# Sensitivity Analysis of Multi-Temporal Sentinel-1 SAR Parameters to Crop Height and Canopy Coverage
## 1 Introduction  
Spatio-temporal monitoring and evaluation of crop types as food resources has substantial importance in socio-economic issues of societies and it is essential for the sustainable management of agricultural activities. Thus, decision makers can have accurate and updated information regarding crops management; agricultural production planning, food security stability promotion, crop trading market etc. Besides, farmers also benefit from obtaining timely information of crop growth as well as yield estimation. The superiority of radar remote sensing techniques and capabilities of SyntheticAperture Radar (SAR) technology have convinced researchers and government officials to apply it as a widely used, practical and efficient tool in such applications [1]. The SAR technique has become increasingly an effective method of providing seasonal agricultural monitoring [1; 2]. SAR is a coherent radar system that generates high-resolution remote sensing imagery. A SAR sensor has capability to collect data in different weather conditions where the cloudy sky in most time of the growing season (particularly in rainy climate) is a serious obstacle to the application of optical images. Moreover, it can acquire data in day-or-night; exclusivity makes it suitable for long-term and multi-seasonal agricultural monitoring [3]. The SAR system is sensitive to the vegetation biophysical variables and dynamical characteristics of plant targets, and underlying soil parameters such as plant water content, geometric property, deflection and irregularity, soil surface roughness and moisture content [4; 5]. Ka, Ku, X, C, and L are different multi-frequency SAR data acquisition configurations regarding the crop biophysical variables investigation. Ka, Ku, and X bands have high frequencies and short wavelengths in compare with C and L bands [6]. In a review paper by [PERSON] and [PERSON] [7], it is discussed that longer wavelength can penetrate into the crop canopy more than the shorter wavelength and therefore it is less affected by soil. Long wavelength such as L-Band (\(\sim\)24 cm) can penetrate subsurface resulting in higher soil scattering contribution while shorter wavelength such as X-Band (\(\sim\)3 cm) and C-band (\(\sim\)6 cm) mainly interacting with upper part of the canopy segment [8]. Therefore, polarimetric SAR C-band data has high potential for biomass and crop coverage estimation [9; 10]. Previous studies have demonstrated the sensitivity of polarimetric SAR to crop variables such as crop leaf area index (LAI), and crop biomass [6; 11; 12]. Processing and analyzing of the radar signals indices at different wavelengths, frequencies, incident angles, and polarization are amongst the techniques used in the studies of the crop biophysical characteristics [6]. In a study of monitoring and estimating wheat yield, [PERSON] et al. [11] investigated the sensitivity of multi-temporal C-band, polarizations (HH and VV) to biophysical parameters, and the relationship between the radar and biophysical measurements on the wheat development stages. In order to maximize the sensitivity of SAR sensors for the maize growth cycle monitoring and mitigating the soil moisture impact on the signal and in SAR time series, [PERSON] et al. [13] developed a model by simulating the signal in all possible configurations (polarization and incidence angles at C-band) for ENVISAT, RADARSAT, and ERS SAR images and they found that dual polarizations indices are more sensitive to maize growth and less sensitive to soil moisture variations. [PERSON] et al. [5] utilized multi-polarized RADARSAT-2 data to set up indicators of crop condition and yield estimation for corn crop growth stages by obtaining polarization signatures from radar data, and applying related crop parameters and vegetation indices in Central Mexico. The results indicate that the application of RADARSAT-2 polarimetric SAR data isoperational in the agricultural activities.