Light can be reflected, transmitted or absorbed by a canopy element.
Considering percentages:
| r + t + a = 1 |
[1] |
r = reflected energyAbsorbed energy is not easy to measure so, it is calculated base on
t = transmitted energy
a = absorbed energy
| a = 1 - r + t |
[1'] |
Measurement technique of optical properties of leaves or canopy elements with an integrating sphere depends on three conditions:
- Is the sample translucent enough so light can transmit through the sample?
- Is there significant difference in the optical properties of the different sides of the sample (top vs. bottom; adaxial vs. abaxial)?
- Do the leaf, leaves or canopy element(s) completely encompass the beam of light from the light source?
For the first condition, if the sample IS translucent enough for light to transmit through the sample then transmitted, reflected and reference measurements can be taken. If the sample is not translucent then only reflected and reference measurements need to be taken. Transmitted energy is assumed zero.
For the second condition, if there is significant differences in the optical properties of the surfaces of the sample then all side of the sample should be measured. Multiple reference measurements should also be measured to represent the effect of each sides contribution to the internal reflectance of the integrating sphere.
For the third condition, a sample can fall into three categories:
- Sample completely covers the light source's beam
- Sample is narrower than the light source's beam, but is long enough to reach across the sample port of the integrating sphere.
- Sample is narrower than the light source's beam and shorter than the integrating sphere's sample port.
Daughtry et al. (1989) and Mesarch et al. (1999) describe measurement techniques and revised measurement techniques for measurements of these three categories.
| View | Measurement | Orientation |
|---|---|---|
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Stray light | No sample in sample port; Light source in reflected port. |
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Stray light reference | No sample in sample port; Light source in reference port. |
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Stray light wall reference | No sample in sample port; Light source in transmitted port. |
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Reflected top | Sample in sample port with top of the sample facing into the sphere. Light source in reflected port. |
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Reference Top | Sample in sample port with top of the sample facing into the sphere. Light source in reference port. |
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Transmitted Bottom | Sample in sample port with top of the sample facing into the sphere. Light source in transmitted port. |
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Transmitted Top | Sample in sample port with bottom of the sample facing into the sphere. Light source in transmitted port. |
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Reference Bottom | Sample in sample port with bottom of the sample facing into the sphere. Light source in reference port. |
|
Reflected Top | Sample in sample port with top of the sample facing into the sphere. Light source in reflected port. |
Spectral Leaf Optical Data of Decidious Leaves
Click on graph to enlarge figure | Click here to get data (ASCII 192 KB)| Species | Reflectance | Transmittance |
|---|---|---|
| Red Maple Leaves |
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| Red Oak Leaves | 
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Spectral Optical Data of Needles and Twigs
Click on graph to enlarge figure | Click here to get needle or twig data (ascii 64 & 69 Kb)| Species | Needles | Twig Reflectance | |
|---|---|---|---|
| Reflectance | Transmittance | ||
| Jack Pine |  |
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| Black Spruce |
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Leaf Optical Measurement Data Format ...
The data format of single measurement by the SE590 consists of two header lines of data description and 121 data values for wavelengths from 400 to 1000 nanometers, every 5 nanometers. The two header lines are different based on type of data collected.Deciduous Leaf Data Header Format
First header line:
Surface code, Observation counter, Day of year (A), HourMinute time (A), Day of Year (B), HourMinute time (B), Year, Site name, Species name, Height in canopy, Location, Branch, Sample code, Age of sample, Replication, Number of scans averaged, Integration time of scans, Month, Day, Year, Hour, Minute, Second.
where Surface code isCode Surface Top Adaxial Bott Abaxial ******* Surface Independent Second header line:
Optical Property, Munsell Color Code for this surface, Description.Needle & Twig Data Header Format
First header line:
Surface code, Observation counter, Day of year (A), HourMinute time (A), Day of Year (B), HourMinute time (B), Year, Site name, Species name, Height in canopy, Location, Branch, Sample code, Age of sample, Replication, Number of scans averaged, Integration time of scans, Month, Day, Year, Hour, Minute, Second.
where Surface code isCode Surface Top Adaxial Bott Abaxial ****** Surface Independent Second header line:
Optical Property, Munsell Color Code for this surface, Gap Fraction.-
Data Block Format
(values listed by wavelength in nanometers)
400 405 410 415 ... 440 445 450 455 460 465 470 ... 495 500 505 ... ... 955 960 965 970 ... 990 995 1000
Daughtry, C.S.T, Biehl, L. L. and Ranson, K. J. 1989. A new technique to measure the spectral properties of conifer needles. Remote Sens. Environ. 27:81-91.
Mesarch, M. A., Walter-Shea, E. A., Asner, G. P., Middleton, E. M. and Chan, S. S. 1999. A revised measurement methodology for conifer needles spectral optical properties: evaluating the influence of gaps between elements. Remote Sens. Environ. 68:177-192.
