Patent Publication Number: US-2022221565-A1

Title: Distance measuring apparatus and method of determining dirt on window

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a bypass continuation application of a currently pending international application No. PCT/JP2020/037118 filed on Sep. 30, 2020 designating the United States of America, the entire disclosure of which is incorporated herein by reference, the international application being based on and claiming the benefit of priority of each of Japanese Patent Application No. 2019-183438 filed on Oct. 4, 2019 and Japanese Patent Application No. 2020-159470 filed on Sep. 24, 2020. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to technologies for determining dirt on a window of a distance measuring apparatus. 
     BACKGROUND 
     A typical distance measuring apparatus emits a light pulse, receives an echo pulse resulting from reflection of the light pulse by a target object, and measures the distance of the target object from the distance measuring apparatus as a function of time of flight defined between the emission of the light pulse and the reception of echo pulse. 
     SUMMARY 
     A distance measuring apparatus according to one aspect of the present disclosure includes a light emitter, a receiver, a calculator, a case having a window, and a determiner for determining that dirt is adhered to the window in response to determination that a dirt determination condition is satisfied. The dirt determination condition includes a first condition that a specified light intensity level at a specified value of a time of flight for at least one pixel of a view region in a histogram is larger than or equal to at least one value of an intensity threshold calculated for the at least one pixel of the view region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a schematic configuration of a distance measuring apparatus; 
         FIG. 2  is a diagram illustrating a schematic configuration of an optical system; 
         FIG. 3  is a diagram illustrating a schematic configuration of a receiver array; 
         FIG. 4  is a diagram illustrating a schematic configuration of a light receiver included in a pixel; 
         FIG. 5  is a block diagram illustrating a schematic configuration of a determination processor; 
         FIG. 6  is a graph illustrating an example of an initial histogram where no dirt is adhered to a window; 
         FIG. 7  is a graph illustrating an example of a histogram generated during execution of a dirt determination routine; 
         FIG. 8  is a diagram illustrating a schematic configuration of a receiver array comprised of pixels used for dirt detection; 
         FIG. 9  is a diagram illustrating that distance measurement and dirt detection are alternately carried out for each of divided pixel blocks; 
         FIG. 10  is a flowchart illustrating a procedure of a dirt determination routine; and 
         FIG. 11  is a view illustrating dirt on an area of a window; the area corresponds to a pixel assembly in a view region. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT 
     Japanese Patent Application Publication No. 2016-176750 discloses a distance measuring apparatus. The distance measuring apparatus emits a light pulse through a window thereof, receives, through the window, an echo pulse resulting from reflection of the light pulse by a target object, and measures the distance of the target object from the distance measuring apparatus as a function of time of flight defined between the emission of the light pulse and the reception of echo pulse. 
     Dirt adhered to the window of the distance measuring apparatus may make it difficult for the distance measuring apparatus to measure the distance of a target object due to a signal-to-noise ratio (S/N ratio) of the echo pulse. Technologies that determine whether there is dirt on the window of the distance measuring apparatus may however be considered sufficiently. 
     From this viewpoint, an exemplary aspect of the present disclosure provides a distance measuring apparatus. The distance measuring apparatus includes a light emitter configured to emit light pulses to a predetermined view region that is comprised of a plurality of pixels. The distance measuring apparatus includes a receiver configured to receive light echoes, each of the light echoes being based on reflection of a corresponding one of the emitted light pulses from a target object. The light echoes respectively have values of time of flight between the light emitter and the receiver. The distance measuring apparatus includes a calculator configured to calculate, in accordance with the received light echoes, a histogram representing an intensity level of each of the light echoes for a corresponding one of the values of the time of flight. The histogram has a predetermined baseline intensity level. The calculator is configured to calculate, in accordance with the values of the time of flight, a distance of the target object from the distance measuring apparatus. 
     The distance measuring apparatus includes a case that houses at least the light emitter and the receiver. The case has a window through which the light pulses and light echoes pass. The distance measuring apparatus includes a storage configured to store a distribution of values of a threshold setting parameter in the view region. The values of the threshold setting parameter are previously determined for the respective pixels of the view region. The distance measuring apparatus includes a determiner. 
     The determiner is configured to add the value of the threshold setting parameter for each of the pixels of the view region to the baseline intensity level to thereby calculate a value of an intensity threshold for a corresponding one of the pixels of the view region. 
     The determiner is configured to determine whether dirt is adhered to the window in accordance with a predetermined dirt determination condition, and determine that the dirt is adhered to the window in response to determination that the predetermined dirt determination condition is satisfied. The predetermined dirt determination condition includes a first condition that a specified light intensity level at a specified value of the time of flight for at least one pixel of the view region in the histogram is larger than or equal to at least one value of the intensity threshold calculated for the at least one pixel of the view region. The specified value of the time of flight corresponds to a length of a light path defined from the light emitter to the window. 
     The distance measuring apparatus of the exemplary aspect is configured to determine that dirt is adhered to the window in response to determination that the dirt determination condition previously determined based on the specified light intensity level at the specified value of the time of flight is satisfied. This configuration therefore enables determination of whether dirt is adhered to the window in accordance with received light-intensity levels of incoming light to the distance measuring apparatus. 
     The following describes an exemplary embodiment of the present disclosure with reference to the accompanying drawings. 
     Referring to  FIG. 1 , a distance measuring apparatus  20  includes a main unit and a case  90  that houses the main unit. The case  90  includes a window  92  constituting a front wall of the case  90 . The main unit of the distance measuring apparatus  20  includes a cleanup unit  400  for performing a cleanup task for cleaning up dirt on the window  92 . The cleanup unit  40  is located adjacent to the window  92 . 
     The cleanup unit  400  of the exemplary embodiment includes first and second washers  410  and  411 , and a heater  420 . Each of the first and second washers  410  and  411  is configured to deliver a jet of water to an outer surface of the window  92  to accordingly remove dirt on the outer surface of the window  92  therefrom. 
     The first washer  410  according to the exemplary embodiment is located to remove dirt adhered to the left side of the outer surface of the window  92 , and the second washer  411  according to the exemplary embodiment is located to remove dirt adhered to the right side of the outer surface of the window  92 . 
     Three or more washers can be provided. That is, a plurality of washers can be provided for cleaning up respective regions, which are different from each other, of the outer surface of the window  92 . Alternatively, a single washer can be provided for cleaning up the whole of the outer surface of the window  92 . 
     Each of the plurality of washers, such as the first and second washers  410  and  411 , can be configured to deliver a jet of air to the outer surface of the window  92  or to deliver both a jet of water and a jet of air to the outer surface of the window  92 . 
     The heater  420  includes a heater wire located along an inner surface of the window  92 . The heater  420  is configured to energize the heater wire to cause the heater wire to generate heat that heats the window  92 . This enables snow and/or ice adhered to the outer surface of the window  92  to melt. 
     The exemplary embodiment can employ, as the cleanup unit  400 , any one of other cleanup units, such as a wiper unit for wiping the outer surface and/or inner surface of the window  92 . 
     The main unit of the distance measuring apparatus  20  includes an optical system  30  and a determination processor  100 . The optical system  30  irradiates an outside object, such as a target object or a target, with light pulses for measurement of the distance to the outside object relative to the apparatus  20 , and receives echo pulses, i.e., light echoes, each of which results from reflection of at least part of the corresponding one of the light pulses by the outside object. The determination processor  100  processes signals obtained by the optical system  30 . 
     The optical system  30  includes a light emitter  40 , a scanner  50 , and a receiver  60 . The light emitter  40  emits laser pulses as the light pulses, and the scanner  50  scans a predetermined view region  80  with each laser pulse. The receiver  60  receives incoming light including echo pulses from the outside object and ambient light. 
     The distance measuring apparatus  20  is, for example, designed as a vehicular lidar apparatus installed in a vehicle, such as an automobile. The lidar apparatus will be referred to simply as a LIDAR, which stands for Light Detection and Ranging. 
     The view region  80  of the distance measuring apparatus  20  has a rectangular shape with a lateral side and a vertical side. The view region  80  is located with the first side being parallel to a horizontal direction X and the vertical side being parallel to a vertical direction Y when the vehicle, in which the distance measuring apparatus  20  is installed, is traveling on a horizontal road surface. 
     Information measured by the distance measuring apparatus  20 , such as the distance of the outside object from the apparatus  20 , is outputted from the apparatus  20  to a distance receiving apparatus  500 , and is used by the distance receiving apparatus  500 . The distance receiving apparatus  500  is a control apparatus that includes an information unit  510  and an electronic control unit (ECU) installed in the vehicle. The information unit  510 , which includes, for example, a display and a speaker, installed in the compartment of the vehicle, informs users of various information items. 
     Referring to  FIG. 2 , the light emitter  40  includes a semiconductor laser device, which is simply referred to as a laser device,  41 , a circuit board  43 , and a collimator lens  45 . 
     The laser device  41  is comprised of a plurality of laser diodes, each of which causes laser oscillation to thereby emit a short-pulsed laser beam as a laser pulse. The laser diodes of the laser device  41  according to the exemplary embodiment are aligned in the vertical direction. This arrangement of the laser diodes of the laser device  41  results in a rectangular laser-irradiation region generated by the short-pulsed laser beams emitted from the laser diodes. The laser device  41  will also be referred to as a light source. The collimator lens  45  is configured to collimate the short-pulsed laser beams, which have passed therethrough, into parallel laser beams. 
     The scanner  50  is configured as a one-dimensional scanner. Specifically, the scanner  50  includes a mirror  54 , a rotor  56 , and a rotary solenoid  58 . 
     The mirror  54  is configured to reflect the parallel laser beams. The rotary solenoid  58 , which includes a rotating portion, is configured to repeat alternate positive and negative rotations of the rotating portion in respective opposing positive and negative directions within a predetermined rotation range in accordance with a control signal received from the determination processor  100 . 
     The rotor  56  is configured to be rotatable on a predetermined axis that is parallel to the vertical direction, and is linked to the rotating portion of the rotary solenoid  58  and to the mirror  54 . The repeated alternate positive and negative rotations of the rotating portion of the rotary solenoid  58  perform repetition of alternative positive and negative rotations of the mirror  54  in the respective positive and negative directions in a direction parallel to the horizontal direction. 
     The parallel laser beams entering the mirror  54  enter the mirror  54 . The repetition of the alternative positive and negative rotations of the mirror  54  cause the parallel laser beams, which have entered the mirror  54 , to pass through the window  92  and thereafter to be scanned over the view region  80 . The view region  80  therefore corresponds to a scanning region of the parallel laser beams. Because the parallel laser beams are scanned over the view region  80 , received light intensities are obtained in respective partitioned pixels of the view region  80 . This results in a distribution of the received light intensity levels in the view region  80  constituting an image. The view region  80  can also be therefore referred to as an image region. 
     The scanner  50  can be eliminated from the optical system  30 . In this modification, the light pulses emitted from the light emitter  40  are irradiated over the view region  80 , and the receiver  60  is configured to receive the light pulses irradiated over the view region  80 . A data assembly representing the distribution of received light intensity levels in the view region  80  will also be refereed to as a frame, i.e., a light intensity frame. In other words, frames, each of which represents the data assembly representing the distribution of received light intensity levels in the view region  80 , are successively obtained. Distance measurement is carried out by the determination processor  100  for each of the frames. 
     The receiver  60  includes a receiver lens  61  and a receiver array  65 . 
     The laser pulses outputted from the distance measuring apparatus  20  are irregularly reflected by the surface of an outside object, such as a person or a vehicle, so that echo pulses resulting from the reflection of at least given number of the laser pulses by the surface of the outside object pass through the window  92  and thereafter enter the receiver lens  61  together with disturbance light as incoming light. 
     The incoming light is focused onto the receiver array  65  through the receiver lens  61 . 
     As illustrated in  FIG. 3 , the receiver array  65  is comprised of a plurality of pixels  66  that are two-dimensionally arranged. Each pixel  66  is, as illustrated in  FIG. 4 , comprised of a plurality of light receivers  68  that constitutes a receiver-element array comprised of (H×V) receiver elements in the horizontal and vertical directions. Reference character H, which is an integer greater than or equal to 1, represents the number of receiver elements in the horizontal direction, and reference character V, which is an integer greater than or equal to 1, represents the number of receiver elements in the vertical direction. Each of the horizontal and vertical receiver-element numbers H and Vis set to 5 in the exemplary embodiment, so that each pixel  66  is comprised of (5×5) receiver elements in the horizontal and vertical directions. 
     Any number of light receivers  68  can constitute each pixel  66 , and therefore a single light receiver  68  can constitute each pixel  66 . The number, i.e., the (H×V), of light receivers  68 , which constitutes each pixel  66 , will also be referred to as a pixel size. The exemplary embodiment employs a single photon avalanche photodiode (SPAD) as each light receiver  68 , but can employ another type of a receiver element, such as a PIN photo diode. Information resulting from the reception of light by each pixel  66  becomes a light intensity of a corresponding one of the partitioned pixels of the view region  80 . As seen by the above descriptions, the pixels  66  constituting the receiver array  65  are hardware components, and therefore used as a different meaning of the partitioned pixels constituting the view region  80 . Because the information resulting from the reception of light by each pixel  66  becomes the light intensity of the corresponding one of the partitioned pixels of the view region  80 , each pixel  66  has a correlative relationship with the corresponding one of the partitioned pixels of the view region  80 . 
     Each of the light receivers  68  is comprised of an avalanche photodiode Da, a quench resistor device Rq, an inverter INV, and an AND circuit SW having a pair of first and second input terminals. Specifically, each light receiver  68  is configured such that the avalanche photodiode Da and the quench resistor device Rq are connected in series between a power source Vcc and a grounded line, and a connection point between the avalanche photodiode Da and the quench resistor device Rq is connected to an input terminal of the inverter INV This configuration of each light receiver  68  enables a predetermined level of voltage at the connection point to be inputted to the inverter INV. This results in an inverted level of voltage being outputted from the inverter INV as a digital signal, i.e., a high-level signal or a low-level signal. The digital signal is inputted to the first input terminal of the AND circuit SW. 
     To the second input terminal of the AND circuit SW, a selection signal Sc is inputted. The selection signal Sc determines an output timing of an output signal Sout, i.e., the digital signal, which reflets the state of the avalanche photodiode Da, from the AND circuit SW. Specifically, changing the level of the selection signal Sout inputted to the second input terminal of the AND circuit SW of each light receiver  68  from a low level to a high level causes the output signal Sout, which reflets the state of the avalanche photodiode Da, to be outputted from the corresponding light receiver  68 . 
     A duration of the selection signal Sc being in the high level corresponds to a time of flight (TOF) Tf for each light receiver  68  defined between the emission of light pulses and the reception of at least one echo pulse causally related to at least one of the emitted light pulses. 
     The emission of one or more light pulses from the light emitter  40  and the reception of at least one echo pulse causally related to at least one of the emitted light pulses by each light receiver  68  will be referred to as light-pulse transceiver sequence. That is, the TOF Tf represents a duration of the light-pulse transceiver sequence. One light-pulse transceiver sequence corresponds to one frame of the data assembly representing the distribution of received light intensity levels in the view region  80 . 
     The selection signal Sc is changed from the low level to the high level each time the TOF Tf of one light-pulse transceiver sequence has elapsed. 
     The output signal Sout outputted from each light receiver  68  is a pulse signal based on received incoming light including (i) at least one echo pulse, which results from the reflection of at least one of the emitted one or more light pulses by an outside object OBJ located in the scanning region returns to the corresponding light receiver  68 , and (ii) disturbance light. The output signals Sout for the respective values of the TOF Tf, which are received by each light receiver  68 , are successively inputted to the determination processor  100 . 
     Referring to  FIG. 5 , the determination processor  100  includes a calculator  200 , a determiner  300 , and a storage  310 . The calculator  200  is configured to calculate the distance of the outside object OBJ from the distance measuring apparatus  20  in accordance with the TOF Tf of each light-pulse transceiver sequence based on echo pulses, each of which results from reflection of a corresponding one of the emitted light pulses by the outside object OBJ. 
     Specifically, the calculator  200  includes a controller  210 , a sum calculator  220 , a histogram generator  230 , a peak detector  240 , and a distance calculator  250 . The controller  210  performs overall control of the determination processor  100 . 
     The sum calculator  220  is configured to receive the output signals Sout from at least some of the light receivers  68  of each pixel  66  constituting the receiver array  65 , and calculates, as a sum result, the number of the received output signals Sout for each pixel  66 . Each light receiver  68  is configured to operate in response to receiving an incoming light pulse. As described above, an SPAD is used as each light receiver  68 , and the plural light receivers  68 , i.e., the plural SPADs, constitute each pixel  66 . An SPAD is capable of responding to a single photon when the single photon is inputted to the SPAD to accordingly detect the single photon. Because the responding of such an SPAD to a single photon occurs probabilistically, each light receiver  68  probabilistically detects an incoming light pulse to thereby output the output signal Sout. 
     The sum calculator  220  is configured to receive, for each light-pulse transceiver sequence, the output signals Sout outputted from at least some of the light receivers  68  of each pixel  66 , and calculate, for each light-pulse sequence, the number of the received output signals Sout as the sum result. Then, the sum calculator  220  is configured to output, for each light-pulse transceiver sequence, the calculated sum result to the histogram generator  230 . 
     The histogram generator  230  is configured to generate, based on the sum results outputted from the sum calculator  220 , a histogram representing an intensity level of the received incoming light for each light-pulse transceiver sequence, i.e., for each TOF  7   f . Then, the histogram generator  230  is configured to output the histogram for each pixel  66  to the peak detector  240 . 
     The histogram generated by the histogram generator  230  for each pixel  66  is a graph of bars; the height of each bar represents a corresponding light intensity level, and the width of each bar represents a class interval corresponding to one of the values of the TOF Tf. The light intensity level for each value of the TOF Tf included in the histogram is the number of the output signals Sout, i.e., the number of light-received light receivers (SPADs) in all the light receivers  68 . 
     The peak detector  240  is configured to analyze the light intensity levels of the histogram for each pixel  66  outputted from the histogram generator  230  to accordingly detect at least one peak, i.e., at least one peak light-intensity level, in all the light intensity levels of the histogram for the corresponding pixel  66 . Then, the peak detector  240  is configured to detect at least one class interval, i.e., at least one value of the TOF Tf, corresponding to the detected at least one peak in the histogram for each pixel  66 . 
     The distance calculator  250  is configured to calculate, based on the at least one value of the TOF Tf of at least one echo pulse, the distance of the outside object OBJ from the distance measuring apparatus  20 . 
     The determiner  300  is configured to perform a dirt determination routine for the window  92  in accordance with information indicative of a light intensity received by the receiver  60  to thereby determine whether there is dirt on the window  92 . The determiner  300  of the exemplary embodiment is configured to use, as the information indicative of the light intensity received by the receiver  60 , the histogram for each pixel  66  generated by the histogram generator  230 . The dirt determination routine will be described later. 
     The determiner  300  is configured to instruct the cleanup unit  400  to perform a dirt removal task of removing dirt on the window  92  in response to determining that there is dirt on the window  92 . 
     Additionally, the distance measuring apparatus  20  includes a temperature sensor  320  connected to the determiner  300 . The temperature sensor  320  is configured to measure an outside-air temperature. The temperature sensor  320  can be omitted. 
     The storage  310  stores a distribution of values of a threshold setting parameter previously determined for the respective pixels in the view region  80 ; the values of the threshold setting parameter are used for respectively setting intensity thresholds used in the dirt determination routine. The values of the threshold setting parameter and the intensity thresholds will be described later. 
     The histogram for each pixel  66  generated by the histogram generator  230  is, as illustrated in each of  FIGS. 6 and 7 , a graph of bars; the height of each bar represents a corresponding light intensity level I, and the width of each bar represents a class interval corresponding to one of the values of the TOF Tf. 
       FIG. 6  represents an example of the histogram generated in an initial state of the window  92  where no dirt is adhered to the window  92 . In contrast,  FIG. 7  represents an example of the histogram generated during execution of the dirt determination routine. In each of  FIGS. 6 and 7 , each reference character, to which 0 is suffixed, is a histogram parameter in the initial state of the window  92 , and each reference character, to which 1 is suffixed, is a histogram parameter during execution of the dirt determination routine. 
     The following mainly describes the meaning of each histogram parameter illustrated in  FIG. 7 . 
     Reference character CL 1  represents a peak, i.e., a peak light-intensity level, in the histogram illustrated in  FIG. 7 ; the peak light-intensity level appears at a previously specified value Tc of the TOF Tf corresponding to the length of a light path defined from the light emitter  40  to the window  92 . A reflected light pulse or echo pulse resulting from reflection of at least one emitted light pulse by the window  92  will be referred to as a clutter light pulse. Reference character CL 0  is used in the histogram illustrated in  FIG. 6  for the same manner as reference character CL 1 . 
     Reference character TP 1  represents a target peak, i.e., a target peak light-intensity level, in the histogram illustrated in  FIG. 7 ; the target peak is based on an echo pulse resulting from reflection of an emitted light pulse by the outside object OBJ. Reference character TP 0  is used in the histogram illustrated in  FIG. 6  for the same manner as reference character TP 1 . 
     Reference character Tt represents a value of the TOF Tf related to each target peak TP 0 , TP 1 , which corresponds to the distance from the light emitter  40  to the outside object OBJ. 
     Reference character Imax represents a predetermined maximum level that the sum of the light intensity levels I of each pixel  66  is able to reach. Specifically, the maximum level Imax for each pixel  66  is defined as the number of light receivers  68  constituting the corresponding pixel  66 . As described above with reference to  FIG. 4 , each pixel  66  is comprised of the (H×V) of light receivers  68 . 
     If the histogram generator  230  generates, for each pixel  66 , the histogram based on the output signals Sout for each of the N times of execution of the light-pulse transceiver sequences (N is an integer greater than or equal to 2), the maximum Imax that the sum of the light intensity levels I of each pixel  66  can reach is equal to the product of (N×H×V). 
     Reference character H 1  is a clutter peak level representing an absolute light-intensity level of the clutter peak CL 1  in the histogram illustrated in  FIG. 7 . The clutter peak level H 1  will also be referred to as a peak level H 1  or a received light-intensity level H 1 . Reference character H 0  is used in the histogram illustrated in  FIG. 7  for the same manner as reference character H 1 . 
     Reference character It 1  is an intensity threshold for the clutter peak CL 1 , which is used for determination of whether a first condition is satisfied. The first condition is that the light intensity level at the specified value Tc of the TOF Tf in the histogram for at least one pixel  66  is larger than or equal to the intensity threshold It 1 . The intensity threshold It 1  is typically set to be lower than the maximum level Imax, but can be set to be equal to the maximum level Imax. How to determine the intensity threshold It 1  during execution of the dirt determination routine will be described later. Reference character It 0  is used in the histogram illustrated in  FIG. 6  for the same manner as reference character It 1 . 
     Reference character BL 1  represents a baseline level of the histogram illustrated in  FIG. 7 ; the baseline level BL 1  of the histogram illustrated in  FIG. 7  is an average level of all the light intensity levels except for the peak light-intensity levels CL 1  and TP 1 . Reference character BL 0  is used in the histogram illustrated in  FIG. 6  for the same manner as reference character BL 1 . 
     Reference character a represents a threshold setting parameter in the histogram illustrated in  FIG. 7  for each pixel in the view region  80 . The threshold setting parameter in the histogram illustrated in  FIG. 7  is for example obtained by subtracting the baseline level BL 1  from the intensity threshold It 1 . In other words, the intensity threshold It 1  in the histogram illustrated in  FIG. 7  for each pixel  66  can be determined based on the sum of a value of the threshold setting parameter and the baseline level BL 1 . The intensity threshold It 1  in the histogram illustrated in  FIG. 7  for each pixel  66  can also be determined in one of the other methods described later. 
     The expression (Imax−BL 1 ) used in the histogram illustrated in  FIG. 7  represents an effective intensity-level width, which is a value obtained by subtracting the baseline level BL 1  from the maximum level Imax. The expression (Imax−BL 0 ) used in the histogram illustrated in  FIG. 6  is substantially identical to the expression (Imax−BL 1 ) used in the histogram illustrated in  FIG. 7 . 
     The target peak TP 0 , which is based on an echo pulse resulting from reflection of an emitted light pulse by the outside object OBJ, appears in the typical histogram illustrated in  FIG. 6 , which is generated in the initial state of the window  92  where no dirt is adhered to the window  92 . This enables the distance of the outside object OBJ from the distance measuring apparatus  20  to be measured as a function of a value Tt of the TOF Tf related to the target peak TP 0  in the histogram illustrated in  FIG. 6 . 
     Additionally, the clutter peak CL 0 , which is based on an echo pulse resulting from reflection of an emitted light pulse by the window  92 , appears in the typical histogram illustrated in  FIG. 6 . As described above, the clutter peak CL 0  represents the peak light-intensity level appearing at the previously specified value Tc of the TOF Tf corresponding to the length of the light path defined from the light emitter  40  to the window  92 . 
     As described above, the clutter peak CL 0  has the peak level H 0 , which will be referred to as an initial clutter peak level H 0 , representing an absolute light-intensity level of the clutter peak CL 0  in the histogram illustrated in  FIG. 6  in the initial state of the window  92  in which no dirt is adhered to the window  92 , i.e., in a factory default state of the apparatus  20 . 
     The specified values Tc of the TOF Tf, at each of which the corresponding clutter peak CL 0  appears, are different from one another for the respective individual locations of the pixels in the view region  80 . This is because the length of the light path from the light emitter  40  to the window  92  through the location of any pixel in the view region  80  is different from that through the location of another pixel in the view region  80 . 
     Similarly, the initial clutter peak levels H 0  of the respective clutter peaks CL 0  are typically different from one another for the respective individual locations of the pixels in the view region  80 . 
     It is unnecessary for typical distance measuring apparatuses to obtain a measured light-intensity level of an echo pulse at the specified value Tc of the TOF Tf at which the clutter peak CL 1  appears, because the typical distance measuring apparatuses has no attention to the location of the window  92  as the measurement target thereof. 
     In other words, the exemplary embodiment has a feature of obtaining a measured light-intensity level of an echo pulse at the specified value Tc of the TOF Tf for determining, using the clutter peak CL 1 , whether there is dirt on the window  92 . 
     The example of the histogram illustrated in  FIG. 7  shows that 
     1. The level of the target peak TP 1  during execution of the dirt determination routine is usually different from the level of the target peak TP 0  in the initial state of the window  92   
     2. The level of the clutter peak CL 1  during execution of the dirt determination routine is usually different from the level of the clutter peak CL 2  in the initial state of the window  92   
     For example, dirt adhered to the window  92  is likely to cause the clutter peak level H 1  to be higher than the initial clutter peak level H 0 . Dirt adhered to the window  92  is likely to cause the level of the target peak TP 1  based on an echo pulse from the outside object OBJ to be lower than the target peak TP 0  based on an echo pulse from the same outside object OBJ. 
     The baseline level BL 1  during execution of the dirt determination routine may fluctuate depending on an external environment in which the distance measuring apparatus  20  is located; the external environment includes whether there is external light radiated from an external light source, such as the sun. For example, strong light radiated from the sun included in the external environment may cause the baseline level BL 1  to become extremely higher, and similarly the clutter peak level H 11  to become higher like the baseline level BL 1 . 
     From this viewpoint, it is preferably to adaptively determine the intensity threshold It 1  during execution of the dirt determination routine in accordance with influence from the external environment. How to adaptively determine the intensity threshold It 1  will be described later. 
     For example, the exemplary embodiment provides the following methods A, B, and C for determining the intensity threshold It 1 . 
     First, the following describes the first method A for determining the intensity threshold It 1 . 
     The first method A determines the intensity threshold It 1  during execution of the dirt determination routine at a constant level. Specifically, the first method A can determine, for all the pixels within the view region  80 , the intensity threshold It 1  within the view region  80  during execution of the dirt determination routine at a common constant level, or can determine, for each of the pixels within the view region  80 , the intensity threshold It 1  within the view region  80  during execution of the dirt determination routine at an individual constant level. The common constant level of the intensity threshold It 1  for all the pixels within the view region  80  can be stored in the storage  310  as a value of a threshold setting parameter α. The individual constant levels of the intensity threshold It 1  for the respective pixels within the view region  80  can be stored in the storage  310  as values of the first threshold setting parameter α. 
     Determining the intensity threshold It 1  at the common constant level for all the pixels within the view region  80  enables the storage  310  to be eliminated. In contrast, determining the intensity threshold It 1  at the individual constant levels for the respective pixels within the view region  80  enables the determined constant levels of the intensity threshold It 1  for the respective pixels within the view region  80  to be higher than the initial clutter peak level H 0 . This makes it possible to perform the dirt determination routine more precisely. 
     Next, the following describes the second method B for determining the intensity threshold It 1 . 
     The second method B adds the baseline level BL 1  of the histogram illustrated in  FIG. 7  to a fixed level as the first threshold setting parameter α to thereby determine the intensity threshold It 1  during execution of the dirt determination routine in accordance with the following expression (1): 
         It 1= BL 1+α  (1)
 
     The first threshold setting parameter α is set to a previously determined level such that the sum of the baseline level BL 1  and the previously determined level of the first threshold setting parameter α is sufficiently larger than the initial clutter peak level H 0 . 
     A common single level can be determined as the first threshold setting parameter a for all the pixels within the view region  80 . Alternatively, individual levels can be determined as the first threshold setting parameter α for the respective pixels within the view region  80 ; the individual levels of the first threshold setting parameter α for the respective pixels within the view region  80  can be stored in the storage  310 . 
     The second method B makes it possible to adaptively determine a value of the intensity threshold It 1  during execution of the dirt determination routine in accordance with influence from the external environment in which the distance measuring apparatus  20  is located; the external environment includes, for example, whether there is external light radiated from an external light source. 
     The first threshold setting parameter α for each pixel  66  can be determined in accordance with the pixel size (H×V) or the N times of execution of the light-pulse transceiver sequences. For example, the first threshold setting parameter a for each pixel  66  can be determined in accordance with the following expressions (1A) to (1C): 
       α=α0×( H×V )  (1A)
 
       α=α0× N   (1B)
 
       α=α0×( H×V )× N   (1C)
 
     where: 
     α0 is a previously determined constant value; and 
     the pixel size (H×V) represents the number of light receivers, i.e., SPADs,  68  constituting each pixel  66 . 
     Additionally, the following describes the third method C for determining the intensity threshold It 1 . 
     The third method C calculates the product of the effective intensity-level width (Imax−BL 0 ) and a second threshold setting parameter β, and adds the calculated product to the baseline level BL 1  to thereby determine the intensity threshold It 1  during execution of the dirt determination routine in accordance with the following expression (2): 
         It 1=( I max− BL 0)×β+ BL 1  (2)
 
     The second threshold setting parameter β is set to a previously determined level such that the calculated result {(Imax−BL 0 )×β+BL 1 } in accordance with the expression (2) is sufficiently larger than the initial clutter peak level H 0 . 
     A common single level can be determined as the second threshold setting parameter β for all the pixels within the view region  80 . Alternatively, individual levels can be determined as the second threshold setting parameter β for the respective pixels within the view region  80 ; the individual levels of the second threshold setting parameter β for the respective pixels within the view region  80  can be stored in the storage  310 . 
     Like the second method B, the third method C makes it possible to adaptively determine a value of the intensity threshold It 1  during execution of the dirt determination routine in accordance with influence from the external environment in which the distance measuring apparatus  20  is located; the external environment includes, for example, whether there is external light radiated from an external light source. 
     Additionally, the third method C maintains a value of the intensity threshold It 1  during execution of the dirt determination routine to be smaller than the maximum level Imax even if the baseline level BL 1  increases due to extremely strong external light. This therefore makes it possible to perform the dirt determination routine more precisely. 
     As described above, if the values of the first threshold setting parameter α or the second threshold setting parameter β for the respective pixels within the view region  80  are individually determined, a distribution of the individually determined values of the first threshold setting parameter α or the second threshold setting parameter β within the view region  80  can be stored in the storage  310 . 
     The values of the first threshold setting parameter a or the second threshold setting parameter β are preferably stored in the storage  310  to correlate with all the respective pixel locations within the view region  80 , but selected values of the first threshold setting parameter α or the second threshold setting parameter β can be stored in the storage  310  to respectively correlate with corresponding selected pixel positions within the view region  80 . This results in a distribution of the selected values of the first threshold setting parameter α or the second threshold setting parameter β in the view region  80  being stored in the storage  310 . 
     If the selected values of the first threshold setting parameter α or the second threshold setting parameter β are stored in the storage  310  to respectively correlate with the corresponding selected pixel positions within the view region  80 , the remaining values of the first threshold setting parameter α or the second threshold setting parameter β for respective unselected pixel positions within the view region  80  can be interpolated based on the selected values of the first threshold setting parameter α or the second threshold setting parameter β. 
     This makes it possible to determine the values of the first threshold setting parameter α or the second threshold setting parameter β for the respective unselected pixel positions within the view region  80  based on interpolation of the selected values of the first threshold setting parameter α or the second threshold setting parameter β stored in the storage  310 , thus calculating a value of the intensity threshold It 1  for each of the pixel positions within the view region  80 . 
     As illustrated in  FIG. 8 , the receiver  65  can include a receiver array  65   a  comprised of a plurality of pixels  67  used for dirt detection in addition to the pixels  66  used for distance measurement. Specifically, the receiver  60  can include the receiver array  65  comprised of the pixels  67  for dirt detection in addition to the pixels  66  used for distance measurement. The pixels  67  used for dirt detection are located adjacent to the pixels  66  for distance measurement. Specifically, the pixels  67  used for dirt detection are preferably arranged in a predetermined region where (i) no clutter light is applied if no dirt is adhered to the window  92  and (ii) clutter light is applied if dirt is adhered to the window  92 . 
     Dirt adhered to the window  92  may increase a clutter peak in each pixel  66  used for distance measurement, and increase clutter light around the pixels  66  used for distance measurement. Locating the pixels  67  for dirt measurement adjacently around the pixels  66  enables determination of whether light is inputted to the pixels  67  to thereby determine whether dirt is adhered to the window  92 . This offers simpler determination of whether dirt is adhered to the window  92 . 
     Additionally, as illustrated in  FIG. 9 , the pixels  66  included in the receiver array  65  are categorized into divided pixel blocks, and at least one of the divided pixel blocks performs distance measurement and at least another of the divided pixel blocks performs dirt detection simultaneously. 
     For example,  FIG. 9  illustrates that, as an example, the pixels  66  are divided into a pixel block A and a pixel block B. One of the pixel blocks A and B alternately performs distance measurement and dirt detection, and the other of the pixel blocks A and B complementarily and alternately performs dirt detection 
     and distance measurement. The pixels  66  can be divided into three or more pixel blocks. In this modification, at least one of the pixel blocks can perform dirt detection, and the at least one remaining pixel block can perform distance measurement. 
     The determiner  300  is configured to cyclically perform the dirt determination routine illustrated in  FIG. 10  under control of the controller  210 . 
     In step S 100  of a current cycle of the dirt determination routine, the determiner  300  determines whether it is time to perform a dirt diagnostic task. For example, the determiner  300  is programmed to determine that it is time to perform the dirt diagnostic task every predetermined period while the distance measuring apparatus  20  is performing the normal distance measurement task. Alternatively, the determiner  300  is programmed to determine a predetermined start time of performing the dirt diagnostic task during each period of self-diagnosis of the distance measuring apparatus  20 . 
     In response to determination that it is time to perform the dirt diagnostic task (YES in step S 100 ), the determiner  300  obtains, from the histogram of the light intensity levels, the peak level H 1  of the clutter peak CL 1  in step S 200 . 
     Next, the determiner  300  determines whether a predetermined dirt determination condition is satisfied in step S 300 . In response to determination that the dirt determination condition is not satisfied (NO in step S 300 ), the determiner  300  terminates the current cycle of the dirt determination routine, and waits for the next cycle of the dirt determination routine. Otherwise, in response to determination that the dirt determination condition is satisfied (YES in step S 300 ), the current cycle of the dirt determination routine proceeds to step S 400 . 
     The determiner  300  is, for example, programmed to use, as the dirt determination condition, any one of the following dirt determination conditions I, II, and III. 
     The dirt determination condition I is satisfied so that it is determined that dirt is adhered to the window  92  in step S 300  if the following first condition C 1  is only satisfied. 
     The first condition C 1  is that the clutter peak level, i.e., the received light-intensity level, H 1  at the previously specified value Tc of the TOF Tf for at least one pixel in the view region  80 , which corresponds to at least one pixel  66 , is larger than or equal to a value of the intensity threshold It 1 ; the previously specified value of the TOF Tf corresponds to the length of the light path defined from the light emitter  40  to the window  92 . 
     Because the dirt determination condition I is a relatively laxer condition, i.e., a relatively more reduced condition as compared with the other determination conditions II and III, the dirt determination condition I provides an advantage of lowering a possibility of missing dirt on the window  92 . The determiner  300  is preferably configured to determine whether the first condition C 1  is satisfied independently of whether the histogram for the at least one pixel in the view region  80  includes the target peak TP 1 . This preferable configuration provides an advantage of detecting dirt on the window  92  even if the histogram for the at least one pixel in the view region  80  includes the target peak TP 1 . 
     The dirt determination condition II is satisfied so that it is deter mined that dirt is adhered to the window  92  in step S 300  if both the above first condition C 1  and the following second condition C 2   a  are satisfied. 
     The second condition C 2   a  is that the number of selected pixels in the view region  80  is greater than or equal to a predetermined number threshold that is defined as an integer greater than or equal to 2; the clutter peak level H 1  at the previously specified value Tc of the TOF Tf for each of the selected pixels in the view region  80  is larger than or equal to a value of the intensity threshold It 1 ; the value of the intensity threshold It 1  corresponding to each of the selected pixels of the view region  80 . 
     The dirt determination condition II enables determination that there is dirt on the window  92  in response to determination that the number of selected pixels in the view region  80  is greater than or equal to the predetermined number threshold; the clutter peak level H 1  at the previously specified value Tc of the TOF Tf for each of the selected pixels in the view region  80  is larger than or equal to a value of the intensity threshold It 1  (see  FIG. 7 ). This therefore provides an advantage of more reliable determination of whether there is dirt on the window  92 . 
     The dirt determination condition III is satisfied so that it is determined that dirt is adhered to the window  92  in step S 300  if both the above first condition C 1  and the following third condition C 2   b  are satisfied. 
     The third condition C 2   b  is that the number of selected pixels in the view region  80  is greater than or equal to the predetermined number threshold and the selected pixels are successively adjacent to each other to constitute a pixel assembly; the clutter peak level H 1  at the previously specified value Tc of the TOF Tf for each of the selected pixels in the view region  80  is larger than or equal to a value of the intensity threshold It 1 . 
     The dirt determination condition III is defined to address an example situation, which is illustrated in  FIG. 11 , where the selected pixels within the view region  80  are successively adjacent to each other to constitute a pixel assembly PA; the clutter peak level H 1  at the previously specified value Tc of the TOF Tf for each of the selected pixels in the view region  80  is larger than or equal to a value of the intensity threshold It 1 ; the value of the intensity threshold It 1  corresponding to each of the selected pixels of the view region  80 . 
     In the exemplary embodiment, pixels are successively adjacent to each other represents that any one of the pixels is located at an upper adjacent position of at least one of the remaining pixels or at a lower adjacent position of at least one of the remaining pixels, or a left-side adjacent position of at least one of the remaining pixels, or a right-side adjacent position of at least one of the remaining pixels. 
     Because dirt is likely to be adhered to a certain size of area on the window  92 , dirt on the window  92  is likely to cause the selected pixels within the view region  80 , which are successively adjacent to each other, to constitute the pixel assembly PA (see  FIG. 11 ); the clutter peak level H 1  at the previously specified value Tc of the TOF Tf for each of the selected pixels in the view region  80  is larger than or equal to a value of the intensity threshold It 1 . For this reason, the dirt determination condition III provides an advantage of still more reliable determination of whether there is dirt on the window  92  as compared with the dirt determination condition II. 
     As an example, the determiner  300  can be programmed to determine whether the dirt determination condition is satisfied in step S 300  for each of successive plural frames. Let us assume that L is defined as an integer greater than or equal to 2. In this assumption, the determiner  300  can be programmed to determine that dirt is adhered to the window  92  in response to determination that the dirt determination condition is satisfied for each of the successive L frames. 
     As another example, let us assume that L is defined as an integer greater than or equal to 3, and M is defined as an integer greater than or equal to 2 and less than or equal to L. In this assumption, the determiner  300  can be programmed to determine that dirt is adhered to the window  92  in response to determination that the dirt determination condition is satisfied for each of the M frames included in the successive L frames. 
     As a further example, let us assume that L is defined as an integer greater than or equal to 2. In this assumption, the determiner  300  can be programmed to determine whether dirt is adhered to the window  92  in accordance with (i) the sum, i.e., the total, or average of the clutter peak levels H 1  for the respective successive L frames and (ii) the sum or average of values of the intensity threshold It 1  for the respective successive L frames. Employing one of the above examples enables stable determination of whether there is dirt on the window  92 , making it possible to prevent erroneous determination that there is dirt on the window  92 . 
     As described above, in response to affirmative determination in step S 300 , the determiner  300  instructs the cleanup unit  400  to perform the dirt removal task. 
     Specifically, as the dirt removal task, at least one of the first and second washers  410  and  411  of the cleanup unit  400  delivers a jet of water or air to the outer surface of the window  92  to accordingly remove dirt on the outer surface of the window  92  therefrom. 
     If the outside-air temperature measured by the temperature sensor  320  points to the possibility of snow and/or ice being adhered to the outer surface of the window  92 , the heater  420  of the cleanup unit  400  energizes the heater wire located along the inner surface of the window  92  to cause the heater wire to generate heat that heats the window  92 . This enables snow and/or ice adhered to the outer surface of the window  92  to melt. 
     The determiner  300  can be configured to select at least one of the above devices  411 ,  412 , and  420 , and instruct the selected at least one of the devices  411 ,  412 , and  420  to perform a corresponding at least one of the above cleanup tasks. 
     For example, the determiner  300  can be configured to select, in accordance with the location of dirt on the outer surface of the window  92 , one of the first and second washers  410  and  420 , which clean up respective different regions on the outer surface of the window  92 , and instruct the selected one of the first and second washers  410  and  420 ; the dirt on the outer surface of the window  92  lies in the region covered by the selected one of the first and second washers  410  and  420 . 
     The first and second washers  410  and  420  can be located adjacent to a selected side in all the sides of the outer surface of the window  92 , and the first washer  410  has a slower rate of delivery of fluid than that of the second washer  420 , and therefore has a lower dirt removal ability than that of the second washer  420 . In this modification, the determiner  300  is configured to 
     (i) Select the first washer  410  and instruct the selected first washer  410  to perform the dirt removal task if dirt on the outer surface of the window  92  lies closer to the selected side of the outer surface of the window  92   
     (ii) Select the second washer  420  and instruct the selected second washer  420  to perform the dirt removal task if dirt on the outer surface of the window  92  lies closer to one of the remaining sides, which is opposite to the selected side, of the outer surface of the window  92   
     The determiner  300  can be configured to select a plurality of cleanup methods described later in accordance with the degree of dirt on the window  92 . Specifically, the determiner  300  can be configured to use, as a dirt indicator for indicating the degree of dirt on the window  92 , any one of the following first to third dirt indicators D 1  to D 3 : 
     The first dirt indicator D 1  represents the absolute difference between the clutter peak level H 1  and a value of the intensity threshold It 1  for the at least one pixel in the view region  80 . 
     The second dirt indicator D 2  represents the number of pixels in the view region  80 , which corresponds to the area of dirt on the window  92 . 
     The third dirt indicator D 3  represents the sum of the absolute differences, each of which is between the clutter peak level H 1  for the corresponding one of the pixels in the view region and the value of the intensity threshold It 1 . 
     The larger each of the first to third dirt indicators D 1 , D 2 , and D 3 , the larger the degree of dirt on the window  92 . 
     That is, the determiner  300  can be configured to calculate any one of the first to third dirt indicators D 1 , D 2 , and D 3 , and send the calculated one of the first to third dirt indicators D 1 , D 2 , and D 3  to the cleanup unit  400 . 
     The cleanup unit  400  can be configured to select one of the plurality of cleanup methods, whose dirt removal abilities are different from one another, in accordance with the degree of dirt on the window  92  specified by one of the first to third dirt indicators D 1 , D 2 , and D 3  sent to the cleanup unit  400 , 
     For example, the degree of dirt on the window  92  is previously divided into, for example, first to third dirt levels, and the cleanup unit  400  can be configured to select, as the plurality of cleanup methods, one of the following first to third cleanup methods E 1  to E 3  in accordance with one of the first to third dirt indicators D 1 , D 2 , and D 3  sent to the cleanup unit  400 . 
     The first cleanup method E 1  is to clean up the window  92  using at least one of the first and second washers  410  and  420  that uses a jet of only air. 
     The second cleanup method E 2  is to clean up the window  92  using at least one of the first and second washers  410  and  420  that uses both a jet of air and a jet of water. 
     The third cleanup method E 3  is to clean up the window  92  using at least one of the first and second washers  410  and  420  and the wiper unit. 
     The first, second, and third cleanup methods E 1 , E 2 , and E 3  have respective first, second, and third different dirt removal abilities that are arranged in an ascending order from the lowest dirt removal ability to the highest dirt removal ability. This enables the first cleanup method E 1  to be employed if the degree of dirt on the window  92  is the first dirt level, the second cleanup method E 2  to be employed if the degree of dirt on the window  92  is the second dirt level, and the third cleanup method E 3  to be employed if the degree of dirt on the window  92  is the third dirt level. 
     The operation in step S 400  can be eliminated. 
     In response to determination that there is dirt on the window  92 , the determiner  300  can be preferably configured to send information indicative of dirt on the window  92  to one or more occupants in the vehicle in which the distance measuring apparatus  20  is installed. For example, the determiner  300  can be configured to instruct the information unit  510 , which includes a display unit or a speaker, to visibly and/or audibly output the information indicative of dirt on the window  92  to one or more occupants in the vehicle. 
     Preferably, the information indicative of dirt on the window  92  to be outputted to one or more occupants in the vehicle can include an area on the outer surface of the window  92  where dirt is located. 
     The calculator  200  can be configured not to output data indicative of the distance of the outside object OBJ through the area on the outer surface of the window  92 , and to output data indicative of the distance of the outside object OBJ through the remaining area of the outer surface of the window  92 ; dirt is not included in the remaining area of the outer surface of the window  92 . 
     Let us assume that the determiner  300  uses one of the dirt determination condition II and the dirt determination condition N. 
     In this assumption, the determiner  300  can be configured to instruct the informing unit  510  to send information indicative of dirt on the window  92  to one or more occupants in the vehicle without instructing the cleanup unit  400  to perform the dirt removal task if 
     (i) The number of selected pixels in the view region  80  is greater than or equal to a predetermined first number threshold; the clutter peak level H 1  at the previously specified value Tc of the TOF Tf for each of the selected pixels in the view region  80  is larger than or equal to a value of the intensity threshold It 1   
     (ii) The number of selected pixels in the view region  80  is larger than or equal to a predetermined second number threshold that is larger than the first number threshold 
     Otherwise, the determiner  300  can be configured to instruct the cleanup unit  400  to perform the dirt removal task if 
     (i) The number of selected pixels in the view region  80  is greater than or equal to the predetermined first number threshold 
     (ii) The number of selected pixels in the view region  80  is smaller than the predetermined second number threshold 
     This configuration enables determination of whether it is difficult for the cleanup unit  400  to remove the dirt on the window  92 . 
     In response to determination that no dirt is adhered to the window  92 , the determiner  300  can be configured to calculate one or more new values of the threshold setting parameter in accordance with the clutter peak level H 1 , and store the calculated one or more new values of the threshold setting parameter in the storage  310  to accordingly update previously stored one or more values of the threshold setting parameter to the new one or more values thereof. 
     In this modification, the determiner  300  can be configured to instruct the cleanup unit  400  to (i) perform the dirt removal task, (ii) measure the clutter peak level H 1  after the dirt removal task, (iii) calculate one or more new values of the threshold setting parameter in accordance with the clutter peak level H 1 , and (iv) store the calculated one or more new values of the threshold setting parameter in the storage  310  to accordingly update previously stored one or more values of the threshold setting parameter to the new one or more values thereof. For example, the determiner  400  can be configured to perform a calculation method of calculating one or more new values of the threshold setting parameter in accordance with the clutter peak level H 1  and the initial clutter peak level H 0 . Using the calculation method enables determination of whether there is dirt on the window  92  in view of age deterioration of the light emitter  40  and/or distortion of the window  92 , making it possible to prevent missing of dirt on the window  92 . 
     If the vehicle, which has traveled normally, is stopped without determination that there is dirt on the window  92 , the determiner  300  can be configured to calculate one or more new values of the threshold setting parameter in accordance with the clutter peak level H 1  which is measured during the normal traveling of the vehicle, and store the calculated one or more new values of the threshold setting parameter in the storage  310  to accordingly update previously stored one or more values of the threshold setting parameter to the new one or more values thereof. This enables determination of whether there is dirt on the window  92  in view of age deterioration of the light emitter  40  and/or distortion of the window  92 , making it possible to prevent missing of dirt on the window  92 . 
     As described above, the distance measuring apparatus  20  of the exemplary embodiment is configured to determine that there is dirt on the window  92  in response to determination that the dirt determination condition previously determined based on the received light intensity H 1  at the specified value Tc of the TOF Tf is satisfied. This configuration therefore enables determination of whether there is dirt on the window  92  in accordance with received light-intensity levels of incoming light to the distance measuring apparatus  20 . 
     The determination processor  100  and methods performed by the determination processor described in the present disclosure can be implemented by a dedicated computer including a memory and a processor programmed to perform one or more functions embodied by one or more computer programs. 
     The determination processor  100  and methods performed by the determination processor described in the present disclosure can also be implemented by a dedicated computer including a processor comprised of one or more dedicated hardware logic circuits. 
     The determination processor  100  and methods performed by the determination processor described in the present disclosure can further be implemented by at least one dedicated computer comprised of a memory, a processor programmed to perform one or more functions embodied by one or more computer programs, and one or more hardware logic circuits. 
     The one or more computer programs can be stored in a non-transitory storage medium as instructions to be carried out by a computer. 
     The present disclosure is not limited to the exemplary embodiment described herein, but can be implemented by various modifications. The specific features described in the present disclosure can be freely combined to each other unless the combined features have a contradiction therebetween.