Abstract:
In order to study the difference of forest phenophases, using the leaf-litter as the reference, three types of digital cameras(Stardot NetCam made in America, Nikon Coolpix made in Japan, and Ltl acorn Ltl-5610 made in China) were used to evaluate the differences in the time series of color indices and phenophases. The influence of white balance mode of camera(sunny, cloudy, auto) on color index and phenology extraction of captured images were evaluated. Compared the differences in observed canopy phenology between NetCam, Coolpix and Ltl-5610 set in fixed(or sunny) white balance mode, and between Lti-5610 and Huawei smartphone. The results showed that: 1) the seasonal variations in greenness indices by all the three cameras tightly correlated with that of leaf-litter, and their phenophases had no significant differences. However, the redness cannot track the dynamics of leaf-litter, and the estimated peaks of color were later than the leaf fall peak by 6~31 d. 2) There was no significant difference in the estimated autumn phenophases of the greenness index of the same Huawei smartphone under different white balance modes(start of fall SOF, middle of fall MOF, and end of fall EOF). 3) The seasonal variations in greenness index of 3 cameras were consistent approximately. There were no significant differences in the six phenophases(start of spring SOS, middle of spring MOS, peak of spring POS, SOF, MOF, and EOF) and two length of growing seasons(the duration from the MOS to MOF, and from SOS to EOF). The MOS and MOF were mostly stable and suitable to define as the start and end of growing season. This study demonstrates that the greenness index of time-lapse camera is able to monitor vegetation phenology and contributes to expand the global phenology network, while the redness to track the autumn phenology should be carefully used.