Real-time frequency management is a vital element in the effective operation of an over-the-horizon backscatter (OTH-B) HF radar. In the case of the Australian project Jindalee OTH-B HF radar, a comprehensive frequency management system has been developed for this purpose. The frequency management system includes subsystems for ionospheric backscatter, vertical and oblique incidence sounding, HF spectral surveillance, and incorporates a low powered backscatter radar. The system is capable of providing real-time frequency management advice to the main radar, and of acquiring synoptic data for off-line analysis. In this paper we describe the hardware architecture and signal processing schemes, together with sample data, for each of the subsystems. We then describe the manipulation of the environmental data in order to provide frequency management advice to the main radar.behavior of the ionosphere can adequately be de-automation, in order that the advice did not require scribed in this manner, the ionosphere is specialist interpretation. The second requirement was characterized by large fluctuations about the for the system to gather data routinely (nominally 24 monthly median [Rush et al., 1974; Paul, 1983]. hours per day) with the objective of building up a Hence, as communicators have sought enhanced per-synoptic data base of the propagation environment, formance from HF circuits (e.g., the transmission of even when the main radar was not in use. In order digital data), it has been recognized that there is a that the data base could be used to provide quantitaneed for real-time frequency management of such cir-tire estimates of radar performance, all data had to cuits [CCIR, 1982]. be calibrated.
The operation of an HF radar represents one ofThe purpose of this paper is to describe the design the most demanding applications of the ionosphere and capabilities of the system together with some as a transmission channel for radiowaves. Successful initial results. We also describe the manipulation of operation of such a radar necessitates careful selec-the environmental data to provide operational data tion of the operating frequency, based upon the cur-to the main radar. The statistical analysis of the derent state of the ionosphere, combined with the spe-tailed synoptic measurements will be reported in subsequent papers, while application of the system to the problem of providing frequency management support Copyright 1987 by the American Geophysical Union. to the main radar for the purpose of remote sea state Paper number 6S0553. sensing has already been reported [Earl and Ward, 0048.6604/87/006s-0553508.00 1986'].
The Shields entrainment function, extrapolated from bed load movement to predict the threshold of particle motion, appears deficient in analyzing incipient shear data for fluid‐sediment combinations encompassing a wide range of relative densities. Equations describing incipient dynamic equilibrium, solved semiempirically, indicate additional density considerations that must be included in an attempt to correlate initial movement for all possible sedimentation density ratios. This and other experimental investigations also indicate any entrainment function to be dependent on the state of the bed and corresponding turbulence. Other factors which might be influential on the threshold of particle movement are mentioned.
A network of oblique angle‐of‐arrival (AoA) ionosondes was installed as part of the Elevation‐scanned Oblique Incidence Sounder Experiment (ELOISE) in September 2015. The ELOISE experimental campaign was designed to study the spatial and temporal structure of ionospheric variability at midlatitudes, of which traveling ionospheric disturbances are a key component. The new AoA sounder makes use of Defence Science and Technology Group's direct‐digital high‐frequency transmitter and receiver technology, to enable multichannel collection of both ionograms and channel scattering functions (Doppler spectra) on a common 2‐D array. In this paper, the array design and onboard signal processing for the AoA sounder is described, along with a sample of results showing typical disturbance signatures across the delay, Doppler frequency, bearing, and elevation measurements. Realistic parameterized models of electron density perturbations, along with geometric ray tracing, were used to synthesize the effects of medium‐ to large‐scale traveling ionospheric disturbances on the sounder observables and aid in interpreting the measured signatures.
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