Spectral Properties of Coniferous Forests: A Review of In Situ and Laboratory Measurements

Rautiainen, Miina; Lukeš, Petr; Homolová, Lucie; Hovi, Aarne; Písek, Jan; Mõttus, Matti

doi:10.3390/rs10020207

Cited by 105 publications

(84 citation statements)

References 105 publications

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“…Younger forest stands appeared to be brighter in NIR spectral region. A similar effect was shown by Rautiainen et al [53] when comparing spectral properties of mature and immature forest stands and by Nilson and Peterson [51] studying successional reflectance trajectories of birch, pine and spruce dominated stands. Changes in canopy closure, LAI, species composition and background reflectance have been shown to control the relationship between stand age and reflectance [51].…”

Section: The Relationships Between Vegetation Indices Single Band Resupporting

confidence: 78%

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Reflectance Properties of Hemiboreal Mixed Forest Canopies with Focus on Red Edge and Near Infrared Spectral Regions

et al. 2019

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This study present the results of airborne top-of-canopy measurements of reflectance spectra in the spectral domain of 350-1050 nm over the hemiboreal mixed forest. We investigated spectral transformations that were originally designed for utilization at very different spectral resolutions. We found that the estimates of red edge inflection point by two methods-the linear four-point interpolation approach (S2REP) and searching the maximum of the first derivative spectrum (D max ) according to the mathematical definition of red edge inflection point-were well related to each other but S2REP produced a continuously shifting location of red edge inflection point while D max resulted in a discrete variable with peak jumps between fixed locations around 717 nm and 727 nm for forest canopy (the third maximum at 700 nm appeared only in clearcut areas). We found that, with medium high spectral resolution (bandwidth 10 nm, spectral step 3.3 nm), the in-filling of the O 2 -A Fraunhofer line (F area ) was very strongly related to single band reflectance factor in NIR spectral region (ρ = 0.91, p < 0.001) and not related to Photochemical Reflectance Index (PRI). Stemwood volume, basal area and tree height of dominant layer were negatively correlated with reflectance factors at both visible and NIR spectral region due to the increase in roughness of canopy surface and the amount of shade. Forest age was best related to single band reflectance at NIR region (ρ = −0.48, p < 0.001) and the best predictor for allometric LAI was the single band reflectance at red spectral region (ρ = −0.52, p < 0.001) outperforming all studied vegetation indices. It suggests that Sentinel-2 MSI bands with higher spatial resolution (10 m pixel size) could be more beneficial than increased spectral resolution for monitoring forest LAI and age. The new index R 751 /R 736 originally developed for leaf chlorophyll content estimation, also performed well at the canopy level and was mainly influenced by the location of red edge inflection point (ρ = 0.99, p < 0.001) providing similar info in a simpler mathematical form and using a narrow spectral region very close to the O 2 -A Fraunhofer line.

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Section: The Relationships Between Vegetation Indices Single Band Resupporting

confidence: 78%

“…Observation Explanation Rautiainen et al (2018) [53] Systematically higher reflectance of the immature spruce forest stand compared to the mature one at all spatial scales…”

Section: Publicationmentioning

confidence: 99%

Reflectance Properties of Hemiboreal Mixed Forest Canopies with Focus on Red Edge and Near Infrared Spectral Regions

et al. 2019

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“…The double sphere is also optimal for quick monitoring type of measurements. As an example, currently only very few studies have examined seasonal variations of needle spectra (see review in Rautiainen et al 2018). In addition to remote sensing applications, these measurements could be utilized e.g.…”

Section: Spectra Of Needle-like Samples and Real Needlesmentioning

confidence: 99%

Evaluating the performance of a double integrating sphere in measurement of reflectance, transmittance, and albedo of coniferous needles

Hovi¹,

Mõttus

Juola³

et al. 2020

Silva Fenn.

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Highlights• Adaptation of a compact double integrating sphere for spectral measurements of coniferous needles. • Double integrating sphere is fast to operate and suitable for monitoring purposes and collection of large spectral databases. • Measured spectra showed negative bias, which could potentially be reduced by building an optimized measurement setup. AbstractLeaf reflectance and transmittance spectra are essential information in many applications such as developing remote sensing methods, computing shortwave energy balance (albedo) of forest canopies, and monitoring health or stress of trees. Measurement of coniferous needle spectra has usually been carried out with single integrating spheres, which has involved a lot of tedious manual work. A small double integrating sphere would make the measurements considerably faster, because of its ease of operation and small sample sizes required. Here we applied a compact double integrating sphere setup, used previously for measurement of broad leaves, for measurement of coniferous needles. Test measurements with the double integrating sphere showed relative underestimation of needle albedo by 5-39% compared to a well-established single integrating sphere setup. A small part of the bias can be explained by the bias of the single sphere. Yet the observed bias is quite significant if absolute accuracy of measurements is required. For relative measurements, e.g. for monitoring development of needle spectra over time, the double sphere system provides notable improvement. Furthermore, it might be possible to reduce the bias by building an optimized measurement setup that minimizes absorption losses in the sample port.Our study indicates that double spheres, after some technical improvement, may provide a new and fast way to collect extensive spectral libraries of tree species.

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“…Here, we use continuous measurements in both spectral space (full spectrum between 400-900 nm) and time (sub-daily over an entire year) to evaluate the potential of hyperspectral canopy reflectance for better understanding VIs sensitive to pigment changes that regulate GPP in evergreen forests. Continuous measurements of spectrally resolved reflectance at the canopy scale have so far been sparse at evergreen forest sites (Gamon et al, 2006;Hilker et al, 2011b;Porcar-Castell et al, 2015;Rautiainen et al, 2018). There are only a few empirical studies on hyperspectral canopy reflectance in evergreen forests (Smith et al, 2002;Singh et al, 2015).…”

mentioning

confidence: 99%

“…components. The spectral changes around the red-edge in the second component is interesting and might be related to structural needle changes in chlorophyll-a and chlorophyll-b contributions(de Tomás Marín et al, 2016;Rautiainen et al, 2018), which are not separated in PROSPECT.…”

mentioning

confidence: 99%

Decomposing reflectance spectra to track gross primary production in a subalpine evergreen forest

Cheng¹,

Magney²,

Dutta³

et al. 2020

Preprint

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Abstract. Photosynthesis by terrestrial plants represents the majority of CO2 uptake on Earth, yet it is difficult to measure directly from space. Estimating Gross Primary Production (GPP) from remote sensing indices is a primary source of uncertainty, in particular for observing seasonal variations in evergreen forests. Recent vegetation remote sensing techniques have highlighted spectral regions sensitive to dynamic changes in leaf/needle carotenoid composition, showing promise for tracking seasonal changes in photosynthesis of evergreen forests. However, continuous daily measurements of spectrally resolved canopy reflectance are limited in these ecosystems. To investigate this potential, we continuously measured vegetation reflectance (400&#8211;900&#8201;nm) using a canopy spectrometer system, PhotoSpec, mounted on top of an eddy-covariance flux tower in a subalpine evergreen forest at Niwot Ridge, Colorado, USA. We analyzed driving spectral components in the measured canopy reflectance using both statistical and process-based approaches. The decomposed spectral components relate directly to carotenoid pigments and co-vary seasonally with GPP, supporting the interpretation of the Photochemical Reflectance Index (PRI) and the Chlorophyll/Carotenoid Index (CCI). We show that using features from the entire 400&#8211;900&#8201;nm range show additional spectral changes near the red-egde but do not outperform the PRI or CCI indices for GPP predictions. In addition, we can quantitatively determine needle-scale chlorophyll to carotenoid ratios as well as anthocyanin contents using full spectrum inversions, both of which tightly correlated with seasonal GPP changes. Reconstructing GPP from vegetation reflectance using Partial Least Squares Regression (PLSR) explained approximately 87&#8201;% of the variability in observed GPP. Our results link the seasonal variation of reflectance to the pool size of photoprotective pigments, highlighting all spectral locations within 400&#8211;900&#8201;nm associated with GPP seasonality in evergreen forests.

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Spectral Properties of Coniferous Forests: A Review of In Situ and Laboratory Measurements

Cited by 105 publications

References 105 publications

Reflectance Properties of Hemiboreal Mixed Forest Canopies with Focus on Red Edge and Near Infrared Spectral Regions

Reflectance Properties of Hemiboreal Mixed Forest Canopies with Focus on Red Edge and Near Infrared Spectral Regions

Evaluating the performance of a double integrating sphere in measurement of reflectance, transmittance, and albedo of coniferous needles

Decomposing reflectance spectra to track gross primary production in a subalpine evergreen forest

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