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

Thanks so much Wietske and João, that is very helpful!

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