Design of Near Infrared Sky Brightness Monitor and Test Running at Ngari Observatory in Tibet

TL;DR

This paper presents the design and deployment of a Near Infrared Sky Brightness Monitor at Ngari Observatory in Tibet, providing initial sky brightness data crucial for astronomical research in this high-altitude site.

Contribution

A novel NIR sky brightness monitor based on InGaAs photodiodes, with improved SNR and data acquisition, and its initial deployment at Ngari Observatory.

Findings

First NIR sky brightness data at Ngari Observatory

Demonstrated effective use of chopper modulation and lock-in amplification

Instrument calibrated and operational since July 2017

Abstract

Tibet is known as the third pole of the earth, as high as the South Pole and North Pole. The Ngari (Ali) observatory in Tibet has the advantage of plenty of photometric night, low precipitable water vapor, high transmittance, good seeing. It is a good site, and promising to be one of the best place for infrared and submillimeter observations in the world. However, there is no data available for sky background brightness in such place, which restrict the astronomical development of the sites. In the near infrared band of J, H, Ks, a NIR sky brightness monitor (NISBM) is designed based on InGaAs photoelectric diode. By using the method of chopper modulation and digital lock-in amplifier processing, the SNR (Signal Noise Ratio), detectivity and the data acquisition speed of the device is greatly improved. For each band of J, H, Ks, an independent instrument is designed and calibrated in laboratory. The NISBM has been installed in Ngari observatory in July of 2017 and obtained the first data of NIR sky brightness at Ngari observatory.