Design and development of ground based radar systems for vegetation studies

Microwave remote sensing is recognized as one of the key technologies to perform radar backscattering analysis of natural and man-made objects. Various airborne and space-borne microwave remote sensing systems have been constructed based on different requirements and applications. Recently, ground based microwave radar technology has become one of the important tools to study and understand the interaction between the microwave signal and the earth terrain. However, it often faces challenges during the in-situ measurement such as lengthy measurement time, offline post-processing and rapid weather changes. In this research work, two ground-based radar systems have been developed namely the near real-time automated C-band scatterometer system (NRT-SCATT) and the wideband VNA ground-based radar system with real and synthetic aperture radar (WRSAR). They have been constructed to surmount the challenges and provide alternative solution to the existing systems.;The full polarimetric NRT-SCATT system is a Frequency Modulated Continuous Wave (FMCW) radar that is constructed from a combination of commercially available Radio Frequency (RF) components and customized circuits by the author. An automated antenna positioning system (AAPS) is included as part of the radar backscattering measurement system, allowing a more efficient and near real-time measurement process.;In order to study wideband radar backscattering responses from vegetation covered area, an automated WRSAR that operates from 2 to 7 GHz has been constructed. A Vector Network Analyzer (VNA) has been employed as the core instrument in the WRSAR to generate the required transmitting signal and to perform data acquisition of the received microwave signal. Custom-made RF circuits have been designed specifically to allow the proposed system to measure full linear polarimetric scattering matrices from the area of interest. Utilizing the two-dimensional scanning capabilities of the AAPS, the WRSAR is able to perform automatic real and synthetic aperture measurements at outdoor environment.;A series of point target measurements has been conducted using the integrated wideband radar system in anechoic chamber. The measured results have been compared with the simulated values from the theoretical model. The comparison shows a good correlation between measured and simulated radar backscattering data.;The constructed systems have been used to perform oil palm measurement and paddy growth monitoring. Season-long radar backscattering coefficient measurement data with 10° angular interval from various growth stages of rice field are presented. It is interesting to show that the radar backscattering response from the rice field can be represented in fifth-order polynomial. Besides, high angular resolution backscattering coefficient of 1° resolution measured from rice fields are also presented. A great advantage of the high resolution measurements is that they provide more detailed information on the actual interactions between the microwave signals and rice crop canopies. This enables a more accurate representation of radar backscattering coefficients at various incident angles and polarizations which in comparisons with simulated results from theoretical models of rice crops.;To study the scattering mechanisms of the rice field, Freeman-Durden target decomposition technique has been used to decompose the polarimetric radar backscattering signature measured by the WRSAR. It is shown that scattering from rice field are dominated by at least two scattering mechanisms. The scattering mechanisms of the rice field provide better illustration and new evidence on the scattering behaviour of the rice field and this finding can be used as the training dataset for a SAR image classification.;Besides performing real aperture measurement, the constructed WRSAR has been used to perform synthetic aperture radar measurement on point targets and rice fields. 3-D target reflectivity images of the measured point targets have been constructed using a 3-D image reconstruction algorithm. The analysis of the results measured by WRSAR in real and synthetic aperture measurement modes show that the system is ready for various environmental monitoring activities such as vegetation growth monitoring, surface roughness study and man-made target analysis.