P-band radars around 435 MHz are receiving an increased interest for Earth observation because they can penetrate the forest canopy and penetrate the soil down to the root zone, allowing to monitor subsurface soil moisture, which is of crucial for crop irrigation management. However, P-band radars face some challenges, such as the potential radio interference (RFI) from long-range radars or radio-amateur emissions, and, because of the long wavelength ~70 cm, they also require large antennas. In this paper, a novel approach using a long sequence Pseudo-Random Noise (PRN) waveform is proposed to mitigate the RFI issue and improve co-existence between different radars, while allowing to reduce the transmitted peak power. This paper presents the P-band SDR polarimetric interferometric ground-based synthetic aperture radar (Pol-In GB-SAR) that has been designed, and it is being developed by the UAE University. Furthermore, the proposed radar system was configured by using GNU Radio, an open-source software. This method has reduced the radar system development process and cost.