Patent Publication Number: US-2022219736-A1

Title: Emergency vehicle audio and visual detection post fusion

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to application Ser. No. ______, titled “MACHINE LEARNING MODEL TO FUSE EMERGENCY VEHICLE AUDIO AND VISUAL DETECTION”, filed on Jan. 14, 2021. The application is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present disclosure relate generally to operating autonomous vehicles. More particularly, embodiments of the disclosure relate to systems and methods for detecting emergency vehicles using information from sources. 
     BACKGROUND 
     Vehicles operating in an autonomous mode (e.g., driverless) can relieve occupants, especially the driver, from some driving-related responsibilities. When operating in an autonomous mode, the vehicle can navigate to various locations using onboard sensors, allowing the vehicle to travel with minimal human interaction or in some cases without any passengers. 
     An ADV needs to take appropriate actions to comply with local traffic rules when emergency vehicles (e.g. police cars, fire trucks and ambulance) are detected on a road. Therefore, accurately detecting emergency vehicles in a surrounding environment of the ADV is important to a travelling ADV such that the AVD does not have to make unnecessary stops. One approach to increasing the accuracy of detection is to use information from multiple sources (e.g., images and voices from sensors on the ADV) to eliminate the instability of a single source. Such an approach requires a fusion of the information from the multiple sources. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the disclosure are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
         FIG. 1  is a block diagram illustrating a networked system according to one embodiment. 
         FIG. 2  is a block diagram illustrating an example of an autonomous vehicle according to one embodiment. 
         FIGS. 3A-3B  are block diagrams illustrating an example of a perception and planning system used with an autonomous vehicle according to one embodiment. 
         FIG. 4  illustrates an example of an emergency vehicle detection system according to one embodiment. 
         FIG. 5  further illustrates the emergency vehicle detection system according to one embodiment. 
         FIGS. 6A-6B  illustrate performance advantages of the emergency vehicle detection system in one embodiment. 
         FIG. 7  illustrates a process of detecting an emergency vehicle according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments and aspects of the disclosures will be described with reference to details discussed below, and the accompanying drawings will illustrate the various embodiments. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosures. 
     Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in conjunction with the embodiment can be included in at least one embodiment of the disclosure. The appearances of the phrase “in one embodiment” in various places in the specification do not necessarily all refer to the same embodiment. 
     According to various embodiments, systems, methods, and mediums for operating an autonomous driving vehicles (ADV) are described. The embodiments use decision-level fusion (post fusion) of audio data and visual data captured by sensors mounted on the ADV. Compared to feature-level fusion of the audio data and the visual data, the embodiments in this disclosure does not require strict timing synchronization between the audio data and the visual data, and can overcome the problems of different feature reliability of different sources of data. 
     In one embodiment, an emergency vehicle detection system can be provided in the ADV travelling on a road to detect the presence of an emergency vehicle in a surrounding environment of the ADV using both audio data and visual data. The emergency vehicle detection system can use a trained neutral network to independently generate a detection result from the audio data, and use another trained network to independently generate another detection result from the visual data. The emergency vehicle detection system can fuse the two detection results to determine the position and moving direction of the emergency vehicle. The ADV can take appropriate actions in response to the position and moving direction of the emergency vehicle. 
     In one embodiment, the emergency vehicle detection system includes an audio submodule and a visual submodule, each submodule being a trained neutral network. The audio submodule can take audio data captured by microphones mounted on the ADV as input, and generate a probability representing how likely a siren sound is present in a surrounding environment of the travelling ADV, and a direction of a source of the siren sound. The visual submodule takes visual data captured by cameras mounted on the ADV as input, and generate a probability representing how likely that an emergency vehicle is present in the surrounding environment, and a distance of the emergency vehicle. 
     A post fusion component in the emergency vehicle detection system can fuse the detection results from the audio submodule and the visual submodule to determine whether an emergency vehicle is present in the surrounding environment. If it is, the post fusion component can determine the position and moving direction of the emergency vehicle. In one embodiment, if at least one of the two probabilities exceeds a threshold, the emergency vehicle detection system can determine that an emergency vehicle is present in the surrounding environment. 
     The emergency vehicle detection system uses both audio and visual data, and fuse the detection results from the two types of data, thus improving the performance of the system. Relying on visual data alone, the emergency vehicle detection system may not accurately detect an emergency vehicle in a low-visibility environment. Relying on audio data alone, the emergency vehicle detection system may not accurately detect an emergency vehicle in a noisy environment. A post fusion combination of both types of data would enable the emergency vehicle detection system to perform well in a variety of environments. 
     The embodiments described herein can include non-transitory machine readable media that store executable computer program instructions that can cause one or more data processing systems to perform the one or more methods described herein when the computer program instructions are executed by the one or more data processing systems. The instructions can be stored in non-volatile memory such as flash memory or other forms of memory. The embodiments can also be practiced as method claims. 
     The above summary does not include an exhaustive list of all embodiments in this disclosure. All systems and methods can be practiced from all suitable combinations of the various aspects and embodiments described in the disclosure. 
     Autonomous Driving Vehicle 
       FIG. 1  is a block diagram illustrating an autonomous driving network configuration according to one embodiment of the disclosure. Referring to  FIG. 1 , network configuration  100  includes autonomous driving vehicle (ADV)  101  that may be communicatively coupled to one or more servers  103 - 104  over a network  102 . Although there is one ADV shown, multiple ADVs can be coupled to each other and/or coupled to servers  103 - 104  over network  102 . Network  102  may be any type of networks such as a local area network (LAN), a wide area network (WAN) such as the Internet, a cellular network, a satellite network, or a combination thereof, wired or wireless. Server(s)  103 - 104  may be any kind of servers or a cluster of servers, such as Web or cloud servers, application servers, backend servers, or a combination thereof. Servers  103 - 104  may be data analytics servers, content servers, traffic information servers, map and point of interest (MPOI) servers, or location servers, etc. 
     An ADV refers to a vehicle that can be configured to in an autonomous mode in which the vehicle navigates through an environment with little or no input from a driver. Such an ADV can include a sensor system having one or more sensors that are configured to detect information about the environment in which the vehicle operates. The vehicle and its associated controller(s) use the detected information to navigate through the environment. ADV  101  can operate in a manual mode, a full autonomous mode, or a partial autonomous mode. 
     In one embodiment, ADV  101  includes, but is not limited to, autonomous driving system (ADS)  110 , vehicle control system  111 , wireless communication system  112 , user interface system  113 , and sensor system  115 . ADV  101  may further include certain common components included in ordinary vehicles, such as, an engine, wheels, steering wheel, transmission, etc., which may be controlled by vehicle control system  111  and/or ADS  110  using a variety of communication signals and/or commands, such as, for example, acceleration signals or commands, deceleration signals or commands, steering signals or commands, braking signals or commands, etc. 
     Components  110 - 115  may be communicatively coupled to each other via an interconnect, a bus, a network, or a combination thereof. For example, components  110 - 115  may be communicatively coupled to each other via a controller area network (CAN) bus. A CAN bus is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other in applications without a host computer. It is a message-based protocol, designed originally for multiplex electrical wiring within automobiles, but is also used in many other contexts. 
     Referring now to  FIG. 2 , in one embodiment, sensor system  115  includes, but it is not limited to, one or more cameras  211 , global positioning system (GPS) unit  212 , inertial measurement unit (IMU)  213 , radar unit  214 , and a light detection and range (LIDAR) unit  215 . GPS system  212  may include a transceiver operable to provide information regarding the position of the ADV. IMU unit  213  may sense position and orientation changes of the ADV based on inertial acceleration. Radar unit  214  may represent a system that utilizes radio signals to sense objects within the local environment of the ADV. In some embodiments, in addition to sensing objects, radar unit  214  may additionally sense the speed and/or heading of the objects. LIDAR unit  215  may sense objects in the environment in which the ADV is located using lasers. LIDAR unit  215  could include one or more laser sources, a laser scanner, and one or more detectors, among other system components. Cameras  211  may include one or more devices to capture images of the environment surrounding the ADV. Cameras  211  may be still cameras and/or video cameras. A camera may be mechanically movable, for example, by mounting the camera on a rotating and/or tilting a platform. 
     Sensor system  115  may further include other sensors, such as, a sonar sensor, an infrared sensor, a steering sensor, a throttle sensor, a braking sensor, and an audio sensor (e.g., microphone). An audio sensor may be configured to capture sound from the environment surrounding the ADV. A steering sensor may be configured to sense the steering angle of a steering wheel, wheels of the vehicle, or a combination thereof. A throttle sensor and a braking sensor sense the throttle position and braking position of the vehicle, respectively. In some situations, a throttle sensor and a braking sensor may be integrated as an integrated throttle/braking sensor. 
     In one embodiment, vehicle control system  111  includes, but is not limited to, steering unit  201 , throttle unit  202  (also referred to as an acceleration unit), and braking unit  203 . Steering unit  201  is to adjust the direction or heading of the vehicle. Throttle unit  202  is to control the speed of the motor or engine that in turn controls the speed and acceleration of the vehicle. Braking unit  203  is to decelerate the vehicle by providing friction to slow the wheels or tires of the vehicle. Note that the components as shown in  FIG. 2  may be implemented in hardware, software, or a combination thereof 
     Referring back to  FIG. 1 , wireless communication system  112  is to allow communication between ADV  101  and external systems, such as devices, sensors, other vehicles, etc. For example, wireless communication system  112  can wirelessly communicate with one or more devices directly or via a communication network, such as servers  103 - 104  over network  102 . Wireless communication system  112  can use any cellular communication network or a wireless local area network (WLAN), e.g., using WiFi to communicate with another component or system. Wireless communication system  112  could communicate directly with a device (e.g., a mobile device of a passenger, a display device, a speaker within vehicle  101 ), for example, using an infrared link, Bluetooth, etc. User interface system  113  may be part of peripheral devices implemented within vehicle  101  including, for example, a keyboard, a touch screen display device, a microphone, and a speaker, etc. 
     Some or all of the functions of ADV  101  may be controlled or managed by ADS  110 , especially when operating in an autonomous driving mode. ADS  110  includes the necessary hardware (e.g., processor(s), memory, storage) and software (e.g., operating system, planning and routing programs) to receive information from sensor system  115 , control system  111 , wireless communication system  112 , and/or user interface system  113 , process the received information, plan a route or path from a starting point to a destination point, and then drive vehicle  101  based on the planning and control information. Alternatively, ADS  110  may be integrated with vehicle control system  111 . 
     For example, a user as a passenger may specify a starting location and a destination of a trip, for example, via a user interface. ADS  110  obtains the trip related data. For example, ADS  110  may obtain location and route data from an MPOI server, which may be a part of servers  103 - 104 . The location server provides location services and the MPOI server provides map services and the POIs of certain locations. Alternatively, such location and MPOI information may be cached locally in a persistent storage device of ADS  110 . 
     While ADV  101  is moving along the route, ADS  110  may also obtain real-time traffic information from a traffic information system or server (TIS). Note that servers  103 - 104  may be operated by a third party entity. Alternatively, the functionalities of servers  103 - 104  may be integrated with ADS  110 . Based on the real-time traffic information, MPOI information, and location information, as well as real-time local environment data detected or sensed by sensor system  115  (e.g., obstacles, objects, nearby vehicles), ADS  110  can plan an optimal route and drive vehicle  101 , for example, via control system  111 , according to the planned route to reach the specified destination safely and efficiently. 
     Server  103  may be a data analytics system to perform data analytics services for a variety of clients. In one embodiment, data analytics system  103  includes data collector  121  and machine learning engine  122 . Data collector  121  collects driving statistics  123  from a variety of vehicles, either ADVs or regular vehicles driven by human drivers. Driving statistics  123  include information indicating the driving commands (e.g., throttle, brake, steering commands) issued and responses of the vehicles (e.g., speeds, accelerations, decelerations, directions) captured by sensors of the vehicles at different points in time. Driving statistics  123  may further include information describing the driving environments at different points in time, such as, for example, routes (including starting and destination locations), MPOIs, road conditions, weather conditions, etc. 
     Based on driving statistics  123 , machine learning engine  122  generates or trains a set of rules, algorithms, and/or predictive models  124  for a variety of purposes. Algorithms  124  can then be uploaded on ADVs to be utilized during autonomous driving in real-time. 
       FIGS. 3A and 3B  are block diagrams illustrating an example of an autonomous driving system used with an ADV according to one embodiment. System  300  may be implemented as a part of ADV  101  of  FIG. 1  including, but is not limited to, ADS  110 , control system  111 , and sensor system  115 . Referring to  FIGS. 3A-3B , ADS  110  includes, but is not limited to, localization module  301 , perception module  302 , prediction module  303 , decision module  304 , planning module  305 , control module  306 , routing module  307 . 
     Some or all of modules  301 - 307  may be implemented in software, hardware, or a combination thereof. For example, these modules may be installed in persistent storage device  352 , loaded into memory  351 , and executed by one or more processors (not shown). Note that some or all of these modules may be communicatively coupled to or integrated with some or all modules of vehicle control system  111  of  FIG. 2 . Some of modules  301 - 307  may be integrated together as an integrated module. 
     Localization module  301  determines a current location of ADV  300  (e.g., leveraging GPS unit  212 ) and manages any data related to a trip or route of a user. Localization module  301  (also referred to as a map and route module) manages any data related to a trip or route of a user. A user may log in and specify a starting location and a destination of a trip, for example, via a user interface. Localization module  301  communicates with other components of ADV  300 , such as map and route data  311 , to obtain the trip related data. For example, localization module  301  may obtain location and route data from a location server and a map and POI (MPOI) server. A location server provides location services and an MPOI server provides map services and the POIs of certain locations, which may be cached as part of map and route data  311 . While ADV  300  is moving along the route, localization module  301  may also obtain real-time traffic information from a traffic information system or server. 
     Based on the sensor data provided by sensor system  115  and localization information obtained by localization module  301 , a perception of the surrounding environment is determined by perception module  302 . The perception information may represent what an ordinary driver would perceive surrounding a vehicle in which the driver is driving. The perception can include the lane configuration, traffic light signals, a relative position of another vehicle, a pedestrian, a building, crosswalk, or other traffic related signs (e.g., stop signs, yield signs), etc., for example, in a form of an object. The lane configuration includes information describing a lane or lanes, such as, for example, a shape of the lane (e.g., straight or curvature), a width of the lane, how many lanes in a road, one-way or two-way lane, merging or splitting lanes, exiting lane, etc. 
     Perception module  302  may include a computer vision system or functionalities of a computer vision system to process and analyze images captured by one or more cameras in order to identify objects and/or features in the environment of the ADV. The objects can include traffic signals, road way boundaries, other vehicles, pedestrians, and/or obstacles, etc. The computer vision system may use an object recognition algorithm, video tracking, and other computer vision techniques. In some embodiments, the computer vision system can map an environment, track objects, and estimate the speed of objects, etc. Perception module  302  can also detect objects based on other sensors data provided by other sensors such as a radar and/or LIDAR. 
     Perception module  302  may include an emergency vehicle detection module  308 , which can detect the presence of an emergency vehicle in a surrounding environment of the ADV using both audio data and visual data. 
     For each of the objects, prediction module  303  predicts what the object will behave under the circumstances. The prediction is performed based on the perception data perceiving the driving environment at the point in time in view of a set of map/rout information  311  and traffic rules  312 . For example, if the object is a vehicle at an opposing direction and the current driving environment includes an intersection, prediction module  303  will predict whether the vehicle will likely move straight forward or make a turn. If the perception data indicates that the intersection has no traffic light, prediction module  303  may predict that the vehicle may have to fully stop prior to enter the intersection. If the perception data indicates that the vehicle is currently at a left-turn only lane or a right-turn only lane, prediction module  303  may predict that the vehicle will more likely make a left turn or right turn respectively. 
     For each of the objects, decision module  304  makes a decision regarding how to handle the object. For example, for a particular object (e.g., another vehicle in a crossing route) as well as its metadata describing the object (e.g., a speed, direction, turning angle), decision module  304  decides how to encounter the object (e.g., overtake, yield, stop, pass). Decision module  304  may make such decisions according to a set of rules such as traffic rules or driving rules  312 , which may be stored in persistent storage device  352 . 
     Routing module  307  is configured to provide one or more routes or paths from a starting point to a destination point. For a given trip from a start location to a destination location, for example, received from a user, routing module  307  obtains route and map information  311  and determines all possible routes or paths from the starting location to reach the destination location. Routing module  307  may generate a reference line in a form of a topographic map for each of the routes it determines from the starting location to reach the destination location. A reference line refers to an ideal route or path without any interference from others such as other vehicles, obstacles, or traffic condition. That is, if there is no other vehicle, pedestrians, or obstacles on the road, an ADV should exactly or closely follows the reference line. The topographic maps are then provided to decision module  304  and/or planning module  305 . Decision module  304  and/or planning module  305  examine all of the possible routes to select and modify one of the most optimal routes in view of other data provided by other modules such as traffic conditions from localization module  301 , driving environment perceived by perception module  302 , and traffic condition predicted by prediction module  303 . The actual path or route for controlling the ADV may be close to or different from the reference line provided by routing module  307  dependent upon the specific driving environment at the point in time. 
     Based on a decision for each of the objects perceived, planning module  305  plans a path or route or trajectory for the ADV, as well as driving parameters (e.g., distance, speed, and/or turning angle), using a reference line provided by routing module  307  as a basis. That is, for a given object, decision module  304  decides what to do with the object, while planning module  305  determines how to do it. For example, for a given object, decision module  304  may decide to pass the object, while planning module  305  may determine whether to pass on the left side or right side of the object. Planning and control data is generated by planning module  305  including information describing how vehicle  300  would move in a next moving cycle (e.g., next route/path segment). For example, the planning and control data may instruct vehicle  300  to move 10 meters at a speed of 30 miles per hour (mph), then change to a right lane at the speed of 25 mph. 
     Based on the planning and control data, control module  306  controls and drives the ADV, by sending proper commands or signals to vehicle control system  111  via a CAN bus module  321 , according to a trajectory (also referred to as a route or path) defined by the planning and control data. The planning and control data include sufficient information to drive the vehicle from a first point to a second point of a route or path using appropriate vehicle settings or driving parameters (e.g., throttle, braking, steering commands) at different points in time along the path or route. 
     In one embodiment, the planning phase is performed in a number of planning cycles, also referred to as driving cycles, such as, for example, in every time interval of 100 milliseconds (ms). For each of the planning cycles or driving cycles, one or more control commands will be issued based on the planning and control data. That is, for every 100 ms, planning module  305  plans a next route segment or path segment, for example, including a target position and the time required for the ADV to reach the target position. Alternatively, planning module  305  may further specify the specific speed, direction, and/or steering angle, etc. In one embodiment, planning module  305  plans a route segment or path segment for the next predetermined period of time such as 5 seconds. For each planning cycle, planning module  305  plans a target position for the current cycle (e.g., next 5 seconds) based on a target position planned in a previous cycle. Control module  306  then generates one or more control commands (e.g., throttle, brake, steering control commands) based on the planning and control data of the current cycle. 
     Note that decision module  304  and planning module  305  may be integrated as an integrated module. Decision module  304 /planning module  305  may include a navigation system or functionalities of a navigation system to determine a driving path for the ADV. For example, the navigation system may determine a series of speeds and directional headings to affect movement of the ADV along a path that substantially avoids perceived obstacles while generally advancing the ADV along a roadway-based path leading to an ultimate destination. The destination may be set according to user inputs via user interface system  113 . The navigation system may update the driving path dynamically while the ADV is in operation. The navigation system can incorporate data from a GPS system and one or more maps so as to determine the driving path for the ADV  101 . 
     Emergency Vehicle Detection 
       FIG. 4  illustrates an example of an emergency vehicle detection system  400  according to one embodiment. 
     As shown in  FIG. 4 , the emergency vehicle detection module  308  can include an audio submodule  407 , and a visual submodule  409 . The audio submodule  407  can be a software module that implements a predetermined algorithm or a neural network. The neural network can be a convolutional neural network (CNN) trained using audio training data (e.g., prior to deployment of the ADV) collected from a large number of emergency vehicles. The training data can include a) audio data that is classified as having an emergency vehicle siren, and b) audio data that is classified as not having an emergency vehicle siren. 
     For example, training data can include numerous audio samples, some of which contain different police sirens, fire truck sirens, and ambulance sirens that are classified as having an emergency vehicle siren, and some of which containing other noises such as, but not limited to, dogs barking, birds chirping, cars honking, music, etc., that are classified as not having an emergency vehicle siren. 
     In one embodiment, the trained neural network can receive  404  audio data (e.g., audio signals) captured by audio sensors  403  mounted on the ADV  101 , and detect, based on the audio data, a presence of an audio signature of an emergency vehicle siren in a surrounding environment of the ADV  101  as the ADV  101  is travelling on a road segment. The audio sensors  403  (also referred to audio capturing devices) can include a number of microphones mounted in different positions of the ADV  101 . The microphones can form a microphone array having fixed and known positions on the ADV, arranged to sense sounds in different directions around the ADV  101 . The audio submodule  407  can output a probability  411  of the presence of a siren sound from an emergency vehicle, and a direction  413  of the siren sound. 
     In one embodiment, the direction  413  of the siren sound can be represented by a numerical number and a moving direction indicator. The numerical number is a degree of an angle between a line representing the ADV  101  and a line from a source of the siren sound to the ADV  101 . The line representing the ADV  101  can be a line that passes through the ADV  101  along the travelling direction of the ADV  101 . The moving direction indicator can indicate whether the source of the siren sound is moving towards the ADV  101  or moving away from the ADV  101 . The moving direction of the source of the siren sound can be determined based on changes in the siren&#39;s amplitude or frequency (e.g., through the Doppler effect). 
     In one embodiment, the visual submodule  409  can be a software module that implements a predetermined algorithm or a neural network. The neural network can also be a CNN trained using visual data collected from a large number of emergency vehicles. In one implementation, the CCN can be a You Only Look Once (YOLO)-based neural network model. 
     The visual submodule  409  can receive  406  visual data captured by visual sensors  405  and determine whether an emergency vehicle exists in the surrounding environment of the ADV  101  as the ADV  101  is travelling on the road. The visual data from the visual sensors  405  and the audio data from the audio sensors  403  are captured simultaneously from the same surrounding environment of the ADV  101 . The audio data can be a stream of audio signals and the visual data can be a sequence of image frames. 
     The visual submodule  409  can output a probability  415  of the presence of an emergency vehicle in the surrounding environment of the ADV  101 , and a distance  417  of the emergency vehicle. 
     When the neural network in the visual submodule  409  is trained, a size of bounding box of each training image frame and extrinsic parameters of the camera used to take the image frame can be used as part of the labeling data of the image frame. Therefore, when an image frame of an emergency vehicle is provided to the trained neutral network, the neutral network model can output a distance of the emergency vehicle to the ADV  101  based on a size of the image frame and extrinsic parameters of the camera used to capture the image frame. 
     Each image frame can be associated with a set of intrinsic parameters and a set of extrinsic parameters. The intrinsic parameters of a camera are unique to the camera. An example of the intrinsic parameters can be a focal length of the camera. The extrinsic parameters of a camera, on the other hand, are not unique to any given camera. The extrinsic parameters include the relative rotation and translation between cameras in a multi-camera arrangement. 
     In one embodiment, the emergency vehicle detection module  308  can further include a post fusion component  420  used to fuse the detection results from the audio submodule  403  and the visual submodule  405 . As shown above, the detection results are represented by the probability  411  of the presence of a siren sound in the surrounding environment, a direction  413  of the siren sound, the probability  415  of the presence of an emergency vehicle in the surrounding environment, and the distance  417  of the emergency vehicle to the ADV  101 . The detection results can also include other outputs (not shown) from the visual submodule  405 , for example, whether the emergency vehicle is driving away from the ADV  101  or driving towards the ADV  101 . 
     The post fusion component  420  can fuse the detection results to output information indicating that an emergency vehicle is present in the surrounding environment of the ADV  101 , a position of the emergency vehicle, and/or a moving direction of the emergency vehicle. 
     The output information from the emergency detection module  308  can be used by the autonomous driving system  110  to generate commands or signals to be sent to the vehicle control system  111  via the CAN bus module  321 . Based on the commands or signals, the vehicle control system  111  can control the ADV  101  to take appropriate actions. 
     In one embodiment, the ADV  101  can steer out of a current driving lane or brake to decelerate or steer to the side of the road, in response to determining that the emergency vehicle is moving towards the ADV  101 . If the emergency vehicle is moving away from the ADV  101 , the ADV  101  can continue along its current path without disturbance. 
       FIG. 5  further illustrates the emergency vehicle detection system  400  according to one embodiment. More specifically,  FIG. 5  illustrates one implementation of the fusion logic in the post fusion component  420 . 
     In one embodiment, the post fusion component  420  can fuse detections results from two different sources of information, namely, the audio sensors  403  and the visual sensors  405 . The detection result from each information source can individually indicate whether an emergency vehicle is present in the surrounding environment of the ADV  101 . For example, the probability  411  of the presence of a siren sound indicates that the probability that an emergency vehicle is present because the presence of a siren sound is strongly correlated to the presence of an emergency vehicle. The process of post fusion can combine the detection results from the audio submodule  407  and the visual submodule  409  into a single detection result. The audio-visual fusion can boost the detection performance of the emergency vehicle detection module  308 , particular in noisy surrounding environments where the performance of audio classifiers tends to be reduced, and where the visual data is unaffected by acoustic noise. 
     In one embodiment, an example of a post fusion process is illustrated in the post fusion component  420 , which can perform a number of operations, including checking the probability  411  and the probability  415 , each of which is associated with a predetermined threshold value, and determining whether at least one of the probability  411  or the probability  415  exceeds its associated threshold, as shown in operation  503 . If neither of the probability  411  and the probability  415  exceeds its associated threshold, the post fusion component  308  determines that no emergency vehicle is present in the surrounding environment as shown in operation  505 . However, if at least one of the probability  411  or the probability  415  exceeds their respective threshold, the post fusion component  420  determines that an emergency vehicle is present in the surrounding environment, as shown in operation  507 . 
     As further shown, if an emergency vehicle is present, the post function component  420  can fuse the distance  417  of the emergency vehicle to the ADV  101  and the direction  413  of the source of the siren sound in operation  509  to obtain the position of the emergency vehicle as shown in operation  511 . 
       FIGS. 6A-6B  illustrate performance advantages of the emergency vehicle detection system  400  in one embodiment. The emergency vehicle detection system  400  uses information from multiple sources for detecting the presence of an emergency vehicle. This multi-source approach would ensure that the emergency vehicle detection system  400  accurately detect the presence of an emergency vehicle in different types of environments. 
       FIG. 6A  shows an example of a surrounding environment that has a low visibility. Although a raining environment is shown, the features and advantages of the emergency vehicle detection system  400  are applicable to other low visibility environments, such as nights. 
     As shown in  FIG. 6A , a microphone array  603  and a camera array  607  are installed on an ADV  601 . The microphone array  603  can be used to capture audio signals from a surrounding environment of the ADV  601  as the ADV  601  is travelling on a road. The microphones and cameras installed on the ADV  601  can be arranged in other manners, for example, in a non-array manner. An emergency vehicle  609  is present in the surrounding environment, driving towards the ADV  601  in a different lane. 
     The emergency vehicle detection system  400  installed in the ADV  601  can receive audio data captured by the microphone array  603 , and visual data captured by the cameras array  707 , and generate a separate detection result from each of the audio data and the visual data. 
     The low-visibility environment negatively impacts the detection accuracy based on the visual data, but has no impact on the detection result based on the audio data. For example, the emergency vehicle detection system  400  can determine that the probability of a siren sound being present in the surrounding environment is 98%, and that the probability of the presence of an emergency vehicle in the surround environment is much lower (67%). The visual submodule of the emergency vehicle detection system  400  cannot accurately detect the shape of the emergency vehicle  609  in the raining day, whereas the audio submodule of the emergency vehicle detection system  400  can still accurate detect the siren sound and the direction. As a result, the overall detection accuracy after the post fusion does not suffer, and the emergency vehicle detection system  400  can still accurately detect the emergency vehicle  609 . 
       FIG. 6B  shows an example of a surrounding environment with a clear sky that has a noisy environment. In such a noisy environment, the detection result of the audio submodule of the emergency vehicle detection system  400  would suffer (66%) while the detection result of the visual submodule of the emergency vehicle detection system  400  would not be negatively impacted (97%). Thus, after the post fusion, the overall detection accuracy of the emergency vehicle detection system  400  is still high. 
       FIG. 7  illustrates a process  700  of detecting an emergency vehicle according to one embodiment. Process  700  may be performed by processing logic which may include software, hardware, or a combination thereof. For example, process  700  may be performed by the autonomous driving system described in  FIG. 4 . 
     As shown in  FIG. 7 , in operation  701 , the processing logic receives a stream of audio signals and a sequence of image frames, the stream of audio signals captured from a surrounding environment of the ADV using one or more audio capturing devices mounted on the ADV, and the sequence of image frames captured from the surrounding environment using one or more image capturing devices mounted on the ADV. In operation  702 , the processing logic determines, using a first neural network model, a first probability that at least a portion of the stream of captured audio signals is from a siren sound. In operation  703 , the processing logic determines, using a second neural network model, a second probability that at least one image frame of the sequence of captured image frames is from an emergency vehicle. In operation  704 , the processing logic determines, based on the first probability and the second probability, that an emergency vehicle is present in the surrounding environment. 
     Note that some or all of the components as shown and described above may be implemented in software, hardware, or a combination thereof. For example, such components can be implemented as software installed and stored in a persistent storage device, which can be loaded and executed in a memory by a processor (not shown) to carry out the processes or operations described throughout this application. Alternatively, such components can be implemented as executable code programmed or embedded into dedicated hardware such as an integrated circuit (e.g., an application specific IC or ASIC), a digital signal processor (DSP), or a field programmable gate array (FPGA), which can be accessed via a corresponding driver and/or operating system from an application. Furthermore, such components can be implemented as specific hardware logic in a processor or processor core as part of an instruction set accessible by a software component via one or more specific instructions. 
     Some portions of the preceding detailed descriptions have been presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the ways used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of operations leading to a desired result. The operations are those requiring physical manipulations of physical quantities. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the above discussion, it is appreciated that throughout the description, discussions utilizing terms such as those set forth in the claims below, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
     Embodiments of the disclosure also relate to an apparatus for performing the operations herein. Such a computer program is stored in a non-transitory computer readable medium. A machine-readable medium includes any mechanism for storing information in a form readable by a machine (e.g., a computer). For example, a machine-readable (e.g., computer-readable) medium includes a machine (e.g., a computer) readable storage medium (e.g., read only memory (“ROM”), random access memory (“RAM”), magnetic disk storage media, optical storage media, flash memory devices). 
     The processes or methods depicted in the preceding figures may be performed by processing logic that comprises hardware (e.g. circuitry, dedicated logic, etc.), software (e.g., embodied on a non-transitory computer readable medium), or a combination of both. Although the processes or methods are described above in terms of some sequential operations, it should be appreciated that some of the operations described may be performed in a different order. Moreover, some operations may be performed in parallel rather than sequentially. 
     Embodiments of the present disclosure are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of embodiments of the disclosure as described herein. 
     In the foregoing specification, embodiments of the disclosure have been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the disclosure as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.