White Reference; Spectralon Reflectance Data - ASD FieldSpec 3 User Manual

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7.11

White Reference

7.11.1

Spectralon Reflectance Data

ASD Document 600540 Rev. J
A material with 95-99% reflectance across the entire spectrum is called a
white reference panel or white reference standard.
The raw measurement made by the spectroradiometer is influenced by both
the sample and the light source. An independent measure of the light source
illumination on a reference of known reflectance is required to calculate the
reflectance of the sample. The use of a white reference standard with near
100% reflectance simplifies this calculation.
The ASD application software, such as RS
ratios for reflectance or transmittance of the material being sampled by the
FieldSpec spectroradiometer using the white reference as the standard.
Spectralon from Labsphere is the white reference standard that is very
suitable for the VNIR and SWIR spectral ranges of ASD instruments.
Spectralon is made of polytetraflouroethylene (PTFE) and cintered halon. It
has the characteristic of being nearly 100% reflective within the wavelength
range of 350 nm to 2500 nm. A Spectralon white reference scatters light
uniformly in all directions within that wavelength range.
Table 7-2 shows the published reflectance data for an uncalibrated SRM-990.
When SRM-990 is used as the white reference for a reflectance measurement
with the FieldSpec spectroradiometer, an even closer reflectance value for the
sample can be calculated.
Table 7-2Labsphere's published reflectance data for uncalibrated Spectralon (+/- 0.5%)
Wavelength (nm)
250
300
400
500
600
700
800
900
1000
1100
Chapter 7 Field Measurements
3
and Indico, can calculate the
SRM-990 "Uncalibrated"
Spectralon Reflectance
0.950
0.985
0.990
0.991
0.992
0.992
0.991
0.991
0.993
0.993
69 FieldSpec® 3 User Manual