Multi-frequency and multi-polarization analysis of onion phenology in south of Italy

In this paper, a multi-frequency analysis of onion crop backscattering is undertaken to monitor crop phenology. Time changes of onion backscattering from C-band Sentinel-1 and X-band COSMO-SkyMed synthetic aperture radar imagery are investigated to infer information on the growth stages of onions. The test site is located in the South of Italy, Avellino province, where a sensors' network on the ground is in place that continuously monitor soil and atmospheric parameters as temperature, moisture, wind field, etc. The test site is also equipped with an optical camera that provides real time pictures of the onion field. In this study, co-polarized (VV at C-band and HH at X-band) and cross-polarized (VH at C-band) backscattering coefficients are analyzed over the onion crop together with ancillary independent ground information. Experimental results show that the considered features have good sensitivity to the onion growth and allow identify four phenologial stages during the time span investigated in this study.