Results of coherent backscatter radar imaging using Capon's method and measurements made by the Sao Luis radar interferometer

Abstract

Interferometric radar imaging of F-region spread F irregularities is used to determine the distribution of scatterers within the radar field of view. In this study, we investigate the use of the Capon's spectral method for estimating the distribution of equatorial spread F (ESF) irregularity structures observed by a small, low power coherent backscatter radar interferometer located at the equatorial site of Sao Luis (2.59°S, 44.21°W, −2.35° dip.), Brazil. To evaluate the performance of the method, we show numerical simulations for typical F-region measurement conditions. Results for the Fourier imaging method are also shown for comparison. The simulation shows that, despite the short baselines of the Sao Luis radar, the Capon technique is capable of distinguishing features with km scale sizes (in the zonal direction) at F-region heights. We also investigated the application of the Capon algorithm to actual measurements made by the Sao Luis radar, and obtained high resolution images of equatorial spread F (ESF) scattering structures. In this presentation, we will show results of the Capon images during different types of equatorial spread F events, and will compare the results with images obtained using the conventional Fourier method. As predicted by the numerical simulations, we are able to distinguish features of the scattering structures with resolution of a few km in the zonal direction. We have been able, in particular, to identify the morphology of scattering structures during bottom-type layers. Signatures of underlying deca-kilometric waves, similar to those observed by [3] and [7] were detected. The observations suggest the action of the so-called collisional shear instability.