Windowed region-of-interest non-uniformity correction and range walk error correction of a 3D flash LiDAR camera

Abstract

We present experimental methods and results for photo-response non-uniformity correction (PRNUC) in range for a 3D flash LiDAR camera from non-optimal static-scene calibration data. Range walk is also corrected. This method breaks up the camera's focal plane array (FPA) into 16 × 16 windowed regions of interest that are incrementally captured and stitched together in post-processing across the entire FPA. The illumination was not uniform, thus requiring additional methods described by our paper to create an acceptable correction. We present the results from a full non-uniformity correction and range walk error correction processed for a set of independently collected validation frames; these validation frames used identical experimental conditions and the same target as was collected for the corrections. We will show that this experimental approach improves range accuracy and range precision of the corrected validation frames despite the sub-optimal conditions of the data used to compute the corrections; the single shot range precision is corrected to 33 cm, as compared to a modeled precision of 15.65 cm, while the accuracy is corrected to 252 cm. This method has implications for simplification of characterization of non-uniformity and range walk error, and its subsequent correction, in 3D flash LiDAR cameras. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Toward snapshot correction of 3D flash LiDAR imagers

“…An estimate of the single shot range precision is provided using the model provided by Reinhardt et al, 4 which is derived from the timing jitter and timing resolution of the detector. The timing resolution, σ 2 res , is provided by E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 0 1 ; 1 1 6 ; 4 3 7…”

“…where σ 2 t;ref is the reference jitter, n ref is the reference signal, and n sig is the input signal on the detector. 4 The range precision, σ r , is therefore provided as a Pythagorean summation of these two previously mentioned noise terms: E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 0 3 ; 1 1 6 ; 2 2 4…”

“…1,2 As with all imaging arrays, 3D flash LiDAR imagers display image non-uniformities, such as dark-frame non-uniformity, otherwise known as fixed pattern noise, or photo-response non-uniformity, otherwise known as gain errors. 3,4 Unlike with 2D imagers, 3D flash LiDAR imagers cannot use an integrating sphere to produce the uniform illumination required for PRNUC as an integrating sphere will randomize pulse time of flight information. 4 Additionally, range walk error acts to correlate the 2D intensity return of the imager with the 3D range return, thus complicating the correction process.…”

“…3,4 Unlike with 2D imagers, 3D flash LiDAR imagers cannot use an integrating sphere to produce the uniform illumination required for PRNUC as an integrating sphere will randomize pulse time of flight information. 4 Additionally, range walk error acts to correlate the 2D intensity return of the imager with the 3D range return, thus complicating the correction process. 1,[5][6][7] In this sense, while a 2D imager can be corrected through calibration methods by obtaining a set of dark frames and a set of photo-response frames, 3 the same is generally assumed to not be true of a 3D flash LiDAR imager.…”

“…This team has previously published work focused on the reduction of SRCN for a time-offlight ranging imager by reducing the footprint of the active FPA through windowed region of interest framing, with the goal of reducing time and effort for capturing data to correct nonuniformity and range walk error in 3D flash LiDAR imagers. 4,14,15 This effort focuses on using the full frame of the return, with the goal of illuminating as many detectors simultaneously as possible. This method is a significant improvement over previous work by this team and any previously published methods.…”