The Antarctica Plateau with high altitude, low water vapor and low thermal emission from the atmosphere is known as one of the best sites on the earth for conducting astronomical observations from the near infrared to the sub-millimeter. Many optical astronomical telescopes are proposed by Chinese astronomical society at present, such as Kunlun Dark Universe Survey Telescope (KDUST), 6.5-meter optical telescopes and 12-meter optical and infrared telescopes. Accurate estimation of the sky background brightness of proposed sites provides the scientific basis for instruments design and observatory site selection. Based on this requirement, a near-infrared sky brightness monitor (NISBM) based on InGaAs photoelectric diode is designed by using the method of chopper modulation and digital lock-in amplifier in the near infrared band of J, H, Ks. The adaptability of the monitor under extremely low temperature conditions in Antarctica is promoted by taking advantage of PID heating and fault detection system. Considering the weak signal of Ks band in Antarctica, a surface blackbody is equipped for real-time calibration. For the adverse circumstances to human, an EPICS and Web based Remote Control Software is implemented for unattended operation. The NISBM has been successfully installed in Dome A, Antarctica on January 2019.
CSTAR2 is a new telescope array which consists of two telescopes with 145mm-aperture and an equatorial mount, which was planned to update the CSTAR (Chinese Small Telescope Array) installed at Dome A, Antarctica in 2008. Since the previous camera was out of product, a brand new CCD camera with 1K*1K pixels was developed for CSTAR2, which was tested function well at -80℃ to prove the ability to work at Antarctica in a long period. The camera has a well performance and the readout noise is as low as 3.99e-rms. An equatorial mount made by NIAOT (Nanjing Institute of Astronomical Optics & Technology) can rotate the telescope to point almost entire sky area. In order to control CSTAR2 in an efficient way, a multi-level software control system was developed which contains three main layers: device control layer, coordinating operation layer, user interface layer. The whole system was planned to achieve automatic observation and remote operation under the conditions of poor satellite-link network.
The Ngari (Ali) observatory is located in Ngari, Tibet, a region known as “the roof of the roof of the world.” The observatory benefits from abundant photometric nights, low perceptible water vapor, high transmittance, and good seeing. Due to these advantages, it promises to be one of the best locations in the world at which to make infrared and submillimeter observations. However, no data on the sky background radiation at this location are available, impacting the planning of future facilities at the observatory. To remedy this deficiency, a near-infrared sky brightness monitor (NISBM) has been designed to obtain data in the J, H, and Ks bands. This monitor is based on an InGaAs photoelectric diode and uses chopper modulation and digital lock-in amplifier processing, which considerably enhance its signal-to-noise ratio, detectivity, and data acquisition speed. An independent device has been designed for each band (J, H, and Ks) and calibrated in the laboratory. The NISBM was installed at the Ngari observatory in July 2017 and has obtained the first NIR sky brightness data for that location.
Tibet is known as the third pole of the earth. The Ngari (Ali) observatory in Tibet 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. 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. The NISBM has been installed in Ngari observatory in July of 2017 and obtained the first data of NIR sky brightness at Ngari observatory.
Infrared sky background level is an important parameter of grounded infrared astronomy observations, which should be firstly measured in a good infrared observatory site, and only the site with low background level is suitable for infrared observations. Infrared sky background level can provide background data for the design of related infrared instruments. However, there is no such data available for major sites in China. Based on the requirement, In order to supplement the current site survey data and guide the design of future infrared instruments, a multiband near-infrared sky brightness monitor (MNISBM) based on an InSb sensor is designed in this paper. The MNISBM consists of optical system, mechanical structure and control system, detector and cooler, high gain readout electronic system, operational software. It is completed and carried out an experimental measurement in the laboratory. The result shows that the sensitivity of the MNISBM meets the requirements of the measurement of near-infrared sky background level.