I'm modeling labor productivity on farm sites spread widely across the US, and I would like to include NDVI (or another vegetation index) as a predictor variable. I'm wondering if there is month during the growing season that makes the most sense for comparing across disparate climate types. Thank you for any suggestions!
Hi Rafter,
If climates are disparate, and probably also the times of planting and harvesting, it might make sense to use not one month throughout the study area, but comparable points in the multitemporal curve of a vegetation index. In literature on monitoring crop development, e.g. for production forecast or for drought detection, you will find ways to detect onset of the growing season, full closure of the crop (peak in green biomass) and harvest date from a time-series of remote sensing images. These dates will also relate to certain labour activities as land preparation, planting , weeding, harvesting etc.
Would that work for your study?
Kind regards,
Wietske
Hi Rafter,
One tool to detect onset and other parameters of vegetation seasonality, as suggested by Wietske, is TimeSat: http://web.nateko.lu.se/timesat/timesat.asp
As in your study you are using isolated farm sites it is probably better and more simpler to use an available map of vegetation phenology (e.g. http://onlinelibrary.wiley.com/doi/10.1029/2006JG000217/epdf) to choose the month when NDVI should be compared (for example the one corresponding to green peak), instead of collecting the NDVI data and running TimeSat or other software.
All the best,
João
Hi Rafter - For NDVI peak healthy vegetation cover with less cloud cover image is best so February and October months is most suitable time.
besides comments of @Wietske Bijker ,
These papers may helpful to you
http://marte.sid.inpe.br/col/dpi.inpe.br/sbsr@80/2008/11.18.12.12/doc/1465-1472.pdf
http://earthobservatory.nasa.gov/Features/MeasuringVegetation/measuring_vegetation_3.php
http://www.eaps.purdue.edu/ebdl/pdfs/2005pub-2.pdf
http://www.gislab.lanl.gov/docs/wang_2003_ijrs.pdf
https://cimss.ssec.wisc.edu/dbs/China2011/Day2/Lectures/MODIS_MOD13_NDVI_referenc.pdf
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