Quantifying the influences of spectral resolution on uncertainty in leaf trait estimates through a Bayesian approach to RTM inversion

Journal Article · Thu Jun 09 00:00:00 EDT 2016 · Remote Sensing of Environment

DOI:https://doi.org/10.1016/j.rse.2016.05.023· OSTI ID:1326737

Shiklomanov, Alexey N.  ^[1]; Dietze, Michael C. ^[1]; Viskari, Toni ^[2]; Townsend, Philip A. ^[3]; Serbin, Shawn P. ^[2]

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1. Boston Univ., Boston, MA (United States)
2. Brookhaven National Lab. (BNL), Upton, NY (United States); Stony Brook Univ., Stony Brook, NY (United States)
3. Univ. of Wisconsin-Madison, Madison, WI (United States)

The remote monitoring of plant canopies is critically needed for understanding of terrestrial ecosystem mechanics and biodiversity as well as capturing the short- to long-term responses of vegetation to disturbance and climate change. A variety of orbital, sub-orbital, and field instruments have been used to retrieve optical spectral signals and to study different vegetation properties such as plant biochemistry, nutrient cycling, physiology, water status, and stress. Radiative transfer models (RTMs) provide a mechanistic link between vegetation properties and observed spectral features, and RTM spectral inversion is a useful framework for estimating these properties from spectral data. However, existing approaches to RTM spectral inversion are typically limited by the inability to characterize uncertainty in parameter estimates. Here, we introduce a Bayesian algorithm for the spectral inversion of the PROSPECT 5 leaf RTM that is distinct from past approaches in two important ways: First, the algorithm only uses reflectance and does not require transmittance observations, which have been plagued by a variety of measurement and equipment challenges. Second, the output is not a point estimate for each parameter but rather the joint probability distribution that includes estimates of parameter uncertainties and covariance structure. We validated our inversion approach using a database of leaf spectra together with measurements of equivalent water thickness (EWT) and leaf dry mass per unit area (LMA). The parameters estimated by our inversion were able to accurately reproduce the observed reflectance (RMSE_VIS = 0.0063, RMSE_NIR-SWIR = 0.0098) and transmittance (RMSE_VIS = 0.0404, RMSE_NIR-SWIR = 0.0551) for both broadleaved and conifer species. Inversion estimates of EWT and LMA for broadleaved species agreed well with direct measurements (CV_EWT = 18.8%, CV_LMA = 24.5%), while estimates for conifer species were less accurate (CV_EWT = 53.2%, CV_LMA = 63.3%). To examine the influence of spectral resolution on parameter uncertainty, we simulated leaf reflectance as observed by ten common remote sensing platforms with varying spectral configurations and performed a Bayesian inversion on the resulting spectra. We found that full-range hyperspectral platforms were able to retrieve all parameters accurately and precisely, while the parameter estimates of multispectral platforms were much less precise and prone to bias at high and low values. We also observed that variations in the width and location of spectral bands influenced the shape of the covariance structure of parameter estimates. Lastly, our Bayesian spectral inversion provides a powerful and versatile framework for future RTM development and single- and multi-instrumental remote sensing of vegetation.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: SC00112704
• OSTI ID: 1326737
• Report Number(s): BNL-112627-2016-JA; R&D Project: 21087; YN0100000
• Journal Information: Remote Sensing of Environment, Vol. 183, Issue C; ISSN 0034-4257
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
leaf optical properties
PROSPECT
radiative transfer modeling
hyperspectral data
Bayesian statistics
spectral inversion