Measuring fractional cover and leaf area index in arid ecosystems: Digital camera, radiation transmittance, and laser altimetry methods

Michael A. White, Gregory P. Asner, Ramakrishna R. Nemani, Jeff L. Privette, Steven W. Running

Research output: Contribution to journalArticlepeer-review

183 Scopus citations

Abstract

Field measurement of shrubland ecological properties is important for both site monitoring and validation of remote sensing information. During the May 1997 NASA Earth Observing System Jornada Prototype Validation Exercise, we calculated plot-level plant area index, leaf area index, total fractional cover, and green fractional cover with data from four instruments: (1) a Dycam Agricultural Digital Camera (ADC), (2) a LI-COR LAI-2000 plant canopy analyzer, (3) a Decagon sunfleck Ceptometer, and (4) a laser altimeter. Estimates from the LAI-2000 and Ceptometer were very similar (plant area index 0.3, leaf area index 0.22, total fractional cover 0.19, green fractional cover 0.14), while the ADC produced values 5% to 10% higher. Laser altimeter values, depending on the height cutoff used to establish total fractional cover, were either higher or lower than the other instruments' values: a 10-cm cutoff produced values ~80% higher, while a 20-cm cutoff produced values ~30% lower. The LAI-2000 and Ceptometer are designed to operate in homogenous canopies, not the sparse and irregular vegetation found at Jornada. Thus, these instruments were primarily useful for relative within-site plant area index monitoring. Calculation of some parameters required destructive sampling, a relatively slow and labor-intensive activity that limits spatial and temporal applicability. Validation/monitoring campaigns therefore should be guided by consideration of the amount of time and resources required to obtain measurements of the desired variables. Our results suggest that the ADC is both efficient and accurate for long-term or large-scale monitoring of arid ecosystems. (C) Elsevier Science Inc., 2000.

Original languageEnglish
Pages (from-to)45-57
Number of pages13
JournalRemote Sensing of Environment
Volume74
Issue number1
DOIs
StatePublished - Oct 2000

Funding

We thank J. Ritchie for providing the laser altimetry results; C. Wessman, S. Zunker, and M. Helmlinger for field assistance; and L. Rocchio for destructive sampling analysis. The JORNEX staff, led by J. Lenz, provided and operated the cherry picker. S. Heinold provided valuable technical assistance with the Agricultural Digital Camera. Logistical support and equipment were provided by the MODLAND project. M.A. White is supported by NASA MODIS grant NAS5-31368 and the NASA ESS Fellowship Program. G. P. Asner is supported by NASA EOS IDS grant NAGW-2662, NASA LCLUC grant NAG5-6134, and the NASA ESS Fellowship Program. R. R. Nemani and S. W. Running are supported by NASA MODIS grant NAS5-31368. J. L. Privette is supported by NASA Headquarters RTOP 622-93-34.

FundersFunder number
National Aeronautics and Space AdministrationNAS5-31368, RTOP 622-93-34, NAG5-6134, NAGW-2662

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