A Test Bed for Short Pulse OA Detection of Optical Directors in Amphibious Operations

This paper describes the design and deployment of a transportable test bed for a short pulse optical augmentation (OA) system to detect optical directors of potential threats in amphibious operations. The use of a short pulse duration allows discrimination of retroreflections from natural sources such as rock formations and vegetation. The test bed has been fielded in experiments on ground ranges and aboard ships in the Chesapeake Bay and Cardigan Bay. The data collected in these trials show that an optical cross section of 300 m/sr can easily be detected at a range of 9 kilometers, proving the feasibility of using such a system aboard vessels in amphibious operations. The test bed was built in a 15’ long trailer that incorporated an optical bench with the probe laser, steering gimbals, detector assembly, visible tracking camera and data acquisition subsystem. Data collection and storage as well as beam control and tracking were performed by a computer system located in the front of the trailer. With a water chiller for the laser attached to the tongue, the trailer became a self contained unit which could then be towed for ground testing, shipped inside a standard ISO container, and lifted onto the decks of ships for testing. In this way the test bed was loaded onto an LCM-8 landing craft and was also deployed aboard the R/V Colonel Templer in the UK to participate in sea trials off the coast of Wales. The probe beam used was a 532 nm Nd:Yag with pulse energy of up to 500 mJ and a repetition rate of 10 pulses per second. The detector was a photomultiplier tube which was connected to a data acquisition system sampling at 1 gigasamples per second. A range gate was set up to collect 1500 samples around a selectable range of interest. A global positioning system (GPS) receiver was used to calculate ranges to known targets. The system incorporated visible image-based beam steering and stabilization. A visible CCD camera coaligned with the probe beam and detector axis was used to calculate ship motion and compensate by moving the gimbals. Motion compensation algorithms were incorporated into the control program which also calculated the range; controlled the data acquisition system; collected, displayed, and archived the data; and provided user interface. Form SF298 Citation Data Report Date ("DD MON YYYY") 00001999 Report Type N/A Dates Covered (from... to) ("DD MON YYYY") Title and Subtitle A Test Bed for Short Pulse OA Detection of Optical Directors in Amphibious Operations Contract or Grant Number Program Element Number Authors Project Number