If at all possible hire a noise engineer.
Search the National Council of Acoustical Consultants.
This industry is booked out months in advance. Start early!
Capture baseline decibel levels with noise meters.
REED Instruments R8050 Dual Range Sound Level Meter
amazon
Use an app on your iPhone
NIOSH Sound Level Meter for iPhone
Purchase a calibrated external microphone specific for recording noise levels.
MicW i437L Omnidirectional Lightning Microphone
from B&H Photo