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incident global flax obtained with a cosine corrected hemispherical receptor (tripod mounted and situated at an 
exposed location); (ii) a scan of a calibrated field reflectance panel (mounted on a stable, blackout covered 
platform) and. (iii) a scan of the target surface. In the case of the mobile arrangement, the latter two scans were 
series of measurements the apertured sensor was tripod mounted for measurements (ii) and (iii). Each data set 
of took approximately 10-15 minutes to complete. During this time the change in solar zenith angle was less 
than 3 degrees and is ignored as a source of variation between the replicate measurements. Clear sky conditions 
prevailed during the measurement period. 
sample variance with the corresponding values for the fixed data set. For the bi-conical data sets, hand-holding 
the sensor potentially influences the target and reference panel measurement, whereas for the cos-conical series 
only the target measurement is affected. Initially, raw data were processed to reflectance (bi-conical and cos- 
conical method). Then the mean reflectance spectrum, standard deviation and coefficient of variance of the 20 
replicate spectra per surface type and method were calculated. 
Figure 7. Coefficient of variation corresponding to figure 6 . 
For the asphalt, the hand-held data set resulted in slightly higher reflectance at all wavelengths, although the 
sample variance was similar for both the fixed and mobile series. In fact the difference between the two mean 
spectra are not significant, since the error limits of the two data sets overlap. There is little difference between 
obtained with the downward-looking sensor supported on a 1.1m pole which was hand-held. For the fixed 
The impact of hand-holding the sensor was examined by comparing the mean reflectance and 
12 
Fixed 
— Fixed + 1 sd 
- - Handheld 
4 
400 
1000 
Wavelength (nm) 
Figure 6 . Mean reflectance of the asphalt surface measured using the sensor hand-held compared with it fixed 
to a support. 
10 
Fixed 
— — Handheld 
0 
400 
1000 
Wavelength (nm)