Italian experiments

Calibration in real conditions in reference to calibrator location

Courtesy of NASA/JPL

Remote Sensing Group, University and Polythecnic of Bari
Research group coordinator  Prof. F. Posa

The activity, coordinated by Prof. F. Posa of the University of Bari, concerns in situ installation of calibrators and data acquisition.

All the measurements will be done in bands C and X, both before and during the mission, in association with passage(s) over the Matera test site, or according to the mission plan.

The corner reflectors used for this mission have already been amply tried out in previous X-SAR/SIR-C missions.

In this activity, as in the previous one, the effects of corner reflector surface curvature on their radar cross-section will be considered.

The corner reflectors

These are trihedral corner reflectors with 1.8 meter sides, whose response to an incident signal is returned in its direction (a feature making them treatable as point targets), and whose radar cross-section is equal to

formula (Robertson, 1947).

This implies a response of approx. 36 dB for band C and 41 dB for band X.

corner reflectors

Corner Reflectors at the Centro Polifunzionale della Protezione Civile

corner reflector

Positioning of a corner reflector on a fire service vehicle
located at the Rondanini hospital, Rome

The ARCs

The devices known as ARCs (Active Radar Calibrators) are electronic apparatuses able to receive the radar signal on the ground, amplify it and send it back to the sensor. They consist of a receiving antenna, a radio-frequency amplifier and a transmitting antenna. The signal reaching the receiving antenna is amplified and sent back to the sensor, which records greater power than supplied by a simple reflector, with an obvious increase in measured RCS.

arc Image of a test site from a microwave sensor, bringing out the different radar cross-section between an active and a passive calibrator.

Scatterometer in band C

A scatterometer in band C has been designed, produced and successfully tested, for in situ measurements of radar cross-sections (RCS). The instrument, operating in FM-CW (Frequency Modulated - Continuous Wave) mode, transmits a wave frequency-modulated in a 300 MHz interval around a central frequency of 5.3 GHz. This frequency modulation allows the signals back-diffused from various scatterers inside the antenna footprint to be resolved. The instrument is able to measure RCSs between +10 and -40 dB, for targets at distances of between 7 and 100 m. The acquisition parameters can be controlled from a PC through a graphic interface.

fir. 1

Microwave and low-frequency sections of the scatterometer in band C

diagram measurements
Measurements with the
scatterometer in band C
Block diagram of the scatterometer in band C

Vectorial Network Analyzer as scatterometer in bands C and X

A Vectorial Network Analyzer can be used as a polarimetric multifrequency microwave scatterometer.
This instrument operates in a broad frequency range (from 0.04 to 13.5 GHz) with a frequency resolution of 1 KHz, and has a wide dynamic range (from 70 to 98 dB, varying with the frequency). The experimental setup includes, as well as the Analyzer, a system of antennas (rectangular horns) operating in bands C and X, with the possibility of selecting the linear polarization states before each data-gathering run. This system enables characterization of the complex frequency response of any network under test, by measuring the scattering parameters and the relation obtaining between them and the scattering matrix.


Configuration of Analyzer for scatterometric measurements

set up

Diagram of experimental setup

wiltron 377225B

The Vectorial Network Analyzer: Wiltron 377225B


Measurements with the Analyzer in C and X bands