tion 
reek 
ze 
di- 
cone 
Or 
cal 
the 
(1) 
| the 
er. 
1a) 
(2) 
(2a) 
- 541 - 
Measurements using the equations (2) or (2a), however, require 
the knowledge of the reflected radiance and of the irradiance 
in absolute units because they cannot be measured with the same 
instrument due to the differing field of view necessary for the 
two measurements. 
We do not recommend any argument or index to the symbol R be- 
cause the specification of the situation of measurement incorpo- 
rates too many points to denote them as arguments or indices. 
In the following, a recommendation of specifications is given 
to make comparisons of different measurements mare reliable. 
It should be specified: 
a) surface: 
type (species), composition, slope and exposition to sun, linear 
or nonlinear texture and its azimuth difference to sun, period 
length (the mean distance of the dominant features of a surface, 
as, e.g. the mean distance of the trees in case of a forest), 
age, growth height, growing status, time of the seasons, envi- 
ronmental factors affecting the spectral properties 
b) conditions of measurement: 
sun's position, direct sun or not, degree of cloudiness, wind, 
wind speed, relation of direct sun to global radiation, atmos- 
pheric turbidity, air temperature and humidity, mean zenith 
(nadir) angle and azimuth difference to sun of the direction of 
view, height of the istrument over ground 
C) instrument: 
field of view, diameter of field of view at the object's dis- 
tance (compare to period length), center wavelengths and half- 
widths or bandwidths of spectral intervals, integration time 
of the electronics 
d) reflection standard: 
type and size, calibration values, time lapse 
References: 
1. CIE, International Lighting Vocabulary (CIE,Paris 1970), 
Publ. 17. (E - 1.1.). 
2. DIN, Deutsches Institut für Normung, DIN 5036 (Draft July 1977). 
K.Ya. Kondratyev, D.N.Lasarev, and Yu.A. Shuba, Appl.Opt.16, 
1770 (1977). 
4. F.E. Nicodemus, Appl. Opt. 9, 1474 (1970) 
5. IAMAP/Radiation Commission, Working Group on Units and Nomen- 
clature, Report 1977. 
6. CIE, Radiometric and Photometric Characteristics of Materials 
and their Measurement, Publ. 38 (TC-2.3), 1977.