Alpine Meadow / Interstate 75 Noise Levels

This noise monitoring system tracks sound levels from Interstate 75 near Alpine Meadow using:

• Raspberry Pi Zero 2 W (512MB RAM)
• PCB Artists I2C Decibel Sound Level Meter
  ARM Cortex M4 processor with pre-calibrated dB SPL output
  Designed according to IEC 61672 Class 2 guidelines, but it is not formally certified
• PiSugar 3 UPS Battery Module
  1200mAh battery with built-in RTC (Real-Time Clock)
  Provides uninterruptible power during outages and maintains accurate time
• MQTT over WebSocket
  For real-time data streaming with local database persistence

Data is measured continuously and stored locally in a SQLite database, then published to a cloud MQTT broker for real-time display. The system operates 24/7 with full offline capability - during internet or power outages, all data is preserved locally and automatically syncs when connectivity returns.

All measurements are in A-weighted decibels (dBA), the standard for environmental noise monitoring.

Standards & Methodology: Hourly noise levels are calculated as L_Aeq,1h using energy averaging (logarithmic mean per IEC 61672), which correctly weights loud events. The daytime threshold of 67 dBA references the FHWA Noise Abatement Criteria for residential land use (23 CFR 772, Activity Category B). The nighttime threshold of 55 dBA references the EPA identified outdoor residential level (EPA 550/9-74-004), applied conservatively as an hourly threshold during nighttime hours (10 PM – 7 AM). L₁₀/L₉₀ statistics use the nearest-rank percentile method.

Weather Flagging: Readings taken during precipitation or high wind (≥15 mph) are automatically flagged. These conditions can affect microphone accuracy, so flagged readings are recorded but may be excluded from statistical calculations.