Attch_2_SOO_FINAL_R1_CALL_002_HF_Backscatter_dtd_20190212.docx

Statement of Objectives (SOO)

Topic 3 a): (Solar, Solar Wind and Ionospheric Effects): Characterization of HF Backscatter and Noise Environment Dated 12 Feb 19

1.0 Scope

To provide real-time modeling capabilities to specify the high frequency (HF) radio backscatter and directional noise environment in order to meet various Air Force ionospheric diagnostic needs for reliable communications and use of over-the-horizon radar (OTHR). These models are to complement current AFRL technology for estimating the HF backscatter and noise environment. In particular, AFRL is seeking a backscatter model that includes real time Bragg scatter from ocean waves and land surface features. Furthermore, we seek real-time directional modeling of HF radio noise from astrophysical radio sources, tropospheric lightning, and anthropogenic sources.

2.0 Performance Objectives

2.1 Overall Objective:

The DoD is heavily invested in HF systems, in terms of communications and their use in OTHR. As part of this investment, AFRL/RVBX has been tasked with understanding and describing HF propagation. In order to meet our research requirements involving HF systems, we must be able to characterize the HF backscatter and noise environment. Specifically, this concerns OTHR backscatter from ocean waves and land features, as well as HF noise from astrophysical radio sources, lightning, and anthropogenic radio sources.

Current efforts utilize a simple ocean wave model that calculates surface waves from local wind estimates. A Bragg scatter model is then applied to these waves to estimate a backscatter Doppler spectra. Non-local sources of ocean waves are ignored. Similarly, HF backscatter from land features is currently ignored in our models. A single backscatter value is used for all types of terrain, regardless of surface features, roughness and conductivity. Along with noise added through the backscatter processes, HF receivers are subject to interference from the HF radio noise associated with the celestial background, lightning, and anthropogenic radio sources. The noise from these sources is variable in both time and angle of arrival, but current efforts assume isotropic noise.

The objectives of this call are to augment current capabilities for modeling the HF backscatter and noise environment, described as follows (1) To receive an OTHR Bragg scatter algorithm that takes into account both local and nonlocal ocean wave sources and has the ability to assimilate real time ocean wave data. (2) To receive an OTHR land surface feature backscatter algorithm that takes into account terrain features, roughness, and conductivity. Such a model would ingest data for terrain features and may also include conductivity changes due to variables such as snow pack, rainfall, and tides. (3) To receive comprehensive HF noise algorithms that take in real-time data to accurately estimate the power as a function of azimuth and elevation coming from astrophysical sources, lightning, and anthropogenic radio noise. These noise models need to be compatible with any given location and time on earth.

2.2 Technical Objectives:

a) Background Scatter Algorithms

i. Real-time driven ocean wave algorithm (local wave structure)

· Develop model of Bragg scatter off of ocean wave spectra

· Incorporate both local and nonlocal generated waves

· Integrate wave measurements into a Bragg model

· Demonstrate validation using data

ii. First order terrain integration backscatter algorithm

· Develop a terrain based backscatter model

· Must utilize a terrain database to estimate backscatter from various land structures

· This algorithm must inform the normal to the surface for each HF ray-ground interaction

· Demonstrate validation using data

b) Directional Noise Climatology Algorithms (can be separate or in one all-inclusive model)

i. HF radio noise from astrophysical sources

· Develop an algorithm that provides the power of HF radio noise from astrophysical sources as a function of azimuth, elevation, time and frequency

· Needs to take into account the maximum frequency of propagation allowed by the ionosphere as a function of position

· Needs to give accurate estimates for any given location on earth

· Should utilize HF or near HF measurements and astrophysical radio noise models

ii. HF radio noise from lightning

· Develop an algorithm that provides the power of HF radio noise from lightning as a function of azimuth, elevation, time and frequency

· Needs to take into account ionospheric parameters dictating over the horizon propagation of lightning radio emissions

· Needs to give accurate estimates for any given location on earth

· May utilize real-time data such as global lightning detector networks and/or weather observations (regional/global sources) for estimates or verification

iii. HF radio noise from anthropogenic sources

· Develop an algorithm that provides the power of HF radio noise from anthropogenic sources as a function of azimuth, elevation, time and frequency

· Needs to take into account ionospheric parameters dictating over the horizon propagation of anthropogenic radio emissions

· Needs to give accurate noise estimates from local and distant sources for any given location on earth

· May utilize real-time or archived data for estimates and verification

· Demonstrate validation of noise estimates using data

SOO To Call 002 FA9453-19-S-0001 1