IACS and MACS: High-Resolution Atmospheric Lidars for Model Verification

Atmospheric effects such as optical turbulence, water vapor, and atmospheric transmission have serious implications on the effectiveness and overall quality of optical communications and long-distance imaging, among other applications. As a result, the ability to measure atmospheric properties to validate meteorological models is of critical importance to estimate and forecast the performance envelope of these systems. More so, the ability to measure these quantities in real-time provides enormous benefits in determining the utility of these systems.

The Integrated Atmospheric Characterization System (IACS) is a deployable LIDAR system that provides single-ended, simultaneous, range-resolved, real-time characterization of aerosols, water vapor, and optical turbulence at more than 10 km on arbitrary slant ranges. The Maritime Atmospheric Characterization System, based upon the IACS aerosol LIDAR, is a maritime ruggedized LIDAR to characterize aerosols. These systems are expected to provide real-time atmospheric measurements to validate or lead to improvement in the underlying physical models for simulators such as the Advanced Navy Aerosol Model (ANAM); the Naval Surface-Layer Optical Turbulence (NSLOT) and its successor, the Navy Atmospheric Vertical Surface-Layer Model (NAVSLaM); and the Coupled Ocean/Atmospheric Mesoscale Prediction System (COAMPS) model. Compared to micro-pulse lidars (MPL), IACS and MACS produce substantially higher temporal and spatial information. This fidelity enables the lidars to detect transient events which a MPL would not be able to measure.

This paper presents an overview of 4 LIDARs: 1.) the IACS Atmospheric Transmission Measurement (ATM) LIDAR, 2.) the IACS Water Vapor Profiler (WVP), 3.) the IACS Optical Turbulence Profiler (OTP), and 4.) the MACS ATM LIDAR. Both ATM systems are elastic backscatter LIDARs operating at 1.064 μm which use the Klett algorithm or Langley calibration method to calculate optical transmission/extinction. The WVP LIDAR uses standard Raman techniques to measure Nitrogen and water vapor content. The OTP LIDAR is a novel system developed at GTRI that uses sets of artificial guide stars focused at varying distances and imaged with a gated Shack-Hartmann wavefront sensor. A set of inversion algorithms converts profiles of differential image motion (DIM) variance to profiles of Cn2. To the author’s knowledge, this is the only operational single-end turbulence LIDAR in the world.