Collaborative Research: Ground-based Very Low Frequency (VLF) and High Frequency (HF) Measurements in Support of the VIPER Sounding Rocket Experiment

众所周知，甚低频（VLF）范围内的无线电发射可以在地球表面和高度接近90公里的高层大气部分电离层（称为D区域）之间传播很长距离。 D区影响用于远程潜艇通信的极低频（ELF）和许多关键通信系统使用的高频（HF）之间的远程无线电通信。 甚低频发射也可以逃离电离层，传播到更高的高度，等离子体密度更高。自然和人为的甚低频发射也可引起磁层中的波粒散射，导致电离层中的粒子沉降。甚低频无线电波传播和信号强度降低一直是具有挑战性的模型和观察，主要是由于缺乏连续的测量在D区和显着的不确定性，在这些高度的等离子体和中性密度的知识。在该项目中，将对现有的甚低频跨电离层传播实验火箭（VIPER）实验进行改进，该实验将于2020年7月从沃洛普斯岛发射。VIPER将提供关于沿其轨道沿着探测到的无线电波的重要信息，从而能够确定通过电离层D区域的甚低频衰减。具体而言，该项目将支持在发射站附近安装地基甚低频和高频接收器，以提供地面实况测量结果，与火箭测量结果进行比较。这些地面测量将限制电离层状态，并将能够准确评估甚低频波随高度的衰减情况。该项目还将支持CU Boulder的一名学生的教育，CU Boulder的一名博士后和UC Berkeley的一名博士后的培训，加强他们的继续教育，并提供一个独特的机会来了解Wallops Flight Facility的宝贵工作。这种合作努力提供直接从源发射机引用的VLF波振幅和相位的直接多点测量。VIPER将测量从缅因州卡特勒广播的NAA（24.0 kHz）发射机信号的高度分辨幅度和相位，从而能够确定通过碰撞D区电离层的甚低频衰减。VIPER还将在穿越电离层期间测量等离子体密度和高频信号幅度。 除了火箭测量外，我们还将在发射机上进行甚低频测量;在地面上进行下靶场测量;并将下靶场测量作为60至150公里的高度剖面。这些测量将提供前所未有的洞察碰撞D区等离子体的VLF波的衰减。反过来，这种衰减将使人们深入了解地面发射机信号对D区电离层的影响及其注入磁层的情况。该项目还有可能对闪电天电（地面）和哨声（电离层以上）进行测量，提供这种衰减的宽带（直流至兆赫）视图。 闪电观测是次要目标，对项目的成功并不重要。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Radio emissions in the Very Low Frequency (VLF) range are known to propagate long distances bouncing between the surface of the Earth and the partially ionized layer of the upper atmosphere near 90 km in altitude called the D region. The D-region impacts long range radio communications between extremely low frequencies (ELF), used for long-range submarine communications, and high frequencies (HF), used by many critical communications systems. VLF emissions can also escape the ionospheric layer and propagate to much higher altitudes with denser plasma. VLF emissions of both natural and man-made origin can also cause wave-particle scattering in the magnetosphere resulting in particle precipitation in the ionosphere. VLF radio wave propagation and signal strength reduction has been challenging to model and observe, mostly due to the lack of continuous measurements in the D region and significant uncertainties in the knowledge of both plasma and neutral densities at these altitudes. In this project, an enhancement will be made to the existing VLF Trans-Ionospheric Propagation Experiment Rocket (VIPER) experiment, to launch from Wallops Island in July 2020. VIPER will provide important information about radio waves detected along its trajectory, enabling a determination of the VLF attenuation through the ionospheric D region. Specifically, this project will support the installation of ground-based VLF and HF receivers near the transmitter site to provide ground-truth measurements to compare to the rocket measurements. These ground measurements will constrain the ionospheric state and will enable an accurate assessment of the attenuation of the VLF wave as a function of altitude. This project will also support the education of a student at CU Boulder, the training of a postdoc at CU Boulder and a postdoc at UC Berkeley, enhancing their continuing educations and providing a unique opportunity to learn about the valuable work at Wallops Flight Facility.This collaborative effort with provide direct multi-point measurements of VLF wave amplitude and phase, referenced directly from the source transmitter. VIPER will measure the height-resolved amplitude and phase of the NAA (24.0 kHz) transmitter signal broadcast from Cutler, Maine, enabling a determination of the VLF attenuation through the collisional D-region ionosphere. VIPER will also measure the plasma density and HF signal amplitudes during the ionospheric traverse. Together with the rocket measurements, we will have VLF measurements at the transmitter; downrange on the ground; and downrange as an altitude profile from 60 to 150 km. These measurements will provide unprecedented insight into the attenuation of VLF waves by the collisional D-region plasma. In turn, this attenuation will yield insight into the effect of ground-based transmitter signals on the D-region ionosphere and their injection into the magnetosphere. The project also has the potential to make measurements of lightning sferics (on the ground) and whistlers (above the ionosphere), providing a broadband (DC to MHz) view of this attenuation. The lightning observations are a secondary goal and are not critical to the success of the project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.