Authored by Don Campbell. Don is an Applications Chemist at Malvern Panalytical, supporting the ASD brand of spectroradiometers. He is focused on pre and post-sale customer support, including feasibility studies and quantitative calibration development for new industrial opportunities, spectrometer installation, and customer training for chemometrics and remote sensing applications. Don has 13+ years of experience with ASD products and accessories and looks forward to helping you obtain the greatest value from your near-infrared (NIR) data.

Using a white reference Spectralon® panel to calibrate the ASD FieldSpec Dual system

As you head out into the field to pursue your remote sensing research, it is important to use a reference panel to perform real-time reflectance measurements and optimize your ASD spectroradiometer’s response. We recommend the use of Spectralon® Diffuse Reflectance Material for these tasks due to its highly diffuse reflectance properties and suitability for field use.

Every attempt should be made to keep the panel as clean as possible and it is particularly important not to allow any oily substances to contact the panel. This includes oils from fingers and hands. Contamination from oils will be difficult or impossible to remove and they can contribute their spectral signature to the panel’s reflectance signature. Significant contamination from dust or dirt will interfere with the near-perfect reflectance qualities of the panel and may contribute a false spectral signature if the contamination is extensive enough. The best practice is to keep the panel as clean as possible.

If your panel is lightly soiled, it may be airbrushed with a jet of clean dry air or nitrogen. Be sure not to use FreonTM or a Freon containing compressed air canister. Our newly designed 3.62” Spectralon round carrying case should aid in keeping the panel cleaner and minimizing contaminant when the panel is not in use.

If your panel is heavily soiled, you can still restore your Spectralon panel to its original or near original condition by following the “Spectralon Material Care and Handling Guidelines,” provided by LabSphere online, or by using the recommendations stated below.

Calibrated panels will retain the specified reflectance properties as part of the panel’s composition, however, there is a specific surface finishing process used with calibrated panels. If you decide to clean your panel by using the procedures below, the calibration may change slightly. This is not a concern for many users but if you require absolute accuracy, you should consider having the panel cleaned and re-calibrated by LabSphere.

To clean a heavily soiled white reference panel:

1. Use a flat surface, such as a thick, flat, glass cutting board.

Glass cutting

2. Attach 220-240 grade wet/dry sandpaper to the cutting board, using tape or binder clips. After wetting the cutting board and sandpaper, they may adhere to each other sufficiently such that binder clips and tape are not required.

Cutting board

3. Place the cutting board into the sink.

4. Turn on faucet at low flow rate to provide a steady stream of clean water to the white reference and sand paper during cleaning. (Optional) Attach Tygon® Tubing to faucet head to reduce splashing and allow for better direction of water flow if necessary.

5. Gently move the white reference panel in a figure-eight motion on the sandpaper. A thin layer of the white reference will be removed and washed away as you continue the cleaning process. To avoid a potentially painful injury, be very careful that you do not allow your fingertips to contact the sandpaper.

6. If the water beads up on the surface of the white reference panel and no longer appears to absorb into the panel, the surface should be sufficiently clean. Examples of heavily soiled and cleaned panels appear below.

7. If the reference panel requires high resistance to deep UV radiation, do one of the following:

  • Flush the reference panel with > 18 milli-ohm distilled, deionized water for 24 hours.
  • Vacuum bake the reference panel at 75° C for a 12-hour period at a vacuum of 1 torr or less. Then purge the vacuum oven with clean dry air or nitrogen.

Examples of heavily soiled, slightly contaminated and clean Spectralon® panels:

Heavily soiled white reference panel. Dirt and debris firmly adhered to panel, panel is discolored.

After initial cleaning, white reference panel remains slightly contaminated. Water still absorbs to a majority of the panel. Additional cleaning still required.

Clean white reference panel. Water beads up uniformly across the entire panel.

Do you require additional assistance or have any questions regarding our ASD brand accessories?