The problem with application of exact biooptical models of PROSPECT and PROSAIL type for description of green vegetation reflectance (GVR) spectra is the necessity for a special supportive study to investigate the influence of rather specific biophysical and computational input parameters on resulting spectra. To simplify this task for designers of cyber-physical systems, we have constructed an empirical easy-to-use approximate compact model for GVR spectrum in wavelength range 400-900 nm. Based on measured spectra and PROSPECT-D simulations, a maximally compact model with 5 setup points at significant wavelength values has been formulated. After further normalization via assigning the unit value to the chlorophyll-caused 670 nm minimum, only 4 easily understood tuning parameters will define the GVR spectrum with a satisfactory accuracy. The Fermi-Dirac like step functions and Gaussian bell functions are used as building blocks to describe the most important spectrum features: flat or slanted ground level, green apex, red 700 nm step and infrared plateau. For fitting of the common 9 wavelength-related parameters and of the 4 sample-dependent amplitude parameters, the 7 datasets measured by hyperspectral camera and compact spectrograph were used. The constructed model may be employed as an easy-to-use simplified submodel in the development of larger cyber-physical systems for civil and military applications where identification or hiding of artificial objects in the presence of natural background is needed. For the rough estimation tasks the offered model can yield approximate GVR spectrum with only 2 parameters defined (relative heights of red step and green apex).