Venkata S. Rao Gudimetla

Moment-matching method for extracting beam jitter and boresight in experiments with satellites of small physical cross section

The boresight and atmospheric jitter errors in a satellite tracking experiment are currently estimated by matching the probability density function (PDF) of the received signal counts with a set of PDFs of the signal for several combinations of jitter and boresight errors and then the best choice of jitter and boresight error is accepted via the chi-square test. Here a technique that can estimate atmospheric beam jitter and boresight error directly in a satellite active tracking experiment using the moments of the returns off the satellites is proposed. That is, we use the theoretical PDF for the signal return from a small target and compute the corresponding theoretical PDF moments. We can then form a few equations from these moments with only two unknowns, namely, the jitter and boresight. Solving for the unknowns is then unambiguous and very rapid. The method is valid for small physical cross-section targets and has been verified by using simulation and experimental data. Extending the case to asymmetric jitter and asymmetric boresight is possible.

Simulation of long-path horizontal propagation through a three-layer non-Kolmogorov atmosphere model

We explore the possibility that a three-layer model including non-Kolmogorov turbulence center section may produce coherent structures in received intensity. Instead, we find that non-Kolmogorov power-law media decreases coherence when log-amplitude variance is fixed.

Simulation of optical plane wave propagation in non-Kolmogorov turbulence

We compare two methods of setting the turbulence strength of phase screens in wave optics simulations involving non-Kolmogorov turbulence: the characteristic length and equivalent energy.

Physically-constrained Multi-frame Blind Deconvolution

We propose statistical constraints for the problem of imaging through turbulence. The constraints describe image variability in three domains: focal plane, pupil plane or Fourier plane. The constraints are incorporated in the maximum a posteriori deconvolution framework.

Progress in image formation in deep turbulence with laser illumination

Formation of images in strong turbulence (spherical-wave log-amplitude variance greater than 0.25) is a well-known challenge. Such imaging with coherent active illumination poses special difficulties due to the presence of laser speckle in the image, which is similar to atmospheric speckle and so it is difficult to separate the two forms of speckle. However, imaging with laser illumination has the potential benefit of enhanced signal and added information in the laser speckle. In this paper, several image processing approaches are investigated with simulation that show promise for good image quality in such conditions. These approaches include pupil-plane techniques that filter phase based on an assumed atmospheric spatial phase structure function, branch-cut filtering and intensity-weighted branch cut minimization. Also included in the analyses are focal-plane techniques. Significant improvements can be found for Rytov variances up to and beyond 0.4 and up to 10 atmospheric coherence lengths (r0) across the aperture, in uniform turbulence scenarios over a 30 km range with objects of limited extent. The approaches are optimized for fast execution and minimal number of image frames required to form an acceptable image. The results are compared using several image metrics and also compared with a corresponding idealized adaptive-optics approach using an incoherent beacon.

Estimating path-averaged refractive index structure constant in deep turbulence using the unwrapped phase information and sub-harmonic simulations

We show that the addition of sub-harmonic frequencies to standard phase screens improve to a high accuracy, the estimation of the refractive index structure constant in deep turbulence from the unwrapped phase information.

Estimating path-averaged Refractive index structure constant) in Non-Kolmogorov deep turbulence using the unwrapped phase variance and correlation information

In this paper, we will show that path-averaged refractive index structure constant can be estimated in non-Kolmogorov deep turbulence from the unwrapped phase information (phase variance and correlation) at the receiver.