Evaluating the Capability of Low-Configuration Spectrometers to Retrieve Far-Red Solar-Induced Chlorophyll Fluorescence and Its Application for Identifying Crop Growth Stages

Abstract

The ground-based continuous hyperspectral remote sensing technique presents a unique opportunity to advance terrestrial ecosystem monitoring. Accurate retrieval of solar-induced chlorophyll fluorescence (SIF) relies heavily on commercially available spectrometers with high spectral resolution (SR). However, high-SR spectrometers are resource-intensive and challenging to maintain, limiting their widespread deployment at observational sites. Here, we explored an alternative low-configuration and low-cost spectrometer for SIF retrieval at 2 sites cultivated with wheat and rice. The results revealed the strong correlations between irradiance and radiance measurements in the selected SIF bands from the high- and low-configuration spectrometers ( R 2 > 0.90, average root mean square error <8.95 mW m −2 nm −1 sr −1 , relative root mean square error < 7%). Far-red SIF retrieved from both spectrometers exhibited marked correlations at both half-hourly and daily averaged scales ( R 2 > 0.90). Additionally, we utilized simulated data to examine the impact of SR and signal-to-noise ratio (SNR) on the far-red SIF retrieval from both high- and low-configuration spectrometers. Strong correlations ( R 2 > 0.80) were found between the simulated data with SNR ≥ 300 and SR < 2 nm. Furthermore, we investigated the relationships between crop gross primary productivity (GPP) and far-red SIF from both types of spectrometers and their ability to identify crop growth stages. SIF from both types of spectrometers exhibited high correlations with GPP ( R 2 > 0.70). The dates of various wheat-specific growth stages observed using the low-configuration spectrometer were consistent with those identified by the high-configuration spectrometer, with less than a 3-d differences for wheat. Our study confirms the capabilities of the low-configuration spectrometers for far-red SIF retrievals and promotes their deployment over large-scale ground observation networks, potentially advancing the large development of low-cost ground-based SIF measurements.