RESUMEN
Planetary caves are desirable environments for the search for biosignatures corresponding to extant or extinct extraterrestrial life due to the protection they offer from surface-level solar radiation and ionizing particles. Near-infrared (NIR) reflectance spectroscopy is one of a multitude of techniques that, when taken together, can provide a comprehensive understanding of the geomicrobiology in planetary subsurface regions. To that end, we developed two portable NIR spectrometers that employ acousto-optic tunable filters and demonstrated them in three geochemically distinct cave environments. The instruments were deployed both as stand-alone spectrometers positioned against the targets manually and as a component of an instrument payload mounted on a quadruped robot capable of vertical excursions of several meters. In situ measurements of calcium carbonates, sulfates, metal oxides, and microbial colonies and mats revealed spectral signatures that enable a distinction between the targets of interest and the underlying substrates. The ruggedness and portability of the instruments, and their low size, weight, and power, spectral agility, and active illumination make AOTF-based spectrometers ideally suited for studies of planetary caves.
RESUMEN
An optical heterodyne array imaging system is described for double-exposure interferometric measurement of objects that change because of stress or vibration. The signal measurement and processing approach is summarized, and the method is demonstrated in the laboratory. An advantage of this technique over other electronic interferometric imaging methods is that complex exposures are created with digital phase and amplitude values at each image pixel. In addition, measurement of object deformation does not require time synchronization between the camera exposure time, or laser pulse time, and object vibration frequency.
RESUMEN
We introduce an incoherent adaptive imaging system based on optimization of an image quality metric measured using a coherent optical system. Experimental results and numerical simulations are presented that demonstrate adaptive correction of phase-distorted extended source images containing objects located at multiple distances.
RESUMEN
Coherent imaging techniques rely on the coherence properties of backscattered radiation to form an image of an illuminated object. These techniques are sensitive to the degree of coherence of the illuminating source. We present an approach for simulating the effects that partial temporal coherent illumination has on these techniques. Computer simulation and laboratory experimental results are presented that illustrate illumination coherence effects on imagery obtained with the technique known as imaging correlography.
RESUMEN
An experimental approach to the measurement of phase of a coherent optical field with a Shack-Hartmann sensor is presented. We demonstrate the usefulness of this sensor by verifying a theoretical model for the distribution of ray directions in a monochromatic speckle pattern.
RESUMEN
We report what are to our knowledge the first coherent images recovered in the laboratory from measurements made with a Shack-Hartmann wave-front sensor of the phase and amplitude of a laser speckle wave front. We discuss the design of our wave-front sensor, which can obtain the phase and amplitude of an optical field with a single intensity measurement, and we point out a particular type of phase jump that cannot be detected by the Shack-Hartmann sensor. We also discuss implementations of this technique that may permit near-diffraction-limited imaging through turbulent media.
RESUMEN
The performance of an imaging technique relying on the spatial correlation of laser-speckle intensity measurements is evaluated on the basis of theoretical analysis, computer simulation, and laboratory results. A theoretical expression for the signal-to-noise ratio of the recovered imaging target's power spectrum is used to estimate the imaging performance expected in the computer simulation and laboratory experiment. Power-spectrum estimates for an imaging target, obtained both in the laboratory and through simulation, are compared with the theoretical results and with the true spectrum of the target. Images recovered from the simulation data and the laboratory data are also compared. Our results suggest that the signal-to-noise ratio expression provides an accurate means for estimating the recoverable frequency content of a simple target.
RESUMEN
We describe a postdetection turbulence compensation technique for obtaining high resolution imagery through the atmosphere. We present preliminary results fromfield experiments.
