Leaf spectroscopy measurements of eucalyptus leaves in the field

doi:10.21203/rs.3.pex-2396/v1

Method Article

Leaf spectroscopy measurements of eucalyptus leaves in the field

https://doi.org/10.21203/rs.3.pex-2396/v1

This work is licensed under a CC BY 4.0 License

This protocol has been posted on Protocol Exchange, an open repository of community-contributed protocols sponsored by Nature Portfolio. These protocols are posted directly on the Protocol Exchange by authors and are made freely available to the scientific community for use and comment.

Version 1

posted

You are reading this latest protocol version

This protocol outlines a simple procedure for the measurement and calculation of reflectance and transmittance radiance of eucalyptus leaves in the field using a handheld spectrometer. This protocol is useful as it allows for rapid measurement of leaf optical properties which provide insights into a range of physical and biochemical traits. The procedure requires specialised equipment to be completed, but the procedure can be followed regardless of the brand of the instrument.

Environmental sciences

Eucalyptus

flammability

fire

drought

leaves

vegetation

leaf material

spectroscopy

spectral signatures

radiance

reflectance

leaf traits.

Handheld spectroradiometer (e.g. ASD Fieldspec or similar).
Batteries for the spectroradiometer.
Integrating sphere for hemispherical reflectance and transmittance measurements.
Laptop computer compatible with required software.
Software for operating spectrometer and viewing spectra.
White reflectance panel (e.g. Spectralon material or similar).
Small brush to clean the reflectance panel.
Ruler or measuring tape
Gazebo (field canopy)
PPE (safety glasses, full body harness, gloves, hat)
Insect repellent
Sun cream (30+ SPF)
Field notebook

Protocol based on Suarez (2015). Additional information can be found in Suarez et al. (2012) and Spectranomics (2011).

Single-leaf sample preparation

Turn on spectrometer and set a station within minutes of the collection tree, preferably on a tarp or vehicle. Leave spectroradiometer to warm up for 10-15 minutes.
Collect leaves. Methods will vary depending on sampling strategy.
Following branch and leaf collection, keep selected branches and leaves in shade and cool conditions for up to 10 minutes, while delivered to the spectrometer. Leaves can also be kept on ice.
Select 5-10 mature, fully-expanded leaves. New undeveloped leaves should be avoided. If different parts of the canopy are being investigated, then take 5-10 leaves from each section of interest (depending on the sampling strategy). Ensure appropriate labelling of the samples.

Measurement procedure

Place each leaf facing inward and tangent to the leaf sample port of the integrating sphere.
Leaves are placed in the sphere so that the field-of-view (approx. 9 mm diameter for ASD instruments) is focused at the adaxial leaf surface during reflectance measurements. The leaf is placed in the sample holder. If present, avoid the large mid-vein entirely.
Reference radiance procedure: Place the light source in the reference position on the sphere to directly illuminate the white reference standard. The reference radiance is measured with the leaf in the sample port, which is not directly illuminated during reference measurements.
Reflectance procedure: Hold the leaf in the same position as during the reference measurement, and move the light source to the reflectance position on the sphere, thereby directly illuminating the leaf sample. Collect a radiance measurement.
Transmittance radiance procedure: Maintaining the leaf in the original position, move the light source to the transmittance position on the sphere, thereby directly illuminating the abaxial side of the leaf. Light passes through the leaf and into the sphere space. Collect a 50-spectrum radiance measurement.
Measure a white reference standard every 10-15 minutes to maximize data quality.
In addition to leaf measurements, measure the ‘stray light’ scattering within the sphere by illuminating the sample port (reflectance mode) with no sample present. Make a similar measurement in the transmittance mode.

Data processing

1. Calculate leaf hemispherical reflectance using the equation:

Refl = [(I_refl - I_stray) * R_ref]/(I_ref- I_stray)

Where:

o I_refl is the radiance measured when the sample is in the port and the light is in the reflectance position;

o I_stray is the radiance measured when no sample is in the port and the light in the reflectance position;

o R_ref is the reflectance (not radiance) of the white reference material;

o I_refis the radiance measured when the light shines directly upon the white reference standard.

2. Calculate leaf hemispherical transmittance using the equation:

Tran = [(I_tran - I_stray) * R_ref]/(I_ref - I_stray)

Where:

o I_tran is the radiance measured when the sample is in the port and the light is in the transmittance position.

3. Following reflectance and transmittance calculations, assess the energy closure and correct using the method provided by Merzlyak et al. (2002).

4. Complete a manual auditing step to ensure that all computed reflectance and transmittance spectra are free from errors, and that final quality is sufficiently high to warrant inclusion of the spectra in the database.

5. Following spectral calibration, reflectance/transmittance calculation and manual audit, calculate the mean and standard deviation spectra for each specimen.

Table 1

Single leaf sample preparation: Total time 10 mins

- Setting up the spectrometer (10 mins)

- Single leaf selection (1 mins). Can be done while instrument is turned on.

Data measurement: Total time for 1 sample (5 leaves) 15 mins

- Measurements of transmittance and reflectance (15 mins)

- Measurement of reference standard every 10 minutes (2 mins). Can be done between leaf measurements.

Data processing: 10 minutes for 25 samples

Each sample, and white reflectance measurement should output a transmittance and reflectance file. Depending on the instrument’s make and model, the file may be in proprietary format, or an open format (e.g. ‘.csv’, ‘.txt’, ‘.sig’).

Reflectance and transmittance data should always be within the range 0-1, or 0-100.

1. Suarez, L. Leaf hemispherical reflectance and transmittance measurement. Source: https://www.crcsi.com.au/assets/Uploads/P9.LEAF-PROCESSING-protocol.pdf (2015).

2. Suarez, L. et al. Chapter 13. Vegetation spectroscopy. In AusCover Good Practice Guidelines: A technical handbook supporting calibration and validation activities of remotely sensed data products. Version 1.2 (eds. Held, A., Phinn, S., Soto-Berelov, M., & Jones, S.) (TERN AusCover, St. Lucia and Canberra, Australia, 2012).

3. Spectranomics. Protocol for Leaf Spectroscopy. https://live-gao.ws.asu.edu/wp-content/uploads/2019/12/Spectranomics_protocol_Leaf_Spectroscopy-1.pdf (2011).

4. Merzlyak, M.N. et al. Does a leaf absorb radiation in the near infrared (780-900 nm) region? A new approach to quantifying optical reflection, absorption and transmission of leaves. Photosynth. Res. 72, 263-270 (2002).

Download PDF

Version 1

posted

You are reading this latest protocol version

Leaf spectroscopy measurements of eucalyptus leaves in the field

Status:

Version 1

Abstract

Figures

Equipment

Procedure

Troubleshooting

Time Taken

Anticipated Results

References

Status:

Version 1

Privacy Policy

Terms of Service

Leaf spectroscopy measurements of eucalyptus leaves in the field

Status:

Version 1

Abstract

Figures

Equipment

Procedure

Troubleshooting

Time Taken

Anticipated Results

References

Status:

Version 1

Privacy Policy

Terms of Service

Manage Cookie Preferences