Radar Imaging Homepage

Note: The MPEG movie viewing tools supplied with Windows distributions do not seem to be able to display the movies posted here. Our movies have unusual aspect ratios with which the Microsoft programs cannot cope. Most shareware viewers have no problems, including The Berkeley Player. A framerate of about 8 fps works well.

Radar interferometry with multiple collinear antenna baselines has been performed at Jicamarca, and high-resolution images of plasma irregularities in the electrojet and in equatorial spread F have been constructed from the data. The images represent the brightness distribution of the coherent radar backscatter, which is the Fourier transform of the visibility or spatial cross correlation of the scattered radar signal on the ground. The horizontal axes for all of the images represent zenith angle in degrees. The vertical axes represent altitude. In the images, the lightness, hue, and saturation of the pixels represent the S/N ratio, Doppler shift, and Doppler width of the backscatter. Red (blue) shifted echoes have red (blue) tones; pure colors denote narrow spectra while broad spectra are more pastel.

The visibility data are noisy and incompletely sampled, and we have used a maximum entropy method to perform the Fourier transform, making optimal use of the data available. Using the current antenna configuration at Jicamarca, the radar imaging technique is able to resolve structures within the radar beam that are a few tenths of a degree or less wide. By animating sequences of images, we can observe the evolution of ionospheric irregularities without confusing spatial and temporal variations.

A new antenna at Jicamarca, physically separated from the main antenna array, provides very long interferometry baselines up to 94 wavelengths long for imaging experiments. Up to 15 interferometry baselines can be constructed, now that Jicamarca has the capability to sample 6 quadrature receivers simultaneously. The particular receiving antenna arrangement we use is shown here. The north and south quarters of the antenna are used for transmission.

Details regarding the generation of the images can be found in a manuscript which is in HTML format. Here we present examples of animated images computed from several different experiments. The RTI maps in each case hint at the behavior of the ionosphere on a given night. Below each map is a selection of animations corresponding to different local time intervals from the map.