The SPHERE-2 balloon-borne detector designed for extensive air shower (EAS) observations using EAS optical Vavilov-Cherenkov radiation (``Cherenkov light''), reflected from the snow-covered surface of Lake Baikal is described. We briefly discuss the concept behind the reflected Cherenkov light method, characterize the conditions at the experimental site and overview the construction of the tethered balloon used to lift the SPHERE-2 telescope above the surface. This paper is mainly dedicated to a detailed technical description of the detector, including its optical system, sensitive elements, electronics, and data acquisition system (DAQ). The results of some laboratory and field tests of the optical system are presented.

中文翻译：

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SPHERE-2 探测器用于观察 1 PeV – 1 EeV 能量范围内的大量风淋

SPHERE-2 气球携带探测器设计用于广泛的空气淋浴 (EAS) 观测，使用 EAS 光学瓦维洛夫-切伦科夫辐射（“切伦科夫光”），从贝加尔湖白雪覆盖的表面反射。我们简要讨论了反射切伦科夫光法背后的概念，描述了实验地点的条件，并概述了用于将 SPHERE-2 望远镜提升到表面上方的系留气球的构造。本文主要对探测器进行详细的技术描述，包括其光学系统、敏感元件、电子器件和数据采集系统（DAQ）。介绍了该光学系统的一些实验室和现场测试结果。