Airborne high-precision imaging system and method for single-photon unmanned aerial vehicles

An airborne high-precision imaging system for single-photon unmanned aerial vehicles, comprising a main control unit, a jitter acquisition unit, a signal acquisition and transmission unit, a two-dimensional scanning unit, and a motion compensation unit;

• where the main control unit is electrically connected with the jitter acquisition unit, the signal acquisition and transmission unit, the two-dimensional scanning unit, and the motion compensation unit, respectively, configured to provide a picosecond global timing synchronization signal;
• the jitter acquisition unit is connected with the motion compensation unit in a manner of communication, configured to transmit IMU data of the inertial navigation unit to the motion compensation unit in real time;
• the signal acquisition and transmission unit is connected with the two-dimensional scanning unit in a manner of an optical path, configured to emit a laser pulse to a target area through the two-dimensional scanning unit;
• the signal acquisition and transmission unit is connected with the motion compensation unit in a manner of data, configured to transmit a timestamp of a photon event to the motion compensation unit;
• the motion compensation unit is configured to align the IMU data of the inertial navigation unit with a timestamp of a photon event, calculate an instantaneous attitude of each photon event, and perform a point-by-point correction on a spatial position of a photon event to eliminate a point cloud motion distortion;
• the signal acquisition and transmission unit comprises a pulse laser, a single-photon detector SPAD, an acousto-optic modulator AOM1, an acousto-optic modulator AOM2 and a time-to-digital converter TDC;
• the acousto-optic modulator AOM1 is set in a transmitting optical path, and the acousto-optic modulator AOM2 is set in a receiving optical path;
• the time-to-digital converter TDC is electrically connected to the single-photon detector SPAD and the main control unit, respectively, to record timestamps of laser transmission and echo photon reception;
• the main control unit sets the acousto-optic modulator AOM1 to the transmitting optical path, and an opening and closing timing of the acousto-optic modulator AOM2 is precisely controlled at a nanosecond level, so that a width of the receiving window only covers an extremely narrow period near an expected signal arrival time;
• according to an approximate distance between the unmanned aerial vehicle and a target, a delay and a width of a receiving window are adjusted in real time to ensure that real signal photons fall when the detector is operating and most of the noise photons are rejected due to asynchrony, so that a transmitting window and the receiving window are strictly separated in time to suppress internal leakage light and near-field scattered light;
• and
• the jitter acquisition unit comprises an inertial navigation unit IMU, and its sampling frequency is higher than a laser pulse frequency through a compensation algorithm;
• data of a pitch angle, a roll angle and a yaw angle of the unmanned aerial vehicle are collected in real time with high time resolution;
• wherein the compensation algorithm is as follows:
• first, the timestamp of IMU data is mapped to a time reference of FPGA to ensure that IMU time is aligned with the FPGA time;
• then, in each time window, a angular velocity and an acceleration of IMU are integrated to calculate increments of attitude, velocity and position;
• when each photon event or FPGA timestamp arrives, the calculated incremental value is used to update a state, and a frequency of the IMU is increased to nanoseconds.