Mark A. Kovacs

HI-CLASS on AEOS: a large-aperture laser radar for space surveillance/situational awareness investigations

The Air Force Research Laboratory/Directed Energy Directorate (AFRL/DE) via the ALVA (Applications of Lidars for Vehicles with Analysis) program installed in late 2000 a wideband, 12 J 15 Hz CO2 laser radar (ladar) on the 3.67 meter aperture AEOS (Advanced Electro-Optics System) telescope. This system is part of the Maui Space Surveillance System (MSSS), on the summit of Haleakala, Maui, HI. This ladar adopts the technology successfully demonstrated by the first generation HI-CLASS (High Performance CO2) Ladar Surveillance Sensor) operating on the nearby 0.6 meter aperture Laser Beam Director (LBD) and developed under the Field Ladar Demonstration program, jointly sponsored by AFRL/DE and the Armys Space and Missile Defense Command. The moderate power (approximately 180 watts) HI-CLASS/AEOS system generates multiple, coherent waveforms for precision satellite tracking and characterization of space objects for 1 m2 targets at ranges out to 10,000 km. This system also will be used to track space objects smaller than30 cm at ranges to 2,000 km. A third application of this system is to provide data for developing satellite identification, characterization, health and status techniques. This paper will discuss the operating characteristics and innovative features of the new system. The paper will also review recent results in support of AF needs, demonstrations, experiments, as well as planned activities that directly support applications in the DoD, scientific, and commercial arenas.

Use of laser radar for small space object experiments

This report briefly reviews the development, capabilities, and current status of pulsed high-power coherent CO2 laser radar systems at the Maui Space Surveillance System (MSSS), HI, for acquisition, tracking, and sizing of orbiting objects. There are two HICLASS systems, one integrated to the 0.6 m Laser Beam Director and one just integrated Summer 2000 to the 3.7 m Advanced E-O System (AEOS). This new system takes full advantage of the large AEOS aperture to substantially improve the ladar range and sensitivity. These improvements make the AEOS HICLASS system potentially suitable for tracking and characterization experiments of small < 30 cm objects in low-earth-orbits.

Real-time image generation with a pulsed coherent laser radar

A kilowatt class, pulsed CO2 laser radar has been developed at Textron under a joint US Army-Air Force program. It is currently undergoing field trials; and successful coherent imaging and tracking experiments have been conducted over the past two years at the Air Force Maui Space surveillance Site. This paper describes the receiver- processor architecture of the laser radar system, the algorithms and waveforms, and the output products which are high resolution range-Doppler and range-amplitude image. Attention will be paid to the hardware and software methods used to achieve real-time, wideband operations.

Prediction and performance measures of atmospheric disturbances on an airborne imaging platform

A series of airborne imaging experiments have been conducted on the island of Maui. The imaging platform was a Twin Otter aircraft, which circled ground target sites. The typical platform altitude was 3000 meters, with a slant range to the target of 9000 meters. This experiment was performed during the day using solar illuminated target buildings, and at night with spotlights used to simulate point sources. Imaging system performance predictions were calculated using standard atmospheric turbulence models, and aircraft boundary layer models. Several different measurement approaches were then used to estimate the actual system performance, and make comparisons with the calculations.

Acquisition, tracking, and sizing of small space objects

High-powered, pulsed CO2 coherent ladar systems and their potential application to space debris tracking and characterization.

Field ladar demonstration (FLD) system, algorithms, and Phase I/Phase II test results

The High Performance CO2 Ladar Surveillance Sensor system (HI-CLASS) is a state-of-the-art coherent ladar system which will provide precision tracking and high resolution imaging at the Air Force Maui Optical Station (AMOS). System development is occurring in 3 phases representing increasing hardware/software complexity and system capability. The recently-completed Phase I HI-CLASS system employs a compact, pulsed, coherent CO2 oscillator, a heterodyne receiver, and signal recorder coupled to the AMOS 0.6 m Laser Beam Director to demonstrate target (satellite) acquisition and tracking, illumination, return signal detection, signal recording, and off-line processing for range and range rate extraction and range- amplitude imaging. A description of the Phase I satellite ranging and ground-based remote sensing tests verifying the FLD system operating concept will be presented. The cooperative target range and range rate measurements, as well as imaging precursor demonstration, will be discussed. The talk will include a discussion of the 21 km demonstration of remote sensing using natural terrain returns. Results generated on phase I data with the phase II algorithm will also be described.

Theoretical and Monte Carlo analyses of the range-Doppler imaging capabilities of mode-locked CO2 ladars

Mode-locked CO2 lasers have been developed which can produce long coherent pulse trains consisting of many narrow subpulses. This laser waveform may be used to numerically generate range-Doppler images (inverse synthetic aperture radar images) of a target wherein the Doppler spread of a spinning target is used to create a synthetic cross-range target dimension. The narrow micro-pulse temporal width provides good range resolution, and the long coherent pulse train provides good frequency resolution of the (cross-range) target Doppler spread. In this paper we examine the algorithms and imaging capabilities of this waveform as implemented for the FLD and Hi-CLASS laser radar (ladar) systems which are now being installed in the AMOS facility on Mt. Haleakala, Maui and in an aircraft testbed.

Comparison of performance capabilities of spread spectrum coherent and direct detection CO2 DIAL systems

This paper compares the performance of a conventional direct detection CO2 Differential Absorption Lidar (DIAL) system with the coherent spread spectrum approach developed and patented by Textron. The analysis shows that the coherent approach is far superior in terms of maximum attainable standoff range at a specified transmitter average power and substantially reduced system power and associated size and weight at a predetermined range. The requirements on local oscillator stability are fairly relaxed and the spread spectrum/coherent DIAL concept is fairly easy to implement. Some comparative validation data are provided.

Doppler spectral scanning differential absorption lidar

Preliminary experiments toward the implementation of Doppler spectral scanning differential absorption lidar (DSS DIAL) are described. In separate tests, CO2 laser pulses were reflected from either a ground-based retroreflector (36-km round-trip distance) or a retroreflector on the GEOS-3 satellite (approximately 2000-km round-trip distance). The returns were split into a reference channel and an absorptive gas-cell channel. The light was coherently detected with heterodyne receivers and analyzed. Results from the ground-based system produced data that matched expected values in one case but its repeatability remains to be determined. We are currently investigating the satellite-based system to assess the DSS DIAL technique.

Differential absorption lidar (DIAL) via atmospheric aerosol (cloud) backscattering: recent results of coherent CO2 lidar measurements conducted at the Maui Space Surveillance Site

Textron Systems, under the US Army Space and Missile Defense Commands Field Ladar Tactical Transition Demonstration program, has been evaluating coherently detected, atmospheric aerosol backscattering as a method to extend the utility of the DIAL technique. This paper present recently obtained long range, multi-wavelength DIAL measurements utilizing cloud formations and a laboratory positioned absorption test cell. Good agreement between cloud and continuous wave laboratory measurements of the absorption spectra of ammonia have been obtained.