An approach to photogrammetric processing of indirect optical location data

The paper proposes an approach to obtaining images of the objects under investigation based on indirect optical location data. The goal of the study is to increase the graphic similarity of the images and to assign them measuring properties. To achieve this goal, the concept of photogrammetric processing of frame images obtained by conducting indirect optical location in a certain way is formulated. The graphical similarity of the images is proposed to be improved by extracting photometric data related to the object and the background from the registered optical radiation. Based on the selected data, a statistical evaluation of the sample average of the optical radiation intensity from these sources is carried out. The obtained estimates are used to form a monochrome digital image. Adding measurement properties is done by converting the coordinates of the digital image to relative coordinates that have a metric expression. The reason for the decrease in the graphical similarity of the images obtained on the basis of indirect optical location data is determined. In particular, the addition of light waves from different sources, during the allotted exposure time of the photodetector, leads to the merging of the object and the background in the resulting image. The paper presents an approach to the separation of photometric data from different sources that is based on the observation of the phase difference between the emitted and recorded light waves. The authors define the mathematical apparatus for linking the obtained images to the relative coordinate system that is adapted for the case of indirect optical location. The concept of conducting indirect optical location using a special optoelectronic complex is proposed. The study describes the requirements for the equipment of an optoelectronic complex that generates and registers optical radiation with the required parameters. The results of an experiment on the formation of images with measuring properties confirm the feasibility of using the proposed method. Conducting an indirect optical location opens the way to obtaining images of an area that is inaccessible to humans. In particular, the results of the experiment demonstrate that the use of the proposed concept provides images of an object placed behind a light-tight obstacle, which are characterized by the presence of measuring properties and reflect the details of the object under study with high graphical similarity

Single-Photon Depth Imaging Using a Union-of-Subspaces Model

Light detection and ranging systems reconstruct scene depth from time-of-flight measurements. For low light-level depth imaging applications, such as remote sensing and robot vision, these systems use single-photon detectors that resolve individual photon arrivals. Even so, they must detect a large number of photons to mitigate Poisson shot noise and reject anomalous photon detections from background light. We introduce a novel framework for accurate depth imaging using a small number of detected photons in the presence of an unknown amount of background light that may vary spatially. It employs a Poisson observation model for the photon detections plus a union-of-subspaces constraint on the discrete-time flux from the scene at any single pixel. Together, they enable a greedy signal-pursuit algorithm to rapidly and simultaneously converge on accurate estimates of scene depth and background flux, without any assumptions on spatial correlations of the depth or background flux. Using experimental single-photon data, we demonstrate that our proposed framework recovers depth features with 1.7 cm absolute error, using 15 photons per image pixel and an illumination pulse with 6.7-cm scaled root-mean-square length. We also show that our framework outperforms the conventional pixelwise log-matched filtering, which is a computationally-efficient approximation to the maximum-likelihood solution, by a factor of 6.1 in absolute depth error.Samsung (Firm) (Scholarship)National Science Foundation (U.S.) (Grant 1422034)Lincoln Laboratory. Advanced Concepts Committe

Revealing hidden scenes by photon-efficient occlusion-based opportunistic active imaging

The ability to see around corners, i.e., recover details of a hidden scene from its reflections in the surrounding environment, is of considerable interest in a wide range of applications. However, the diffuse nature of light reflected from typical surfaces leads to mixing of spatial information in the collected light, precluding useful scene reconstruction. Here, we employ a computational imaging technique that opportunistically exploits the presence of occluding objects, which obstruct probe-light propagation in the hidden scene, to undo the mixing and greatly improve scene recovery. Importantly, our technique obviates the need for the ultrafast time-of-flight measurements employed by most previous approaches to hidden-scene imaging. Moreover, it does so in a photon-efficient manner based on an accurate forward model and a computational algorithm that, together, respect the physics of three-bounce light propagation and single-photon detection. Using our methodology, we demonstrate reconstruction of hidden-surface reflectivity patterns in a meter-scale environment from non-time-resolved measurements. Ultimately, our technique represents an instance of a rich and promising new imaging modality with important potential implications for imaging science.Comment: Related theory in arXiv:1711.0629

Computational Microwave Imaging Using 3D Printed Conductive Polymer Frequency-Diverse Metasurface Antennas

A frequency-diverse computational imaging system synthesized using three-dimensional (3D) printed frequency-diverse metasurface antennas is demonstrated. The 3D fabrication of the antennas is achieved using a combination of PolyLactic Acid (PLA) polymer material and conductive polymer material (Electrifi), circumventing the requirement for expensive and time-consuming conventional fabrication techniques, such as machine milling, photolithography and laser-etching. Using the 3D printed frequency- diverse metasurface antennas, a composite aperture is designed and simulated for imaging in the K-band frequency regime (17.5-26.5 GHz). The frequency-diverse system is capable of imaging by means of a simple frequency-sweep in an-all electronic manner, avoiding mechanical scanning and active circuit components. Using the synthesized system, microwave imaging of objects is achieved at the diffraction limit. It is also demonstrated that the conductivity of the Electrifi polymer material significantly affects the performance of the 3D printed antennas and therefore is a critical factor governing the fidelity of the reconstructed images.Comment: Original manuscript as submitted to IET Microwaves, Antennas & Propagation (2017). 17 pages, 8 figure