Device and method for real-time measuring the spectrum of airborne hyperspectral imaging LiDAR

A device for real-time measuring the spectrum of airborne hyperspectral imaging LiDAR, comprising a laser, a reference module, an emitting module, and a receiving module, wherein the reference module comprises a first reflecting mirror (2) and a second reflecting mirror (6) with a given transmittance;

• the first reflecting mirror (2) and the second reflecting mirror (6) are arranged with a focusing mirror (3) and an optical fiber (4) in sequence therebetween;
• the laser emits a laser light to the first reflecting mirror (2) with a given transmittance, and the beam of the laser light transmitted through the first reflecting mirror (2) after passing the focusing mirror (3) is used as a reference beam after passing the optical fiber (4);
• the emitting module comprises a laser and a rotating mirror (14);
• the rotating mirror (14) is used to reflect the laser light reflected by the first reflecting mirror (2) to the target;
• and the receiving module further comprises a receiving telescope (5), a second reflecting mirror (6), a diaphragm (7), a collimating paraboloidal mirror (8), a grating (9), a telecentric lens (10), a beam coupler (11) and a detecting and processing unit arranged in sequence;
• the detecting and processing unit comprises a detector that receives the light output by the beam coupler (11) and a processor (15) that receives and processes the signal from the detector;
• the reference beam is emitted to the back side of the second reflecting mirror (6) and transmitted to converge with the detecting beam emitted by the receiving telescope (5) to the front side of the second reflecting mirror (6);
• and the optical fiber (4) is a multi-mode optical fiber (4) with a core diameter of 200 μm;
• wherein the device for real-time measuring the spectrum of airborne hyperspectral imaging LiDAR is used according to a method comprising the following steps:
• S1. according to the return signal power PR (λ, z) in the hyperspectral LiDAR equation and the power spectrum of the reference light (13) PRef (λ) detected by the detector, where
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• λ is the central wavelength λNCW of each channel obtained during spectrum calibration, PR (λ, z) is the optical power of the return signal received by the LiDAR channel with the central wavelength of λ, in the unit of W;
• βG (λ) is the reflectivity of the ground object;
• DR is the effective clear aperture of the receiving telescope (5), in the unit of m;
• z is the distance between the LiDAR and the measured ground surface, in the unit of m, and z can be measured in real time through the ranging channel;
• Tatm (λ, O, z) is the transmittance of the atmosphere between the LiDAR and the measured ground surface at wavelength of λ;
• c(λ)=ρ0η(λ)Δλε, c (λ) is the power intensity of the light pulse energy emitted by the laser (1) into the detector in the radar system, and ρ0 is the average spectral power density output by the laser (1), in the unit of W/nm;
• η (λ) is a normalized function of the power density spectrum of the average spectral power density of the laser (1);
• Δλ is the corresponding spectral bandwidth in one channel, in the unit of nm;
• ε(λ) is the optical efficiency of the LiDAR system;
• wherein a corner reflector is adopted to introduce part of the laser light scanning the ground object target (12) through a rotating mirror (14) to the receiving module, and to obtain a power spectrum PCor (λ) of the laser light received by the detector;
• S2. according to the data from each formula in step S1, the power intensity c (λ) is obtained of the light pulse energy emitted by the laser (1) into the detector in the radar system.