRemote Sensing of Environment, 2020, v. 246, p. article no. 111865-
dc.identifier.issn0034-4257-
dc.identifier.urihttp://hdl.handle.net/10722/283324-
dc.description.abstractIn tropical forests, leaf phenology—particularly the pronounced dry-season green-up—strongly regulates biogeochemical cycles of carbon and water fluxes. However, uncertainties remain in the understanding of tropical forest leaf phenology at different spatial scales. Phenocams accurately characterize leaf phenology at the crown and ecosystem scales but are limited to a few sites and time spans of a few years. Time-series satellite observations might fill this gap, but the commonly used satellites (e.g. MODIS, Landsat and Sentinel-2) have resolutions too coarse to characterize single crowns. To resolve this observational challenge, we used the PlanetScope constellation with a 3 m resolution and near daily nadir-view coverage. We first developed a rigorous method to cross-calibrate PlanetScope surface reflectance using daily BRDF-adjusted MODIS as the reference. We then used linear spectral unmixing of calibrated PlanetScope to obtain dry-season change in the fractional cover of green vegetation (GV) and non-photosynthetic vegetation (NPV) at the PlanetScope pixel level. We used the Central Amazon Tapajos National Forest k67 site, as all necessary data (from field to phenocam and satellite observations) was available. For this proof of concept, we chose a set of 22 dates of PlanetScope measurements in 2018 and 16 in 2019, all from the six drier months of the year to provide the highest possible cloud-free temporal resolution. Our results show that MODIS-calibrated dry-season PlanetScope data (1) accurately assessed seasonal changes in ecosystem-scale and crown-scale spectral reflectance; (2) detected an increase in ecosystem-scale GV fraction (and a decrease in NPV fraction) from June to November of both years, consistent with local phenocam observations with R2 around 0.8; and (3) monitored large seasonal trend variability in crown-scale NPV fraction. Our results highlight the potential of integrating multi-scale satellite observations to extend fine-scale leaf phenology monitoring beyond the spatial limits of phenocams.-
dc.languageeng-
dc.publisherElsevier Inc. The Journal's web site is located at http://www.elsevier.com/locate/rse-
dc.relation.ispartofRemote Sensing of Environment-
dc.subjectMulti-scale satellite observations-
dc.subjectPlanetScope-
dc.subjectMODIS-
dc.subjectBRDF correction-
dc.subjectReflectance cross-calibration-
dc.titleMulti-scale integration of satellite remote sensing improves characterization of dry-season green-up in an Amazon tropical evergreen forest-
dc.typeArticle-
dc.identifier.emailWang, J: lucyjing@hku.hk-
dc.identifier.emailWu, S: shengwu@hku.hk-
dc.identifier.emailYan, Z: zbyan@hku.hk-
dc.identifier.emailWu, J: jinwu@hku.hk-
dc.identifier.authorityWu, J=rp02509-
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1016/j.rse.2020.111865-
dc.identifier.scopuseid_2-s2.0-85084846617-
dc.identifier.hkuros310538-
dc.identifier.volume246-
dc.identifier.spagearticle no. 111865-
dc.identifier.epagearticle no. 111865-
dc.publisher.placeUnited States-

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