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Articles containing the keyword 'albedo'

Category: Research article

article id 10270, category Research article
Aarne Hovi, Matti Mõttus, Jussi Juola, Farshid Manoocheri, Erkki Ikonen, Miina Rautiainen. (2020). Evaluating the performance of a double integrating sphere in measurement of reflectance, transmittance, and albedo of coniferous needles. Silva Fennica vol. 54 no. 2 article id 10270. https://doi.org/10.14214/sf.10270
Keywords: vegetation; albedo; reflectance; transmittance; needle carrier; spectra
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.
Abstract | Full text in HTML | Full text in PDF | Author Info

Leaf 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.

  • Hovi, Aalto University, School of Engineering, Department of Built Environment, P.O.Box 14100, FI-00760 Aalto, Finland ORCID https://orcid.org/0000-0002-4384-5279 E-mail: aarne.hovi@aalto.fi (email)
  • Mõttus, VTT Technical Research Centre Finland, P.O. Box 1000, FI-02044 VTT, Finland ORCID https://orcid.org/0000-0002-2745-1966 E-mail: matti.mottus@gmail.com
  • Juola, Aalto University, School of Engineering, Department of Built Environment, P.O.Box 14100, FI-00760 Aalto, Finland E-mail: jussi.juola@aalto.fi
  • Manoocheri, Aalto University, School of Electrical Engineering, Metrology Research Institute, Maarintie 8, FI-02150 Espoo, Finland ORCID https://orcid.org/0000-0003-3935-3930 E-mail: farshid.manoocheri@aalto.fi
  • Ikonen, VTT Technical Research Centre Finland, P.O. Box 1000, FI-02044 VTT, Finland; Aalto University, School of Electrical Engineering, Metrology Research Institute, Maarintie 8, FI-02150 Espoo, Finland ORCID https://orcid.org/0000-0001-6444-5330 E-mail: erkki.ikonen@aalto.fi
  • Rautiainen, Aalto University, School of Engineering, Department of Built Environment, P.O.Box 14100, FI-00760 Aalto, Finland; Aalto University, School of Electrical Engineering, Department of Electronics and Nanoengineering, P.O. Box 15500, FI-00760 Aalto, Finland ORCID https://orcid.org/0000-0002-6568-3258 E-mail: miina.a.rautiainen@aalto.fi
article id 7753, category Research article
Aarne Hovi, Pekka Raitio, Miina Rautiainen. (2017). A spectral analysis of 25 boreal tree species. Silva Fennica vol. 51 no. 4 article id 7753. https://doi.org/10.14214/sf.7753
Keywords: albedo; leaf; needle; reflectance; transmittance; integrating sphere; spectrometer
Highlights: An extensive spectral library containing leaf and needle reflectance and transmittance spectra was collected; The spectra openly available in SPECCHIO Spectral Information System; Effects of tree species, leaf/needle side, canopy position, and needle age on spectra were quantified; Seasonal variations were measured for four species; Spectra analysis highlights the importance of shortwave-infrared region in separating tree species.
Abstract | Full text in HTML | Full text in PDF | Author Info

Spectral libraries have a fundamental role in the development of interpretation methods for airborne and satellite-borne remote sensing data. This paper presents to-date the largest spectral measurement campaign of boreal tree species. Reflectance and transmittance spectra of over 600 leaf and needle samples from 25 species were measured in the Helsinki area (Finland) using integrating sphere systems attached to an ASD FieldSpec 4 spectroradiometer. Factors influencing the spectra and red edge inflection point (REIP) were quantified using one-way analysis of variance. Tree species differed most in the shortwave-infrared (1500–2500 nm) and least in the visible (400–700 nm) wavelength region. Species belonging to same genera showed similar spectral characteristics. Upper (adaxial) and lower (abaxial) leaf sides differed most in the visible region. Canopy position (sunlit/shaded) had a minor role in explaining spectral variation. For evergreen conifers, current and previous year needles differed in their spectra, current-year needles resembling those of broadleaved and deciduous conifers. Two broadleaved species were monitored throughout the growing season (May–October), and two conifers were measured twice during summer (June, September). Rapid changes were observed in the spectra in early spring and late autumn, whereas seasonal variations during summer months were relatively small for both broadleaved and coniferous species. Based on our results, shortwave-infrared seems promising in separating tree species, although it is to-date least studied. The spectral library reported here (Version 1.0) is publicly available through the SPECCHIO Spectral Information System.

  • Hovi, Aalto University, Department of Built Environment, P.O. Box 14100, FI-00076 Aalto, Finland E-mail: aarne.hovi@aalto.fi (email)
  • Raitio, Aalto University, Department of Built Environment, P.O. Box 14100, FI-00076 Aalto, Finland E-mail: pekka.raitio@aalto.fi
  • Rautiainen, Aalto University, Department of Built Environment, P.O. Box 14100, FI-00076 Aalto, Finland; Aalto University, Department of Electronics and Nanoengineering, P.O. Box 15500, FI-00076 Aalto, Finland E-mail: miina.a.rautiainen@aalto.fi

Category: Research note

article id 10683, category Research note
Aarne Hovi, Petr Lukeš, Lucie Homolová, Jussi Juola, Miina Rautiainen. (2022). Small geographical variability observed in Norway spruce needle spectra across Europe. Silva Fennica vol. 56 no. 2 article id 10683. https://doi.org/10.14214/sf.10683
Keywords: albedo; remote sensing; reflectance; transmittance; land surface modeling; leaf optical properties; radiative transfer modeling
Highlights: Spectra of Norway spruce needles were collected from three sites in Europe (49°–62°N); The same acquisition and processing parameters were applied throughout the campaign; Geographical variability in the needle spectra was small; Comparison of the spectra of coniferous needles and broadleaved tree foliage is also presented.
Abstract | Full text in HTML | Full text in PDF | Author Info

Foliage spectra form an important input to physically-based forest reflectance models. However, little is known about geographical variability of coniferous needle spectra. In this research note, we present an assessment of the geographical variability of Norway spruce (Picea abies (L.) H. Karst.) needle albedo, reflectance, and transmittance spectra across three study sites covering latitudes of 49–62°N in Europe. All spectra were measured and processed using exactly the same methodology and parameters, which guarantees reliable conclusions about geographical variability. Small geographical variability in Norway spruce needle spectra was observed, when compared to variability observed between previous measurement campaigns (employing slightly varying measurement and processing parameters), or to variability between plant functional types (broadleaved vs. coniferous). Our results suggest that variability of needle spectra is not a major factor introducing geographical variability to forest reflectance. The results also highlight the importance of harmonizing measurement protocols when collecting needle spectral libraries. Furthermore, the data collected for this study can be useful in studies where accurate information on spectral differences between broadleaved and coniferous tree foliage is needed.

  • Hovi, Aalto University, School of Engineering, Department of Built Environment, P.O. Box 14100, FI-00760 Aalto, Finland ORCID https://orcid.org/0000-0002-4384-5279 E-mail: aarne.hovi@aalto.fi (email)
  • Lukeš, Global Change Research Institute of the Czech Academy of Sciences, Bělidla 986/4a, 603 00 Brno, Czech Republic ORCID https://orcid.org/0000-0002-3707-6557 E-mail: lukes.p@czechglobe.cz
  • Homolová, Global Change Research Institute of the Czech Academy of Sciences, Bělidla 986/4a, 603 00 Brno, Czech Republic ORCID https://orcid.org/0000-0001-7455-2834 E-mail: homolova.l@czechglobe.cz
  • Juola, Aalto University, School of Engineering, Department of Built Environment, P.O. Box 14100, FI-00760 Aalto, Finland ORCID https://orcid.org/0000-0002-6050-7247 E-mail: jussi.juola@aalto.fi
  • Rautiainen, Aalto University, School of Engineering, Department of Built Environment, P.O. Box 14100, FI-00760 Aalto, Finland; Aalto University, School of Electrical Engineering, Department of Electronics and Nanoengineering, P.O. Box 15500, FI-00760 Aalto, Finland ORCID https://orcid.org/0000-0002-6568-3258 E-mail: miina.a.rautiainen@aalto.fi
article id 228, category Research note
Aku Riihelä, Terhikki Manninen. (2008). Measuring the vertical albedo profile of a subarctic boreal forest canopy. Silva Fennica vol. 42 no. 5 article id 228. https://doi.org/10.14214/sf.228
Keywords: boreal forest; albedo; validation; canopy transmission
Abstract | View details | Full text in PDF | Author Info
The validation of airborne and satellite-derived albedo measurements suffers from the fact that the surface albedo of forest is difficult to measure in-situ over large areas. The goal of this study is to examine whether or not the estimation of the surface albedo of a forest stand from ground level measurements is possible. In addition, knowledge about the vertical behavior of albedo, and therefore transmitted solar radiation, is important in the modeling of interactions of sunlight with the forest canopy. Such modeling is useful for forest growth estimations among other things. To achieve these goals, an albedometer set-up capable of vertical albedo profiling has been used to obtain data from a boreal forest stand in Northern Finland during periods in summer 2006 and winter 2007. The results show a strong relationship between the data and fitted power-law regression curves. Power-law regression fits best likely because of the radiation transmission characteristics of boreal forest.
  • Riihelä, Finnish Meteorological Institute, P.O. Box 503, FI-00200 Helsinki, Finland E-mail: aku.riihela@fmi.fi (email)
  • Manninen, Finnish Meteorological Institute, P.O. Box 503, FI-00200 Helsinki, Finland E-mail: tm@nn.fi

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