236
ATSR-2 is representative of the surrounding region to scales of tens of
kilometers.
Chapter 24
4.
SPECTRAL BRDF MEASUREMENTS
CSIRO measures the surface-leaving spectral radiance with a triple
grating CCD spectrometer. The spectrometers operate over three overlapping
wavelength ranges: 380-540 nm, 480-870 nm and 500-1000 nm. Each has
1024 detector elements and is fed through a fiber-optic cable from input
optics with a roughly 10° field of view. Single spectra are acquired over 200
ms and are logged onto a notebook computer on which they can be
immediately displayed.
The spectrometer input optics are mounted on a computer-pointable dualaxis mount (the Remote AXis Controller - RAXC). For the results presented
here, the upwelling radiance was sampled on one side of the principal plane,
at zenith angle increments of 15° and azimuth increments of 30°, and then
symmetry in the principal plane was assumed to fill the unmeasured
azimuths. The measurements were repeated at several places across an area
of a few
at each site to assess and reduce the effect of spatial variability.
Figure 5 shows the hemispherical distribution of directional spectral
reflectance measured at Amburla and integrated over the ATSR-2 555 nm
band. The distribution has the characteristic bowl shape expected from
vegetation, and a distinct hot-spot in the backscatter direction. Figure 6
shows that the Roujean three-parameter model (Roujean et al., 1992) of the
bi-directional reflectance distribution function (BRDF) fits the
measurements well.
ATSR-2 is representative of the surrounding region to scales of tens of
kilometers.
Chapter 24
4.
SPECTRAL BRDF MEASUREMENTS
CSIRO measures the surface-leaving spectral radiance with a triple
grating CCD spectrometer. The spectrometers operate over three overlapping
wavelength ranges: 380-540 nm, 480-870 nm and 500-1000 nm. Each has
1024 detector elements and is fed through a fiber-optic cable from input
optics with a roughly 10° field of view. Single spectra are acquired over 200
ms and are logged onto a notebook computer on which they can be
immediately displayed.
The spectrometer input optics are mounted on a computer-pointable dualaxis mount (the Remote AXis Controller - RAXC). For the results presented
here, the upwelling radiance was sampled on one side of the principal plane,
at zenith angle increments of 15° and azimuth increments of 30°, and then
symmetry in the principal plane was assumed to fill the unmeasured
azimuths. The measurements were repeated at several places across an area
of a few
at each site to assess and reduce the effect of spatial variability.
Figure 5 shows the hemispherical distribution of directional spectral
reflectance measured at Amburla and integrated over the ATSR-2 555 nm
band. The distribution has the characteristic bowl shape expected from
vegetation, and a distinct hot-spot in the backscatter direction. Figure 6
shows that the Roujean three-parameter model (Roujean et al., 1992) of the
bi-directional reflectance distribution function (BRDF) fits the
measurements well.