Index


Proceedings of
TECOM Test Technology Symposium '97

"The Army After Next ­ How Will We Test?"

March 18-20, 1997



Radiant Outlaw Technology
for Non-Cooperative Identification

Alex Lovett
SEMCOR, Inc.
Suite. 400 145020 Greenview Drive
Laurel, MD 20724

Chyau Shen
NAWC AD 4.5.5.6
EO Sensors Branch
Bldg 2187, Suite 3190
48110 Shaw Road Unit 5
Patuxent River, MD 20607-1906

19 March 1997

1.0 Introduction

(U) The Low Probability of Intercept Sensors was a U.S. Navy Advanced Technology Demonstration that ran from FY93-FY96. The program consisted of two parts: Radiant Mist and Radiant Outlaw. Radiant Mist was an advanced electro-optic (EO) sensor for shipboard application, while Radiant Outlaw, its sister program, consisted of the same sensors packaged for airborne applications. Both contained passive visible, infrared (IR), and (active) laser radar sensors. These sensors were used to detect, track, and identify targets at unresolved ranges. These sensor systems are now being evaluated for utility in cooperation with the Forward Area Air Defense (FAAD) Testing at FT Bliss in August 1997. The Office of the Secretary of Defense has also sponsored an Advanced Concept Technology Demonstartion (ACTD) titled Precision Targeting and Identification (PTI) which will explore advanced packaging options for mobile ground forces.

(U) The Radiant Mist sensor system was a multi-mode passive/active sensor for detecting, tracking, and identifying targets from a shipboard platform. This EO system, when cued by shipboard radars or Infrared Search and Track (IRSTs), passively acquired and tracked targets for handover to a laser radar system for precision tracking and identification. A 3-D state vector (bearing, range, range rate ) on targets was generated and provided to the ship's combat system for weapons fire control and battle damage assessment. The high resolution thermal imaging sensors which direct the laser system also performed surveillance functions. The multi-functional system was integrated onto a McDonnell Douglas Mast Mounted Sight (NMMS) gimbal to perform a functional demonstration in an operational environment during the summer of 1996.

(U) A new effort is being undertaken by the U.S. Army/U.S. Navy to re-configure the shipboard sensor system. The system will then be tested to determine its performance as a land based system. The sensors will be integrated into the Forward Area Air Defense System (FAADS) to demonstrate an enhanced combat identification capability to permit Beyond Visual Identification Range (BVIDR) engagements.

2.0 Non-Cooperative Identification

(U) Laser radar (ladar) benefits from its relatively small beam width as compared to a conventional radar. Precise angular information is available because of the small beam width. The inherently small wave length of the ladar produces very high Doppler velocity sensitivity to target motions. This sensitivity is so precise that target Doppler skin vibrations or displacements can be measured which are on the order of micrometers. A one to two second illumination of a target allows for low probability of intercept while collecting enough information to classify a target with out being counter-detected. Signal processing techniques for target identification using target signatures (both passive and active) are very similar to current Anti-Submarine Warfare (ASW) techniques that are well understood. The laser radar return signal is passed through the signal processing algorithms to extract a target-unique vibration signature. The vibration signature is compared with a library of signatures on file to identify the target platform. This technique provides aspect invariant target classification.

(U) A variety of NCID techniques have been evaluated in search of one method that can provide reliable aspect-invariant identification at stand-off ranges.

(U) The Radiant Outlaw/Mist program developed hardware to perform target signature collections for all of the previous techniques mentioned. The Radiant Mist system is capable of collection simultaneous IR, Visible and 3-D ladar imagery as well as range profiles and vibration sensing. The program fielded expert systems to perform autonomous classification using image based, range profiles, or vibration sensing. For unresolved targets it was determined that vibration sensing produced the best aspect invariant results. Vibration sensing is the only classification technique which is not tied to making a spatial measurement or comparison of key features, which drives sensor resolution requirements. The limiting performance factor for vibration sensing is the energy received on target not the targets size or geometry.

(U) The ladar system utilizes coherent optical heterodyne detection. The process is accomplished by mixing the ladar target return signal with the local oscillator (LO) signal. Just as an inbound or outbound target produces a gross Doppler shift on the return signal, a target vibration produces a micro-Doppler vibrational spectrum on the return signal.

(U) The optically mixed signals produce a frequency difference, or beat frequency signal, on the detector. A low pass filter responds primarily to the optical difference frequency to produce an electrical signal called the first Intermediate Frequency (IF). This IF signal is further mixed down to remove the gross Doppler shift of the target and a second IF is generated. This second IF signal is demodulated and the deviation of the signal frequency from the second IF's center frequency identifies the micro-Doppler vibration spectrum.

(U) The U.S. Naval Air Warfare Center, Patuxent River (NAWCPAX) has developed and fielded an automatic target recognition (ATR) system for fixed-wing aircraft and helicopters. NAWCPAX in conjunction with the Night Vision Lab, FT Belvior, has initiated the process to develop a database and software upgrade to the classification software to provide the capability to perform automatic classification of ground vehicles.

2.1 Sensors

2.1.1 Passive Sensors

(U) Two uses of the passive sensors are target aimpoint selection and target recognition. Aimpoint selection supports three dimensional tracking as well as collection of surface vibration signatures on localized areas of a target by pointing the laser beam. In addition, IR imagery may augment target recognition performance by providing auxiliary information that can be incorporated into the sensor fusion process thereby increasing overall NCID performance.

(U) The IR sensors used to collect imagery on targets by the Radiant Mist system are the MWIR provided by Rockwell and the LWIR sensor from McDonnell Douglas. The Rockwell camera (see Figure 2-1) is the primary IR data collection system since it is co-boresighted with the Rockwell ladar system. IR target data must coincide with ladar data to support the evaluation of aimpoint selection and NCID. The MWIR camera operates in the 3 µm - 5 µm region of the spectrum with a six inch aperture and two fields of views.

Figure 2-1: The Rockwell Six Inch Aperture 320x240
with Dither Scan MWIR Camera

(U) The long wave infrared (LWIR) sensor has been retained by the Radiant Mist sensor from the Naval Mast Mounted Sight (NMMS) sensor. The LWIR camera serves as a comparison between LWIR and MWIR imagery. Also included in the passive sensor package is a visible sensor provided by McDonnell Douglas. This sensor operates from about 0.6 µm to about 0.9 µm and incorporates two fields of view subtending two and eight degrees, respectively. Visible data is for reference only to help describe the difference between IR and visible imagery in terms of resolution and environmental effects. See Table 2-1 below for specifications of all the passive sensors in the optical director turret head.

Sensor Parameter
MWIR Camera
Visible Camera
LWIR Camera
Spectral Bandpass
3µm - 5µm
.65mm - .95mm
8µm - 12µm
FOV
2 o NFOV / 8 o WFOV
2o NFOV, 8 o WFOV
2.8o
Aperture
6" (15.24 cm)
4" (10.16 cm)
6" (15.24 cm)
Resolution
81 µrads / 326 µrads
N/A
100 µrads
FPA Material
HgCdTe
Si
HgCdTe
Array Dimensions
320 x 240 Staring
1" Diameter Tube
180 x 1 Scanning

Table 2-1: List of Passive Sensors and Baseline Specifications

2.1.2 Active Sensor

(U) The active sensor subsystem in Radiant Mist is a CO2 laser radar (ladar). The laser operates in the LWIR region of the EO spectrum. The transmit/receive aperture is six inches and the transmit power output can be varied from 5-80 watts. The detector used is a 1x1 HgCdTe detector in quadrature. The laser hardware itself is located in the bottom of the beam director (see Figure 2-2). The laser beam is passed through the aperture by the Off Gimbal Optical Transfer System (OGOTS), a mirror relay with an optical path of 1.5 meters.

Figure 2-2: Picture of the Laser Master Oscillator

2.2 Radiant Mist System Configuration

(U) The Radiant Mist Sensor System includes three separate sets of equipment. They are the Optical Director/Turret (OD/T), which contains the passive and active sensors, the support electronics boxes (SEB),and the control and display console (CDC).

2.2.1 Optical Director/Turret

(U) The sensors are housed in a modified (NMMS) turret, pictured in Figure 2-3. The gimbal limits are +190o in azimuth and +30 o in elevation. The gimbal maximum slew rate is 45o/sec and the maximum slew acceleration is 45o/sec2. The NMMS took feeds from the ship for water, using the fire main, and air, using dried low pressure (LP) air. The stability of the NMMS is 30 µrad, but with the modifications made for Radiant Mist, the jitter in the pod grew to over 200 µrad. This jitter caused a great many problems in collecting active sensor data. Only at the end of the tests was the jitter successfully controlled. Also located near the turret base are two thermal control units to monitor and control the temperature of the laser oscillator. The temperature of the oscillator must remain steady in order to attain the required coherence length for the laser beam.

Figure 2-3: Radiant Mist Turret Installed on the Navy Self
Defense Test Ship.

2.2.2 Support Electronics Boxes

(U) The next piece of equipment in the Radiant Mist sensor system are the Support Electronics Boxes. They contain the executive controller, the imaging tracker, the master power supply, and the thermal control unit for the laser.

2.2.3 Control and Display Console

(U) The CDC (see Figure 2-4) controls the Radiant Mist system. The CDC includes a situation display, an imagery display, a ladar control computer, a system controller, the turret controls, and the AFAPS computer. The situation display, a 19" BARCO monitor displaying the sensor line of sight (LOS), sensor status, and sensor controls, is located on top of the CDC. Figure 2-5 shows a sample of the situation display screen. The imagery display is a green and black monitor on the bottom of the CDC which displays the imagery from the passive sensor which the user has selected (MWIR, LWIR, VIS) for the tracker. The operator can control the tracking sensor, the FOV selection, the LOS control, and the tracking control with the keyboard joystick.

Figure 2-4: The CDC Installed on the Self Defense Test Ship

Figure 2-5: A Diagram of a Sample Situation Display Screen

2.3 Radiant Mist Testing

(U) The Radiant Mist system was tested continuously from its inception to the end of FY96. The final test occurred in Port Hueneme, CA, aboard the Self Defense Test Ship (SDTS). The SDTS (see Figure 2-6), the former USS Decatur, is a ship dedicated to weapon systems engineering, testing, and evaluation. During typical operations, air and/or surface launched threats simulate live attacks on the SDTS. The system under test, whether a new combat system or an individual element (sensors, weapon systems, etc.), respond to the threats to defend the ship. Since the SDTS represents a considerable Navy investment, it tows a decoy barge approximately 300 feet astern during live fire events, which serves as the target of attack.

Figure 2-6: The Self Defense Test Ship, ex-U.S.S. Decatur

2.3.1 Objectives

(U) In an effort to assess the overall performance characteristics of the Radiant Mist sensor system, tests were conducted at Pt. Hueneme, California from January 1996 to April 1996. By having a dedicated instrumented ship, Radiant Mist's anti-ship missile defense (ASMD) capability as a stand alone sensor was assessed. These tests were used to evaluate the ability of the Radiant Mist sensor system to perform anti-ship missile defense functions such as detecting and tracking anti-ship missile threats. The ship tests also included testing of the vibration sensing functions of the system for several pre-planned aircraft scenarios as well as for targets of opportunity. This data collection effort has helped answer or characterize important issues such as MWIR camera performance, cueing requirements within a Ship Self Defense (SSD) architecture, required laser power for operation, required laser stability, adaptive vibration compensation requirements, and software operability.

(U) The primary goal of this test was to determine the overall performance capabilities of the sensor system when employed in near real world conditions against stand-off air and surface targets. A secondary goal was to validate existing sensor prediction models by simulating operational atmospheric transmission paths. Other test objectives included target ladar cross section characteristics, atmospheric effects, laser stability effects and adaptive vibration compensation requirements. Although many objectives were set for this test period, the following prioritized list provides some of the more important objectives:

(i) Demonstrate the end-to-end functionality of the Radiant Mist system,

(ii) Demonstrate the Radiant Mist operational concept of passive acquisition and hand-over to ladar for precision tracking to perform ASMD,

(iii) Evaluation of environmental effects,

(iv) Characterization of target ladar cross section at various aspect angles as well as collection of target IR signatures versus predicted values,

(v) Verification of ladar receiver sensitivity for sufficient signal to noise (SNR),

(vi) Verification of adaptive vibration compensation to remove own-platform vibration,

(viii) Assessment of target distinguishability via skin vibration measurement for ship and aircraft targets of opportunity, and spatial characterization of their vibration signatures.

2.3.2 Operational Concept

(U)The operational concept of the Radiant Mist system is to take a cue from a radar, IRST, or electronic support measures (ESM) sensor, to slew the gimbal head to the proper coordinates, and to passively detect the target. If the cue is tight enough, narrow field of view (NFOV) may be used. If, however, the cue is in a basket greater than 2o, wide field of view (WFOV) is necessary. The WFOV must then switch to NFOV without losing the target. When the NFOV detects the target, auto-tracking software centers the target in the field of view (FOV) for laser illumination in order to find target range or identification information.

2.3.3 Target Detectability

(U) ASMD is the primary issue of concern for the planned tests. During the tests from Jan 1996 - April 1996 signatures were collected on a number of missile targets in order to evaluate the fidelity of several of the models used to predict target signatures. The tests will also be used to determine the effectiveness of the IR cameras in the Radiant Mist Phase IIB testbed, the long wave infrared (LWIR) from McDonnell Douglas and the mid-wave infrared (MWIR) from Rockwell, to detect the relatively small and fast targets associated with ASMD Testing. The effects of the atmosphere on the passive and active sensors on target detectability were also evaluated. Also to be evaluated were the models used to predict sensor performance for the passive and active subsystems of Radiant Mist.

2.3.4 Adaptive Vibration Cancellation Functions

(U) Another secondary objective of the SDTS testing was to demonstrate successful own-platform vibration cancellation. The vibrations of the host platform are present in any skin vibration spectrum. They must be canceled out in processing or they will corrupt the spectrum presented by the target. Therefore, any successful demonstration of target skin vibrational measurements also would prove the successful removal of the vibrations of the sensor platform.

2.4 General Conclusions from Shipboard Testing

(U) The Radiant Mist system accomplished many of its testing objectives during the period from January through April 1996. The system demonstrated its end-to-end functionality with only minor difficulties. The passive cameras were thermally cycled over 100 times with no ill effects. There were no electromagnetic interference (EMI) effects Internal to the system, however there were EMI problems with the remote link. The gimbal bearings failed and had to be replaced but had lasted for over two years prior. There was functionality between all above decks equipment and the below decks equipment. The major hardware failing occurred in the system remote link, which was not part of the original design.

(U) The concept of passive acquisition and hand-over to ladar for tracking was demonstrated, although not with ASCM targets. All ladar data that was collected during the tests was collected from cues from the passive cameras. The system ran in all weather conditions short of pouring rain and, although it was found to have degraded performance in hazy and foggy conditions, it always outperformed visible-only performance. IR target signatures were gathered and they matched well with predicted values. Ladar receiver sensitivity was verified and although the receiver exhibited 10 dB excess noise, it was sensitive enough to perform the tasks at shipboard testing.

3.0 U.S. Army Need

3.1 Operational Threat

(U) The mission of the U.S. Army Air Defense Artillery (ADA) is to prevent airborne attacks on friendly forces in the theater of operations. The FAAD addresses this need by denying the enemy aerial reconnaissance and in the event of leakage, defense against close-air support fixed wing (FW), rotary wing (RW), unmanned aerial vehicle (UAV), and cruise missile (CM) threats.

(U) The functions of the air defense system are to: (1) maintain air surveillance to provide early warning, (2) identify targets as friend, foe, or neutral (IFFN), (3) provide communication between command post and weapons, (4) cue/handover targets to the weapon system and/or gunners, (5) execute fire control, and (6) perform battle damage assessment (BDA).

(U) The key elements of the FAAD system are the Ground Based Sensor (GBS), with its three dimensional multi-function radar, the distributed Command, Control, and Information (C2I) units, and the weapon systems such as the Avenger, Bradley Fighting Vehicle (BFV), and gunners (Man-Portable Air Defense Systems - MANPADS). All of these elements are linked by a digital data distribution system that provides rapid and robust communications.

(U) The evolving threat characteristics and variable environmental factors present formidable challenges to the FAAD system performance. Threat upgrades involving low-observable technology, low altitude penetrations, and higher speed coupled with electronic countermeasures, such as jammers, chaff, anti-radiation missiles, and direction finders, require continual improvements in the FAAD system to be effective. Environmental factors such as weather, day/night operations, clutter, and friendly or neutral air vehicles, further complicate the engagement scenarios.

(U) A single-sensor system will be severely taxed to meet the numerous operational requirements, evolving threat characteristics, and variable environmental factors. In particular, the need for addressing IFFN, low radar cross-section threats, low altitude penetrations, and anti-radiation missiles places a critical limit on the performance of the FAAD elements.

3.2 Testing Scenarios

(U) The objective of the new effort is to demonstrate the long range NCID capability of the Radiant Mist/Outlaw Technology and to develop cost-effective operational concepts for integrating an enhanced combat ID capability into FAAD. The incorporation of a long range NCID capability will make it possible for FAAD rules of engagement to be changed to permit BVIDR engagements, allowing the FAAD weapons to be used to their full potential. This effort also addresses the concerns documented by the Department of Defense's (DOD) director of Operational Test and Evaluation (T&E), which found FAAD C3I operationally suitable, but fratricide experienced during testing was "unacceptably high."

(U) Radiant Outlaw technology will aid in extending engagements of potential threats by adding to the FAAD architecture in the following way. When the Radiant Mist/Outlaw system receives a cue from a radar, in this case, the FAAD GBS, its OD/T slews to the proper coordinates. The IR camera in the system will detect the target or, if no target is detected, perform a limited sector search to attempt to locate the target. Once the target is detected by the MWIR camera, tracking software will be activated to provide fine tracking. This track will contain azimuth and elevation bearings and their rates of change. Once the passive target track is established, the ladar beam can be activated. The ladar output will contain range, range rate, instantaneous velocity, and target vibration spectrum. To produce a fire control-quality track, continuous illumination of the target is necessary. However, a vibration spectrum is produced with only a one to two second illumination. The vibration spectrum provides target classification as explained above. Target classification information can then be handed over to a commander to make a decision about weapon release.

(U) For the FAAD application, the Radiant Misty/Outlaw technology can be integrated with either the GBS or the Avenger and Bradley weapons units. The MFOS system can be cued by the GBS for initial target detection and track, so that it can perform precision track and NCID functions. The MFOS system could also perform an independent area search.

(U) The testing will occur at Ft. Bliss. The system will be tested to demonstrate its capability to detect and classify targets when cued properly. Targets will include helicopters, propeller aircraft, jets, and a cruise missile surrogate. The anticipated ranges will be greater than 15 km depending on weather constraints. Pending a successful test, the technology could be incorporated into the FAAD GBS system architecture to provide long range, standoff target classification to allow BVIDR engagements.

(U) Future tests could be devised to show the utility of Radiant Mist/Outlaw technology in many other operational scenarios. For instance, a low power model could be integrated into ground combat vehicles to demonstrate the utility of positive ID of ground targets. The system could also be flown on platforms providing CAS to ground units.

3.3 System Reconfiguration

(U) The passive and active EO systems must be re-configured for integration with FAAD either as a stand alone or integrated into C2I. This effort will adapt both the passive and active test-beds to these conditions. The following sections describe the adaptions to be performed.

3.3.1 OD/T

(U) The stability of the sensors in the ODT requires that the internal turret temperature be maintained within a specific range. A custom thermal control system was designed for shipboard operation and will be adapted for the Fort Bliss environment. The turret will also be kept under positive pressure to keep dust and other particulates, heavy in the land environment, from entering the turret.

(U) Since the GBS radar produces a high degree of RF radiation, the MFOS testbed will be located out its direct line of radiation and specifically shielded from its X-band radiation. Because the OD/T is designed for helicopter and shipboard operation, the vibration and shock encountered when it is mounted on a trailer in typical field conditions must be investigated and appropriate measures must be taken. An approach must also be taken to establish a handover from the GBS to the MFOS so that correct pointing of the ODT is insured.

3.3.2 SEB

(U) The SEB must likewise be adapted to the environmental conditions, vibration and shock of transportation, and EMI conditions of the field environment. As required, the SEB will be repackaged and integrated on the same trailer as the ODT. As part of this repackaging, space will be provided to accommodate equipment from the CDC, which will be reconfigured into a portable workstation.

3.3.3 CDC

(U) The CDC has been developed for operation in the Command Information Center on a Naval Vessel. For the FAAD operation, a portable workstation is preferable. Therefore, a portable workstation consisting of a monitor display, system processor, hand controller, LAN interfaces, and keyboard, will be constructed from the current CDC. Additional software upgrades will be added to the CDC by McDonnell Douglas.

4.0 Conclusion

The Radiant Mist/Outlaw sensor system is a mature technology for providing advanced day/night surveillance and target identification. The U.S. Navy has developed an ATR system to perform autonomous target classification of aircraft and is in development of a ground database. The Precision Targeting and Identification ACTD program will produce a compact low cost ID system that could be fielded on close air support aircraft, helicopters, and mobile ground forces to assist in the classification friendly forces.

References

1. Mid-Wave Thermal Imaging Sensors in the Maritime Environment, A. Lovett and C. Shen, March 1995 Passive IRIS

2. Test Results of the Radiant Mist Electro-Optic Fire Control System, A. Lovett and C. Shen, May 1996 Active IRIS

3. Radiant Mist Testing Aboard the Self Defense Test Ship Final Report January-April 1996.

4. McDonnell Douglas Proposal for Multi-Functional Optical System Tesating in a FADDS Environment, 6 August 1996

5. IR/EO Systems Handbook, Volume 6, Active Elctro-Optical Systems, ERIM, SPIE Press, 1993