Roger M. Smith

Radiometric one-second camera (ROSCAM) airborne evaluation

The rapidly developing market for passive millimeter-wave imaging cameras with a frame time of one second or less includes several commercial as well as military applications. A mechanical scanning antenna system has demonstrated the ability to meet a one second frame time for a 1000 pixel scene, using only one receiving channel. That camera has been updated to provide an airborne imaging capability, in both a raster scanning mode, and a cross- track in-light mode. The results of a helicopter test program will be described.

ROSCAM: a 95-GHz radiometric one-second camera

The ability to obtain millimeter wave images under a variety of environmental conditions, such as rain, snow, fog, smoke, dust, etc., has numerous DoD as well as commercial applications. The demonstrated ability to look through doors, walls and clothing has recently extended potential millimeter wave applications to contraband detection and surveillance within buildings. Though the phenomenology supports the generation of high quality millimeter wave images, present-day frame time capabilities limit the use of millimeter wave cameras. Several solutions to frame time reduction are currently being investigated within government and industry. Two popular approaches include: (1) Electronic scanning focal plane arrays (FPA); (2) Mechanical raster scanning of a single antenna beam. One significant difference between the two approaches noted above is the number of receiving channels required. This is important because camera cost is driven by the number of receiver channels used in a camera, as well as the added complexities associated with inter-channel gain stability. There are a number of applications that do not require a motion picture capability. Images obtained sequentially at a nominal rate of one per second would satisfy the needs of a wide range of applications. It is evident, however, that the motion picture quality of a starring FPA may ultimately reduce the market for one-second cameras. In the interim, the one-second camera fills an important need. The goal of the Radiometric One Second Camera (ROSCAM) investigation is to demonstrate a practical millimeter-wave imaging (MMWI) camera, with a frame time of approximately one second. The approach combines a high-speed mechanical raster scanning antenna system with a single-channel radiometric receiving system. For baseline comparison, it is assumed that the scene is comprised of 1,000 pixels, each sampled for one millisecond, to generate a single frame in one second. The ROSCAM is based on combining a state-of-the-art radiometric receiver with a high-speed mechanical antenna scanning mechanism. One purpose of the initial measurement program described here, was to determine the ability of an existing high-speed raster scanning antenna to meet ROSCAM antenna requirements, specifically, a Field of View (FOV) consisting of 1,000 pixels scanned in a frame time of one second. A by- product of this investigation was the determination of the number of radiometer channels needed to generate a motion picture with a similar FOV. This paper includes: (1) Description of the ROSCAM Breadboard; (2) ROSCAM Performance Capabilities; (3) Measurement Results; (4) Conclusions.

All-weather capabilities of passive millimeter-wave sensors

A Passive MMW sensor capability of 0.5 Krms, at W-Band, achieved with an integration time of less than 0.1 ms is now considered state-of-the-art. Though some engineering details remain concerning Passive Millimeter Wave (PMMW) configurations best suited for imaging applications, motion picture frame rates for most applications appear to be a near future reality. The efficacy of applying these new capabilities to all-weather sensing may in many cases be determined by the characteristics of the all-weather scenario. The Munitions Directorate of the Air Force Research Laboratory is currently investigating phenomenology associated with the PMMW scenario that will influence the achievable capabilities of PMMW sensors, when used under adverse weather conditions. Model predictions and verification measurements are described along with preliminary results.

Flight test of a MMW imaging radarometer

An imaging radarometer mode integrates a radar with a radiometer in a manner which allows simultaneous use of a common imaging antenna. The goal of this research effort was the design of a MMW camera capable of obtaining simultaneous passive and active airborne images, in the radarometer mode. An ETU was assembled to verify the design of an Engineering Model and to determine if any significant design changes were needed. ETU flight test data is presented and discussed in terms of sensor system capabilities and the Engineering Model design approach.

Passive millimeter-wave imaging device for naval special warfare

The U.S. Navy Coastal Systems Station (CSS) is currently executing a program to develop a small, lightweight, low power passive millimeter wave imager. The end user will be Naval Special Operations Forces (SOF). The program began by conducting a feasibility assessment of the potential Passive Millimeter Wave (PMMW) technology that would meet the Naval Special Warfare (NSW) mission requirements. A performance analysis was conducted to compare the capabilities of the various PMMW imager technologies. Finally, a technology development road map is under development, which will include all recommendations for hardware development and image processing. Other DoD and industrial programs are being monitored for leveraging potential to insure the imager program will use the latest technology available. As a result of a technology survey, CSS decided to leverage their development funds with Eglin Air Force Base to develop an antenna-coupled microbolometer. This paper will discuss the program plans, and the potential applications of PMMW technology to Naval Special Warfare.

Millimeter-wave analysis of passive signatures (MAPS)

The STAG program was hiitiated at Eglin Air Force Base in 1990 under the sponsorship of the Armament Directorate of Wright Laboratory. The purpose of the STAG program is to investigate and support passive millimeter wave activities associated with the development of mart tactical gutonomous guidance systems. Development of the associated sensor technology focuses attention on a data collection/phenomenology effort to provide a firm foundation for sensor design and algorithm development. The center piece of the data collection/phenomenology effort is the mobile test bed referred to as MAPS, an acronym taken from Millimeter Wave Analysis of Passive Signatures. As shown in Figure 1, the MAPS will provide the data base of passive millimeter wave information concerning terrain, atmospheric and target signatures needed to support the critical development technologies associated with the STAG program. MAPS low-bed trailer includes an equipment enclosure which is 8 ft. wide and 25 ft. long. Photographs ofMAPS are shown in Figures 2a through 2d.

Passive millimeter-wave imaging technology and phenomenology: a common denominator approach

Passive imaging technology has been recognized and reduced to practice for sensing targets in the battlefield environment for several decades. Most imaging is done at optical and infrared wavelengths which require favorable weather conditions. This paper describes what is on the horizon for a new imaging technology passive millimeter wave (PMMW) imaging that can operate in all weather conditions. It will introduce the reader to the unique world of PMMW imaging by describing the technical approach underway at the Wright Laboratory Armament Directorate, Advanced Guidance Division, Eglin AFB, Florida. A PMMW analytical model has been developed and a data collection/phenomenology testbed is being built to validate this model. This will be a mobile test facility that will provide the needed ground truth for an Airborne PMMW Captive Flight Test program in the FY97/98 timeframe. The thrust of this analytical model is the treatment of theoretical equations that allow low altitude imaging in and out of the millimeter wave spectral window frequencies. PMMW sensors at 35, 60 (non- window), and 95 GHz are being fabricated and will be collocated on the same platform to validate this model. This testbed will be the hardware used to begin a radiometric imaging program that will serve not only military needs for advanced munition sensor development, but commercial and academic endeavors as well.