Field Calibration of the Optical Properties of Pedestrian Targets in Autonomous Emergency Braking Tests Using a Three-Dimensional Multi-Faceted Standard Body

Abstract

Highlights: What are the main findings? Novel calibration apparatus: This manuscript introduces a three-dimensional multi-faceted standard body used as a value transfer medium to calibrate the optical properties (expressed as BRDF values) of pedestrian test targets. This approach is innovative because it addresses the challenges of traditional BRDF measurement methods, especially in outdoor, real-world testing scenarios. Integration of imaging and algorithmic methods: The proposed method combines a camera-based analytical algorithm with imaging techniques to map and transfer calibration values from a standard white plate to complex pedestrian surfaces. This integration is shown to improve the reliability of sensor calibration on non-ideal and dynamically changing targets. What are the implications of the main findings? Enhanced calibration reliability: The development of an SI-traceable, field-applicable calibration method fills an important gap in ensuring that pedestrian target test objects used in AEB evaluations maintain consistent and reliable optical properties. This directly influences the accuracy of sensor-based safety systems in autonomous vehicles. Quantitative insights into target degradation: This article documents how repeated usage (i.e., crash–scatter–reassembly cycles) affects the BRDF properties of targets—showing measurable changes such as decreased uniformity and altered reflectivity. These insights have strong implications for interpreting AEB test data and for establishing maintenance or replacement schedules for test targets. To address the growing need for field calibration of the optical properties of pedestrian targets used in autonomous emergency braking (AEB) tests, a novel three-dimensional multi-faceted standard body (TDMFSB) was developed. A camera-based analytical algorithm was proposed to evaluate the bidirectional reflectance distribution function (BRDF) characteristics of pedestrian targets. Additionally, a field calibration method applied in AEB testing scenarios (CPFAO and CPLA protocols) on one new and one aged typical pedestrian target of the same type revealed a 21% decrease in the BRDF uniformity of the aged target compared to the new one, confirming optical degradation due to repeated “crash–scatter–reassembly” cycles. The surface wear of the aged target on the side facing the vehicle produced a smoother surface, increasing its BRDF magnitude by 25% compared to the new target and making it easily detectable by the vehicle’s perception system. This led to “reverse scoring,” a safety risk in performance evaluation, necessitating timely calibration of AEB pedestrian targets to ensure reliable test results. The findings provide valuable insights into the development of regulatory techniques, evaluation standards, and technical specifications for test targets and offer a practical path toward full-life-cycle traceability and quality control.