Incoherent Integration Detection Method of Airborne Phased Array Radar in a Multipath Environment

Airborne phased array radar (PAR) suffers from multipath problems when flying over a calm sea surface. The existence of a multipath phenomenon will cause the electromagnetic echo of the same target to be reflected back to the airborne PAR from two paths, namely, direct path (DP) and multipath. Compared with the ground-based radar, the target echo received by airborne PAR in the multipath environment has two important characteristics: one is that the DP signal and the multipath signal exist in different range bins, and the other is that the radar cross section (RCS) in the DP direction may be smaller than that in the multipath direction. Considering these two characteristics, this paper first proposes a target pairing algorithm for matching the DP range and multipath range of the same target in signal detection, and then, combined with the cell-averaging constant false alarm rate (CA-CFAR) detection model, an incoherent integration detection method for airborne PAR in the multipath environment is proposed. In the target pairing process, the geometric structure relationship of the airborne PAR model can be fully utilized. After a successful target pairing process, the energy of the multipath signal will be incoherently accumulated into the corresponding DP range bin, so as to improve the probability of DP range bin data passing the detection threshold. In essence, the proposed method makes full use of multipath energy to improve the detection capability of airborne PAR in the multipath environment. Finally, the detection probability of the proposed method is given, and the detection performance is analyzed.

Overview of the Airborne Phased Array Radar Observing Simulator

<p>The proposed airborne phased array radar (APAR) system consists of four removable, dual-polarized, C-band AESAs (Active Electronic Scanning Array) strategically located on the fuselage of the NSF/NCAR C-130. Conceptually, the radar system is divided into the front-end, the backend, and aircraft-specific section with the front-end primarily consisting of AESAs and the signal processor is in the backend. The aircraft specific section includes a power system and a GPS antenna.</p><p>As part of the risk reduction of the APAR development, the APAR Observing Simulator (AOS) system has been developed to provide simulated APAR data collection sampled from a C-130 flying by/through realistic numerical weather simulations of high-impact weather events. Given that APAR is designed to extend beyond capabilities of the existing airborne tail Doppler radars (e.g., NOAA TDRs and the retired NSF/NCAR ELDORA), a verification of signal processing software and algorithms is needed before the radar is physically built to ensure that the signal processing software infrastructure can handle high data rates and complicated, multiplex scanning that will be part of normal APAR operations.  Furthermore, several algorithms that will need to ingest large amounts of APAR data at very high rates are under development, including dual-Doppler wind synthesis, radar reflectivity attenuation correction, rain rate estimation, and hydrometeor classification. These algorithms need to be tested and verified before the implementation. </p><p>The AOS will also serve as a planning tool for future Principal Investigators (PIs) who will use it to design and test different flight and scanning strategies based on simulated storms to yield the best scientific outcomes before their field deployment takes place. This will enable better understanding of trade-offs among various sampling regimes/strategies during the planning and enhance future field programs' efficiency and effectiveness.</p>

APAR: The Next Generation of Airborne Polarimetric Doppler Weather Radar

<p>A novel, airborne phased array radar (APAR) is currently under design at the NCAR Earth Observing Laboratory. This novel airborne radar is to be carried by the NSF/NCAR C-130 aircraft. The APAR system will consist of four removable C-band active electronically scanned arrays (AESA), strategically placed on the fuselage of the aircraft. Conceptually, the radar system is divided into the front-end, the backend, and the aircraft-specific section. The front-end primarily consists of AESAs, the backend of the signal processor, and the aircraft specific section includes a power system and a GPS antenna.</p><p>APAR, with dual-Doppler and dual polarization capabilities at a lesser attenuating C-band wavelength, is designed to enable further advancement in understanding of in-cloud microphysical and dynamical processes within a variety of precipitation systems. Such unprecedented observations, in conjunction with the advanced radar data assimilation systems, is anticipated to significantly improve understanding and predictability of hazardous weather events.</p><p>At present, and with funding from both the National Science Foundation and the National Oceanic and Atmospheric Administration, NCAR is engaged in the risk reduction and APAR preliminary design activities. In this talk, we will provide an update on the status of these activities for various system components as well as the system-level design. For the final design and development of APAR, NCAR plans to apply for the NSF Mid-scale Research Infrastructure funds in 2021. It is anticipated that the APAR final design and development will be a five-year effort.</p>

STAP Optimization of Airborne Phased Array Radar in Nonuniform Environment Based on EFA Algorithm

EFA (extended factored approach) algorithm is the main method of space-time adaptive processing technology (STAP) for airborne phased array radar, but it is faced with many problems, such as large number of samples and large amount of calculation. Therefore, this paper uses a method of spatial data dimensionality reduction processing based on cyclic iterative calculation to optimize its STAP. The final experimental results show that, after spatial data dimensionality reduction processing optimization, the STAP performance of EFA algorithm is further expanded in the range of sample number adaptation; especially in the case of small sample number, the optimized STAP performance has been basically close to the ideal compared with other optimization schemes; tap performance also proves that the optimization scheme in this paper has better convergence speed and STAP performance.

Airborne Phased-Array Radar (APAR): The Next Generation of Airborne Polarimetric Doppler Weather Radar

<p>This paper presents a configuration of a novel, airborne phased array radar (APAR) motivated by major advances in cellular technology, component miniaturization, and radar antenna simulation software. This has paved the way for a next-generation radar being designed by NCAR/EOL to be installed on the NSF/NCAR C-130 aircraft. The APAR system will consist of four removable C-band active electronically scanned arrays (AESA) strategically placed on the fuselage of the aircraft. Each AESA measures approximately 1.5 x 1.5 m and is composed of 2368 active radiating elements arranged in a total of 37 line replaceable units (LRU). Each LRU is composed of 64 radiating elements that are the building block of the APAR system.</p><p> </p><p>Polarimetric measurements are not available from current airborne tail Doppler radars. However, APAR, with dual-Doppler and dual polarization diversity at a lesser attenuating C-band wavelength, will further advance the understanding of the microphysical processes within a variety of precipitation systems<em>. </em>Such unprecedented observations, in conjunction with the advanced radar data assimilation schema, will be able to address the key science questions to improve understanding and predictability of significant weather.</p><p>A Mid-scale Research Infrastructure proposal is submitted to the National Science Foundation to request the implementation cost. The development is expected to take ~5 years after the funding is in place. It adopts a phased approach as an active risk assessment and mitigation strategy. At the present time, both the National Science Foundation and the National Oceanic and Atmospheric Administration are funding the APAR project for risk reduction activities. The APAR Team is actively seeking partners in industry and in the university community. An APAR science and engineering advisory panel has been organized.</p><p> </p><p>The authors will review the overall design and current progress of APAR and outline ambitious future development work needed to bring this exceptional tool into full operation.</p>

Airborne polarimetric Doppler weather radar: trade-offs between various engineering specifications

NCAR EOL is investigating potential configurations for the next-generation airborne phased array radar (APAR) that is capable of retrieving dynamic and microphysical characteristics of clouds and precipitation. The APAR will operate at C band. The APAR will use the electronic scanning (e-scan) feature to acquire the optimal number of independent samples for recording research-quality measurements. Since the airborne radar has only a limited time for collecting measurements over a specified region (moving aircraft platform ∼ 100 m s−1), beam multiplexing will significantly enhance its ability to collect high-resolution, research-quality measurements. Beam multiplexing reduces errors in radar measurements while providing rapid updates of scan volumes. Beamwidth depends on the size of the antenna aperture. Beamwidth and directivity of elliptical, circular, and rectangular antenna apertures are compared and radar sensitivity is evaluated for various polarimetric configurations and transmit–receive (T/R) elements. In the case of polarimetric measurements, alternate transmit with alternate receive (single-channel receiver) and simultaneous reception (dual-channel receiver) is compared. From an overall architecture perspective, element-level digitization of T/R module versus digital sub-array is considered with regard to flexibility in adaptive beamforming, polarimetric performance, calibration, and data quality. Methodologies for calibration of the radar and removing bias in polarimetric measurements are outlined. The above-mentioned engineering options are evaluated for realizing an optimal APAR system suitable for measuring the high temporal and spatial resolutions of Doppler and polarimetric measurements of precipitation and clouds.