What Is an Inertial Profiler?
An inertial profiler is a vehicle-mounted system that measures the longitudinal profile of a pavement with laser sensors and accelerometers.
How it works
It has four parts. An accelerometer measures the movement of the vehicle frame. Noncontact sensors, commonly lasers, measure the distance between the frame and the road. A distance-measuring instrument records how far the vehicle has travelled. A computer combines the three signals into a longitudinal profile of the surface. ASTM E950 is the test method for this principle (title only, see references).
A high-speed profiler is mounted on a data-collection vehicle and collects data at posted speed. A lightweight profiler uses the same method on a smaller vehicle and suits new concrete that cannot yet carry normal traffic. The method does not work well below about 15 to 20 mph, in stop-and-go traffic, or in falling rain or strong wind.
Roughness indices
Most agencies turn the profile into a smoothness number. The most common is the International Roughness Index (IRI). A quarter-car model is run over the measured profile at 50 mph (80.5 km/h). The suspension movement is summed and divided by the length. The result is a slope in inches per mile or meters per kilometer.
Use on airfields
Two FAA documents use inertial profilers on airfield pavement.
- New pavement. AC 150/5370-10H, Item P-401, lets the engineer require a roughness test of a new or reconstructed runway or taxiway. The test uses a profilograph to ASTM E1274 or a Class I inertial profiler to ASTM E950. The average profile index must be below 15 inches per mile per 1/10 mile. The text applies only to projects longer than 500 feet and not to aprons.
- In-service runways. AC 150/5380-9 sets the method for runway roughness. Airfield roughness is defined by the effect on the aircraft, not by ride quality. The AC gives the Boeing Bump Index for this and says that a high-pass filtered inertial profiler is not recommended for it.
AC 150/5380-7B says that roughness measurement helps when pilots often complain. AC 150/5320-6G says to evaluate profiles with programs such as ProVAL or ProFAA.
Limits
An inertial profiler measures profile only. It does not rate cracking, weathering or other surface distress. Those are the subject of a Pavement Condition Index survey (ASTM D5340). TarmacView does not run inertial profilers.
Frequently Asked Questions
- What is the difference between an inertial profiler and a profilograph?
- A profilograph records the surface as a profilogram and gives a Profile Index. An inertial profiler is a vehicle with a laser, an accelerometer and a distance sensor. FAA AC 150/5370-10H accepts either one for the roughness test of a new runway or taxiway pavement. It names a profilograph to ASTM E1274 or a Class I inertial profiler to ASTM E950.
- Does an inertial profiler measure the Boeing Bump Index on a runway?
- Yes, but only with the right data processing. FAA AC 150/5380-9 does not recommend an inertial profiler that applies a high-pass filter to the accelerometer signal for the Boeing Bump Index. The filter removes the long wavelengths that this index needs. The AC also says that threshold-to-threshold runway profiles are difficult to measure with a vehicle that accelerates or brakes.
- Does TarmacView measure pavement roughness?
- No. A drone survey rates the distress that a camera can see. The TarmacView pavement page lists roughness measurement as work that needs equipment on the surface.
References
- fhwa-inertial-profiler
- Pavements - Inertial Profiler - Pavement (IP) FHWA, Infotechnology
- faa-ac-150-5380-9
- AC 150/5380-9, Guidelines and Procedures for Measuring Airfield Pavement Roughness FAA
- faa-ac-150-5370-10h
- AC 150/5370-10H, Standard Specifications for Construction of Airports FAA
- faa-ac-150-5320-6g
- AC 150/5320-6G, Airport Pavement Design and Evaluation FAA
- faa-ac-150-5380-7b
- AC 150/5380-7B, Airport Pavement Management Program (PMP) FAA
This is a reference entry. TarmacView provides drone inspection services and doesn't sell the equipment or materials described in this glossary.
