Abstract:
A continuous environmental noise level recording and analysis system is provided. The system is capable of sampling, processing and storing Equivalent Sound Level values over a period of about two weeks. The recorded data is downloaded and analyzed to show graphs, and to automatically detect noise events of interest. The measurement system conforms to ANSI/IEC Type I or Type II standards for noise level monitoring

Description:
RELATED APPLICATIONS 
   This patent application claims priority to U.S. Provisional Patent Application Ser. No. 60/335,675, entitled “LOW COMPLEXITY, SELF-POWERED, CONTINUOUS ENVIRONMENTAL NOISE MONITORING SYSTEM FOR COMMUNITIES, AIRPORTS AND REMOTE AREAS”, filed Oct. 25, 2001 and hereby incorporated by reference to the extent as though fully replicated herein. 

   FIELD OF THE INVENTION 
   The present invention relates to the field of remote environmental noise monitoring. 
   BACKGROUND OF THE INVENTION 
   For airports and communities, it is useful to conduct medium-term (one to two week) continuous measurements of sound levels. At the present time, there are no sound level meters or systems that can do this type of monitoring at costs that are affordable for small regional airports and smaller communities. Existing monitors of this type cost in excess of $10,000, and are so complicated that only professional noise consultants can use them. 
   SUMMARY OF THE INVENTION 
   Systems and methods herein provide for continuous measuring and recording of sound levels over the course of a one to two week period, in accordance with national and international noise measurement standards. In one aspect, a system has a remote power supply unit to power the system, a microphone to convert the sound source to an electrical signal, an analog circuit to condition the signal, a digital circuit to digitize, process and store the information, and an interface to transfer the stored data to an analysis unit. The analysis unit may be accessed and/or used for further statistical analysis and automatic noise event detection. 
   One method of monitoring environmental noise levels includes of detecting and converting sound waves into two identical analog electrical signals. The first signal is filtered to leave only A-weighted information. A new signal is then generated representing an envelope of the A-weighted information. The second signal is filtered to leave only C-weighted information; and another signal is generated representing an envelope of the C-weighted information. Logarithmic amplifiers compress the envelope signals into a range that is suitable for digitization. An analog-to-digital converter is used to convert the logarithmic signals into digital data. A processor calculates 1-second Leq values and exponential averages of the Leq values from the digital data. The processor may also calculate maximum, minimum, 1/10th percentile, 1/50th percentile, and 1/90th percentile statistical information from the Leq values. Leq values and statistical information may be stored in non-volatile memory. The method may further include steps of transferring the stored data from the non-volatile memory to a noise analysis unit. The noise analysis unit may display the transferred data in graphical form. The noise analysis unit may also process the transferred data to produce statistical information and/or detect noise events. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram illustrating one system for capturing and analyzing environmental noise. 
       FIG. 2  illustrates one monitoring unit [ 12   FIG. 1 ] in use within an environment. 
       FIG. 3  is a block diagram illustrating further details of one monitoring unit. 
       FIG. 4  shows a flow chart illustrating one process for controlling the monitoring unit of  FIG. 1 . 
       FIG. 5  shows a flow chart illustrating one sub-process for handling user input. 
       FIG. 6  shows a flow chart illustrating one sub-process for processing sampled data. 
       FIG. 7  shows a flow chart illustrating one sub-process for controlling data transfer. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a block diagram showing one environmental noise monitoring and analysis system  10 . System  10  includes a portable environmental noise monitoring unit  12  and an environmental noise analysis unit  14 , connected together by a communication path  16 . Monitoring unit  12  is ideally a weatherproof, self-contained, shock resistant, easy to operate unit and may be deployed in an environment to continuously record equivalent sound level (“Leq”) data for a period of about two weeks. Monitoring unit  12  may be connected to analysis unit  14  using communication path  16  for transfer of recorded Leq data. Analysis unit  14  includes a processor (e.g., within a workstation) running noise analysis software capable of displaying the data graphically, performing statistical analysis on the data, and recognizing individual sound sources and their characteristics in the data. 
     FIG. 2  illustrates a portable environmental noise monitoring unit  20  in environment  22 . Sound waves  24  represent background sounds in environment  22 . Aircraft  26  flying through environment  22  generates aircraft sounds  28 , and vehicle  30  traveling through environment  22  generates vehicle sounds  32 . 
   Analog section  34  of monitoring unit  20  converts sound waves  24 ,  28 , and  32  into electrical signals  36 . Digital section  38  digitizes, processes and records electrical signals  36 . Analog section  34  and digital section  38  are powered by power supply section  40  via power connectors  42  and  44 , respectively. Monitoring unit  20  is described in more detail in  FIG. 3 . 
     FIG. 3  is a block diagram illustrating one monitoring unit  50 . Monitoring unit  50  has three main sections: analog section  52 , processing and control section  54 , and power supply section  56 . 
   Analog section  52  includes microphone  58  that converts sound waves (e.g., sound  28  of  FIG. 2 ) into analog electrical signal  60 . Pre-amplifier  62  conditions and splits signal  60  into two identical signals  64  and  66 . ANSI/IEC defines standards for both Type I and Type II microphone selection, including two frequency bands of interest, A and C. A-frequency weighted circuit  68  filters signal  64  to leave only the A-frequency information of signal  64  and produces DC output signal  70  representative of an envelope of the filtered signal. C-frequency weighted circuit  72  filters signal  66  to leave only the C-frequency information of signal  66  and produces DC output signal  74  representative of an envelope of the filtered signal. 
   Logarithmic amplifier  76  compresses signal  70  into signal  78  that has a range suitable for digitization. Logarithmic amplifier  80  compresses signal  74  into signal  82  that has a range suitable for digitization. Signals  78  and  82  are fed into analog-to-digital converter  84  of processing and control section  54 . 
   Processing and control section  54  contains embedded processor  86 . Processor  86  uses analog-to-digital converter  84  to digitize signals  78  and  82 . Processor  86  calculates 1-second Leq values with either fast or slow user selectable weighting for each signal. Processor  86  performs statistical calculations on the 1-second Leq values to produce exponential time response sound levels, and, based on these levels, determines hourly Lmax, Lmin, L10, L50 and L90 sound levels (maximum, minimum, 10th, 50th and 90th percentile sound levels respectively). 
   Processor  86  may record the 1-second Leq data and hourly statistical data for each frequency band (A, C) in non-volatile data memory  88 . 
   Processing and control section  54  may contain user interface  90  that includes a keypad  91  and a display  93 . Processor  86  reads user input from keypad  91  and may display user selected information screens on display  93 . Display  93  may be used to show current measurements and statistical information. 
   Processing and control section  54  may also contain data transfer interface  92  that transfers stored Leq and statistical information to an analysis unit (e.g.,  14  of  FIG. 1 ). Interface  92  may be used to control monitoring unit  50  remotely. Communication path  16 ,  FIG. 1 , may be a physical bus, or may be a wireless link. 
   Power supply section  56  contains power control circuit  94 , which stabilizes power received from rechargeable battery  96  and supplies power to analog section  52  and processing and control section  54  via power connectors  98  and  100 , respectively. Solar panel  102  extends the life of battery  96  by recharging it when sufficient light is available. 
     FIG. 4  shows a flow chart illustrating process  110  for controlling the portable noise monitoring unit  20  of  FIG. 2 . Process  110  illustrates an outer control loop of software used with processor  86 ,  FIG. 3 .  FIGS. 5 ,  6  and  7  illustrate sub-processes  140 ,  170  and  190 , respectively, referenced in process  110 . 
   Process  110  begins at step  112 , at which point the unit is powered on and initialized. Steps  114  to  130  are performed continuously until the user elects to shut the system off. Process  110  continues with step  114 . 
   Step  114  is a decision. If there is input from the user, process  110  continues with step  116 ; otherwise process  110  continues with step  118 . Step  116  is the execution of sub-process  140 , shown in  FIG. 5 . Sub-process  140  returns to step  118  upon completion. 
   Step  118  is a decision. If the user has elected to record, process  110  continues with step  120 ; otherwise process  110  continues with step  122 . Step  120  is the execution of sub-process  170 , shown in  FIG. 6 . Sub-process  170  returns to step  122  upon completion. 
   Step  122  is a decision. If the user has selected a display that shows measurement values, process  110  continues with step  124 ; otherwise process  110  continues with step  126 . Step  124  updates the display with the latest measurement values. Process  110  continues with step  126 . 
   Step  126  is a decision. If the user has elected to transfer data to an analysis unit, process  110  continues with step  128 ; otherwise process  110  continues with step  130 . Step  128  is the execution of sub-process  190 , shown in  FIG. 7 . Sub-process  190  returns to step  130  upon completion. 
   Step  130  is a decision. If the user has elected to exit, process  110  continues with step  132 ; otherwise process  110  continues with step  114 . 
   Step  132  performs shutdown operations. Process  110  terminates at step  134 . 
     FIG. 5  shows a flow chart illustrating sub-process  140 . Sub-process  140  handles user input. Sub-process  140  starts at step  142 , and continues with step  144 . 
   Step  144  is a decision. If the user has elected to start recording equivalent noise level (“Leq”) data, sub-process  140  continues with step  146 ; otherwise sub-process  140  continues with step  148 . Step  146  initializes the recording mechanism, and sets a flag to cause sub-process  170  execution from process  110 . Sub-process  140  continues with step  152 . 
   Step  148  is a decision. If the user has elected to stop recording Leq data, sub-process  140  continues with step  150 ; otherwise sub-process  140  continues with step  152 . Step  150  terminates recording. Sub-process  140  continues with step  152 . 
   Step  152  is a decision. If the user has selected a different display, sub-process  140  continues with step  154 ; otherwise sub-process  140  continues with step  156 . Step  154  changes the display contents, and selects the appropriate screen update mechanism. Sub-process  140  continues with step  156 . 
   Step  156  is a decision. If the user has elected to start downloading recorded data, sub-process  140  continues with step  158 ; otherwise sub-process  140  continues with step  160 . Step  158  initializes the download sequence and sets a transfer flag to cause sub-process  190  execution in process  110 . Sub-process  140  continues with step  160 . 
   Step  160  is a decision. If the user has elected to shut the unit down, sub-process  140  continues with step  162 ; otherwise sub-process  140  terminates at step  164 . Step  162  sets the Exit flag and sub-process  140  terminates at step  164 . 
     FIG. 6  shows a flow chart illustrating sub-process  170 , which processes the sampled sound level signal information. Sub-process  170  starts at step  172 , and continues with step  174 . 
   Step  174  converts analog signals  78  and  82  of  FIG. 3  to digitized data using analog-to-digital converter  84  of  FIG. 3 . Sub-process  170  continues with step  176 . 
   Step  176  calculates the 1-second Leq values from the digitized data. Sub-process  170  continues with step  178 . 
   Step  178  calculates the hourly exponential time response values from the 1-second Leq values. Sub-process  170  continues with step  180 . 
   Step  180  stores the calculated values in non-volatile data memory  88  of  FIG. 2 . Sub-process  170  terminates at step  182 . 
     FIG. 7  shows a flow chart illustrating sub-process  190 , which transfers stored data to data transfer interface  92  of  FIG. 3 . Sub-process  190  starts at step  192 , and continues with step  194 . 
   Step  194  reads the next data item from the non-volatile data memory  88  of  FIG. 2 . Sub-process  190  continues with step  196 . 
   Step  196  transfers the data to data transfer interface  92  of  FIG. 3 . Sub-process  190  continues with step  198 . 
   Step  198  is a decision. If the last data item from memory was transferred, sub-process  190  continues with step  200 ; otherwise sub-process  190  terminates at step  202 . 
   Step  200  stops the transfer process. Sub-process  190  terminates at step  202 . 
   Those skilled in the art will appreciate that variations from the specified embodiments disclosed above are contemplated herein. The description should not be restricted to the above embodiments, but should be measured by the following claims.