The magnitude of random errors in determining the ZLF can 
indirectly be judged by the values of the MSE computed for 
various realizations of objects of one and the same class. 
These values are governed both by the decree of uniformity 
of the objects combined into a class and by the errors in 
determining the ZLF, Numerous results of practical measurements 
of the ZLF have shown that in most cases the random measure 
ment errors do not exceed 10%, For illustration, Table 1 shows 
the results of determining the values of ZLF of desert areas 
subjected to different anthropogenic effect. The first class 
corresponded to the surface in immediate vicinity of the wells, 
the second class - to the surfaces located at a distance of 
5-7 km from them and the third class - to the background 
surface located at a considerable distance from the wells. 
In season (September) no plants vegetation was practically 
observed. 
Table 1 
Values of ZLF of desert areas 
Class of 
obj ects 
Number 
of 
objects 
Spectral zones 
500- 
•560 nm 
620- 
-710 nm 
660- 
-870 nm 
ME 
MSE % 
ME 
MSE % 
ME 
MSE % 
1 
38 
0.20 
- 7*6 
0.31 
- 5.9 
o.36 
- 8.5 
2 
76 
0.18 
- 6.0 
0.28 
- 6.9 
0.33 
- 4.9 
3 
76 
0.16 
- 6.7 
0.25 
- 8.0 
0.32 
— 6.8 
Thus, the random errors of measurement of the ZLF are 
small in magnitude, whereas the systematic errors, particu 
larly for low-brightness objects, may be considerable, which 
makes difficult comparison of the data obtained by different 
survey means at different time.' To disclose and eliminate the 
systematic errors it is necessary that artificial or natural 
photometric reference standard be available on the terrain.