The Canopy Semi-analytic Pgap And Radiative Transfer (CanSPART) model: Formulation and application
► Developed semi-analytic multi-layer model to predict gap probability and radiation transfer in clumped canopies. ► Analytic approximation to the crown porosity: computationally efficient and demonstrated validity. ► Applied to complex canopy structures. ► Can be formulated in terms of a clumping f...
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| Veröffentlicht in: | Agricultural and forest meteorology 2012-07, Vol.160, p.14-35 |
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| creator | Haverd, V. Lovell, J.L. Cuntz, M. Jupp, D.L.B. Newnham, G.J. Sea, W. |
| description | ► Developed semi-analytic multi-layer model to predict gap probability and radiation transfer in clumped canopies. ► Analytic approximation to the crown porosity: computationally efficient and demonstrated validity. ► Applied to complex canopy structures. ► Can be formulated in terms of a clumping factor: single clumping factor shown to perform well compared to height- and angle-resolved clumping factor. ► Results agree well with site observations of albedo, provided the effect of clumping on scattered radiation interception is included.
We present CanSPART: a model of gap probability (Pgap) based on a simple but flexible geometric vegetation canopy structure, coupled to a one-dimensional radiative transfer scheme, to account for the effects of crown structure and trunks on vertically resolved canopy radiation fluxes. The Pgap component of the model is intended for use in inverting ground-based and airborne gap-frequency data for biometric variables, while the full CanSPART model is intended for application within a one-dimensional multilayer soil-vegetation-atmosphere-transfer model. Our approach to modelling Pgap is novel because it uses an analytic approximation to the crown porosity, which makes it computationally efficient. Further, it can accommodate any distribution of crown and trunk heights and dimensions, allowing the model to be applied to complex canopy structures with multiple layers. The Pgap model is readily rewritten in terms of a clumping factor as a function of height and angle. Simulations of Pgap(θ,z) for idealised canopies compared favourably with those of two other models: the Analytical Clumped Two-Stream (ACTS) model (Ni-Meister et al., 2010) and an adaptation of the Nilson (1999) model. We test the analytic approximation to the crown porosity, also inherent in the Nilson (1999) model, and the applicability of a single clumping factor without angle nor height dependence. Both simplifications are demonstrated to be valid. Lovell et al. (2012, this issue) provide quantitative assessment of the Pgap component of CanSPART against ground-based lidar measurements from sites spanning a range of canopy structures.
The radiative-transfer part of the model is an extension of the two-stream scheme, using Pgap as input and requiring the solution of a single matrix equation. In contrast to existing modified two-stream models which use a clumping factor, we account for both the primary effect of clumping (enhanced uncollided flux intensities) and |
| doi_str_mv | 10.1016/j.agrformet.2012.01.018 |
| format | Article |
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We present CanSPART: a model of gap probability (Pgap) based on a simple but flexible geometric vegetation canopy structure, coupled to a one-dimensional radiative transfer scheme, to account for the effects of crown structure and trunks on vertically resolved canopy radiation fluxes. The Pgap component of the model is intended for use in inverting ground-based and airborne gap-frequency data for biometric variables, while the full CanSPART model is intended for application within a one-dimensional multilayer soil-vegetation-atmosphere-transfer model. Our approach to modelling Pgap is novel because it uses an analytic approximation to the crown porosity, which makes it computationally efficient. Further, it can accommodate any distribution of crown and trunk heights and dimensions, allowing the model to be applied to complex canopy structures with multiple layers. The Pgap model is readily rewritten in terms of a clumping factor as a function of height and angle. Simulations of Pgap(θ,z) for idealised canopies compared favourably with those of two other models: the Analytical Clumped Two-Stream (ACTS) model (Ni-Meister et al., 2010) and an adaptation of the Nilson (1999) model. We test the analytic approximation to the crown porosity, also inherent in the Nilson (1999) model, and the applicability of a single clumping factor without angle nor height dependence. Both simplifications are demonstrated to be valid. Lovell et al. (2012, this issue) provide quantitative assessment of the Pgap component of CanSPART against ground-based lidar measurements from sites spanning a range of canopy structures.
The radiative-transfer part of the model is an extension of the two-stream scheme, using Pgap as input and requiring the solution of a single matrix equation. In contrast to existing modified two-stream models which use a clumping factor, we account for both the primary effect of clumping (enhanced uncollided flux intensities) and the secondary effect (enhanced interception of scattered radiation). Application of CanSPART to three contrasting Australian field sites show that Pgap, the absorption of radiation by leaves, Qleaf, and albedo are sensitive to the clumping of leaves into crowns. Except for the most sparsely vegetated site, albedo predictions were significantly too high, unless both primary and secondary effects of clumping were included. This highlights the importance of accounting for the enhanced interception of radiation scattered by leaves in a clump (relative to the unclumped case) and suggests why modified two-stream canopy radiative transfer models using a clumping factor approach may systematically underestimate Qleaf and overestimate albedo.</description><identifier>ISSN: 0168-1923</identifier><identifier>EISSN: 1873-2240</identifier><identifier>DOI: 10.1016/j.agrformet.2012.01.018</identifier><identifier>CODEN: AFMEEB</identifier><language>eng</language><publisher>Amsterdam: Elsevier B.V</publisher><subject>Agricultural and forest climatology and meteorology. Irrigation. Drainage ; Agronomy. Soil science and plant productions ; Albedo ; Biological and medical sciences ; Canopies ; Canopy ; Clumping ; Clumping factor ; Fluxes ; Fundamental and applied biological sciences. Psychology ; General agronomy. Plant production ; Interception ; Leaves ; Life Sciences ; Mathematical analysis ; Mathematical models ; Pgap ; Radiative transfer ; Savanna</subject><ispartof>Agricultural and forest meteorology, 2012-07, Vol.160, p.14-35</ispartof><rights>2012 Elsevier B.V.</rights><rights>2015 INIST-CNRS</rights><rights>Distributed under a Creative Commons Attribution 4.0 International License</rights><lds50>peer_reviewed</lds50><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-c2909-7fdc12a0efa365dccbb47c94d66bcaf57777b54529f845880ed154303247e0463</citedby><cites>FETCH-LOGICAL-c2909-7fdc12a0efa365dccbb47c94d66bcaf57777b54529f845880ed154303247e0463</cites><orcidid>0000-0002-5966-1829</orcidid></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><linktohtml>$$Uhttps://dx.doi.org/10.1016/j.agrformet.2012.01.018$$EHTML$$P50$$Gelsevier$$H</linktohtml><link.rule.ids>230,314,780,784,885,3550,27924,27925,45995</link.rule.ids><backlink>$$Uhttp://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetail&idt=25906452$$DView record in Pascal Francis$$Hfree_for_read</backlink><backlink>$$Uhttps://hal.inrae.fr/hal-02643378$$DView record in HAL$$Hfree_for_read</backlink></links><search><creatorcontrib>Haverd, V.</creatorcontrib><creatorcontrib>Lovell, J.L.</creatorcontrib><creatorcontrib>Cuntz, M.</creatorcontrib><creatorcontrib>Jupp, D.L.B.</creatorcontrib><creatorcontrib>Newnham, G.J.</creatorcontrib><creatorcontrib>Sea, W.</creatorcontrib><title>The Canopy Semi-analytic Pgap And Radiative Transfer (CanSPART) model: Formulation and application</title><title>Agricultural and forest meteorology</title><description>► Developed semi-analytic multi-layer model to predict gap probability and radiation transfer in clumped canopies. ► Analytic approximation to the crown porosity: computationally efficient and demonstrated validity. ► Applied to complex canopy structures. ► Can be formulated in terms of a clumping factor: single clumping factor shown to perform well compared to height- and angle-resolved clumping factor. ► Results agree well with site observations of albedo, provided the effect of clumping on scattered radiation interception is included.
We present CanSPART: a model of gap probability (Pgap) based on a simple but flexible geometric vegetation canopy structure, coupled to a one-dimensional radiative transfer scheme, to account for the effects of crown structure and trunks on vertically resolved canopy radiation fluxes. The Pgap component of the model is intended for use in inverting ground-based and airborne gap-frequency data for biometric variables, while the full CanSPART model is intended for application within a one-dimensional multilayer soil-vegetation-atmosphere-transfer model. Our approach to modelling Pgap is novel because it uses an analytic approximation to the crown porosity, which makes it computationally efficient. Further, it can accommodate any distribution of crown and trunk heights and dimensions, allowing the model to be applied to complex canopy structures with multiple layers. The Pgap model is readily rewritten in terms of a clumping factor as a function of height and angle. Simulations of Pgap(θ,z) for idealised canopies compared favourably with those of two other models: the Analytical Clumped Two-Stream (ACTS) model (Ni-Meister et al., 2010) and an adaptation of the Nilson (1999) model. We test the analytic approximation to the crown porosity, also inherent in the Nilson (1999) model, and the applicability of a single clumping factor without angle nor height dependence. Both simplifications are demonstrated to be valid. Lovell et al. (2012, this issue) provide quantitative assessment of the Pgap component of CanSPART against ground-based lidar measurements from sites spanning a range of canopy structures.
The radiative-transfer part of the model is an extension of the two-stream scheme, using Pgap as input and requiring the solution of a single matrix equation. In contrast to existing modified two-stream models which use a clumping factor, we account for both the primary effect of clumping (enhanced uncollided flux intensities) and the secondary effect (enhanced interception of scattered radiation). Application of CanSPART to three contrasting Australian field sites show that Pgap, the absorption of radiation by leaves, Qleaf, and albedo are sensitive to the clumping of leaves into crowns. Except for the most sparsely vegetated site, albedo predictions were significantly too high, unless both primary and secondary effects of clumping were included. This highlights the importance of accounting for the enhanced interception of radiation scattered by leaves in a clump (relative to the unclumped case) and suggests why modified two-stream canopy radiative transfer models using a clumping factor approach may systematically underestimate Qleaf and overestimate albedo.</description><subject>Agricultural and forest climatology and meteorology. Irrigation. Drainage</subject><subject>Agronomy. Soil science and plant productions</subject><subject>Albedo</subject><subject>Biological and medical sciences</subject><subject>Canopies</subject><subject>Canopy</subject><subject>Clumping</subject><subject>Clumping factor</subject><subject>Fluxes</subject><subject>Fundamental and applied biological sciences. Psychology</subject><subject>General agronomy. Plant production</subject><subject>Interception</subject><subject>Leaves</subject><subject>Life Sciences</subject><subject>Mathematical analysis</subject><subject>Mathematical models</subject><subject>Pgap</subject><subject>Radiative transfer</subject><subject>Savanna</subject><issn>0168-1923</issn><issn>1873-2240</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2012</creationdate><recordtype>article</recordtype><recordid>eNqFkV1r2zAUhk3ZYFm33zDdFNoLZ5IsW9LuTOjHILDSZtfiWD5uFeSPSU4g_77KUnJbcUBIPK_O0ftm2Q9Gl4yy6ud2CS-hG0OP85JTxpeUpVIX2YIpWeScC_opWyRS5Uzz4kv2NcYtTaCUepE1m1ckKxjG6UCesXc5DOAPs7Pk8QUmUg8teYLWwez2SDYBhthhINdJ8fxYP21uSD-26H-RuzTAzidsHAgkEUyTd_b_-Vv2uQMf8fv7fpn9vbvdrB7y9Z_736t6nVuuqc5l11rGgWIHRVW21jaNkFaLtqoaC10p02pKUXLdKVEqRbFlpShowYVEKqriMrs5vfsK3kzB9RAOZgRnHuq1Od5RXomikGrPEnt9Yqcw_tthnE3vokXvYcBxF01yq5RaSaE_RimnSmjJVULlCbVhjDFgdx6DUXMMy2zNOSxzDMtQluqovHpvAtGC75LR1sWznJeaVunriatPHCYj9w6DidbhYLF1Ae1s2tF92OsNJO2sYA</recordid><startdate>20120715</startdate><enddate>20120715</enddate><creator>Haverd, V.</creator><creator>Lovell, J.L.</creator><creator>Cuntz, M.</creator><creator>Jupp, D.L.B.</creator><creator>Newnham, G.J.</creator><creator>Sea, W.</creator><general>Elsevier B.V</general><general>Elsevier</general><general>Elsevier Masson</general><scope>IQODW</scope><scope>AAYXX</scope><scope>CITATION</scope><scope>7ST</scope><scope>7TG</scope><scope>7UA</scope><scope>C1K</scope><scope>KL.</scope><scope>SOI</scope><scope>8FD</scope><scope>FR3</scope><scope>H8D</scope><scope>KR7</scope><scope>L7M</scope><scope>1XC</scope><orcidid>https://orcid.org/0000-0002-5966-1829</orcidid></search><sort><creationdate>20120715</creationdate><title>The Canopy Semi-analytic Pgap And Radiative Transfer (CanSPART) model: Formulation and application</title><author>Haverd, V. ; Lovell, J.L. ; Cuntz, M. ; Jupp, D.L.B. ; Newnham, G.J. ; Sea, W.</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c2909-7fdc12a0efa365dccbb47c94d66bcaf57777b54529f845880ed154303247e0463</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2012</creationdate><topic>Agricultural and forest climatology and meteorology. Irrigation. Drainage</topic><topic>Agronomy. Soil science and plant productions</topic><topic>Albedo</topic><topic>Biological and medical sciences</topic><topic>Canopies</topic><topic>Canopy</topic><topic>Clumping</topic><topic>Clumping factor</topic><topic>Fluxes</topic><topic>Fundamental and applied biological sciences. Psychology</topic><topic>General agronomy. Plant production</topic><topic>Interception</topic><topic>Leaves</topic><topic>Life Sciences</topic><topic>Mathematical analysis</topic><topic>Mathematical models</topic><topic>Pgap</topic><topic>Radiative transfer</topic><topic>Savanna</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Haverd, V.</creatorcontrib><creatorcontrib>Lovell, J.L.</creatorcontrib><creatorcontrib>Cuntz, M.</creatorcontrib><creatorcontrib>Jupp, D.L.B.</creatorcontrib><creatorcontrib>Newnham, G.J.</creatorcontrib><creatorcontrib>Sea, W.</creatorcontrib><collection>Pascal-Francis</collection><collection>CrossRef</collection><collection>Environment Abstracts</collection><collection>Meteorological & Geoastrophysical Abstracts</collection><collection>Water Resources Abstracts</collection><collection>Environmental Sciences and Pollution Management</collection><collection>Meteorological & Geoastrophysical Abstracts - Academic</collection><collection>Environment Abstracts</collection><collection>Technology Research Database</collection><collection>Engineering Research Database</collection><collection>Aerospace Database</collection><collection>Civil Engineering Abstracts</collection><collection>Advanced Technologies Database with Aerospace</collection><collection>Hyper Article en Ligne (HAL)</collection><jtitle>Agricultural and forest meteorology</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Haverd, V.</au><au>Lovell, J.L.</au><au>Cuntz, M.</au><au>Jupp, D.L.B.</au><au>Newnham, G.J.</au><au>Sea, W.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>The Canopy Semi-analytic Pgap And Radiative Transfer (CanSPART) model: Formulation and application</atitle><jtitle>Agricultural and forest meteorology</jtitle><date>2012-07-15</date><risdate>2012</risdate><volume>160</volume><spage>14</spage><epage>35</epage><pages>14-35</pages><issn>0168-1923</issn><eissn>1873-2240</eissn><coden>AFMEEB</coden><abstract>► Developed semi-analytic multi-layer model to predict gap probability and radiation transfer in clumped canopies. ► Analytic approximation to the crown porosity: computationally efficient and demonstrated validity. ► Applied to complex canopy structures. ► Can be formulated in terms of a clumping factor: single clumping factor shown to perform well compared to height- and angle-resolved clumping factor. ► Results agree well with site observations of albedo, provided the effect of clumping on scattered radiation interception is included.
We present CanSPART: a model of gap probability (Pgap) based on a simple but flexible geometric vegetation canopy structure, coupled to a one-dimensional radiative transfer scheme, to account for the effects of crown structure and trunks on vertically resolved canopy radiation fluxes. The Pgap component of the model is intended for use in inverting ground-based and airborne gap-frequency data for biometric variables, while the full CanSPART model is intended for application within a one-dimensional multilayer soil-vegetation-atmosphere-transfer model. Our approach to modelling Pgap is novel because it uses an analytic approximation to the crown porosity, which makes it computationally efficient. Further, it can accommodate any distribution of crown and trunk heights and dimensions, allowing the model to be applied to complex canopy structures with multiple layers. The Pgap model is readily rewritten in terms of a clumping factor as a function of height and angle. Simulations of Pgap(θ,z) for idealised canopies compared favourably with those of two other models: the Analytical Clumped Two-Stream (ACTS) model (Ni-Meister et al., 2010) and an adaptation of the Nilson (1999) model. We test the analytic approximation to the crown porosity, also inherent in the Nilson (1999) model, and the applicability of a single clumping factor without angle nor height dependence. Both simplifications are demonstrated to be valid. Lovell et al. (2012, this issue) provide quantitative assessment of the Pgap component of CanSPART against ground-based lidar measurements from sites spanning a range of canopy structures.
The radiative-transfer part of the model is an extension of the two-stream scheme, using Pgap as input and requiring the solution of a single matrix equation. In contrast to existing modified two-stream models which use a clumping factor, we account for both the primary effect of clumping (enhanced uncollided flux intensities) and the secondary effect (enhanced interception of scattered radiation). Application of CanSPART to three contrasting Australian field sites show that Pgap, the absorption of radiation by leaves, Qleaf, and albedo are sensitive to the clumping of leaves into crowns. Except for the most sparsely vegetated site, albedo predictions were significantly too high, unless both primary and secondary effects of clumping were included. This highlights the importance of accounting for the enhanced interception of radiation scattered by leaves in a clump (relative to the unclumped case) and suggests why modified two-stream canopy radiative transfer models using a clumping factor approach may systematically underestimate Qleaf and overestimate albedo.</abstract><cop>Amsterdam</cop><pub>Elsevier B.V</pub><doi>10.1016/j.agrformet.2012.01.018</doi><tpages>22</tpages><orcidid>https://orcid.org/0000-0002-5966-1829</orcidid></addata></record> |
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| ispartof | Agricultural and forest meteorology, 2012-07, Vol.160, p.14-35 |
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| subjects | Agricultural and forest climatology and meteorology. Irrigation. Drainage Agronomy. Soil science and plant productions Albedo Biological and medical sciences Canopies Canopy Clumping Clumping factor Fluxes Fundamental and applied biological sciences. Psychology General agronomy. Plant production Interception Leaves Life Sciences Mathematical analysis Mathematical models Pgap Radiative transfer Savanna |
| title | The Canopy Semi-analytic Pgap And Radiative Transfer (CanSPART) model: Formulation and application |
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