Spectrometer stray light can bias retrievals of solar-induced fluorescence

Published

May 14, 2019

Author(s)

Loren Albert, Katherine Cushman, Yuqin Zong, David Allen, Luis Alonso, James Kellner

Abstract

Remote sensing of solar induced chlorophyll fluorescence (SIF) promises a significant advance in our ability to quantify gross primary productivity across spatial scales. Because the fluorescence emission is usually < 5 % of recorded canopy radiance, sources of error must be reduced for accurate estimation of SIF (SIF retrieval). Stray light, an unwanted signal in measurements from all gratings-based spectrometers, is a source of systematic error in spectroscopy. Here we evaluate whether and how much stray light may bias SIF retrievals. Using the Fraunhofer line depth principle (sFLD) equations, we first show that stray light in recorded canopy and reference spectra could compensate for each other, but only under the strong assumptions that SIF, reflectance, and stray light are constant across the wavelengths used in the sFLD retrieval. In practice however, SIF and reflectance are known to vary across the wavelengths used in the sFLD retrieval, and spectral stray light also varies because it is a function of the light source radiance spectrum and instrument properties. To test for the effect of stray light on retrieved SIF under more realistic conditions, we used simulations. We applied two retrieval methods—the sFLD method and the modified FLD (3FLD) method—to twelve Fraunhofer lines and the Oxygen A band to examine effects of stray light across the fluorescence emission spectrum. To represent spectrometers with high, medium, low, and very low stray light, we scaled an empirically derived spectral stray light distribution matrix such that stray light was approximately 10-1, 10-2, 10-3, and 10-4 of the measured radiance, respectively. These simulations showed that, on average, stray light introduced a greater error for SIF retrievals using Fraunhofer lines than the Oxygen A band. For Fraunhofer lines, high simulated stray light introduced a mean bias on SIF of 21.14 % for sFLD and 7.275 % for 3FLD retrievals. By contrast, using the Oxygen-A band, high stray light

Citation

Remote Sensing of Environment

Pub Type

Journals

Download Paper

Local Download

Keywords

chlorophyll fluorescence, near-surface remote sensing, spectral imaging, stray light, sensor characterization

Citation

Albert, L. , Cushman, K. , Zong, Y. , Allen, D. , Alonso, L. and Kellner, J. (2019), Spectrometer stray light can bias retrievals of solar-induced fluorescence, Remote Sensing of Environment, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=929523 (Accessed October 10, 2025)