Abstract
A polarization lidar with dual Geiger-mode avalanche photodiodes (Gm-APDs) is designed to obtain the high-precision depth image of shallow semitransparent media by using a wide laser pulse. The first surface of the semitransparent media is smooth and can nearly preserve the incident polarization, whereas the second surface is rough and can depolarize the incident polarization. A polarization splitting prism is utilized to separate the two echo signals, which will be detected by dual Gm-APDs. It gives the ability to obtain the extremely shallow depth independent of laser pulse width and dead time of Gm-APD. The theory of laser polarization transmission of dual Gm-APD polarization lidar is analyzed. Signal restoration & center-of-mass algorithm method is used to restrain the range walk error and obtain high range precision. The depth image of shallow semitransparent media with a thickness and distance of 10 cm and 6 m, respectively, is obtained in the experiment with a range precision of 1.1 cm. An experiment of real shallow water layer with different depth features is also performed to verify the result.
Highlights
Photon counting lidar has attracted amount of attentions for three-dimensional (3D) imaging for many applications in recent years [1]–[5].Geiger-mode avalanche photodiode (Gm-APD) is widely used in the 3-D imaging lidar system to detect weak signals because of their single-photon sensitivity and picosecond magnitude time precision [6]–[9]
A polarization splitting prism is utilized to separate the two echo signals, which will be detected by dual Geiger-mode avalanche photodiodes (Gm-APDs)
This novel polarization optical system can separate the two echo signals, which will be detected by the dual Gm-APDs, to obtain extremely shallow depths that are independent of the laser pulse width and dead time of Gm-APD
Summary
Photon counting lidar has attracted amount of attentions for three-dimensional (3D) imaging for many applications in recent years [1]–[5].Geiger-mode avalanche photodiode (Gm-APD) is widely used in the 3-D imaging lidar system to detect weak signals because of their single-photon sensitivity and picosecond magnitude time precision [6]–[9]. Achieving a shallow depth measurement is limited by the requirements of the short laser pulse width, rapid detector response time, and high-resolution analog-to-digital conversion, all of which increase the cost and complexity of the system [23].The polarization-preserving nature of the water surface and volume and the depolarizing nature of rough floor topographies, has been demonstrated [24]. This study designs a dual Gm-APD polarization lidar to measure the depth image of shallow semitransparent media by using a wide laser pulse It uses a polarization-splitting prism to isolate the adjacent echoes from the front and rear surfaces of the shallow semitransparent media by exploiting the different polarization attributes of scattered signals from the two surfaces. A high-precision depth image of the shallow semitransparent media can be obtained independent of the laser pulse width
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