Linking Phenological Indices from Digital Cameras in Idaho and Montana to MODIS NDVI

Joseph St Peter,Nicole Hupp,Mark Hebblewhite,Kelly Proffitt,John Hogland,Mark Hurley

doi:10.3390/rs10101612

Abstract

Digital cameras can provide a consistent view of vegetation phenology at fine spatial and temporal scales that are impractical to collect manually and are currently unobtainable by satellite and most aerial based sensors. This study links greenness indices derived from digital images in a network of rangeland and forested sites in Montana and Idaho to 16-day normalized difference vegetation index (NDVI) from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS). Multiple digital cameras were placed along a transect at each site to increase the observational footprint and correlation with the coarser MODIS NDVI. Digital camera phenology indices were averaged across cameras on a site to derive phenological curves. The phenology curves, as well as green-up dates, and maximum growth dates, were highly correlated to the satellite derived MODIS composite NDVI 16-day data at homogeneous rangeland vegetation sites. Forested and mixed canopy sites had lower correlation and variable significance. This result suggests the use of MODIS NDVI in forested sites to evaluate understory phenology may not be suitable. This study demonstrates that data from digital camera networks with multiple cameras per site can be used to reliably estimate measures of vegetation phenology in rangelands and that those data are highly correlated to MODIS 16-day NDVI.

Highlights

Vegetation phenology is the seasonal timing of vegetation development; it can be characterized by events such as emergence, bud burst, flowering date and senescence for individual or groups of vegetative species
The results of our site-level comparisons show that in the Idaho study area, the excess green index (ExG) and Green chromatic coordinate (GCC) camera index values were highly correlated to Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) (Pearson correlations of 0.80 to 0.95, respectively), while the VIgreen camera index had the lowest correlation to MODIS NDVI (Table 1)
The lower correlation found between the VIgreen camera index and MODIS NDVI compared to the GCC and ExG index is primarily in the rapid decline of VIgreen in autumn (Figure 5)

Summary

Introduction

Vegetation phenology is the seasonal timing of vegetation development; it can be characterized by events such as emergence, bud burst, flowering date and senescence for individual or groups of vegetative species. One method used to link digital camera indices to traditional vegetation indices; like NDVI compares the level of agreement between phenophase transition dates such as start, end, and length of growing season for indices from infrared and visible portions of the electromagnetic spectrum [20,21,22,23,24]. These studies have found that camera and satellite phenology. After removing malfunctioning and unusable camera data, the Idaho camera network consisted of 26 cameras on six sites in the year 2014 and 31 cameras on eight sites in 2015 producing over 41,000 images

Processing Phenological Indices

Statistical Analysis

Results

Discussion

Conclusions

27. Phenocam