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Ansari, Homayoon

Publications and source records attributed to Ansari, Homayoon.

Camera Simulation for the Perseverance Rover’s Lander Vision System

On February 18, 2021, the Perseverance Rover safely landed on Mars at Jezero Crater. Part of the successful landing was due to the Lander Vision System (LVS), which takes descent images from the LVS Camera (LCAM) and IMU measurements and estimates the lander position relative to a map of the Jezero landing site. The LVS Simulation LCAM (LVSS LCAM) model is an image rendering program developed to test the LVS in a variety of scenarios to ensure performance amid uncertainty. The LVSS LCAM model includes a pointing misalignment model, an exposure timing model, shadowing, a terrain reflectance model, atmospheric attenuation from dust, and sensor effects. This model was used for performance analysis, verification, and validation of the LVS algorithms in a Mars-like simulation prior to landing. This paper describes the LVSS LCAM rendering algorithm and compares flight images from LVS operation during the Perseverance landing with their rendered counterparts.

Zheng, Jason

Image Processing In Laser-Beam-Steering Subsystem

Conceptual design of image-processing circuitry developed for proposed tracking apparatus described in "Beam-Steering Subsystem For Laser Communication" (NPO-19069). In proposed system, desired frame rate achieved by "windowed" readout scheme in which only pixels containing and surrounding two spots read out and others skipped without being read. Image data processed rapidly and efficiently to achieve high frequency response.

Lesh, James R.

Digital Controller For Laser-Beam-Steering Subsystem

Report presents additional information about proposed apparatus described in "Beam-Steering Subsystem for Laser Communication" (NPO-19069). Discusses design of digital beam-steering control subsystem and, in particular, that part of design pertaining to digital compensation for frequency response of steering mirror.

Ansari, Homayoon

Digital Controller For Laser-Beam-Steering Subsystem: Part 2

A report presents additional information about laser-beam-steering apparatus described in "Digital Controller for Laser-Beam-Steering Subsystem" (NPO-19193) and "More About Beam-Steering Subsystem for Laser Communication" (NPO-19381). Reiterates basic principles of operation of beam-steering subsystem, with emphasis on modes of operation, basic design concepts, and initial experiments on partial prototype of apparatus.

Ansari, Homayoon

Beam-Steering Subsystem For Laser Communication

Proposed free-space laser communication system contains fewer optical and mechanical components. Involves novel fast beam-steering subsystem stabilizing only angle between transmitting and receiving beams instead of stabilizing both transmitting and receiving lines of sight individually. Received and transmitted beams of light both imaged onto CCD array at focal plane. Relative angular positions of beams computed from centroids of their images.

Lesh, James R.

Lasercom system architecture with reduced complexity

Spatial acquisition and precision beam pointing functions are critical to spaceborne laser communication systems. In the present invention, a single high bandwidth CCD detector is used to perform both spatial acquisition and tracking functions. Compared to previous lasercom hardware design, the array tracking concept offers reduced system complexity by reducing the number of optical elements in the design. Specifically, the design requires only one detector and one beam steering mechanism. It also provides the means to optically close the point-ahead control loop. The technology required for high bandwidth array tracking was examined and shown to be consistent with current state of the art. The single detector design can lead to a significantly reduced system complexity and a lower system cost.

Lesh, James R.

Eliminating Bias In Acousto-Optical Spectrum Analysis

Scheme for digital processing of video signals in acousto-optical spectrum analyzer provides real-time correction for signal-dependent spectral bias. Spectrum analyzer described in "Two-Dimensional Acousto-Optical Spectrum Analyzer" (NPO-18092), related apparatus described in "Three-Dimensional Acousto-Optical Spectrum Analyzer" (NPO-18122). Essence of correction is to average over digitized outputs of pixels in each CCD row and to subtract this from the digitized output of each pixel in row. Signal processed electro-optically with reference-function signals to form two-dimensional spectral image in CCD camera.

Ansari, Homayoon

Three-Dimensional Acousto-Optical Spectrum Analyzer

Experimental acousto-optical Bragg-cell spectrum analyzer achieves subhertz frequency resolution. System represents extension to three dimensions of two-dimensional spectrum-analyzer concept described in, "Two-Dimensional Acousto-Optical Spectrum Analyzer" (NPO-18092). First and second dimensions two spatial dimensions of charge-coupled-device (CCD) imaging array. Third dimension time, as sampled at frame rate of CCD array.

Ansari, Homayoon

Two-Dimensional Acousto-Optical Spectrum Analyzer

State-of-the-art two-dimensional acousto-optical spectrum analyzer processes input radio-frequency signal in real time into components in any number of spectral channels up to about 10(Sup5). Input radio-frequency signal to be analyzed launched via transducer into acousto-optical device along x axis. Acousto-optical device becomes Bragg cell. Pulsed plane waves of light from laser aimed at Bragg cell, which spatially modulates phases of plane waves and diffracts waves according to pattern of acoustic signal.

Ansari, Homayoon

Superfine resolution acoustooptic spectrum analysis

High resolution spectrum analysis of RF signals is required in applications such as the search for extraterrestrial intelligence, RF interference monitoring, or general purpose decomposition of signals. Sub-Hertz resolution in three-dimensional acoustooptic spectrum analysis is theoretically and experimentally demonstrated. The operation of a two-dimensional acoustooptic spectrum analyzer is extended to include time integration over a sequence of CCD frames.

Ansari, Homayoon

Experimental considerations for 2-D acoustooptic spectrum analysis

Two-dimensional acoustooptic spectrum analysis (AOSA) with the associated reference function generator and real-time image processor is presented. The resolution, bandwidth, and analysis time of the two-dimensional AOSA depend on the characteristics. The operation of the two-dimensional AOSA and the experimental considerations for obtaining a high-resolution two-dimensional spectrum in real time are described.

Ansari, Homayoon

Three-dimensional acousto-optic spectrum analysis

A three-dimensional acoustooptic spectrum analyzer with subhertz resolution is demonstrated experimentally. The first and second dimensions are the two spatial dimensions of the output detector array, and the third dimension is time as sampled by the detector array frame rate. A superfine resolution of 0.12 Hz has been achieved.

Ansari, Homayoon