Lidar system model for use with path obscurants and experimental validation

Abstract

When lidar pulses travel through a short path that includes a relatively high concentration of aerosols, scattering phenomena can alter the power and temporal properties of the pulses significantly, causing undesirable effects in the received pulse. In many applications the design of the lidar transmitter and receiver must consider adverse environmental aerosol conditions to ensure the desired performance. We present an analytical model of lidar system operation when the optical path includes aerosols for use in support of instrument design, simulations, and system evaluation. The model considers an optical path terminated with a solid object, although it can also be applied, with minor modifications, to cases where the expected backscatter occurs from nonsolid objects. The optical path aerosols are characterized by their attenuation and backscatter coefficients derived by the Mie theory from the concentration and particle size distribution of the aerosol. Other inputs include the lidar system parameters and instrument response function, and the model output is the time-resolved received pulse. The model is demonstrated and experimentally validated with military fog oil smoke for short ranges (several meters). The results are obtained with a lidar system operating at a wavelength of 0.905 microm within and outside the aerosol. The model goodness of fit is evaluated using the statistical coefficient of determination whose value ranged from 0.88 to 0.99 in this study.

Influence of fog on the signal to interference plus noise ratio of the imaging laser radar using a 16-element APD array

“…However, it is not straight forward to quantify the distribution of fog droplet sizes due to the influence of different physical processes, thus the introduction of a number of drop size distribution (DSD) based models. One of the classical and widely used model is the lognormal distribution, which is given by [12,19,[21][22][23][24]…”

“…1. The angular distribution of the intensity of scattered light by article suspended in the channel is best characterized by the phase function, which is given by [22]:…”

The irradiating field of view of imaging laser radar under fog conditions in a controlled laboratory environment

“…For fog particles with spherical shapes and r≈λ Mie theory can be adopted as in [18,[20][21][22]. The extinction coefficient ext m is obtained by integrating the droplet extinction cross sections C ext weighted by DSD, which is given as follows:…”

“…In an outdoor environment with fog, BRPs of a standard Lambertian target, which are larger than the arrived laser spot, are given by [4,21,28]: where P 0 is the initial laser power, e h and r h are the transmittance of the laser beam at the source and receiver (Rx), respectively. O l ( ) is the overlap function, which represents the proportion of the overlap area between the spot zone and the aiming field of the laser spot at the Rx [29].…”

“…In [20] laser radar expressions based on the beam spreading function for a system with a multiple-scattering beam induced spreading and pulse stretching, which represented a significant extension beyond historical laser radar models with no pulse stretching. In [21], an analytical model for the laser radar system in the presence of aerosols was presented, which accurately predicted the shape of actual target pulses and backscattered return pulses (BRPs) due to fog or smoke.…”