Nothing Special   »   [go: up one dir, main page]
Scribd Logo
Upload

Welcome to Scribd!

  • 108 views

    FMCW Lidar: Figure 1. A Conceptual Diagram of FMCW Ladar

    Uploaded by

    adrianioantoma
    0000

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd

    FMCW Lidar: Figure 1. A Conceptual Diagram of FMCW Ladar

    Uploaded by

    adrianioantoma
    108 views2 pages
    0000

    Original Title

    FMCW_LiDAR

    Copyright

    © © All Rights Reserved

    Available Formats

    PDF, TXT or read online from Scribd

    Did you find this document useful?

    Is this content inappropriate?

    0000

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    108 views2 pages

    FMCW Lidar: Figure 1. A Conceptual Diagram of FMCW Ladar

    Uploaded by

    adrianioantoma
    0000

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 2

    FMCW LiDAR

    Bridger’s distance measurement technology is based on frequency-modulated continuous-wave


    (FMCW) LiDAR shown in Figure 1. Light from a frequency-swept, or “chirped”, laser is split into
    two portions; one portion (Tx) is transmitted to the target while the second portion (LO) is kept
    local and does not travel to the target. The laser light returning from the target (Rx) is
    interferometrically recombined with the LO and detected. Figure 1 (top right), shows the LO
    (black) and Rx (gray) optical frequencies (linear chirps) as functions of time. Because the Rx has
    traveled to the target and back, it is simply a time-delayed replica of the LO waveform. The time
    delay, 𝜏𝐷 , is related to the target range (distance), 𝑅, through the relation

    𝜏𝐷 = 2𝑅⁄𝑐, (1)

    where 𝑐 is the speed of light. A detector measures the heterodyne beat (difference frequency)
    between the two optical fields. The heterodyne beat frequency is given by

    𝑓𝑏𝑒𝑎𝑡 = 𝜅𝜏𝐷 , (2)

    where 𝜅 is the chirp rate. Figure 1 (bottom right) shows the Fourier transform of the heterodyne
    beat on a logarithmic vertical axis, with the horizontal frequency axis converted to range. This
    representation is referred to as the full-waveform range profile. Eqns. (1) and (2) can be combined
    to determine the target range through the equation

    𝑅 = 𝑓𝑏𝑒𝑎𝑡 𝑐⁄2𝜅, (3)

    Scene

    Figure 1. A conceptual diagram of FMCW ladar.

    © copyright Bridger Photonics, Inc. All rights reserved. No reproduction without permission.
    Often times, one desires to know the range to one or more targets along the beam path. Figure
    2 shows a range profile, this time with a linear vertical axis, with three targets on the same bearing,
    but at different ranges. The following definitions follow from those of the radar community.

    As shown in Figure 2, the range resolution is defined as the minimum resolvable separation (full
    width at half maximum) between two targets on the same bearing, and is given by

    ∆𝑅 = 𝑐⁄2𝐵, (4)

    where 𝐵 is the information bandwidth (chirp bandwidth for this case). However, it is often possible
    to determine the range of a target much more precisely than the resolution.

    As shown in Figure 2, the range precision is defined as the standard deviation of a statistically
    meaningful number of range measurements of the same target under the same conditions, and
    is given by the Cramér Rao lower bound,

    𝜎𝑅 ≈ ∆𝑅⁄√𝑆𝑁𝑅, (5)

    where SNR is the signal-to-noise ratio (in RF power) of the measurement. The beauty of Eqns. (4)
    and (5) are that they apply to any LiDAR system. To determine the range to a target with the best
    precision, one simply desires large information bandwidth and high signal-to-noise ratio.

    Figure 2. A conceptual diagram of FMCW ladar.

    A portion of Bridger’s intellectual property includes methods to actively linearize very broadband
    frequency chirps, which is important for achieving the fundamental limits of resolution, precision,
    and measurement range.

    The FMCW LiDAR technique can offer a number of advantages over conventional “direct detect”
    LiDAR techniques including:

    1. Improved range resolution, enabling the measurement and separation of multiple


    closely spaced surfaces.
    2. Improved dynamic range, enabling the measurement of both bright and dim objects
    simultaneously.
    3. Single-photon sensitivity, enabling small apertures, long range operation, and obscurant
    penetration.
    4. Velocity sensitivity, enabling the ability to detect and quantify motion.

    Copyright © 2019 Bridger Photonics, Inc. Specifications are subject to change without notice. 2

    You might also like