KEYWORDS: Radar, Synthetic aperture radar, Prototyping, X band, Receivers, Ku band, Sensors, Human-machine interfaces, Commercial off the shelf technology, Oscillators
The FlexSAR radar system was designed to be a high quality, low-cost, flexible research prototype instrument. Radar researchers and practitioners often desire the ability to prototype new or advanced configurations, yet the ability to enhance or upgrade existing radar systems can be cost prohibitive. FlexSAR answers the need for a flexible radar system that can be extended easily, with minimal cost and time expenditures. The design approach focuses on reducing the resources required for developing and validating new advanced radar modalities. Such an approach fosters innovation and provides risk reduction since actual radar data can be collected in the appropriate mode, processed, and analyzed early in the development process. This allows for an accurate, detailed understanding of the corresponding trade space. This paper is a follow-on to last years paper and discusses the advancements that have been made to the FlexSAR system. The overall system architecture is discussed and presented along with several examples illustrating the system utility.
KEYWORDS: Radar, Synthetic aperture radar, Prototyping, Commercial off the shelf technology, L band, X band, Clocks, Algorithm development, Antennas, Computing systems
The FlexSAR radar system was designed to be a high quality, low-cost, flexible prototype instrument. Many radar researchers and practitioners desire the ability to efficiently prototype novel configurations. However, the cost and time required to modify existing radar systems is a challenging hurdle that can be prohibitive. The FlexSAR system couples an RF design that leverages connectorized components with digital commercial-off-the-shelf (COTS) cards. This design allows for a scalable system that supports software defined radio (SDR) capabilities. This paper focuses on the RF and digital system design, discussing the advantages and disadvantages. The FlexSAR system design objective was to support diverse configurations with minimal non-recurring engineering (NRE) costs. Multiple diverse applications are examined, demonstrating the flexible system nature. The configurations discussed utilize different system parameters (e.g., number of phase-centers, transmit configurations, etc.). The resultant products are examined, illustrating that high-quality data products are still attained.
Unmanned aerial systems (UASs) have become a critical asset in current battlespaces and continue to play an increasing role for intelligence, surveillance and reconnaissance (ISR) missions. With the development of medium-to-low altitude, rapidly deployable aircraft platforms, the ISR community has seen an increasing push to develop ISR sensors and systems with real-time mission support capabilities. This paper describes recent flight demonstrations and test results of the RASAR (Real-time, Autonomous, Synthetic Aperture Radar) sensor system. RASAR is a modular, multi-band (L and X) synthetic aperture radar (SAR) imaging sensor designed for self-contained, autonomous, real-time operation with mission flexibility to support a wide range of ISR needs within the size, weight and power constraints of Group III UASs. The sensor command and control and real-time image formation processing are designed to allow integration of RASAR into a larger, multi-intelligence system of systems. The multi-intelligence architecture and a demonstration of real-time autonomous cross-cueing of a separate optical sensor will be presented.
The utilization of unmanned aerial systems (UASs) for intelligence, surveillance and reconnaissance (ISR) applications
continues to increase and unmanned systems have become a critical asset in current and future battlespaces. With the
development of medium-to-low altitude, rapidly deployable aircraft platforms, the ISR community has seen an
increasing push to develop ISR sensors and systems with real-time mission support capabilities. This paper describes the
design and development of the RASAR (Real-time, Autonomous, Synthetic Aperture Radar) sensor system and presents
demonstration flight test results. RASAR is a modular, multi-band (L and X) synthetic aperture radar (SAR) imaging
sensor designed for self-contained, autonomous, real-time operation with mission flexibility to support a wide range of
ISR needs within the size, weight and power constraints of Group III UASs. SAR waveforms are generated through
direct digital synthesis enabling arbitrary waveform notching to enable operations in cluttered RF environments. RASAR
is capable of simultaneous dual-channel receive to enable polarization based target discrimination. The sensor command
and control and real-time image formation processing are designed to enable integration of RASAR into larger, multi-intelligence
system of systems. The multi-intelligence architecture and a demonstration of real-time autonomous cross-cueing
of a separate optical sensor will be presented.
The capabilities of tactical intelligence, surveillance, and reconnaissance (ISR) payloads are expanding from single
sensor imagers to integrated systems-of-systems architectures. Increasingly, these systems-of-systems include multiple
sensing modalities that can act as force multipliers for the intelligence analyst. Currently, the separate sensing modalities
operate largely independent of one another, providing a selection of operating modes but not an integrated intelligence
product. We describe here a Sensor Management System (SMS) designed to provide a small, compact processing unit
capable of managing multiple collaborative sensor systems on-board an aircraft. Its purpose is to increase sensor
cooperation and collaboration to achieve intelligent data collection and exploitation. The SMS architecture is designed to
be largely sensor and data agnostic and provide flexible networked access for both data providers and data consumers. It
supports pre-planned and ad-hoc missions, with provisions for on-demand tasking and updates from users connected via
data links. Management of sensors and user agents takes place over standard network protocols such that any number
and combination of sensors and user agents, either on the local network or connected via data link, can register with the
SMS at any time during the mission. The SMS provides control over sensor data collection to handle logging and routing
of data products to subscribing user agents. It also supports the addition of algorithmic data processing agents for
feature/target extraction and provides for subsequent cueing from one sensor to another. The SMS architecture was
designed to scale from a small UAV carrying a limited number of payloads to an aircraft carrying a large number of
payloads. The SMS system is STANAG 4575 compliant as a removable memory module (RMM) and can act as a
vehicle specific module (VSM) to provide STANAG 4586 compliance (level-3 interoperability) to a non-compliant
sensor system. The SMS architecture will be described and results from several flight tests and simulations will be
shown.
The availability of imagery simultaneously collected from sensors of disparate modalities enhances an image analyst's
situational awareness and expands the overall detection capability to a larger array of target classes. Dynamic
cooperation between sensors is increasingly important for the collection of coincident data from multiple sensors either
on the same or on different platforms suitable for UAV deployment. Of particular interest is autonomous collaboration
between wide area survey detection, high-resolution inspection, and RF sensors that span large segments of the
electromagnetic spectrum. The Naval Research Laboratory (NRL) in conjunction with the Space Dynamics Laboratory
(SDL) is building sensors with such networked communications capability and is conducting field tests to demonstrate
the feasibility of collaborative sensor data collection and exploitation. Example survey / detection sensors include:
NuSAR (NRL Unmanned SAR), a UAV compatible synthetic aperture radar system; microHSI, an NRL developed
lightweight hyper-spectral imager; RASAR (Real-time Autonomous SAR), a lightweight podded synthetic aperture
radar; and N-WAPSS-16 (Nighttime Wide-Area Persistent Surveillance Sensor-16Mpix), a MWIR large array gimbaled
system. From these sensors, detected target cues are automatically sent to the NRL/SDL developed EyePod, a high-resolution,
narrow FOV EO/IR sensor, for target inspection. In addition to this cooperative data collection, EyePod's
real-time, autonomous target tracking capabilities will be demonstrated. Preliminary results and target analysis will be
presented.
NuSAR (Naval Research Laboratory Unmanned Synthetic Aperture Radar) is a sensor developed under the ONRfunded
FEATHAR (Fusion, Exploitation, Algorithms, and Targeting for High-Altitude Reconnaissance) program.
FEATHAR is being directed and executed by the Naval Research Laboratory (NRL) in conjunction with the Space
Dynamics Laboratory (SDL). FEATHAR's goal is to develop and test new tactical sensor systems specifically designed
for small manned and unmanned platforms (payload weight < 50 lbs). NuSAR is a novel dual-band (L- and X-band)
SAR capable of a variety of tactically relevant operating modes and detection capabilities. Flight test results will be
described for narrow and wide bandwidth and narrow and wide azimuth aperture operating modes.
The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS), developed for the NASA New Millennium
Program (NMP) Earth Observing-3 (EO-3) mission, has recently completed a series of uplooking atmospheric
measurements. The GIFTS development demonstrates a series of new sensor and data processing technologies that can
significantly expand geostationary meteorological observational capability. The resulting increase in forecasting
accuracy and atmospheric model development utilizing this hyperspectral data is demonstrated by the uplooking data.
The GIFTS sensor is an imaging FTS with programmable spectral resolution and spatial scene selection, allowing
spectral resolution and area coverage to be traded in near-real time. Due to funding limitations, the GIFTS sensor module
was completed as an engineering demonstration unit that can be upgraded to flight quality. This paper reviews the
GIFTS system design considerations and the technology utilized to enable a nearly two order performance increase over
the existing GOES sounder and shows its capability. While not designed as an operational sensor, GIFTS EDU provides
a flexible and accurate testbed for the new products the hyperspectral era will bring. Efforts to find funding to upgrade
and demonstrate this amazing sensor in space are continuing.
J. Elwell, G. Cantwell, D. Scott, R. Esplin, G. Hansen, S. Jensen, M. Jensen, S. Brown, L. Zollinger, V. Thurgood, M. Esplin, R. Huppi, G. Bingham, H. Revercomb, F. Best, D. Tobin, J. Taylor, R. Knuteson, W. Smith, R. Reisse, R. Hooker
The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) was developed for the NASA New Millennium
Program (NMP) Earth Observing-3 (EO-3) mission. This paper discusses the GIFTS measurement requirements and the
technology utilized by the GIFTS sensor to provide the required system performance. Also presented are preliminary
results from the recently completed calibration of the instrument. The GIFTS NMP mission challenge was to
demonstrate new and emerging sensor and data processing technologies to make revolutionary improvements in
meteorological observational capability and forecasting accuracy using atmospheric imaging and hyperspectral sounding
methods. The GIFTS sensor is an imaging FTS with programmable spectral resolution and spatial scene selection,
allowing radiometric accuracy and atmospheric sounding precision to be traded in near-real time for area coverage.
System sensitivity is achieved through the use of a cryogenic Michelson interferometer and two large-area, IR focal
plane detector arrays. Due to funding limitations, the GIFTS sensor module was completed as an engineering
demonstration unit, which can be upgraded for flight qualification. Capability to meet the next generation
geosynchronous sounding requirements has been successfully demonstrated through thermal vacuum testing and
rigorous IR calibration activities.
The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, a 10-channel infrared (1.27 - 16.9 μm) radiometer, was launched on the TIMED (Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics) satellite in December 2001 from Vandenburg Air Force Base. SABER is being used to measure earthlimb emissions and to characterize infrared radiation, allowing calculation of cooling rates and determination of composition and temperature profiles in the mesosphere, lower thermosphere, and ionosphere (60-180 km). The SABER telescope is an on-axis Cassegrain design with a picket-fence tuning fork chopper at the first focus and a clamshell re-imager to focus the image on the focal plane. The telescope was designed to reject stray light from the Earth and atmosphere outside the instrument's instantaneous field-of-view (IFOV). The baffle assembly contains a single-axis scan mirror, which permits the 2 km vertical IFOV of each detector to be scanned from the Earth to a 400 km tangent height. The telescope and baffle assembly are cooled to 220 K by a dedicated radiator. The focal plane assembly is cooled to 75 K by a miniature cryogenic refrigerator. Field programmable gate arrays are used to implement state machine algorithms for control and operation of the instrument and subsystems. Although originally designed for a two-year lifetime requirement, the SABER instrument has been in continuous operation since January 2002. This paper discusses the SABER instrument design and innovations developed to achieve the required performance, along with instrument performance and lessons learned from the program.
This paper describes the design of a 10-channel infrared (1.27 to 16.9 micrometers ) radiometer instrument known as SABER (sounding of the atmosphere using broadband emission radiometry) that will measure earth-limb emissions from the TIMED (thermosphere- ionosphere-mesosphere energetics and dynamics) satellite. The instrument telescope, designed to reject stray light from the earth and the atmosphere, is an on-axis Cassegrain design with a clam shell reimager and a one-axis scan mirror. The telescope is cooled below 210 K by a dedicated radiator. The focal plane assembly (consisting of a filter array, a detector array, a Lyot stop, and a window) is cooled to 75 K by a miniature cryogenic refrigerator. The conductive heat load on the refrigerator is minimized by a Kevlar support system that thermally isolates the focal plane assembly from the telescope. Kevlar is also used to thermally isolate the telescope from the spacecraft. Instrument responsivity drifts due to changes in telescope and focal plane temperatures as well as other causes are neutralized by an in-flight calibration system. The detector array consists of discrete HgCdTe, InSb, and InGaAs detectors. Two InGaAs detectors are a new long wavelength type, made by EG&G, that have a long wavelength cutoff of 2.33 micrometers at 77 K.
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