Evaluation of protection measures against laser dazzling for imaging sensors

Abstract

Abstract. We present our work regarding the evaluation of protection measures against laser dazzling for imaging devices. Different approaches for the evaluation of dazzled sensor images are investigated to estimate the loss of information due to the dazzle spot: (1) counting the number of overexposed pixels, (2) based on triangle orientation discrimination, and (3) using the structural similarity index. The evaluation approaches are applied on experimental data obtained with two different sensors hardened against laser dazzling. The hardening concept of the first sensor is based on the combination of a spatial light modulator and wavelength multiplexing. This protection concept allows spatially and spectrally resolved suppression of laser radiation within the sensor's field-of-view. The hardening concept of the second sensor utilizes the principle of "complementary bands." The optical setup resembles a common three-chip camera, with the difference that dedicated filters with steep edges replace the regular spectral band filters. Although this concept does not really represent a "protection measure," it allows the sensor to provide information even in laser dazzling situations. The data for the performance evaluation were acquired both in a laboratory setup using test charts comprising triangles of different size and orientation as well as in field trials. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Preventing image information loss of imaging sensors in case of laser dazzle

“…[21][22][23][24][25][26] For this sensor system, we were able to realize a mean attenuation of laser light up to 45.5 dB in the visible spectral range. 21 However, by using quantitative methods to assess the sensor's protection performance, [27][28][29][30] we found out that this protection concept was good mainly at lower dazzle levels. At larger dazzle levels, i.e., when nearly the complete sensor's field of view was dazzled, the protection performance strongly degraded due to contrast loss and color distortions.…”

“…In the last years, we focused our research also on the quantitative assessment of protection measures for imaging sensors against laser dazzle. [27][28][29][30] Three different methods were studied:…”

“…to quantify laser dazzle is to calculate the SSIM index. [27][28][29][30] The SSIM index is a metric for measuring the quality of an image by comparing it to a distortionfree reference image. 35 This metric is based on the assumption that the human visual system is designed to recognize structures in images and estimates to what extent two images exhibit the same structures.…”

“…In earlier publications, we already presented various measurements to assess quantitatively the three-band sensor. 27,28 We recognized that the OPC method is not Ritt, Schwarz, and Eberle: Preventing image information loss of imaging sensors in case of laser dazzle applicable to the three-band sensor since the image fusion algorithm filters out the overexposed pixels. Therefore, in the fusion image, no overexposed pixels occur, which apparently results in a perfect protection performance.…”

Use of complementary wavelength bands for laser dazzle protection

“…In recent work, we examined the quantitative assessment of laser protection measures for imaging sensors. 34,35 The main objective of this work is to assess how protection measures influence the information content of sensor images. This may be seen from a very general point of view like sensor performance with/without laser protection as well as for the cases of laser dazzle.…”