SPECTRAL T1 BL D MEASUREMENTS
FOR THE DETERMINATION OF
REFLECTANCE CHARACTERISTICS
OF VEGETATED SURFACES
H.-J. Boehnel, W. Fischer, G. Knoll
Institut fur physikalische Weltraumforschung
D-7800 Freiburg, Heidenhofstrasse 8, Fed. Rep. of Germany
Introduction
Many applications of remote sensing techniques are based
on the concept of multispectral discrimination. In the
visible and the near infrared part of the electromagnetic
radiation spectrum the spectral characteristics of objects
depend on their reflection properties. Natural targets
are commonly not flat and homogeneous surfaces. The
reflected radiation shows an anisotropic distribution of
energy and varies with the irradiation of the scene, its
general state and specific structure, certain environmental
factors, etc.
For a better understanding of the reflection properties of
vegetated surfaces we are carrying out systematic field
measurements with spectroradiometers in the wavelength
range from O.4 to 2.5 um. These measurements are performed
at different zenith angles of observation and various solar
positions. This paper describes the methodology, the in-
strumentation and some of the results of this investigation
which is sponsored by the Federal Ministry of Research and
S
s or Technology.
Methodology
The geometry of reflection is shown in Figure 1. The sub-
scripts i and r denote the
zm incident and the reflected
radiation, respectively. d@
is the element of the radiant
ser power propagating within the
element of solid angle dn.
The zenith angles A} are
angles from the reflection
plane normal, the azimuth
Reflexions -
- 2 SHE pm angles ÿ are angles from an
e : . :
Paw. arbitrary reference direction
in the reflection plane
(South has been taken in the
following.)