POWER-LINES - RADAR MEASUREMENTS AND DETECTION ALGORITHM FOR POLARIMETRIC SAR IMAGES

Polarimetric radar backscattering measurements of a variety of powerli ne cables are presented. The objective of the first part of the invest igation was to study the effect of braiding of the cables on the backs cattering at skew incidence. The measurements were performed for four different actual size powerline samples at C-, X-, and Ka-band over a wide range of incidence angles. The data were collected over a 500 MHz bandwidth at C- and X- band with a 1.25 MHz increment and a 1 GHz ban dwidth at Ka-band with a 2.5 MHz increment. Also the effect of nonunif orm illumination and measurement in the near field of the cables were studied. Experimental data shows a significant radar backscatter for V V-polarization (sigma(nunu)) at angles away from normal incidence. Thi s backscatter is proportional to the number and diameter of the strand s on the surface of the cables. There is also noticeable backscatter f or the HH and VH components of the scattering matrices. Their magnitud es, relative to that of the VV component, are proportional to the pitc h angle of the helix. Since detection of these cables is an important safety issue for low-flying airplanes a detection algorithm using pola rimetric synthetic aperture radar (SAR) images was developed using the knowledge gleaned from the measurements. The detection algorithm was tested on a simulated image and worked well, detecting a power line wh ose backscatter power was 6 dB below the average background power.