Phenology is the study of recurring natural phenomena. The seasonal "greening-up" and "greening-down" of dominant vegetation can be used as a predictor for a variety of processes and variables at local to global scales. The use of satellites to monitor land surface phenology is important for understanding local and regional ecosystem variability, identifying change over time, and potentially predicting ecosystem response to short and long-term changes in climate. However, the relationship between how phenology is expressed on the ground and how it is interpreted from satellites is poorly understood because phenological stages do not always correspond well to changes in spectral reflectance. In this study, we explored the relationship between greenness as measured by digital camera, the human eye, and ASTER imagery in two perennial grasslands at the Sevilleta National Wildlife Refuge in central New Mexico.
Visual observations: While facing south, a "niner" (i.e., a 30 cm x 30 cm frame partioned into nine squares, each equal to an area of 1% of 1m2) was placed with one corner at a pinflag to the north and the other at a pinflag to the south. Four substrates were measured: bare Soil (S), brown vegetation (B), green vegetation (G), and green forbs (F).
The total cover of substrates at a sampling location equalled 9% (i.e., the entire niner). If the substrate had < 0.25% cover, T (i.e., trace) was recorded. If the cover of a substrate was > 0.25% it was rounded up to 1. If a substrate did not exist at a location, a zero was recorded
Time of day: The date/time stamp on a digital camera was used so that date/time was recorded on each photo.
Plot layout: Two sites were chosen to represent semi-arid grasslands. Site B was dominated by blue grama and site G by black grama. At each site six plots were established. Each plot was comprised of twelve quadrats that measured 50 X 50 cm for digital photographs and 30 X 30 cm for visual observations in a 3 X 4 grid.
Digital images: A 50 X 50 cm pvc frame was used to delineate area. Laminated markers placed next to the frame denoted the plot and quadrat number. A camera was held directly over a quadrat to get the entire PVC frame in the picture. Every effort was made to minimize shadow.
All data was checked for errors. Both years were combined and put online. 6/25/09, KRW.
Data Collection Period:
5/3/2007, 7/2/2007, 7/16/2007, 7/31/2007, 8/17/2007, 9/4/2007, 9/18/2007, 10/4/2007, 4/14/2008, 5/30/2008, 8/4/2008, 8/19/2008, 9/5/2008, 9/22/2008, and 10/6/2008.