Characterization of background reflectivity for MEDUSA

The DARPA MEDUSA program goal is to detect, locate, and identify electro-optical threats in the vicinity of a moving platform. Laser sensing will be employed to find these threats by looking for anomalous reflections from threat sensors. However, the reflectivity variability (clutter) in both natural and manmade backgrounds will inherently limit target detection levels. In parallel with advanced component development by several aerospace contractors, a study of this clutter limitation was initiated in the long-wave (LW) and midwave (MW) infrared spectral regions to properly drive system design parameters. The analysis of clutter and associated limits on detection has been a major component of LANL efforts in laser remote sensing for non-proliferation. LANL is now analyzing existing data and conducting additional selected measurements in both the LWIR (9 and 10.6 pm) and MWIR (4.6 pm) in support of the DARPA program to increase our understanding of these clutter limitations and, thereby aid in the design and development of the MEDUSA system. The status of the LANL effort will be discussed. A variety of different natural and manmade target types have been investigated. Target scenes range from relatively low clutter sites typical of a southwestern desert to higher clutter downtown urban sites. Images are created by conducting raster scans across a scene interest. These images are then analyzed using data clustering techniques (e g K-means) to identify regions within the scene that contain similar reflectivity profiles. Data will be presented illustrating the reflectivity variability among different samples of the same target type, Le. within the same cluster, and among different data clusters. In general, it is found that the variability of reflectivities among similar targets is well represented by a log-normal distribution. Furthermore, manmade target tend to have higher reflectivities and more variability than natural targets. The implications of this observation for MEDUSA systems designed to locate and identify threat sensors will be discussed. The implications for chemical sensing applications will also be addressed

Title: Target Characterization in 3D Using Infrared Lidar Target Characterization in 3D Using Infrared Lidar

ABSTRACT We report examples of the use of a scanning tunable CO 2 laser lidar system in the 9-11 µm region to construct images of vegetation and rocks at ranges of up to 5 km from the instrument. Range information is combined with horizontal and vertical distances to yield an image with three spatial dimensions simultaneous with the classification of target type. Object classification is made possible by the distinct spectral signatures of both natural and man-made objects. Several multivariate statistical methods are used to illustrate the degree of discrimination possible among the natural variability of objects in both spectral shape and amplitude

Atmospheric effects on CO{sub 2} differential absorption lidar sensitivity

The ambient atmosphere between the laser transmitter and the target can affect CO{sub 2} differential absorption lidar (DIAL) measurement sensitivity through a number of different processes. In this work, we will address two of the sources of atmospheric interference with CO{sub 2} DIAL measurements: effects due to beam propagation through atmospheric turbulence and extinction due to absorption by atmospheric gases. Measurements of atmospheric extinction under different atmospheric conditions are presented and compared to a standard atmospheric transmission model (FASCODE). We have also investigated the effects of atmospheric turbulence on system performance. Measurements of the effective beam size after propagation are compared to model predictions using simultaneous measurements of atmospheric turbulence as input to the model. These results are also discussed in the context of the overall effect of beam propagation through atmospheric turbulence on the sensitivity of DIAL measurements

Huygens-Fresnel wave-optics simulation of atmospheric optical turbulence and reflective speckle in CO2 differential absorption LIDAR (DIAL)

The measurement sensitivity of C02 differential absorption lidar (DIAL) can be affected by a number of different processes. We have previously developed a Huygens-Fresnel wave optics propagation code to simulate the effects of two of these processes: effects caused by beam propagation through atmospheric optical turbulence and effects caused by reflective speckle. Atmospheric optical turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has been shown to have a major impact on the sensitivity of C02 DIAL. However, in real DIAL systems it is a combination of these phenomena, the interaction of atmospheric optical turbulence and reflective speckle, that influences the results. In this work, we briefly review a description of our model including the limitations along with previous simulations of individual effects. The performance of our modified code with respect to experimental measurements affected by atmospheric optical turbulence and reflective speckle is examined. The results of computer simulations are directly compared with lidar measurements and show good agreement. In addition, advanced studies have been performed to demonstrate the utility of our model in assessing the effects for different lidar geometries on RMS noise and correlation "size" in the receiver plane.U.S. Department of EnergyW-7405-ENG-3