A new technique to measure the spectral properties of conifer needles

Daughtry, Craig S. T.; Biehl, L. L.; Ranson, K.J.

doi:10.1016/0034-4257(89)90039-4

Cited by 136 publications

(85 citation statements)

References 3 publications

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“…Our formula for T (Equation (2)) is slightly different from that given in the RTS-3ZC user manual [19]. We derived Equation (2) in literature [20][21][22], often without theoretical justifications. The difference between Equation (2) and version reported in RTS-3ZC user manual is however small, provided that the proportion of stray light is small and that the reflectance factor of the white reference is close to unity.…”

Section: Asd Rts-3zc Single Integrating Sphere (Sis)mentioning

confidence: 99%

“…We took samples from a maple and a birch tree (heights 15.6 m and 18.0 m, respectively) located in the close surroundings of Otaniemi Campus of Aalto University (60 • 11 14 N, 24 • 49 36 E). Measurements for one species were performed within a 3-4 days period (19)(20)(21)(22) June for maple, 3-5 June for birch) so that sample branches from selected trees were always collected in the morning (8:40-9:10 a.m. local time), stored in a refrigerator (temperature 3.9-7.5 • C), and measurements of leaves were performed within 6 h from the collection of the branch. Branches (length approx.…”

Section: Measurement Protocolsmentioning

confidence: 99%

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Evaluation of Accuracy and Practical Applicability of Methods for Measuring Leaf Reflectance and Transmittance Spectra

et al. 2017

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Leaf reflectance and transmittance spectra are urgently needed in interpretation of remote sensing data and modeling energy budgets of vegetation. The measurement methods should be fast to operate and preferably portable to enable quick collection of spectral databases and in situ measurements. At the same time, the collected spectra must be comparable across measurement campaigns. We compared three different methods for acquiring leaf reflectance and transmittance spectra. These were a single integrating sphere (ASD RTS-3ZC), a small double integrating sphere (Ocean Optics SpectroClip-TR), and a leaf clip (PP Systems UNI501 Mini Leaf Clip). With all methods, an ASD FieldSpec 4 spectrometer was used to measure white paper and tree leaves. Single and double integrating spheres showed comparable within-method variability in the measurements. Variability with leaf clip was slightly higher. The systematic difference in mean reflectance spectra between single and double integrating spheres was only minor (average relative difference of 1%), whereas a large difference (14%) was observed in transmittance. Reflectance measured with leaf clip was on average 14% higher compared to single integrating sphere. The differences between methods influenced also spectral vegetation indices calculated from the spectra, particularly those that were designed to track small changes in spectra. Measurements with double integrating sphere were four, and with leaf clip six times as fast as with single integrating sphere, if slightly reduced signal level (integration time reduced from optimum) was allowed for the double integrating sphere. Thus, these methods are fast alternatives to a conventional single integrating sphere. However, because the differences between methods depended on the measured target and wavelength, care must be taken when comparing the leaf spectra acquired with different methods.

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Section: Asd Rts-3zc Single Integrating Sphere (Sis)mentioning

confidence: 99%

Section: Measurement Protocolsmentioning

confidence: 99%

Evaluation of Accuracy and Practical Applicability of Methods for Measuring Leaf Reflectance and Transmittance Spectra

et al. 2017

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“…This is because the conifer needles are very small and do not cover the sample port of the integrating sphere, which has a port diameter of 15 mm for reflectance and 13.5 mm for transmittance. Therefore, the technique first developed by Daughtry et al (1989) and later revised by (Mesarch et al 1999) was applied to measure the spectral property of the conifer needles. A universal sample holder that could accommodate all lengths of conifer needles was designed, following Malenovsky et al (2006).…”

Section: Spectral Measurementsmentioning

confidence: 99%

“…A universal sample holder that could accommodate all lengths of conifer needles was designed, following Malenovsky et al (2006). Needles were detached from each sample shoot, placed on the sample holder, secured with scotch tape and leaving a space of approximately one needle's width between needles to avoid multiple reflectance from adjacent needles (Daughtry et al 1989). The sample holder was carefully placed at the sample port of the integrating sphere, and reflectance and transmittance spectra were acquired following the port configuration procedures of the ASD integrating sphere.…”

Section: Spectral Measurementsmentioning

confidence: 99%

Prospect inversion for indirect estimation of leaf dry matter content and specific leaf area

Ali

Darvishzadeh

Skidmore

et al. 2015

Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci.

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ABSTRACT:Quantification of vegetation properties plays an indispensable role in assessments of ecosystem function with leaf dry mater content (LDMC) and specific leaf area (SLA) being two important vegetation properties. Methods for fast, reliable and accurate measurement of LDMC and SLA are still lacking. In this study, the inversion of the PROSPECT radiative transfer model was used to estimate these two leaf parameters. Inversion of PROSPECT traditionally aims at quantifying its direct input parameters rather than identifying the parameters which can be derived indirectly from the input parameters. The technique has been tested here to indirectly model these parameters for the first time. Biophysical parameters such as leaf area, as well as fresh and dry weights of 137 leaf samples were measured during a field campaign in July 2013 in the mixed mountain forests of the Bavarian Forest National Park, Germany. Reflectance and transmittance of the leaf samples were measured using an ASD field spec III equipped with an integrating sphere. The PROSPECT model was inverted using a look-up table (LUT) approach for the NIR/SWIR region of the spectrum. The retrieved parameters were evaluated using their calculated R 2 and normalized root mean square error (nRMSE) values with the field measurements. Among the retrieved variables the lowest nRMSE (0.0899) was observed for LDMC. For both traits higher R 2 values (0.83 for LDMC and 0.89 for SLA) were discovered. The results indicate that the leaf traits studied can be quantified as accurately as the direct input parameters of PROSPECT. The strong correlation between the estimated traits and the NIR/SWIR region of the electromagnetic spectrum suggests that these leaf traits could be assessed at canopy and in the landscape by using hyperspectral remote sensing data.

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“…A key parameter entering these models is the shoot silhouette to total area ratio (STAR) (Oker-Blom & Smolander, 1988), which is conceptually analogous to the G-function, or the mean projection of unit foliage area, defined for flat leaves (Nilson, 1971). These models have been designed specifically for the estimation of photosynthesis, and the spectral properties of shoots have not been considered important because the scattering of photosynthetically active radiation (PAR) by conifer needles is known to be very small (Daughtry, Ranson, & Biehl, 1989). Some recent canopy reflectance models (Knyazikhin et al, 1998;Kuusk & Nilson, 2000;Shabanov et al, 2000) have accounted for the effect of smallscale clumping by modifying the G-function but in these approaches the shoot has not been explicitly used as the basic element in evaluating the area scattering phase function of the transport equation.…”

Section: Introductionmentioning

confidence: 99%

A method to account for shoot scale clumping in coniferous canopy reflectance models

Smolander¹,

Stenberg²

2003

Remote Sensing of Environment

124

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The three-dimensional structure of a coniferous shoot gives rise to multiple scattering of light between the needles of the shoot, causing the shoot spectral reflectance to differ from that of a flat leaf. Forest reflectance models based on the radiative transfer equation handle shoot level clumping by correcting the radiation attenuation coefficient with a clumping index. The clumping index causes a reduction in the interception of radiation by the canopy at a fixed leaf area index (LAI). In this study, we show how within-shoot multiple scattering is related to shoot scale clumping and derive a similar, but wavelength dependent, correction to the scattering coefficient. The results provide a method for integrating shoot structure into current radiative transfer equation based forest reflectance models. The method was applied to explore the effect of shoot scale clumping on canopy spectral reflectance using simple model canopies with a homogeneous higher level structure. The clumping of needles into shoots caused a wavelength dependent reduction in canopy reflectance, as compared to that of a leaf canopy with similar interception. This is proposed to be one reason why coniferous and broad-leaved canopies occupy different regions in the spectral space and exhibit different dependency of spectral vegetation indices on LAI. D

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A new technique to measure the spectral properties of conifer needles

Cited by 136 publications

References 3 publications

Evaluation of Accuracy and Practical Applicability of Methods for Measuring Leaf Reflectance and Transmittance Spectra

Evaluation of Accuracy and Practical Applicability of Methods for Measuring Leaf Reflectance and Transmittance Spectra

Prospect inversion for indirect estimation of leaf dry matter content and specific leaf area

A method to account for shoot scale clumping in coniferous canopy reflectance models

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