SAR signature modeling of the Pampas region main crops

On October 7th, 2018 the SAOCOM (Satélite Argentino de Observación Con Microondas) 1A was launched, carrying an L band, full-polarimetric SAR on board. The SAOCOM 1B, an identical satellite allowing a revisit time of 8 days, is planned to be launched on March 30th, 2020. Both SAOCOM satellites belong to CONAE (National Space Activities Commission of Argentina) and form part of the ItalianArgentine System of Satellites for Emergency Management (SIASGE) constellation, also including four X band (~9.6 GHz) SAR-equipped COSMO-SkyMed satellites from the Italian Space Agency (ASI). One of the main objectives of the SAOCOM project is related to land and agricultural applications. Extracting land information from radar signatures is a complex issue and the present thesis shows part of the trip we are doing to develop crop applications. This thesis is focused on backscattering simulations over some of the most important crop fields in Argentina, that is, soybeans, maize and wheat. The dedicated area to each crop is 17, 7 and 6 million hectares correspondingly. Simulations are carried out at L- and X-band, and at HH, VV, and HV polarizations, and are based on the application of a discrete scattering model and detailed ground truth collected over the Argentinean Pampas region, used to simulate the backscattering coefficients of crop fields during the entire growth cycle. The wheat fields simulations show that the backscattering coefficient is driven by variations of soil moisture at L-band, particularly at HH polarization, with low vegetation effects. Conversely, the attenuation of vegetation is dominant in producing variations of backscattering coefficients at X-band, particularly at VV polarization. Simulations are compared against experimental data collected over the same Pampas region, using airborne SARAT SAR at L-band and COSMO-SKYMED at X-band. Assuming a surface height standard deviation in a 0.4-0.7 cm range, the simulations generally agree with experimental data, with an RMSE of about 2 dB at L-band and X-band. Discrepancies observed in specific conditions are discussed in the thesis. Overall, the results indicate that a joint use of L- and X-bands has good potential to monitor both soil moisture and vegetation growth. We carried out a test using measurements over US maize fields collected by airborne PALS (Passive and Active L and S band) sensor during the SMEX-2002 campaign, finding that simulations (from Argentinean crop inputs) produce a general agreement on the trend of backscattering coefficient vs. vegetation water content. However, experimental data show some outliers, particularly at HH polarization, which are not explained by the model and the available ground measurements. A completely developed soybeans model was tested against ALOS-2 (Advanced Land Observing Satellite-2; SAR mission) signatures collected over Argentinean soybean fields during 2017 on the site of Monte Buey, located in Pampas. A general agreement is observed also in this case, with some underestimation which can be due to the appearance of the sheath, not yet considered by the model.