1. Filippo Parrini Technologies for Environmental and Cultural Heritage Laboratory (TECHLab) Department of Electronics and Telecommunications University of Firenze (Italy)

2. Ground based radar interferometry

3. LINE OF SIGHT DISPLACEMENT

4. Multi-bistatic radar: operating principle Three independent interferometric measurements: 1.TX1 - RX (monostatic) 2.TX2 - RX (bistatic) 3.TX3 - RX (bistatic)

5. Multi bistatic radar: operating principle d: target displacementd1,d2,d3: target displacement projections

6. Multi bistatic radar: issues Instrumental issuesGeometric issuesRadar issues Cable thermal driftMulti-bistatic RCS of natural/artificial targets Measurement geometry determination Displacement components estimation

7. Instrumental issues: cable’s thermal drift Highly phase stable cable This effect has not been compensated yet

8. Radar issues: bistatic RCS Natural or man-made reflectors usually have a very low RCS in multi bistatic mode It is more difficult to have radar reflectors with a good RCS in several directions in order to perform a robust interferometric analysis

9. Geometric issues 2) The targets position in the reference system has to be determined (it can be retrieve from radar range measurement) 3) Target displacement vector (d x, d y, d z ) has to be estimated (made with the following relation) A measurement setup geometry which assure a small condition number for matrix A is necessary for a good accuracy in displacement vector estimation 1) The multi-bistatic radar position in the reference system has to be known (it can be easily measured with additional instruments) (d 1,d 2,d 3 ) interferometric measurements

10. Experimental tests in controlled environment No vertical baseline was achieved

11. Experimental tests Special multi-bistatic target automatically positioned and rotated Side view Front view

12. Experimental test #1: displacement along y axis Direction of the displacement during the 1 st test

13. Displacement of target measured by three radar channels (d 1,d 2,d 3 ) Experimental test #1: displacement along y axis

14. Measurement displacement along the reference system axis (X = red, Y= blue) Errors: Mean: -0.01 mm  : 0.03 mm Experimental test #1: displacement along y axis

15. Experimental test #2: displacement along any direction Direction of the displacement during the 2 st test (  =23.5)

16. Experimental test #2: displacement along any direction Errors: Mean: -0.02 mm  : 0.03 mm

17. Conclusions The novel sensor was tested in a controlled environment showing good performances in term of measurement accuracy. A novel multi-bistatic radar sensor has now been designed and set up in order to provide three dimensional measurement capabilities. Only LOS component of displacement is provided by traditional interferometric radar. Measurement of displacement vector is of paramount importance in static and dynamic tests on civil structures.