Ground-penetrating radar for precision radio cosmology

宇宙中的第一批恒星诞生于大爆炸后的几亿年后。这些恒星与今天存在的任何恒星都不一样，这段被称为“宇宙黎明”的宇宙历史在很大程度上是未知的领域。通过对天空的无线电频率测量，可以观测到第一批恒星。氢是宇宙中最丰富的元素，自然发出的光波长为21厘米。因为宇宙在膨胀，这个波长的延伸与氢发出的光的距离成正比（或者，等价地，与多久以前成正比）。氢的射电辐射敏感地依赖于第一批恒星，因此是阐明它们的物理性质和形成历史的有力工具。然而，这些频率（< 200mhz）的观测异常困难，因为来自天空的信号很容易被仪器行为的不确定性所污染。特别是，接收入射光的天线受到下面地面电磁特性的微妙影响：从本质上讲，地面是仪器的一个组成部分，因此必须作为实验的一部分进行表征。该提案将支持一个探地雷达（GPR）系统，该系统将用于执行宇宙黎明实验中土壤电磁特性的高精度测量。宇宙黎明仪器已经在麦吉尔开发，子系统已经广泛表征。我们将从魁北克中部的麦吉尔北极研究站和乌皮什卡站进行观察，我们的团队认为这是杰出的无线电安静地点，代表了加拿大独特的地理优势。有了新颖的宇宙黎明仪器，以及极好的观测位置，GPR将为宇宙黎明测量带来新的精度水平，并将帮助打开射电天空的新窗口。

The first stars in the universe were born a few hundred million years after the big bang. These stars were unlike any that exist today, and this period of the universe's history, known as "cosmic dawn," is largely uncharted territory. Observations of these first stars are possible via radio-frequency measurements of the sky. Hydrogen, which is the most abundant element in the universe, naturally emits light with a wavelength of 21 cm. Because the universe is expanding, this wavelength is stretched in proportion to how far away (or, equivalently, how long ago) the hydrogen emitted its light. The radio emission from hydrogen depends sensitively upon the first stars and is therefore a powerful tool for elucidating their physical properties and formation history. However, observations at these frequencies (<200 MHz) are exceptionally difficult because the signal from the sky can be easily contaminated by uncertainties in the instrument behavior. In particular, the antenna that receives incoming light is influenced in subtle ways by the electromagnetic properties of the underlying earth: in essence, the ground is an integral part of the instrument and therefore must be characterized as part of the experiment. This proposal will support a ground-penetrating radar (GPR) system that will be used to perform high-precision measurements of soil electromagnetic properties for cosmic dawn experiments. The cosmic dawn instrumentation has already been developed at McGill, and the subsystems have been extensively characterized. We will observe from the McGill Arctic Research Station and Uapishka Station in central Quebec, which our team has identified as outstanding radio-quiet sites that represent a unique Canadian geographic advantage. With novel cosmic dawn instrumentation in hand, as well as superb observing locations, the GPR will bring a new level of precision to cosmic dawn measurements and will help open a new window on the radio sky.