Comparison of Smartphone and Drone Lidar Methods for Characterizing Spatial Variation in PAI in a Tropical Forest
Estimating leaf area index (LAI) and assessing spatial variation in LAI across a landscape is crucial to many ecological studies. Several direct and indirect methods of LAI estimation have been developed and compared; however, many of these methods are prohibitively expensive and/or time consuming....
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| Format: | Article |
| Language: | English |
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MDPI AG
2020-05-01
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| Series: | Remote Sensing |
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| Online Access: | https://www.mdpi.com/2072-4292/12/11/1765 |
| _version_ | 1797566546336284672 |
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| author | Tamara E. Rudic Lindsay A. McCulloch Katherine Cushman |
| author_facet | Tamara E. Rudic Lindsay A. McCulloch Katherine Cushman |
| author_sort | Tamara E. Rudic |
| collection | DOAJ |
| description | Estimating leaf area index (LAI) and assessing spatial variation in LAI across a landscape is crucial to many ecological studies. Several direct and indirect methods of LAI estimation have been developed and compared; however, many of these methods are prohibitively expensive and/or time consuming. Here, we examine the feasibility of using the free image processing software CAN-EYE to estimate effective plant area index (PAI<sub>eff</sub>) from hemispherical canopy images taken with an extremely inexpensive smartphone clip-on fisheye lens. We evaluate the effectiveness of this inexpensive method by comparing CAN-EYE smartphone PAI<sub>eff</sub> estimates to those from drone lidar over a lowland tropical forest at La Selva Biological Station, Costa Rica. We estimated PAI<sub>eff</sub> from drone lidar using a method based in radiative transfer theory that has been previously validated using simulated data; we consider this a conservative test of smartphone PAI<sub>eff</sub> reliability because above-canopy lidar estimates share few assumptions with understory image methods. Smartphone PAI<sub>eff</sub> varied from 0.1 to 4.4 throughout our study area and we found a significant correlation (<i>r</i> = 0.62, <i>n</i> = 42, <i>p</i> < 0.001) between smartphone and lidar PAI<sub>eff</sub>, which was robust to image processing analytical options and smartphone model. When old growth and secondary forests are assumed to have different leaf angle distributions for the lidar PAI<sub>eff</sub> algorithm (spherical and planophile, respectively) this relationship is further improved (<i>r</i> = 0.77, <i>n</i> = 42, <i>p</i> < 0.001). However, we found deviations in the magnitude of the PAI<sub>eff</sub> estimations depending on image analytical options. Our results suggest that smartphone images can be used to characterize spatial variation in PAI<sub>eff</sub> in a complex, heterogenous tropical forest canopy, with only small reductions in explanatory power compared to true digital hemispherical photography. |
| first_indexed | 2024-03-10T19:29:24Z |
| format | Article |
| id | doaj.art-29a0849bfd8d4b878f79a68d110fd0cc |
| institution | Directory Open Access Journal |
| issn | 2072-4292 |
| language | English |
| last_indexed | 2024-03-10T19:29:24Z |
| publishDate | 2020-05-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Remote Sensing |
| spelling | doaj.art-29a0849bfd8d4b878f79a68d110fd0cc2023-11-20T02:15:40ZengMDPI AGRemote Sensing2072-42922020-05-011211176510.3390/rs12111765Comparison of Smartphone and Drone Lidar Methods for Characterizing Spatial Variation in PAI in a Tropical ForestTamara E. Rudic0Lindsay A. McCulloch1Katherine Cushman2Department of Earth, Environmental and Planetary Sciences, Brown University, 324 Brook St., Providence, RI 02912, USAInstitute at Brown for Environment and Society, Brown University, 85 Waterman St., Providence, RI 02912, USAInstitute at Brown for Environment and Society, Brown University, 85 Waterman St., Providence, RI 02912, USAEstimating leaf area index (LAI) and assessing spatial variation in LAI across a landscape is crucial to many ecological studies. Several direct and indirect methods of LAI estimation have been developed and compared; however, many of these methods are prohibitively expensive and/or time consuming. Here, we examine the feasibility of using the free image processing software CAN-EYE to estimate effective plant area index (PAI<sub>eff</sub>) from hemispherical canopy images taken with an extremely inexpensive smartphone clip-on fisheye lens. We evaluate the effectiveness of this inexpensive method by comparing CAN-EYE smartphone PAI<sub>eff</sub> estimates to those from drone lidar over a lowland tropical forest at La Selva Biological Station, Costa Rica. We estimated PAI<sub>eff</sub> from drone lidar using a method based in radiative transfer theory that has been previously validated using simulated data; we consider this a conservative test of smartphone PAI<sub>eff</sub> reliability because above-canopy lidar estimates share few assumptions with understory image methods. Smartphone PAI<sub>eff</sub> varied from 0.1 to 4.4 throughout our study area and we found a significant correlation (<i>r</i> = 0.62, <i>n</i> = 42, <i>p</i> < 0.001) between smartphone and lidar PAI<sub>eff</sub>, which was robust to image processing analytical options and smartphone model. When old growth and secondary forests are assumed to have different leaf angle distributions for the lidar PAI<sub>eff</sub> algorithm (spherical and planophile, respectively) this relationship is further improved (<i>r</i> = 0.77, <i>n</i> = 42, <i>p</i> < 0.001). However, we found deviations in the magnitude of the PAI<sub>eff</sub> estimations depending on image analytical options. Our results suggest that smartphone images can be used to characterize spatial variation in PAI<sub>eff</sub> in a complex, heterogenous tropical forest canopy, with only small reductions in explanatory power compared to true digital hemispherical photography.https://www.mdpi.com/2072-4292/12/11/1765leaf area indexlidarhemispherical photographytropical forestLa Selva Biological Station |
| spellingShingle | Tamara E. Rudic Lindsay A. McCulloch Katherine Cushman Comparison of Smartphone and Drone Lidar Methods for Characterizing Spatial Variation in PAI in a Tropical Forest Remote Sensing leaf area index lidar hemispherical photography tropical forest La Selva Biological Station |
| title | Comparison of Smartphone and Drone Lidar Methods for Characterizing Spatial Variation in PAI in a Tropical Forest |
| title_full | Comparison of Smartphone and Drone Lidar Methods for Characterizing Spatial Variation in PAI in a Tropical Forest |
| title_fullStr | Comparison of Smartphone and Drone Lidar Methods for Characterizing Spatial Variation in PAI in a Tropical Forest |
| title_full_unstemmed | Comparison of Smartphone and Drone Lidar Methods for Characterizing Spatial Variation in PAI in a Tropical Forest |
| title_short | Comparison of Smartphone and Drone Lidar Methods for Characterizing Spatial Variation in PAI in a Tropical Forest |
| title_sort | comparison of smartphone and drone lidar methods for characterizing spatial variation in pai in a tropical forest |
| topic | leaf area index lidar hemispherical photography tropical forest La Selva Biological Station |
| url | https://www.mdpi.com/2072-4292/12/11/1765 |
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