This has been done with the GB-PolSAR instrument, designed and built by members of ARS group of CommSensLab. The incidence angles are similar to those of geosynchronous satellite observations over Europe. The measurement campaign has been designed to provide a continuous monitoring of an agricultural field with a temporal resolution of 10 minutes and a spatial resolution in the order of a square meter providing calibrated quad-pol Single Look Complex (SLC) images with a large number of resolution cells.
Two different crops have been sown and monitored. In the spring phase of the campaign, barley, a typical cereal cultivated in southern Europe, was sown and monitored until beginning of summer. Immediately after barley harvest, the field was ploughed, and corn was sown supported by an irrigation system. The corn crop was monitored through its life cycle until harvesting time in November. The different densities, sizes and water content of both crops will allow to assess GeoSAR capabilities to provide soil moisture and crop water content data.
The field is in front of the North North-West facade of the EEABB building. The cultivated area is 25 m far from the façade, its depth is approx. 22 m, and its width is around 60 m. The GB-SAR is mounted on the roof of the building, centred respect the cultivated area in order to minimize the squint angles
The main instrument is a Full-Polarimetric Ground Based Synthetic Aperture Radar, with two independent Zero-IF receivers and one transmitter chain. A Solid State Microwave Switch is connected among the transmitter and two orthogonal polarized antennas. Each of the two receiver chains is connected respectively to one of the two orthogonally polarized receiving antennas. The frequency generation unit is a DDS that generates a stepped linear frequency modulated continuous wave (SLFM-CW) chirp signal.The RADAR is mounted on a linear motion unit, capable of performing up to 2m long apertures. The aperture length and rail speed are fully controllable, with a speed limit of 1m/s. The linear motion unit is attached to a rigidized steel frame .
A Corner Reflector was placed along the scenario. It facilitated the identification of the field extension and provided information of the polarimetric image calibration.
The set of four pyramidal horns were characterized in the Anechoic chamber
Soil moisture ground-truth was based on gravimetric measurements from samples taken at different positions of the field
Soil roughness was measured by means of a laser profiler
Different corner reflectors were permanently deployed for radiometric calibration of radar data
Long-term backscattering evolution of the barley crop. Different ancillary data has been included as rain, leaf area index (LAI), plant water content, plant height and soil moisture.
Long-term backscattering evolution of copolar and cross-polar channels of the corn crop. Different ancillary data has been included as rain, LAI and plant water content. Important peaks in the evolution of the backscattering can be clearly seen at the beginning of the corn campaign due to some rain events and the irrigation periods.
Time series of 10 min, 1h, 4h, 1 day, 3 days and 6 days temporal baseline coherence of the whole corn crop campaign for HH, VV, HV and VH channels for Mid Range: incidence angles (59.1 to 63 ). The evolution can be compared with ancillary data (plant height, rain and irrigation)