Applicability of digital camera images to estimate vegetation parameters in semi-arid grasslands of Mongolia

Greenness indices derived from near-surface photography are increasingly being used for the continuous and automated monitoring of vegetation within various ecosystems. In the present study, we examined the characteristics and applicability of the green chromatic coordinate (GCC) index for monitoring vegetation parameters in semi-arid grasslands. From 2016 to 2019, digital images were collected using time-lapse cameras at 10-min intervals at two grassland sites in Mongolia. The GCC was calculated from the digital number values of red, green, and blue channels of the images. The results demonstrated that GCC values on sunny days were nearly constant between 1100 local time (LT) and 1500 LT regardless of solar altitude and direction. However, the GCC showed erroneous values under low illumination conditions on cloudy and rainy days. In addition, the GCC showed clear seasonal changes similar to the satellite-based normalized difference vegetation index (NDVI) and greenery ratio (GR). The variation in GCC agreed better with that in GR than in NDVI. Finally, the GCC value was highly correlated with plant aboveground biomass and was probably related to CO2 fluxes. Thus, our findings suggest the feasibility of using a digital camera system for continuous long-term monitoring of vegetation parameters and phenology in semi-arid grasslands.