Patent Publication Number: US-2023135132-A1

Title: Methods and Systems for Dithering Active Sensor Pulse Emissions

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/556,207, filed Dec. 20, 2021, which is a continuation of U.S. patent application Ser. No. 16/134,985, filed Sep. 19, 2018. The foregoing applications are incorporated herein by reference. 
    
    
     BACKGROUND 
     Active sensors, such as light detection and ranging (LIDAR) sensors, radio detection and ranging (RADAR) sensors, sound navigation and ranging (SONAR) sensors, among others, are sensors that can scan a surrounding environment by emitting signals toward the surrounding environment and detecting reflections of the emitted signals. 
     For example, a LIDAR sensor can determine distances to environmental features while scanning through a scene to assemble a “point cloud” indicative of reflective surfaces in the environment. Individual points in the point cloud can be determined, for example, by transmitting a laser pulse and detecting a returning pulse, if any, reflected from an object in the environment, and then determining a distance to the object according to a time delay between the transmission of the pulse and the reception of the reflected pulse. As a result, for example, a three-dimensional map of points indicative of locations of reflective features in the environment can be generated. 
     SUMMARY 
     In one example, a device comprises a plurality of emitters including at least a first emitter and a second emitter. The first emitter emits light that illuminates a first portion of a field-of-view (FOV) of the device. The second emitter emits light that illuminates a second portion of the FOV. The device also comprises a controller that obtains a scan of the FOV. Obtaining the scan involves the controller causing each emitter of the plurality of emitters to emit a respective light pulse during an emission time period associated with the scan. Causing each emitter to emit the respective light pulse involves the controller causing the first emitter to emit a first-emitter light pulse at a first-emitter time offset from a start time of the emission time period, and causing the second emitter to emit a second-emitter light pulse at a second-emitter time offset from the start time of the emission time period. 
     In another example, a method involves causing a plurality of emitters to emit a plurality of light pulses during a first emission time period associated with a first scan of a field-of-view (FOV). A first emitter of the plurality of emitters may be configured to illuminate a first portion of the FOV. A second emitter of the plurality of emitters may be configured to illuminate a second portion of the FOV. Causing the plurality of emitters to emit the plurality of light pulses may involve causing the first emitter to emit a first-emitter light pulse at a first-emitter time offset from an end time of the first emission time period, and causing the second emitter to emit a second-emitter light pulse at a second-emitter time offset from the end time of the first emission time period. The method also involves obtaining the first scan based on a first measurement of light from the FOV received during a first detection time period that begins after the end time of the first emission time period. 
     In yet another example, a device includes a transmitter that transmits a plurality of light beams during a first emission time period associated with a first scan of a field-of-view (FOV) of the device. The plurality of light beams is spatially arranged to illuminate respective portions of the FOV. The first emission time period has a start time and an end time. The transmitter illuminates a first portion of the FOV at a first-portion time offset from the start time of the first emission time period. The transmitter illuminates a second portion of the FOV at a second-portion time offset from the start time of the first emission time period. The device also includes a receiver that intercepts light from the FOV illuminated by the plurality of light beams. 
     In still another example, a system comprises means for causing a plurality of emitters to emit a plurality of light pulses during a first emission time period associated with a first scan of a field-of-view (FOV). A first emitter of the plurality of emitters may be configured to illuminate a first portion of the FOV. A second emitter of the plurality of emitters may be configured to illuminate a second portion of the FOV. Causing the plurality of emitters to emit the plurality of light pulses may involve causing the first emitter to emit a first-emitter light pulse at a first-emitter time offset from an end time of the first emission time period, and causing the second emitter to emit a second-emitter light pulse at a second-emitter time offset from the end time of the first emission time period. The system also comprises means for obtaining the first scan based on a first measurement of light from the FOV received during a first detection time period that begins after the end time of the first emission time period. 
     These as well as other aspects, advantages, and alternatives will become apparent to those of ordinary skill in the art by reading the following detailed description with reference where appropriate to the accompanying drawings. Further, it should be understood that the description provided in this summary section and elsewhere in this document is intended to illustrate the claimed subject matter by way of example and not by way of limitation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a simplified block diagram of a device, according to example embodiments. 
         FIG.  2    illustrates a LIDAR device, according to example embodiments. 
         FIG.  3    illustrates a cross-section view of a plurality of emitted beams spatially arranged to scan respective portions of a FOV, according to example embodiments. 
         FIG.  4    is a flowchart of a method, according to example embodiments. 
         FIG.  5    is a flowchart of another method, according to example embodiments. 
         FIG.  6 A  illustrates conceptual timing diagrams for a first scan of a FOV, according to example embodiments. 
         FIG.  6 B  illustrates conceptual timing diagrams for a second scan of the FOV, according to example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary implementations are described herein. It should be understood that the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any implementation or feature described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations or features. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The example implementations described herein are not meant to be limiting. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations. 
     I. Overview 
     Within examples, an active sensing system (e.g., LIDAR, RADAR, SONAR, etc.) may include a transmitter that transmits a plurality of signals (e.g., beams, pulses, etc.) spatially arranged (e.g., in a grid arrangement or other arrangement of adjacent signals) to scan respective portions of a field-of-view (FOV). 
     In one example, a LIDAR device may include multiple transmit/receive channels arranged to scan respective portions of a FOV. For instance, the LIDAR device may include a transmitter that transmits a plurality of light beams toward the FOV. Each light beam may illuminate a respective portion of the FOV. The LIDAR device may also include a plurality of detectors and a lens that focuses light from the FOV for receipt by the plurality of detectors. A first detector of the plurality may be arranged to intercept a first portion of the focused light from a first portion of the FOV that was illuminated by a first light beam of the plurality of light beams. Similarly, a second detector may be arranged to intercept a second portion of the focused light from a second portion of the FOV that was illuminated by a second light beam, and so on. Thus, each detector may be aligned with a corresponding transmitted light beam to define a respective transmit/receive channel of the LIDAR device. 
     With this arrangement, the multiple transmit/receive channels can interrogate different portions of the FOV. For instance, each channel can emit a pulse of light during an emission time period, and then “listen” for a reflected pulse during a detection time period following the emission time period. In some implementations, the LIDAR device may then perform a subsequent scan of the FOV, which similarly includes another emission time period followed by another detection time period, and so on. With this arrangement for instance, the LIDAR device can obtain a sequence of scans (e.g., periodically) of the FOV. 
     In some scenarios, a reflected portion of light that was originally transmitted by a particular channel may be detected in one or more other channels (e.g., neighboring channels that scan portions of the FOV adjacent to the portion scanned by the particular channel), thereby resulting in spurious signal detection (e.g., “cross-talk”) by the other channel(s). Various factors may cause such cross-talk, such as optical distortions in the lens, distortions caused by dust particles on the lens, and/or reflectivity characteristics of objects in the scanned environment, among other factors. 
     In one scenario, transmitted light in a particular channel may be reflected by a retroreflector in a portion of the FOV scanned by the particular channel. A retroreflector may include a device or surface that reflects a relatively higher fraction of incident light back (e.g., into a relatively narrower cone, etc.) toward its source as compared to other types of reflectors. For instance, a road traffic sign may be coated with a retroreflector to improve visibility of the sign to vehicle drivers on the road. In this scenario, some portions of the (strong) reflected signal from the retroreflector may have sufficient amounts of energy to be detected by other (e.g., neighboring) channels (spuriously) as well as the particular channel that illuminated the retroreflector. 
     By way of example, a retroreflector may be located within a portion of the FOV scanned by a first channel. In this example, a light pulse emitted by the first channel may be reflected by the retroreflector, and the reflected light pulse may then be detected at the first channel as a relatively strong signal. In this example, a time difference between the emission time of the emitted light pulse and the detection time of the reflected light pulse can be used to determine that the retroreflector is at a distance of 50 meters from the LIDAR device. However, as noted above, N additional channels may also receive portions of the reflected light pulse from the retroreflector as spurious signals. If the N additional channels had also emitted N respective light pulses at the same emission time as the light pulse of the first channel, then the spurious signals detected by the N channels may be interpreted as reflections of the N light pulses from objects (at a distance of 50 meters) within respective portions of the FOV scanned by the N channels. As a result, the spurious signals may prevent or interfere with detection of actual objects present at the same distance of 50 meters within the respective portions of the FOV scanned by the N additional channels. For instance, a computing system that processes data from the LIDAR to generate a 3D map of the environment may render a map that shows “ghost” retroreflectors at the 50 meter distance (e.g., instead of showing objects actually present at this distance). 
     Reducing this type of cross-talk error may be desirable in some applications. For example, a LIDAR-equipped vehicle may be configured to use the LIDAR to detect objects (e.g., other vehicles, pedestrians, etc.) in the environment of the vehicle. In this example, if the LIDAR is unable to scan significant portions of the environment near every retroreflector (e.g., pedestrian standing next to a stop sign, etc.), then the LIDAR may be less reliable for object detection and/or safe operation of the vehicle. 
     To mitigate the effects of such cross-talk, in some examples, the LIDAR device may include one or more light filters interposed between the lens and the plurality of detectors. The light filter(s) may reduce (or prevent) relatively weak spurious signals propagating toward an unintended transmit/receive channel. However, an extent of filtration by the light filter(s) may be limited to allow propagation of non-spurious signals through the light filter(s). Thus, the light filter(s) may still allow propagation of some (relatively stronger) spurious signals (e.g., having a similar amount of energy as that of non-spurious signals), such as spurious signals associated with retroreflectors for instance. 
     Accordingly, some implementations herein may involve operating a multi-channel active sensor (e.g., LIDAR, SONAR, etc.) to mitigate the effects of channel cross-talk associated with retroreflectors or other sources of spurious signals. 
     In a first example, one or more of the multiple transmit/receive channels of the LIDAR device described above can be configured to emit respective light pulses at different respective time offsets during a first emission time period of a first scan of the FOV of the LIDAR. For instance, a first channel may emit a light pulse near the beginning of the first emission time period, a second channel may emit a light pulse near the end of the first emission time period, and so on. After the first emission time period ends, the multiple channels of the LIDAR may then begin “listening” for reflections of their respective emitted light pulses during a first detection time period of the first scan. With this arrangement for instance, if a retroreflector present at a distance of 50 meters in a first portion of the FOV scanned by the first channel causes spurious signal detections at N other channels that scan other portions of the FOV, then the spurious signal detections may be mapped to a variety distances (e.g., 40-60 meters) due to the differences between the emission times of the first channel and the N channels. Thus, in this example, the LIDAR can improve the quality of object detection at the range of 50 meters by spreading the spurious signal detections associated with the retroreflector over a range of distances. 
     In a second example, where the LIDAR device obtain a sequence of scans of the FOV (e.g., periodically), the LIDAR device may be configured to adjust the respective emission time offsets assigned to a particular channel for each scan in the sequence. For instance, in a first scan of the sequence, the first channel may emit a light pulse near the beginning of the first emission time period and the second channel may emit a light pulse near the end of the first emission time period. Next, in a second scan subsequent to the first scan, the first channel may instead emit a light pulse near the end of a second emission time period of the second scan, and the second channel may instead emit a light pulse near the beginning of the second emission time period, and so on. 
     Thus, with this arrangement, the emission times used by a particular channel over the sequence of scans may be effectively dithered (e.g., relative to a start or end of the respective emission time periods of the sequence of scans). As a result, for instance, if the particular channel is “blinded” from detecting an object at a particular distance (e.g., 50 meters) during a first scan (due to a spurious signal from another channel), then the particular channel may be able to detect the object during a subsequent second scan (because the spurious signal will be instead mapped to a different distance in the second scan). For instance, actual signals reflected by an object illuminated by the particular channel may be detected repeatedly as being at the same particular distance during successive scans by the particular channel (e.g., “coherent” detections). Whereas, spurious signals caused by a retroreflector illuminated by another channel may be detected repeatedly as being at different distances (e.g., “incoherent” detections) during the successive scans. 
     In some implementations, the time offsets assigned to a particular channel in each respective emission time period of the sequence of scans can be based on a pseudo-random time offset sequence. For example, a computing system can determine the pseudo-random time offset sequence that is applied to one or more particular channels prior to the LIDAR performing the sequence of scans. However, in other implementations, varying the time offsets from one scan to another can be performed in a variety of different ways. 
     II. Example Sensor Systems and Devices 
     A non-exhaustive list of example sensors that can be employed herein includes LIDAR sensors, RADAR sensors, SONAR sensors, active IR cameras, and microwave cameras, among others. To that end, some example sensors herein may include active sensors that emit a signal (e.g., visible light signal, invisible light signal, radio-frequency signal, microwave signal, sound signal, etc.), and then detect reflections of the emitted signal from the surrounding environment. 
       FIG.  1    is a simplified block diagram of a device  100 , according to example embodiments. As shown, device  100  includes a power supply arrangement  102 , a controller  104 , a transmitter  106 , one or more optical elements  108 , a receiver  114 , a rotating platform  116 , one or more actuators  118 , a stationary platform  120 , a rotary link  122 , and a housing  124 . In some embodiments, device  100  may include more, fewer, or different components. Additionally, the components shown may be combined or divided in any number of ways. 
     Power supply arrangement  102  may be configured to supply, receive, and/or distribute power to various components of device  100 . To that end, power supply arrangement  102  may include or otherwise take the form of a power source (e.g., battery cells, etc.) disposed within device  100  and connected to various components of the device  100  in any feasible manner, so as to supply power to those components. Additionally or alternatively, power supply arrangement  102  may include or otherwise take the form of a power adapter configured to receive power from one or more external power sources (e.g., from a power source arranged in a vehicle to which device  100  is mounted) and to transmit the received power to various components of device  100 . 
     Controller  104  may include one or more electronic components and/or systems arranged to facilitate certain operations of device  100 . Controller  104  may be disposed within device  100  in any feasible manner. In one embodiment, controller  104  may be disposed, at least partially, within a central cavity region of rotary link  122 . 
     In some examples, controller  104  may include or otherwise be coupled to wiring used for transfer of control signals to various components of device  100  and/or for transfer of data from various components of device  100  to controller  104 . For example, the data that controller  104  receives may include sensor data indicating detections of signals by receiver  114 , among other possibilities. Moreover, the control signals sent by controller  104  may operate various components of device  100 , such as by controlling emission of signals by transmitter  106 , controlling detection of signals by the receiver  114 , and/or controlling actuator(s)  118  to rotate rotating platform  116 , among other possibilities. 
     To that end, in some examples, controller  104  may include one or more processors, data storage, and program instructions (stored on the data storage) executable by the one or more processors to cause device  100  to perform the various operations described herein. The processor(s) may comprise one or more general-purpose processors and/or one or more special-purpose processors. To the extent that controller  104  includes more than one processor, such processors could work separately or in combination. The data storage, in turn, may comprise one or more volatile and/or one or more non-volatile storage components, such as optical, magnetic, and/or organic storage, and the data storage may be optionally integrated in whole or in part with the processor(s). 
     In some instances, the controller may communicate with an external controller or the like (e.g., a computing system arranged in a vehicle to which device  100  is mounted) so as to help facilitate transfer of control signals and/or data between the external controller and the various components of device  100 . 
     Additionally or alternatively, in some examples, controller  104  may include circuitry wired to perform one or more of the operations described herein. For example, controller  104  may include one or more pulser circuits that provide pulse timing signals for triggering emission of pulses or other signals by transmitter  106 . For instance, each pulser circuit may drive a respective emitter that provides one or more beams arranged to scan one or more respective portions of the FOV of device  100 . 
     Additionally or alternatively, in some examples, controller  104  may include one or more special purpose processors, servos, or other types of controllers. For example, controller  104  may include a proportional-integral-derivative (PID) controller or other control loop feedback mechanism that operates actuator(s)  118  to cause the rotating platform to rotate at a particular frequency or phase. Other examples are possible as well. 
     Transmitter  106  may be configured to transmit signals toward an environment of device  100 . As shown, transmitter  106  may include one or more emitters  140 . Emitters  140  may include various types of emitters depending on a configuration of device  100 . 
     In a first example, where device  100  is configured as a LIDAR device, transmitter  106  may include one or more light emitters  140  that emit one or more light beams and/or pulses having wavelengths within a wavelength range. The wavelength range could be, for example, in the ultraviolet, visible, and/or infrared portions of the electromagnetic spectrum. In some examples, the wavelength range can be a narrow wavelength range, such as that provided by lasers. A non-exhaustive list of example light emitters  140  includes laser diodes, diode bars, light emitting diodes (LED), vertical cavity surface emitting lasers (VCSEL), organic light emitting diodes (OLED), polymer light emitting diodes (PLED), light emitting polymers (LEP), liquid crystal displays (LCD), microelectromechanical systems (MEMS), fiber lasers, and/or any other device configured to selectively transmit, reflect, and/or emit light to provide a plurality of emitted light beams and/or pulses. 
     In a second example, where device  100  is configured as an active infrared (IR) camera, transmitter  106  may include one or more emitters  140  configured to emit IR radiation to illuminate a scene. To that end, transmitter  106  may include any type of emitter (e.g., light source, etc.) configured to provide the IR radiation. 
     In a third example, where device  100  is configured as a RADAR device, transmitter  106  may include one or more antennas, waveguides, and/or other type of RADAR signal emitters  140 , that are configured to emit and/or direct modulated radio-frequency (RF) signals toward an environment of device  100 . 
     In a fourth example, where device  100  is configured as a SONAR device, transmitter  106  may include one or more acoustic transducers, such as piezoelectric transducers, magnetostrictive transducers, electrostatic transducers, and/or other types of SONAR signal emitters  140 , that are configured to emit a modulated sound signal toward an environment of device  100 . In some implementations, the acoustic transducers can be configured to emit sound signals within a particular wavelength range (e.g., infrasonic, ultrasonic, etc.). Other examples are possible as well. 
     In some implementations, device  100  (and/or transmitter  106 ) can be configured to emit a plurality of signals (e.g., light beams, IR signals, RF waves, sound waves, etc.) in a relative spatial arrangement that defines a FOV of device  100 . For example, each beam (or signal) may be configured to propagate toward a portion of the FOV. In this example, multiple adjacent (and/or partially overlapping) beams may be directed to scan multiple respective portions of the FOV during a scan operation performed by device  100 . Other examples are possible as well. 
     To that end, optical element(s)  108  can be optionally included in or otherwise coupled to transmitter  106  and/or receiver  114 . In one example, optical element(s)  108  can be arranged to direct light from light sources or emitters in transmitter  106  toward the environment. In another example, optical element(s)  108  can be arranged to focus light from the environment toward receiver  114 . As such, optical element(s)  108  may include any feasible combination of mirror(s), waveguide(s), lens(es), or other types optical components, that are arranged to guide propagation of light through physical space and/or to adjust certain characteristics of the light. 
     Receiver  114  may include one or more detectors  110  configured to detect reflections of the signals emitted by transmitter  106 . 
     In a first example, where device  100  is configured as a RADAR device, receiver  114  may include one or more antennas (i.e., detectors  110 ) configured to detect reflections of the RF signal transmitted by transmitter  106 . To that end, in some implementations, the one or more antennas of transmitter  106  and receiver  114  can be physically implemented as the same physical antenna structures. 
     In a second example, where device  100  is configured as a SONAR device, receiver  114  may include one or more sound sensors  110  (e.g., microphones, etc.) that are configured to detect reflections of the sound signals emitted by transmitter  106 . 
     In a third example, where device  100  is configured as an active IR camera, receiver  114  may include one or more light detectors  110  (e.g., charge-coupled devices (CCDs), etc.) that are configured to detect a source wavelength of IR light transmitted by transmitter  106  and reflected off a scene toward receiver  114 . 
     In a fourth example, where device  100  is configured as a LIDAR device, receiver  114  may include one or more light detectors  110  (e.g., photodiodes, avalanche photodiodes, etc.) that are arranged to intercept and detect reflections of the light pulses or beams emitted by transmitter  106  (and reflected from one or more objects in the environment of device  100 ). To that end, receiver  114  may be configured to detect light having wavelengths in the same wavelength range as the light emitted by transmitter  106 . In this way, for instance, device  100  may distinguish reflected light pulses originated by device  100  from other light in the environment. 
     In some implementations, receiver  114  may include a photodetector array, which may include one or more detectors configured to convert detected light into an electrical signal indicating a measurement of the detected light. The photodetector array could be arranged in a variety ways. For instance, the detectors can be disposed on one or more substrates (e.g., printed circuit boards (PCBs), flexible PCBs, etc.) and arranged to detect incoming light that is traveling along an optical path of an optical lens of device  100  (e.g., optical element(s)  108 ). Also, such a photodetector array could include any feasible number of detectors aligned in any feasible manner. Additionally, the detectors in the array may take various forms. For instance, the detectors may take the form of photodiodes, avalanche photodiodes (APDs), silicon photomultipliers (SiPMs), single photon avalanche diodes (SPADs), multi-pixel photon counters (MPPCs), phototransistors, cameras, active pixel sensors (APS), charge coupled devices (CCD), cryogenic detectors, and/or any other sensor of light configured to receive focused light having wavelengths in the wavelength range of the emitted light. 
     In some examples, device  100  can select or adjust a horizontal scanning resolution by changing a rate of rotation of device  100  (and/or transmitter  106  and receiver  114 ). Additionally or alternatively, the horizontal scanning resolution can be modified by adjusting a pulse rate of signals emitted by transmitter  106 . In a first example, transmitter  106  may be configured to emit pulses at a pulse rate of 15,650 pulses per second, and to rotate at 10 Hz (i.e., ten complete 360° rotations per second) while emitting the pulses. In this example, receiver  114  may have a 0.23° horizontal angular resolution (e.g., horizontal angular separation between consecutive pulses). In a second example, if device  100  is instead rotated at 20 Hz while maintaining the pulse rate of 15,650 pulses per second, then the horizontal angular resolution may become 0.46°. In a third example, if transmitter  106  emits the pulses at a rate of 31,300 pulses per second while maintaining the rate of rotation of 10 Hz, then the horizontal angular resolution may become 0.115°. In some examples, device  100  can be alternatively configured to scan a particular range of views within less than a complete 360° rotation of device  100 . Other implementations are possible as well. 
     It is noted that the pulse rates, angular resolutions, rates of rotation, and viewing ranges described above are only for the sake of example, and thus each of these scanning characteristics could vary according to various applications of device  100 . 
     Rotating platform  116  may be configured to rotate about an axis. To that end, rotating platform  116  can be formed from any solid material suitable for supporting one or more components mounted thereon. For example, transmitter  106  and receiver  114  may be arranged on rotating platform  116  such that each of these components moves relative to the environment based on rotation of rotating platform  116 . In particular, these components could be rotated about an axis so that device  100  may obtain information from various directions. In this manner, a pointing direction of device  100  can be adjusted horizontally by actuating the rotating platform  114  to adjust a FOV of device  100  in various directions. 
     In order to rotate platform  116  in this manner, one or more actuators  118  may actuate the rotating platform  114 . To that end, actuators  118  may include motors, pneumatic actuators, hydraulic pistons, and/or piezoelectric actuators, among other possibilities. 
     With this arrangement, controller  104  could operate actuator  118  to rotate rotating platform  116  in various ways so as to obtain information about the environment. In one example, rotating platform  116  could be rotated in either direction. In another example, rotating platform  116  may carry out complete revolutions such that device  100  scans a 360° view of the environment. Moreover, rotating platform  116  could rotate at various frequencies so as to cause device  100  to scan the environment at various refresh rates. In one embodiment, device  100  may be configured to have a refresh rate of 10 Hz (e.g., ten complete rotations of device  100  per second). Other refresh rates are possible. 
     Alternatively or additionally, device  100  may be configured to adjust the pointing direction of an emitted signal (emitted by transmitter  106 ) in various ways. In one implementation, signal emitters (e.g., light sources, antennas, acoustic transducers, etc.) of transmitter  106  can be operated according to a phased array configuration or other type of beam steering configuration. 
     In a first example, where device  100  is configured as a LIDAR device, light sources or emitters in transmitter  106  can be coupled to phased array optics that control the phase of light waves emitted by the light sources. For instance, controller  104  can be configured to adjust the phased array optics (e.g., phased array beam steering) to change the effective pointing direction of a light signal emitted by transmitter  106  (e.g., even if rotating platform  116  is not rotating). 
     In a second example, where device  100  is configured as a RADAR device, transmitter  106  may include an array of antennas, and controller  104  can provide respective phase-shifted control signals for each individual antenna in the array to modify a pointing direction of a combined RF signal from the array (e.g., phased array beam steering). 
     In a third example, where device  100  is configured as a SONAR device, transmitter  106  may include an array of acoustic transducers, and controller  104  can similarly operate the array of acoustic transducers (e.g., via phase-shifted control signals, phased array beam steering, etc.) to achieve a target pointing direction of a combined sound signal emitted by the array (e.g., even if rotating platform  116  is not rotating, etc.). 
     Stationary platform  120  may take on any shape or form and may be configured for coupling to various structures, such as to a top of a vehicle, a robotic platform, assembly line machine, or any other system that employs device  100  to scan its surrounding environment, for example. Also, the coupling of the stationary platform may be carried out via any feasible connector arrangement (e.g., bolts, screws, etc.). 
     Rotary link  122  directly or indirectly couples stationary platform  120  to rotating platform  116 . To that end, rotary link  122  may take on any shape, form and material that provides for rotation of rotating platform  116  about an axis relative to the stationary platform  120 . For instance, rotary link  122  may take the form of a shaft or the like that rotates based on actuation from actuator  118 , thereby transferring mechanical forces from actuator  118  to rotating platform  116 . In one implementation, rotary link  122  may have a central cavity in which one or more components of device  100  may be disposed. In some examples, rotary link  122  may also provide a communication link for transferring data and/or instructions between stationary platform  120  and rotating platform  116  (and/or components thereon such as transmitter  106  and receiver  114 ). 
     Housing  124  may take on any shape, form, and material and may be configured to house one or more components of device  100 . In one example, housing  124  can be a dome-shaped housing. Further, in some examples, housing  124  may be composed of a material that is at least partially non-transparent, which may allow for blocking of at least some signals from entering the interior space of the housing  124  and thus help mitigate thermal and noise effects of ambient signals on one or more components of device  100 . Other configurations of housing  124  are possible as well. 
     In some examples, housing  124  may be coupled to rotating platform  116  such that housing  124  is configured to rotate based on rotation of rotating platform  116 . In these examples, transmitter  106 , receiver  114 , and possibly other components of device  100  may each be disposed within housing  124 . In this manner, transmitter  106  and receiver  114  may rotate along with housing  124  while being disposed within housing  124 . In other examples, housing  124  may be coupled to stationary platform  120  or other structure such that housing  124  does not rotate with the other components rotated by rotating platform  116 . 
     It is noted that this arrangement of device  100  is described for exemplary purposes only and is not meant to be limiting. As noted above, in some examples, device  100  can be alternatively implemented with fewer components than those shown. In one example, device  100  can be implemented without rotating platform  100 . For instance, transmitter  106  can be configured to transmit a plurality of signals spatially arranged to define a particular FOV of device  100  (e.g., horizontally and vertically) without necessarily rotating transmitter  106  and receiver  114 . Other examples are possible as well. 
       FIG.  2    illustrates a LIDAR device  200 , according to an example embodiment. In some examples, LIDAR  200  may be similar to device  100 . For example, as shown, LIDAR device  200  includes a lens  208 , a rotating platform  216 , a stationary platform  220 , and a housing  224  which may be similar, respectively, to optical element  108 , rotating platform  216 , stationary platform  120 , and housing  124 . In the scenario shown, light beams  280  emitted by LIDAR device  200  may propagate from lens  108  along a viewing (or pointing) direction of LIDAR  200  toward a FOV of LIDAR  200 , and may then reflect off one or more objects in the environment as reflected light  290 . 
     In some examples, housing  224  can be configured to have a substantially cylindrical shape and to rotate about an axis of LIDAR device  200 . In one example, housing  224  can have a diameter of approximately 10 centimeters. Other examples are possible. In some examples, the axis of rotation of LIDAR device  200  is substantially vertical. For instance, a three-dimensional map of a 360-degree view of the environment of LIDAR device  200  can be determined by rotating housing  224  about a vertical axis. Additionally or alternatively, in some examples, LIDAR device  200  can be configured to tilt the axis of rotation of housing  224  to control a field of view of LIDAR device  200 . Thus, in some examples, rotating platform  216  may comprise a movable platform that may tilt in one or more directions to change the axis of rotation of LIDAR device  200 . 
     In some examples, lens  208  can have an optical power to both collimate (and/or direct) emitted light beams  280  toward the environment of device  200 , and to focus reflected light  290  from one or more objects in the environment of LIDAR device  200  onto detectors in LIDAR device  200 . In one example, lens  208  has a focal length of approximately 120 mm. Other examples are possible. By using the same lens  208  to perform both of these functions, instead of a transmit lens for collimating and a receive lens for focusing, advantages with respect to size, cost, and/or complexity can be provided. 
     In other examples, instead of the single lens  208  configuration as shown in  FIG.  2   , LIDAR  200  could be alternatively implemented to include separate transmit lens (for manipulating emitted light  280 ) and receive lens (for focusing reflected light  290 ). 
       FIG.  3    illustrates a cross-section view of a plurality of emitted beams, exemplified by beams  302 ,  304 ,  306 ,  308 ,  312 ,  318 , that are spatially arranged to scan respective portions of a FOV  300 , according to example embodiments. 
     FOV  300  may correspond to a FOV that is illuminated by transmitter(s)/emitter(s) (e.g., transmitter  106 , emitter(s)  140 , etc.) of an active sensor (e.g., devices  100 ,  200 ) during a scan of the FOV. 
     For example, referring back to  FIG.  2   , FOV  300  may correspond to the region of the environment of device  200  toward which light beams  280  are emitted. In this example, the beams shown in  FIG.  3    may be propagating through the page in the direction of the arrow  280  shown in  FIG.  2   . 
     In some examples, a device or system herein may transmit the plurality of beams  302 ,  304 ,  306 ,  308 ,  312 ,  318 , etc., in a relative spatial arrangement such as the arrangement shown in  FIG.  3   , during an emission time period of a particular scan of FOV  300 . Thus, as shown, each of the emitted beams may scan a respective portion of FOV  300 . For example, beam  302  may have a particular (elevational and azimuthal) angular position within the spatial arrangement of the plurality of beams shown. In a LIDAR device configuration for instance, the particular angular position of beam  302  may be defined by one or more optical elements (e.g., lenses, apertures, waveguides, etc.) that direct beam  302  in a particular transmit path. Thus, for instance, the various respective portions of FOV  300  scanned by the emitted beams may together define the vertical and horizontal extents of FOV  300  that are scanned by multiple channels of an active sensor. 
     In some examples, where a device performs a sequence of scans of FOV  300 , the device can then perform a second scan of FOV  300  by transmitting a second plurality of beams, in a similar spatial arrangement as that shown for the beams of  FIG.  3   , to scan the respective portions of FOV  300  another time, and so on. 
     In some examples, a device herein may include a plurality of emitters (e.g., emitters  140 ) that emit the plurality of beams shown in  FIG.  3   . A first emitter of the plurality may emit signals toward a first portion of FOV  300 , and a second emitter may emit light that illuminates a second portion of FOV  300 . In a first example, the first emitter may be coupled to optical elements (e.g., waveguide(s), aperture(s), lens(es), etc.) that direct its emitted light to the angular position of beam  302  in the spatial arrangement of the emitted beams. Similarly, in this example, signals emitted by the second emitter may be directed to the angular position of  312 , and so on. In a second example, the signals from each emitter may be split into multiple beams. For instance, signals from the first emitter can be split into the row of beams including beams  302 ,  304 ,  306 ,  308 . Similarly, for instance, signals from the second emitter may be split to provide the row of four beams including beams  312  and  318 . Other examples are possible. 
     In some examples, a device herein may include a plurality of detectors for receiving reflected signals (e.g., light) from respective portions of FOV  300  illuminated by beams  302 ,  304 ,  306 ,  308 ,  312 ,  318 , etc. Referring back to  FIG.  2    for example, lens  208  may be configured to focus received light  290  for receipt by a plurality of detectors (e.g., detectors  110  of device  100 ). Moreover, referring back to  FIG.  1   , a first detector of detectors  110  can be arranged to receive a first portion of the focused light that includes a reflection of beam  302 , a second detector of detectors  110  can be arranged to receive a second portion of the focused light that includes a reflection of beam  304 , and so on. 
     It is noted that the arrangement, shapes, and/or number of the plurality of emitted beams shown in  FIG.  3    may vary, and are only illustrated as shown for convenience in description. For example, FOV  300  could be scanned by an example device herein that emits more or fewer beams for scanning various respective portions of FOV  300 . As another example, the beams can be arranged in a different spatial arrangement (e.g., circular arrangement, linear arrangement, grid arrangement, etc.) than the arrangement shown in  FIG.  3   . 
     III. Example Methods and Computer Readable Media 
       FIG.  4    is a flowchart of a method  400 , according to example embodiments. Method  400  presents an embodiment of a method that could be used with any of devices  100  and/or  200 , for example. Method  400  may include one or more operations, functions, or actions as illustrated by one or more of blocks  402 - 404 . Although the blocks are illustrated in a sequential order, these blocks may in some instances be performed in parallel, and/or in a different order than those described herein. Also, the various blocks may be combined into fewer blocks, divided into additional blocks, and/or removed based upon the desired implementation. 
     In addition, for method  400  and other processes and methods disclosed herein, the flowchart shows functionality and operation of one possible implementation of present embodiments. In this regard, each block may represent a module, a segment, a portion of a manufacturing or operation process, or a portion of program code, which includes one or more instructions executable by a processor for implementing specific logical functions or steps in the process. The program code may be stored on any type of computer readable medium, for example, such as a storage device including a disk or hard drive. The computer readable medium may include a non-transitory computer readable medium, for example, such as computer-readable media that stores data for short periods of time like register memory, processor cache and Random Access Memory (RAM). The computer readable medium may also include non-transitory media, such as secondary or persistent long term storage, like read only memory (ROM), optical or magnetic disks, compact-disc read only memory (CD-ROM), for example. The computer readable media may also be any other volatile or non-volatile storage systems. The computer readable medium may be considered a computer readable storage medium, for example, or a tangible storage device. 
     In addition, for method  400  and other processes and methods disclosed herein, each block in  FIG.  4    may represent circuitry that is wired to perform the specific logical functions in the process. 
     At block  402 , method  400  involves causing a plurality of emitters to emit a plurality of light pulses during a first emission time period associated with a first scan of a field-of-view (FOV). The plurality of emitters may include at least a first emitter and a second emitter. The first emitter may be configured to illuminate a first portion of the FOV, and the second emitter may be configured to illuminate a second portion of the FOV. 
     Referring back to  FIG.  3    for example, a first emitter (e.g., one of emitters  140  of device  100 , etc.) may emit light that includes a first row of light beams  302 ,  304 ,  306 ,  308  to scan a first portion of FOV  300  illuminated by the first row. Further, a second emitter (e.g., another one of emitters  140 , etc.) may emit light that includes a second row of light beams (e.g., including beams  312 ,  318  and the two beams in between) to scan a second portion of FOV  300  illuminated by the second row, and so on. 
     In some implementations, method  400  involves obtaining the first scan of the FOV, where obtaining the first scan involves causing each emitter of the plurality of emitters to emit a respective light pulse during the first emission time period. For example, the first emission time period may have a start time (e.g., t=0 ns) and an end time (e.g., t=499 ns), and each emitter of the plurality of emitters may be coupled to a respective pulser circuit (e.g., controller  140 ) that triggers emission of a respective light pulse by the emitter during a time offset between the start time and end time of the first emission time period. In one embodiment, a first pulser circuit can be configured to trigger pulse emissions by two or more particular emitters of the plurality of emitters. For instance, the two or more emitters may be configured to emit respective light pulses at a same time offset within the first emission time period. In another embodiment, the first pulser circuit can be configured to trigger pulse emissions by one emitter and a second pulser circuit can be configured to trigger emissions by another emitter. 
     Thus, in some implementations, method  400  involves causing a first emitter (of the plurality of emitters) to emit a first-emitter light pulse at a first-emitter time offset from the start time (or the end time) of the first emission time period, and causing a second emitter to emit a second-emitter light pulse at a second-emitter time offset from the start time (or the end time) of the first emission time period. In an example scenario, where the first emission time period extends from t=0 ns to t=499 ns, the first emitter can be configured to emit a light pulse at the first-emitter time offset of 0 ns from the start time (i.e., at t=0 ns) or from the end time (i.e., at t=499 ns) of the first emission time period. Similarly, in this scenario, the second emitter may emit a light pulse at the second-emitter time offset of 10 ns from the start time (i.e., at t=10 ns) or from the end time (i.e., at t=489 ns). 
     In some examples, as noted above, the first-emitter light pulse (and/or the second-emitter light pulse) can be split into multiple light beams of multiple channels scanned by a system of method  400 . Referring back to  FIG.  3    for example, light from a single emitter (e.g., LED, etc.) may be split (e.g., using mirrors, waveguides, beam splitters, etc.) into four light beams  302 ,  304 ,  306 ,  308  to scan four separate portions of FOV  300 . Alternatively or additionally, in some examples, the first-emitter light pulse (and/or the second-emitter light pulse) can be transmitted as a single respective light beam toward the FOV. Referring back to  FIG.  3    for example, beam  302  can be emitted by the first emitter, beam  304  can be emitted the second emitter, and so on. Other examples are possible. 
     At block  404 , method  400  involves obtaining the first scan based on a first measurement of light from the FOV received during a first detection time period that begins after (or at) the end time of the first emission time period. 
     In an example scenario, the first emission time period may extend from a start time of t=0 ns to an end time of t=499 ns. In this scenario, the first detection time period may begin after the end time (e.g., at t=500 ns) or at the end time (i.e., at t=499 ns) of the first emission time period. Referring back to  FIG.  3    for instance, a system of method  400  may transmit light beams  302 ,  304 ,  306 ,  308  at respective time offsets (e.g., at t=0 ns, t=100 ns, t=200 ns, and t=400 ns) within the first emission time period. Further, the system may then obtain the first measurement of light incident on detectors  110  (shown in  FIG.  1   ) during the first detection time period (e.g., from t=500 ns to t=2500 ns). Thus, in some examples, the first measurement of light from the FOV at block  404  may include one or more measurements of incident light associated with one or more channels that illuminate one or more respective portions of the FOV. 
     In some implementations, method  400  involves obtaining a sequence of scans of the FOV including at least the first scan and a second scan subsequent to the first scan. For instance, consider a scenario where the first scan has a first emission time period from a start time of t=0 ns to an end time of t=499 ns, and a first detection time period from t=500 ns to t=2500 ns. In this scenario, the second scan may have a second emission time period that begins at a start time of t=5000 ns and ends at an end time of t=5499 ns, and a second detection time period from t=5500 ns to t=7500 ns. In this scenario, a device of method  400  may be configured to obtain a scan of the FOV every 5000 ns. Referring back to  FIG.  3    for instance, the device may be configured to emit all of the plurality of beams shown to illuminate FOV  300  during the first emission time period, and then a second similar plurality of beams during the second emission time period. 
     In some implementations, method  400  involves illuminating the first portion of the FOV using the first emitter during the first scan, and illuminating a different portion of the FOV using the first emitter during the second scan. Referring back to  FIG.  1    for example, transmitter  106  (and/or optical element  108 ) can be configured to adjust the source (e.g., emitter A of emitters  140 , emitter B of emitters  140 , etc.) of light beams  302 ,  304 ,  306 ,  308 ,  312 ,  318 , etc. For instance, device  100  may include mirrors, switches, actuators, and/or any other type of circuitry to allow controlling which portions of the scanned FOV are illuminated by which emitter during a particular scan. In this example, during the first scan, beam  302  could be emitted by the first emitter to illuminate the first portion of FOV  300 . In this example, during the second scan, beam  304  could be emitted by the first emitter instead of beam  302  to illuminate a different portion of the FOV, and so on. Similarly, the scanning channel(s) illuminated by the second emitter (and/or any other emitter of the plurality of emitters) can be changed between successive scans of the FOV. 
     Thus, in these implementations, a mapping between emitters and scanning channels can be varied to dither the relative emission times of pulses during consecutive scans of the FOV. By way of example, referring back to  FIG.  3   , pulse  302  during the first scan can be emitted by the first emitter at the first-emitter time offset from the start time (or end time) of the first emission time period, then another pulse  302  can be emitted by the second emitter at the second-emitter time offset from the start time (or end time) of the second emission time period, and so on. 
     Alternatively or additionally, in some implementations, method  400  may involve modifying the first-emitter time offset for the second scan. In these implementations, obtaining the second scan described above may comprise causing the first emitter to emit another first-emitter light pulse at the modified first-emitter time offset (from a start time or end time) of the second emission time period associated with the second scan. In the scenario above for instance, a first-emitter time offset of 0 ns may be used for the first emitter during the first scan (e.g., first-emitter light pulse emitted at t=0 ns if the first-emitter offset is from the start time, or at t=499 ns if the first-emitter offset is from the end time). Further, in this scenario, the first-emitter time offset may then be adjusted to 50 ns for the second scan. For instance, another first-emitter light pulse emitted during the second scan may be emitted at t=5000+50=5050 ns (offset from start time of second emission time period), or at t=5500−50=5450 ns (offset from end time of second emission time period. Further, in some examples, similarly to the first scan, obtaining the second scan may be based on a second measurement of light from the FOV received (e.g., collected by detectors  410 ,  412 ,  414 ,  416 , etc., of system  400 ) during the second detection time period that begins after (or at) the end time of the second emission time period. 
     In some implementations, method  400  may also involve modifying the second-emitter time offset for the second scan. In these implementations, obtaining the second scan may also involve causing the second emitter to emit another second-emitter light pulse at the modified second-emitter time offset from the start time (or the end time) of the second emission time period. For instance, similarly to the discussion above for the modification of the first-emitter time offset, the second-emitter offset can be adjusted for each successive scan in the sequence. 
     In some implementations, method  400  involves determining a pseudo-random time offset sequence. For example, controller  104  (or another external computing system) can be configured to generate a sequence of time offsets within a typical emission period (e.g., between 0 and 499 ns, etc.) for a certain number of scans of the FOV by a particular emitter (e.g.,  50  offsets for 50 pulse emissions by a first emitter during 50 consecutive scan periods, etc.) of emitters  140 . In some examples, the sequence of pseudo-random time offsets may be computed as random time offset values within a particular range (e.g., 0 to 499 ns, etc.). Additionally or alternatively, in some examples, the values of the time offsets in the sequence can be selected from the particular range according to one or more rules (e.g., to constrain the extent of their randomness). 
     In a first example, the time offsets in the sequence can be selected to be non-repeatable. For instance, the first emitter can be assigned a specific number (e.g., 50, 60, etc.) of unique time offset values for the same number (e.g., 50, 60, etc.) of consecutive scans of the FOV (i.e., the sequence of scans). Accordingly, in some implementations, determining the pseudo-random time offset sequence may comprise determining a sequence of time offset values that are different from one another. With this arrangement for instance, a system of method  400  can prevent (or reduce the likelihood of) the first emitter being assigned the same time offset value randomly (at least for a particular number of consecutive scans). 
     In a second example, the time offsets in the sequence can be selected to be different from corresponding time offsets assigned to other emitters of the LIDAR device during a same scan of the FOV. For instance, a computing device of method  400  may pre-compute a plurality of pseudo-random time offset sequences for use with the plurality of emitters during the sequence of scans. The respective time offset values ordered at a same position in each sequence can be selected to be different from one another. For instance, consider a scenario where a first time offset sequence is generated to include the time offsets of 0 ns, 100 ns, 50 ns (in that order). In this scenario, every other sequence may be generated to include a first time offset different than 0 ns, a second time offset different than 100 ns, a third time offset different than 50 ns, and so on. Thus, in this example, a system of method  400  can provide a different time offset value for each emitter of the LIDAR device during any particular scan of the sequence of scans by assigning the first pseudo-random time offset sequence to the first emitter, a second pseudo-random time offset sequence to the second emitter, and so on. 
     Accordingly, in some implementations, method  400  may involve determining a plurality of pseudo-random time offset sequences for the plurality of emitters. In these implementations, a given time offset of a given sequence may have a different value than corresponding time offsets having a same order-position in other sequences of the plurality of pseudo-random time offset sequences. 
     Due to the varying of the relative emission times of the plurality of emitters within the respective emission time periods of the sequence of scans, a spurious signal received at a first detector aligned with a first emitter (e.g., reflection of a light beam that was not emitted by the first emitter) may correspond to a different distance in each successive scan of the sequence (e.g., incoherent detections of the spurious signal by the first detector). However, because the respective detection time period of each scan begins after the respective emission time period of the scan ends, a minimum range measured by each detector may also vary in each scan of the sequence. 
     For example, consider a scenario where the first emission time period of the first scan is between t=0 ns and t=500 ns, the first detection time period of the first scan is between t=500 ns and t=2500 ns, the second emission time period of the second scan is between t=5000 ns and t=5500 ns, and the second detection time period of the second scan is between t=5500 ns and t=7500 ns. In this scenario, the first emitter may emit a first-emitter light pulse in the first scan at t=500 ns (i.e., first-emitter time offset is 0 ns from the end time of the first emission time period). Thus, during the first scan, the first detector aligned with the first emitter may begin detecting reflections of the first-emitter light pulse as soon as it is emitted (i.e., at t=500 ns), and may thus detect an object that is 0 meters away from a LIDAR device of method  400 . In this scenario, during the second scan of the FOV, the first-emitter time offset may be modified to 500 ns (e.g., another first-emitter light pulse is emitted 500 ns prior to the end time of the second emission time period or at t=5500−500=5000 ns). Thus, in the second scan, reflections of the (another) first-emitter light pulse that arrive at the LIDAR device within 500 ns (i.e., between t=5000 ns and t=5500 ns) after the first-emitter light pulse is emitted might not be detected by the first detector aligned with the first emitter. More specifically, in this scenario, reflections off objects that are 75 meters or less from the LIDAR device might not be detected by the first detector because they would arrive before the second detection time period of the second scan begins (i.e., before t=5500 ns). 
     Accordingly, in some examples, the randomness of the pseudo-random time offset sequence can be constrained to achieve a minimum scanning range by the first emitter at least once within a particular number of consecutive scans. For instance, the pseudo-random time offset sequence may be constrained such that every 10 successive time offsets in the pseudo-random time offset sequence includes at least one time offset of 0 ns (e.g., from the end time of the respective emission time period of the scan). With this arrangement, a particular channel of the LIDAR device a may be configured to scan objects near the LIDAR device at least once in every 10 scans in the sequence of scans. By way of an example scenario, referring back to  FIG.  3   , a channel that scans the portion of FOV  300  illuminated by beam  302  may emit ten successive beams/pulses similar to beam  302  during ten successive scans of FOV  300  according to the pseudo-random time sequence. For this scenario, in at least one of the ten scans, the respective emitted beam may be triggered at the end of the respective emission time period of the at least one scan to ensure the portion of the FOV scanned by that channel can detect objects at a 0 meter range at least once during the ten successive scans. 
     Similarly, in some examples, the randomness of the pseudo-random time offset sequence can be constrained to achieve multiple minimum scanning ranges using the first emitter during the sequence of scans. For example, the time offset sequence may be generated to include at least one time offset for a 0 meter minimum range, at least one time offset for a 10 meter minimum range, at least one offset for a 20 meter minimum range, and so on. 
     Thus, in some implementations, determining the pseudo-random time offset sequence may involve determining at least one time offset that is less than or equal to a predetermined threshold offset (e.g., &lt;=0 ns, &lt;=50 ns, etc.). Additionally or alternatively, determining the pseudo-random time offset sequence may involve determining at least one time offset that is within a threshold predetermined threshold range (e.g., between 95 ns and 105 ns, etc.). 
     In some implementations, method  400  may involve selecting the first-emitter time offset for each scan of the sequence of scans from the pseudo-random time offset sequence based on an order of the scan in the sequence of scans. For example, a first time offset may be selected from the pseudo-random time offset sequence for a first scan of the sequence of scans, a second time offset subsequent to the first offset in the pseudo-random time offset sequence may be selected for a second scan subsequent to the first scan in the sequence of scans, and so on. 
     In some examples, determining the pseudo-random time offset sequence may involve obtaining a predetermined pseudo-random time offset sequence. For instance, the time offset sequences may be precomputed (e.g., by a controller of the LIDAR device, or by another external computing system) and/or retrieved from data storage prior to obtaining a scan of the environment. In other examples however, determining the pseudo-random time offset sequence may alternatively involve generating the pseudo-random time offset sequence at any other time (e.g., between scans, during scans, etc.). 
     In some implementations, method  400  involves obtaining a first sequence of scans (e.g., 50 scans) and a second sequence of scans (e.g., 50 additional scans) subsequent to the first sequence of scans. In these implementations, method  400  may also involve adjusting the second-emitter time offset for one or more of the second sequence of scans according to the determined pseudo-random time offset sequence. For example, in line with the discussion above, the pseudo-random time offset sequence may be used to adjust the respective first-emitter time offsets assigned to the first emitter during the first sequence of scans. Then, during the second sequence of scans, the same pseudo-random time offset sequence can be re-used to instead modify the respective second-emitter time offsets assigned to the second emitter during the second sequence of scans. By doing so for instance, additional randomization of the light pulse emissions by the channels can be achieved as compared to implementations where the same pseudo-random offset sequence for every sequence of scans by a particular channel. 
     Referring back to  FIG.  3    for example, a first emitter that illuminates the portion of FOV  300  illuminated by the row of beams  302 ,  304 ,  306 ,  308  can be assigned a particular pseudo-random time offset sequence for a first sequence of N scans. Then, during a subsequent sequence of N additional scans, a different portion of the FOV illuminated by the row of beams  312 ,  318  (and the three other beams in between) can be assigned the particular pseudo-random time offset sequence (which was previously used with the first emitter), and so on. 
     In other implementations however, a same pseudo-random time offset sequence can be alternatively re-used with the first emitter during both the first sequence of scans and the second subsequent sequence of scans. 
     In some implementations, method  400  may involve illuminating a first portion of the FOV using the first emitter during the first sequence of scans, and illuminating a second portion of the FOV using the first emitter during the second sequence of scans subsequent to the first sequence of scans. Thus, referring now to  FIG.  3    for example, the first emitter can be configured to illuminate the portions of FOV  300  corresponding to beams  302  and  304  during a first sequence of scans (e.g., 50 scans), and then the first emitter can be configured to illuminate the portion of the FOV corresponding to beams  308  and  318  during a second subsequent sequence of scans (e.g., the next 50 scans), and so on. With this arrangement for instance, even if a same pseudo-random time offset sequence is re-used with the first emitter during consecutive sequences of scans, a particular channel (e.g., portion of FOV associated with beam  302 ) may effectively be scanned according to a different pseudo-random time offset sequence of the second emitter during the second sequence of scans. 
     In some implementations, method  400  involves determining, based on the first measurement of block  404 , respective distances between a device of method  400  and objects in the FOV illuminated by the plurality of beams. For instance, in an implementation where device  100  illuminates FOV  300 , controller  104  may be configured to compute a time difference between an emission time of beam  302  (shown in  FIG.  3   ) and a detection time of a reflection of beam  302  (e.g., by receiver  114 ), and then compute the distance between device  100  and an object within the portion of the FOV illuminated by beam  302  based on the time difference. 
     In some implementations, method  400  involves determining that a likelihood of false signal detections by one or more detectors of the LIDAR device is greater than a threshold based on signal characteristics of a first signal received by a first detector of the LIDAR device. For example, controller  104  may receive a measurement of the first signal from the first detector, and then determine that the first signal has a signal intensity outside a given range (e.g., greater than an expected intensity, a threshold high intensity expected when a retroreflector is illuminated by an emitter of the plurality of emitters, etc.). In this example, the one or more detectors (e.g., of other transmit/receive channels) may detect false (e.g., spurious) signals due to portions of the light associated with the first signal having sufficient power to be also detected (spuriously) by the one or more detectors. Further, in this example, the spurious signals at the one or more channels may be received at substantially the same time when the first signal was received at the first channel. 
     Accordingly, in some implementations, method  400  may also involve storing an indication of a time of receipt of the first signal. For instance, a computing device (e.g., controller  104 , external computer, etc.) that processes LIDAR data from the LIDAR device may access the stored indication to identify the one or more signals detected by other detectors at (substantially) the same time when the first signal was also detected by the first detector. In this instance, the computing device may then remove the one or more signals (e.g., if they are deemed to correspond to spurious detections) from the LIDAR data, or keep the one or more signals (e.g., if they are deemed to correspond to true detections). 
     Accordingly, in some implementations, method  400  may also involve identifying one or more error signals detected by one or more detectors of the LIDAR device based on signal characteristics of a given signal detected by a given detector other than the one or more detectors. Further, in some implementations, the identification of the one or more error signals may be based on a comparison of detection times of the one or more error signals and a detection time of the given signal. 
     In some examples, the portion of the FOV scanned by a particular LIDAR channel during a sequence of scans may correspond to different physical regions in the environment of the LIDAR device. Referring back to  FIG.  2    for example, LIDAR  200  may be configured to rotate about an axis (e.g., vertical axis, etc.) while obtaining the sequence of scans of the environment. In this example, the portion of the FOV scanned by a first channel of LIDAR  200  (e.g., a portion of the FOV illuminated by the first emitter of method  400  and observed by the first detector of method  400 , etc.) during a first scan (when LIDAR  200  is at a first angular position about its axis of rotation) may correspond to a different physical region in the environment of LIDAR  200  than the region scanned by the first channel during a second scan (e.g., performed after LIDAR  200  rotates to a second angular position about the axis). Referring back to  FIG.  3    for example, beam  302  may point toward a first angular direction (relative to the axis of rotation of the LIDAR) during the first scan, and toward a second angular direction during the second scan. In a scenario where the LIDAR rotates in a counterclockwise direction after the first scan for instance, beam  302  may move to the left of its position shown in  FIG.  3   . 
     In some scenarios, where the LIDAR is rotating and the first channel illuminates a retroreflector in the environment for instance, varying the respective emitter time offsets during the respective emission time periods of the sequence of scans in accordance with method  400  could still result in incoherent distance measurements indicated by spurious signals received in a second channel due to the retroreflector illuminated by the first channel. For instance, the retroreflector (e.g., street sign) may have a sufficient spatial extent such that multiple light pulses emitted by the first channel (in the sequence of scans) while the LIDAR is rotating would still reflect off portions of the retroreflector (and therefore cause a sequence of spurious detections in the second channel). Thus, the present method may facilitate identification of spurious signal detections (e.g., due to channel cross-talk, presence of retroreflectors, etc.) even in some scenarios where the LIDAR is moving (e.g., rotating, etc.) while obtaining the sequence of scans. 
       FIG.  5    is a flowchart of another method  500 , according to example embodiments. Method  500  presents an embodiment of a method that could be used with any of devices  100  and/or  200 , for example. Method  500  may include one or more operations, functions, or actions as illustrated by one or more of blocks  502 - 504 . Although the blocks are illustrated in a sequential order, these blocks may in some instances be performed in parallel, and/or in a different order than those described herein. Also, the various blocks may be combined into fewer blocks, divided into additional blocks, and/or removed based upon the desired implementation. 
     At block  502 , method  500  involves transmitting a plurality of beams toward respective portions of a field-of-view (FOV) during a first emission time period associated with a first scan of the FOV. Referring back to  FIG.  3    for example, a LIDAR transmitter (e.g., transmitter  106  of device  100 ) may transmit the plurality of light beams  302 ,  304 ,  306 ,  308 ,  312 ,  318 , etc., that are spatially arranged to illuminate respective portions of FOV  300 . 
     In some implementations, method  500  also involves transmitting a second plurality of beams to illuminate the respective portions of the FOV during a second emission time period associated with a second scan of the FOV. Continuing with the example of  FIG.  3   , a device of method  500  may emit the plurality of light beams  302 ,  304 ,  306 ,  308 ,  312 ,  318 , etc., shown in  FIG.  3    during the first scan of FOV  300 . In this example, the device may then emit the second plurality of beams (in a similar spatial arrangement) during the second scan of FOV  300 . 
     At block  504 , method  500  involves illuminating a first portion of the FOV at a first-portion time offset, and a second portion of the FOV at a second-portion time offset. Referring back to  FIG.  3    for example, beams  302  and  304  may correspond to the first portion of the FOV illuminated at a the first-portion time offset (e.g., t=100 ns) from a start time (or end time) of the first emission time period, and beams  306  and  308  may correspond to the second portion of the FOV illuminated at the second-portion time offset (e.g., t=200 ns) from the start time (or end time) of the first emission time period. 
     In some implementations, method  500  may also involve illuminating the first portion of the FOV at a modified first-portion time offset from a start time (or end time) of a second emission time period of a second scan of the FOV (after the first scan). In line with the discussion above for instance, the modified first-portion time offset (e.g., 100 ns) may thus be different from the first-portion time offset (e.g., 400 ns) associated with the first scan. 
     In some implementations, method  500  involves intercepting light from the FOV illuminated by the plurality of beams. Referring back to  FIG.  1    for example, a first detector of detectors  110  may be aligned with a first portion of the FOV illuminated by a first beam of the plurality of beams described at block  502 , a second detector of detectors  110  may be aligned with a second portion of the FOV illuminated by a second beam of the plurality of beams, and so on. 
     IV. Example Timing Diagrams 
       FIG.  6 A  illustrates conceptual timing diagrams for a first scan  600  of a FOV, according to example embodiments. In particular,  FIG.  6 A  shows timing diagrams for transmit/receive signals associated with multiple channels (labeled as CH1, CH2, CH3, CH4) of an example device or system herein (e.g., devices  100 ,  200 , etc.). Each channel may be configured to scan a respective portion of a FOV. Referring back to  FIG.  3    for example, transmit signal  602  of CH1 may indicate emission of a pulse or beam  302  at t=500 ns, transmit signal  604  of CH2 may indicate emission of beam  304  at t=125 ns, transmit signal  606  of CH3 may indicate emission of beam  306  at t=375 ns, and transmit signal  608  of CH4 may indicate emission of beam  308  at t=250 ns. 
     Thus, in line with the discussion above, an example system may scan respective portions of a FOV using a spatial arrangement of transmit/receive channels that emit signals at varying (e.g., dithered, etc.) times within an emission time period of first scan  600 . For instance, in the scenario shown, the emission time period (500 ns) of first scan  600  may have a start time of t=0 ns and an end time of t=500 ns. Further, as shown, a detection time period (2000 ns) of first scan  600  begins after the emission period lapses (at t=500 ns). 
     During the detection time period (e.g., from t=500 ns to t=2500 ns), each channel may listen for returning reflections of its respective transmitted signal. For instance, in the scenario shown, CH1 may detect receive signal  622  at t=1500 ns. Thus, an example system or device herein may determine a distance “d” to an object that reflected a particular receive signal detected by a particular channel as: 
         d=c *(channel_detection_time−channel_emission_time)/2;
 
     where c is the speed of light (and/or other signal type of transmit signal  602  such as sound, etc.). Thus, for CH1 in this scenario, d=c*(1500 ns−500 ns)/2≈150 meters. In turn, an example system that performs the first scan  600  may determine that an object is present in the portion of the FOV scanned by CH1 at a distance of 150 meters from the system. Similarly, the system can determine distances to objects present in respective portions of the FOV scanned by CH2, CH3, CH4 based on the respective channel emission times (e.g., of signals  604 ,  606 ,  608 ) and the respective channel detection times. 
     As noted above however, in some scenarios, a reflected portion of a transmit signal from a first channel may be spuriously detected by a second channel. For instance, in a scenario where a retroreflector (or other strong reflector) is scanned by the first channel, portions of the reflected signal from the retroreflector may have sufficient energy to be detected by the second channel as well. 
     For example, consider a scenario where transmit signal  602  is reflected by a retroreflector and detected at CH1 as a (relatively strong) receive signal  622 . In this scenario, portions of the reflected signal from the retroreflector may also be detected spuriously at CH2 and CH3 as, respectively, (relatively weaker) receive signals  624  and  626 . In some examples, the (spurious) receive signals  624  and  626  may interfere with (and/or prevent) detection of non-spurious receive signals (not shown) that also arrive at t=1500 ns in CH2 and CH3. 
     However, in line with the discussion above, the effect of the spurious signals on the quality of the scan can be mitigated by varying the respective channel emission times during the emission period. For instance, a system that computes distance to an object associated with spurious signal  624  may determine a distance of d=c*(1500 ns−125 ns)/2≈206 meters in the portion of the FOV scanned by CH2. Similarly, the computing system may compute a distance of d=c*(1500 ns−375 ns)/2≈169 meters for the spurious receive signal  626  in CH3. Thus, with this arrangement, the errors associated with the spurious signal detections  624  and  626  may be spread over a range of distances from the scanning device. 
     Whereas, in an alternative implementation, if transmit signals  604  (of CH2) and 606 (of CH3) where instead transmitted at the same time (t=500 ns) as the emission time of transmit signal  602  (of CH1), then all three channels (CH1, CH2, CH3) would perceive presence of the retroreflector at the same distance of d=150 meters in their respective portions of the FOV. As a result, in the alternative implementation, a relatively larger portion of the scanned FOV at d=150 meters would be affected by errors associated with the spurious signals, as compared to the implementation described in  FIG.  6 A  (where the respective channel emission times are varied and/or dithered during the emission time period). 
     As noted above, some example methods herein involve obtaining a sequence of scans of a FOV. For instance, an example system that performs the first scan  600  may then perform a second scan, which begins after the detection period of the first scan lapses (i.e., at or after t=2500 ns), and so on. In some examples, the second scan may have a similar emission period (500 ns), in which each of CH1, CH2, CH3, CH4 emits another respective transmit signal (e.g., pulse, beam, etc.), followed by a similar detection period (2000 ns). In one example, the system may be configured to obtain the sequence of scans periodically. For instance, each scan may be assigned a predetermined scanning period (e.g., 5 microseconds, 10 microseconds, etc.). In some instances, each scanning period may be divided into a series of time windows (e.g., initialization time period, background and/or noise detection time period, signal emission time period, reflected signal detection time period, data collection time period, etc.). However, for convenience in description,  FIG.  6 A  only shows the emission period and the detection period of the first scan  600 . 
       FIG.  6 B  illustrates conceptual timing diagrams for a second scan  650  of the FOV, according to example embodiments. For instance, second scan  650  may be the second scan subsequent to first scan  600  in the sequence of scans described above. To that end, transmit signals  652 ,  654 ,  656 ,  658  and receive signals  672 ,  674 ,  676  may be similar, respectively, to transmit signals  602 ,  604 ,  606 ,  608  and receive signals  622 ,  624 ,  626  of first scan  600 . 
     Referring back to  FIG.  3    for example, transmit signal  652  may indicate emission of another pulse or beam  302  at t=5000 ns, transmit signal  654  of CH2 may indicate emission of another beam  304  at t=5500 ns, transmit signal  656  of CH3 may indicate emission of another beam  306  at t=5125 ns, and transmit signal  658  of CH4 may indicate emission of another beam  308  at t=5375 ns. 
     As noted above, some example systems herein may obtain the sequence of scans periodically or intermittently. For the sake of example, consider a scenario where the illustrations of  FIGS.  6 A- 6 B  involve an example system configured to obtain the sequence of scans periodically (i.e., one scan every 5 microseconds). In this scenario, similarly to first scan  600 , second scan  650  is shown to have a similar emission period (500 ns) from t=5000 ns to t=5500 ns, followed by a similar detection period (2000 ns) from t=5500 ns to t=7500 ns. 
     However, as shown, the transmit signals of CH1, CH2, CH3, CH4 are assigned different time offsets within the emission period of second scan  650  as compared to the time offsets assigned to the corresponding transmit signals of first scan  600 . 
     Referring back to  FIG.  6 A  for example, transmit signal  602  (of CH1) is assigned a time offset of 500 ns−0 ns=500 ns from the start time (t=0 ns) of the emission period of first scan  600 , transmit signal  604  (of CH2) is assigned a time offset of 125 ns−0 ns=125 ns, transmit signal  606  (of CH3) is assigned a time offset of 375 ns−0 ns=375 ns, and transmit signal  608  (of CH4) is assigned a time offset of 250 ns−0 ns=250 ns. 
     In contrast, returning now to  FIG.  6 B , transmit signal  652  (of CH1) is assigned a time offset of 5000 ns−5000 ns=0 ns from the start time (t=5000 ns) of the emission period of second scan  650 , transmit signal  654  (of CH2) is assigned a time offset of 5500 ns−5000 ns=500 ns, transmit signal  656  (of CH3) is assigned a time offset of 5125 ns−5000 ns=125 ns, and transmit signal  658  (of CH4) is assigned a time offset of 5375 ns−5000 ns=375 ns. 
     In some examples, in accordance with the present disclosure, such varying (e.g., dithering) of relative channel emission times within respective emission periods of a sequence of scans may facilitate identification and/or mitigation of errors associated with spurious signal detection. For example, consider the scenario described above for  FIG.  6 A , where a retroreflector in the portion of the FOV scanned by CH1 causes the detection of non-spurious receive signal  622  in CH1 as well as spurious receive signals  624  (in CH2) and 626 (in CH3) during the first scan  600 . Continuing with this scenario, returning now to  FIG.  6 B , the retroreflector may similarly result in the detection (at t=6000 ns) of non-spurious receive signal  672  (in CH1) and spurious receive signals  674  (in CH2) and 676 (in CH3). 
     In this scenario, the distance to the retroreflector perceived by CH1 during the second scan  650  may be d=c*(6000−5000)/2≈150 meters, which is the same as the distance computed for CH1 during the first scan  600 . However, due to the change in the emission time offsets associated with transmit signals  652 ,  654 ,  656 , the distances to the retroreflector computed for CH2 and CH3 in the second scan  650  may be different than the corresponding distances computed in the first scan  600 . For instance, the distance computed for CH2 in the second scan  650  may be d=c*(6000−5500)/2≈75 meters (compared to 206 meters in the first scan  600 ); and the distance computed for CH3 in the second scan  650  may bed=c*(6000−5125)/2≈131 meters (compared to 169 meters in the first scan  600 ). 
     Thus, with this arrangement for example, consecutive detections of an object that is actually present in a portion of the FOV scanned by a particular channel may remain “coherent” (e.g., the perceived distance to the object may remain substantially the same in consecutive scans by the particular channel). On the other hand, consecutive detections of an object that is not actually present in the portion of the FOV scanned by the particular channel may be “incoherent” (e.g., the perceived distance to the object may change in consecutive scans by the particular channel). In various examples, a system herein can improve the quality of LIDAR sensor data based on the incoherent nature of the spurious signals. 
     In one example, a device herein may determine that a received signal at a first channel has signal characteristics associated with presence of a retroreflector. For instance, as shown in  FIG.  6 B , the device may detect that receive signal  672  in CH1 has a signal intensity greater than a threshold (e.g., a sufficiently high intensity expected when a retroreflector is present in the portion of the FOV scanned by the first channel). In response to such determination, the device may identify other signals that were received at other channels (e.g., signals  674  and  676 ) at a same time (t=6000 ns) when signal  672  was received at the first channel. The device may then store an indication of the identified other signals as potential spurious signal detections by the other channels (CH2 and CH3). Upon further processing of the sensor data from the LIDAR (e.g., by a computing device, etc.) for instance, the potential spurious signal detections can be removed from the sensor data (or otherwise modified) if the received signal at the first channel is determined to be a reflection from a retroreflector. 
     Additionally, due to the incoherent nature of the potential spurious signals, the effect of removing the spurious signals on the quality of sensor data from a particular channel can be mitigated. Referring back to  FIG.  6 A  for example, removal of data associated with spurious signal  624  may result in a missing measurement from CH2 at the distance of 206 meters in the first scan  600 . However, during the second scan  650 , CH2 can scan for objects at the distance of 206 meters even if spurious signal  674  is also removed because spurious signal  674  corresponds to a distance of 75 meters in the second scan  650  (instead of a distance of 206 meters). On the other hand, if spurious signals  624  and  674  were instead coherent, then CH2 would be blinded from detecting true objects at a particular distance (e.g., 75 meters) during several consecutive scans by CH2. 
     Accordingly, some example methods herein (e.g., methods  400 ,  500 ) may involve determining that a first signal received by a first detector has an intensity greater than a threshold, identifying one or more additional signals received by one or more other detectors at a same time as a time of receipt of the first signal, and storing an indication of the one or more additional signals. 
     Alternatively or additionally, some example methods herein (e.g., methods  400 ,  500 ) may involve identifying an error detection based on a comparison of sensor data collected during a sequence of scans of a FOV. Referring back to  FIG.  1    for example, a computing device (e.g., controller  104 ) may compare distance measurements obtained using a first detector of detectors  110  in a plurality of successive scans of the sequence of scans. If the distance measurements indicated by the first detector are coherent (e.g., within a threshold tolerance range), then the computing device may determine that the measurements associated with the plurality of scans indicate presence of an actual object in the portion of the FOV scanned by the first detector. Whereas, if the distance measurements are incoherent (e.g., outside the threshold tolerance range), then the computing device may determine that the measurements may be associated with channel cross-talk or other source of noise. 
     To that end, in some examples, a method herein (e.g., methods  400 ,  500 ) may also involve filtering sensor data obtained from a receiver (e.g., receiver  114 ) based on a comparison of distance measurements associated with the sequence of scans. For example, the sensor data can be pruned to remove given data associated with spurious signals (associated with incoherent distance measurements in successive scans of the sequence of scans). For instance, referring back to  FIG.  1   , device  100  may analyze the sensor data to remove data points (e.g., signal detections, etc.) that are inconsistent over a given number (e.g., two, three, etc.) of successive scans by a same detector of detectors  110 . 
     V. Conclusion 
     The particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other implementations may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an exemplary implementation may include elements that are not illustrated in the Figures. Additionally, while various aspects and implementations have been disclosed herein, other aspects and implementations will be apparent to those skilled in the art. The various aspects and implementations disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. Other implementations may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations.