Agile Adaptive Radar Sampling of Fast‐Evolving Atmospheric Phenomena Guided by Satellite Imagery and Surface Cameras
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54 ENVIRONMENTAL SCIENCES↗
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Adaptive Quantizer for Burst Synthetic-Aperture Radar
Adaptive quantizer for burst-mode synthetic-aperture radar reduces data rate of return signal. Device, called block floating-point quantizer (BFPQ) basically analog-to-digital converter that covers wide dynamic range and discards appropriate lower order bits. BFPQ is, in effect, digital approximator with automatic gain control. Moves floatingpoint marker binary representation of signal data in accordance with perceived dynamic range. Available step sizes thus limited to multiples of underlying smallest quantization step (represented by lowest order bit). Retains only first K most significant bits of signal; (L,K) BFPQ is one that does K-bit quantization of signal originally quantized to L bits. Quantization error simply difference between actual signal level and its binary approximation. Other potential applications for BFPQ include speech compression and picture data compression.
Joo, T. H.↗
Ocean waves and turbulence as observed with an adaptive coherent multifrequency radar
An adaptive coherent multifrequency radar system is developed for several applications. The velocity distribution (Doppler spectrum) and spectral intensity of 15 different irregularity scales (waves and turbulence) can be measured simultaneously. Changing the azimuth angle of the antennas at regular intervals, the directivity of the wave/turbulence pattern on the sea surface can also be studied. A series of measurements for different air/sea conditions are carried out from a coast based platform. Experiments in the Atlantic are also performed with the same equipment making use of the NASA Electra aircraft. The multifrequency radar allows the measurement of the velocity distribution (""coherent and incoherent component'') associated with 15 different ocean irregularity scales simultaneously in a directional manner. It is possible to study the different air/sea mechanisms in some degree of detail.
Gjessing, D. T.↗
Adaptive OFDM Radar Waveform Design for Improved Micro-Doppler Estimation
Here we analyze the performance of a wideband orthogonal frequency division multiplexing (OFDM) signal in estimating the micro-Doppler frequency of a rotating target having multiple scattering centers. The use of a frequency-diverse OFDM signal enables us to independently analyze the micro-Doppler characteristics with respect to a set of orthogonal subcarrier frequencies. We characterize the accuracy of micro-Doppler frequency estimation by computing the Cramer-Rao bound (CRB) on the angular-velocity estimate of the target. Additionally, to improve the accuracy of the estimation procedure, we formulate and solve an optimization problem by minimizing the CRB on the angular-velocity estimate with respect to the OFDM spectral coefficients. We present several numerical examples to demonstrate the CRB variations with respect to the signal-to-noise ratios, number of temporal samples, and number of OFDM subcarriers. We also analysed numerically the improvement in estimation accuracy due to the adaptive waveform design. A grid-based maximum likelihood estimation technique is applied to evaluate the corresponding mean-squared error performance.
47 OTHER INSTRUMENTATION↗
Adapt: A Weather Radar Data Analysis and Nowcasting Platform for Informed Adaptive Scanning
SF-26-021 Adapt is a data processing platform for real-time data analysis, short term prediction of targets convective cells and tracking for archived data. It provides tools for downloading, processing, segmenting, projecting, analyzing, and visualizing storm cell data from weather radar. The pipeline includes cell detection, motion estimation using optical flow, cell property extraction, and persistence to NetCDF and SQLite/Parquet for guiding adaptive scanning.
Raut, Bhupendra Ashokrao [Argonne National Laborat↗
Radar, Insect Population Ecology, and Pest Management
Discussions included: (1) the potential role of radar in insect ecology studies and pest management; (2) the potential role of radar in correlating atmospheric phenomena with insect movement; (3) the present and future radar systems; (4) program objectives required to adapt radar to insect ecology studies and pest management; and (5) the specific action items to achieve the objectives.
Vaughn, C. R.↗
Target Detection via Cognitive Radars Using Change-Point Detection, Learning, and Adaptation
Many radar detection algorithms that assume a stationary environment (clutter) have been proposed and analyzed over the years. However, in practice, changes in the nonstationary environment can perturb the parameters of the clutter distribution, or even alter the clutter distribution family, which can greatly deteriorate the target detection capability. To avoid such potential performance degradation, cognitive radar systems are envisioned which are required to rapidly realize the nonstationarity, accurately learn the new characteristics of the environments, and adaptively update the detector. In this paper, aiming to develop a fully cognitive radar for target detection in nonstationary environments, we propose a unifying framework that integrates (i) change-point detection of clutter distributions by using a data-driven cumulative sum (CUSUM) algorithm and its extended version, (ii) learning/identification of clutter distribution by applying sparse theory and kernel density estimation methods, and (iii) adaptive target detection by automatically modifying the likelihood-ratio test and corresponding detection threshold. Further, with extensive numerical examples, we demonstrate the achieved improvements in detection performance due to the proposed framework in comparison to a nonadaptive case, an adaptive matched filter (AMF) method, and the clairvoyant case. Herein, we also use Wilcoxon rank-sum tests to evaluate the statistical significance of the performance improvements
42 ENGINEERING↗
Adaptively pointing spaceborne radar for precipitation measurements
An auxiliary concept of adaptive pointing applicable to meteorological radar is discussed. This control technique would resolve the conflicts among speed of scan or scan width, resolution, and dwell time per resolution element. At T1(orbital position) a passive infrared radiometer imager scans a swath ahead of the spacecraft; an appropriate algorithm indicates which clouds are probably producing precipitation. These locations are then used by the on-board antenna controller to program the antenna scan so that the radar samples clouds A and B at times T2 and T3 respectively.
Atlas, D.↗
Adaptively pointing spaceborne radar for precipitation measurements
An auxiliary concept of adaptive pointing is presented as an aid to space-based measurements of precipitation using microwave radar. It is recommended that the instantaneous field of view (IFOV) be limited to cloudy regions of possible precipitation rather than scanning clear-sky areas of no interest. A microwave imager is proposed for scanning ahead of the satellite in order to identify areas of precipitation, and then an on-board antenna controller can reposition the scanning antenna to obtain reflectivities for use in rainfall-reflectivity relationships. The precursor beam could delineate the storm boundaries and determine points of peak intensity which can then be selectively sampled to find the rainfall rate distribution for the storm. The adaptive-beam system is suggested to be implementable using an IR sensor on-board geosynchronous satellites.
Atlas, D.↗
Implications from Near-Shoemaker Imaging of Eros for Small-Scale Structure and Surface Sampling
What we know about asteroids has always been bifurcated by the enormous gap between astronomical studies of small, distant bodies, and the close-up laboratory measurements of hand-sample sized meteorites. The gulf has been narrowed somewhat by improvements in Earth-based astronomical techniques (e.g. Hubble Space Telescope, radar, adaptive optics) and especially by spacecraft fly-bys of asteroids. But the Near Earth Asteroid Rendezvous (NEAR)-Shoemaker mission has gone considerably more in the direction of bridging the gap. Any consideration of intelligent sample-return from an asteroid must be based on the best possible knowledge of the asteroid at the spatial scales pertinent to operations at the asteroid and of the sample/s. Otherwise, we are in danger of succumbing to the 'Martian Horror Story' that Bruce Murray, in the 1960's, envisioned might impair our exploration of the surface of the red planet if we tried to land on it without first bolstering the information content of our database about Mars, especially at high resolutions. NEAR-Shoemaker is helping to bridge that gap in the case of Eros. The best resolution obtained by the Galileo spacecraft on Ida was 25 m/pixel. As of this writing, NEAR has already obtained images with resolutions at least five times better (information content 25 times better) and vastly better images may be available at the time of this Workshop from the late October low flyby. Already, we are seeing that the Martian horror story looks tame compared with Eros. Everywhere we have landed on Mars, the surface has been covered with rocks and boulders, with much higher spatial coverage than seen anywhere on the lunar surface. We have, in fact, been rather lucky that none of our Martian landers have tipped over so far, and there were justified fears in the early aftermath of last year's failure of Mars Polar Lander that it had suffered from inadequate high-resolution characterization of polar regions on Mars (the failure is now known to have had another cause). Eros looks potentially even more terrifying. Additional information is contained in the original extended abstract.
Chapman, C. R.↗
Environmentally Adaptive, Multiband Software-Defined-Radar for Monitoring of Item of Interest in a Dynamically Cluttered Room
High-resolution multi-frequency radars when networked together, form a robust and seamless monitoring system for high-valued items. The multi-look-direction radar network investigated by LLNL and DSI, operates at 77 GHz and 5.8GHz, and is capable of detection at centimeter resolution movement of objects of interest. This dual frequency radar (unlike optical methods) can operate under various environments with conditions such a smoke, dust, and other natural or manmade obscurations. In addition, the multiband network radar is based on low-cost FCC approved EM specifications and can be scaled with the dimensions of the room and objects under consideration by user-defined inputs. Furthermore, the underlying radar signal processing based on software-defined radar engine is adaptive to its operational environment, where operators can input the size of the facility and object of interest and the distance between the object and radar. Finally, this multi-frequency radar employs a host of change detection and machine learning algorithms to reach performance levels in terms of high probability of detection and low false alarm rates while the monitoring state of the object can be reported remotely.
42 ENGINEERING↗
An adaptive filter for smoothing noisy radar images
A spatial domain adaptive Wiener filter for smoothing radar images corrupted by multiplicative noise is presented. The filter is optimum in a minimum mean squared error sense, computationally efficient, and preserves edges in the image better than other filters. The proposed algorithm can also be used for processing optical images with illumination variations that have a multiplicative effect.
Frost, V. S.↗
Precipitation measurements from space - Workshop summary 28 April-1 May 1981, Greenbelt, MD
The goals and methods for global precipitation measurements from space are examined. Records currently exist only for visible and IR scans of cloud properties, and are applied from GEO for detecting diurnal variations in precipitation. Microwave radiometry is noted to be a suitable method for supplementing the visible and IR data for measuring stratiform oceanic precipitation, and when used at up to 3 microns can detect areas, if not amounts, of precipitation from GEO. Applications of radar altimeters are proposed in terms of modifications to the Seasat-type 2.2 cm radar, the use of surface target attentuation radar, of frequency agile rain radar, or of adaptive pointing radar. Soil moisture sensing is available with passive microwave radiometry in the 20-50 cm bands, or active sensing in the 5-8 cm bands. The utilization of GARP ground truth data is explored, along with statistical methods for treating the data samples.
Atlas, D.↗
Adaptive filtering of radar images for autofocus applications
Autofocus techniques are being designed at the Jet Propulsion Laboratory to automatically choose the filter parameters (i.e., the focus) for the digital synthetic aperture radar correlator; currently, processing relies upon interaction with a human operator who uses his subjective assessment of the quality of the processed SAR data. Algorithms were devised applying image cross-correlation to aid in the choice of filter parameters, but this method also has its drawbacks in that the cross-correlation result may not be readily interpretable. Enhanced performance of the cross-correlation techniques of JPL was hypothesized given that the images to be cross-correlated were first filtered to improve the signal-to-noise ratio for the pair of scenes. The results of experiments are described and images are shown.
Stiles, J. A.↗
Radar Range Sidelobe Reduction Using Adaptive Pulse Compression Technique
Pulse compression has been widely used in radars so that low-power, long RF pulses can be transmitted, rather than a highpower short pulse. Pulse compression radars offer a number of advantages over high-power short pulsed radars, such as no need of high-power RF circuitry, no need of high-voltage electronics, compact size and light weight, better range resolution, and better reliability. However, range sidelobe associated with pulse compression has prevented the use of this technique on spaceborne radars since surface returns detected by range sidelobes may mask the returns from a nearby weak cloud or precipitation particles. Research on adaptive pulse compression was carried out utilizing a field-programmable gate array (FPGA) waveform generation board and a radar transceiver simulator. The results have shown significant improvements in pulse compression sidelobe performance. Microwave and millimeter-wave radars present many technological challenges for Earth and planetary science applications. The traditional tube-based radars use high-voltage power supply/modulators and high-power RF transmitters; therefore, these radars usually have large size, heavy weight, and reliability issues for space and airborne platforms. Pulse compression technology has provided a path toward meeting many of these radar challenges. Recent advances in digital waveform generation, digital receivers, and solid-state power amplifiers have opened a new era for applying pulse compression to the development of compact and high-performance airborne and spaceborne remote sensing radars. The primary objective of this innovative effort is to develop and test a new pulse compression technique to achieve ultrarange sidelobes so that this technique can be applied to spaceborne, airborne, and ground-based remote sensing radars to meet future science requirements. By using digital waveform generation, digital receiver, and solid-state power amplifier technologies, this improved pulse compression technique could bring significant impact on future radar development. The novel feature of this innovation is the non-linear FM (NLFM) waveform design. The traditional linear FM has the limit (-20 log BT -3 dB) for achieving ultra-low-range sidelobe in pulse compression. For this study, a different combination of 20- or 40-microsecond chirp pulse width and 2- or 4-MHz chirp bandwidth was used. These are typical operational parameters for airborne or spaceborne weather radars. The NLFM waveform design was then implemented on a FPGA board to generate a real chirp signal, which was then sent to the radar transceiver simulator. The final results have shown significant improvement on sidelobe performance compared to that obtained using a traditional linear FM chirp.
Li, Lihua↗
Random sampling adaptively focusing synthetic aperture radar
A high resolution narrow angle of view imaging radar system is considered that employs an airborne synthetic aperture of 600 meters operating at X-band to produce a beamwidth of approximately 0.05 mr. This system differs from a conventional SAR in that only a smaller number of wavefront samples, spaced randomly over the aperture are processed, and adaptive beamforming with open loop scanning is used. As a result, the processing requirements are reduced to within the capability of present day small computer technology, and the tolerance on flight stability is loosened by about 100:1. The system is described and initial analysis and evaluation results are presented.
Powers, E. N.↗
The New Weather Radar for America's Space Program in Florida: A Temperature Profile Adaptive Scan Strategy
A new weather radar is being acquired for use in support of America s space program at Cape Canaveral Air Force Station, NASA Kennedy Space Center, and Patrick AFB on the east coast of central Florida. This new radar replaces the modified WSR-74C at Patrick AFB that has been in use since 1984. The new radar is a Radtec TDR 43-250, which has Doppler and dual polarization capability. A new fixed scan strategy was designed to best support the space program. The fixed scan strategy represents a complex compromise between many competing factors and relies on climatological heights of various temperatures that are important for improved lightning forecasting and evaluation of Lightning Launch Commit Criteria (LCC), which are the weather rules to avoid lightning strikes to in-flight rockets. The 0 C to -20 C layer is vital since most generation of electric charge occurs within it and so it is critical in evaluating Lightning LCC and in forecasting lightning. These are two of the most important duties of 45 WS. While the fixed scan strategy that covers most of the climatological variation of the 0 C to -20 C levels with high resolution ensures that these critical temperatures are well covered most of the time, it also means that on any particular day the radar is spending precious time scanning at angles covering less important heights. The goal of this project is to develop a user-friendly, Interactive Data Language (IDL) computer program that will automatically generate optimized radar scan strategies that adapt to user input of the temperature profile and other important parameters. By using only the required scan angles output by the temperature profile adaptive scan strategy program, faster update times for volume scans and/or collection of more samples per gate for better data quality is possible, while maintaining high resolution at the critical temperature levels. The temperature profile adaptive technique will also take into account earth curvature and refraction when geo-locating the radar beam (i.e., beam height and arc distance), including non-standard refraction based on the user-input temperature profile. In addition to temperature profile adaptivity, this paper will also summarize the other requirements for this scan strategy program such as detection of low-level boundaries, detection of anvil clouds, reducing the Cone Of Silence, and allowing for times when deep convective clouds will not occur. The adaptive technique will be carefully compared to and benchmarked against the new fixed scan strategy. Specific environmental scenarios in which the adaptive scan strategy is able to optimize and improve coverage and resolution at critical heights, scan time, and/or sample numbers relative to the fixed scan strategy will be presented.
Carey, L. D.↗
Dedicated short range communications used as fail-safe in autonomous navigation
Here in this paper, we have analyzed scenarios for leader-follower vehicle convoys that have the potential to be unsafe, hazardous, or even fatal in order to provide insight on dangerous driving conditions for autonomous vehicle platoons. These scenarios were created in a simulation software called Prescan, and are made to reflect the behavior of the vehicle dynamics and sensor characteristics of a real-world vehicle convoy that is currently being tested at the American Center for Mobility (ACM) and sponsored by the Department of Energy (DOE), National Renewable Energy Laboratory (NREL), the U.S. Army Combat Capabilities Development Command - Ground Vehicle Systems Center (U.S. Army CC-DEVCOM) and the Michigan Department of Transportation (MDOT). The follower vehicle in this study is tested under multiple scenarios, equipped with a Dedicated Short Range vehicle-to-vehicle communication system (DSRC), a radar-based adaptive cruise control system (ACC) and a precision global positioning system (GPS).
42 ENGINEERING↗