Cloud Detector measurements made at Davis Station, Antarctica

It had been shown that remote cloud detection can be performed with the use of new generation Thermopile detectors. The detection method is based on the fact that a cloudy sky will be warmer than a clear sky. An ideal cloud detection system would also need to account for the effects of relative humidity and barometric pressure, however good performance can still be obtained by ignoring these effects. AAD Thermopile Detector=====================A Thermopile detector is used to remotely measure the temperature of the sky. The TPS 534 Thermopile detector chosen is fitted with a 5.5um Longpass (standard) IR filter, which allows precise remote temperature measurement of an ideal black body source. The TPS 534 Thermopile detector produces an output voltage that is positive when the temperature of the scene it is viewing is higher than the temperature of itself, and a negative output voltage when the temperature of the scene it is viewing is lower than the temperature of itself. For this reason it is necessary to compensate for the temperature of the detector. The TPS 534 Thermopile detector has an internal NTC Thermistor which can be used for temperature compensation. This Cloud Detector design implements a very simple analogue form of temperature compensation. The main drawback of an analogue temperature compensation system is that the NTC Thermistor has a very non-linear response with temperature which can only be partially corrected using a linearization resistance network. The other main drawback of an analogue temperature compensation system is that the system gains and voltage levels must be precisely adjusted by trial and error to guarantee correct operation over the desired operational temperature range.The Cloud Detector is designed for an operational temperature range of -30 degrees to +25 degrees Celsius. Operation outside of this range may cause internal signal saturation, and incorrect temperature compensation performance. The Cloud Detector optical field of view has been constrained to a 30 degrees full angle with the use of a cylindrical baffle assembly fitted directly to the Thermopile detector. The dimensions of the cylindrical baffle assembly could in theory be defined such that any field of view up to 80 degrees could be achieved.The Cloud Detector provides three plus or minus 10V output voltage signals to the data logging hardware :- Uncompensated Sensor Output Signal :Thermopile detector output signal without any analogue temperature compensation.The output voltage is proportional to the amount of cloud detected within the field of view of the     instrument.- Compensated Sensor Output Signal :Thermopile detector output signal with analogue temperature compensation.The output voltage is proportional to the amount of cloud detected within the field of view of the     instrument.- Temperature Output Signal :Linearised NTC Thermistor output signal used to apply analogue temperature compensation to the Thermopile detector output signal.The output voltage is proportional to the temperature of the Thermopile detector. The output voltage is uncalibrated, however the temperature verses output voltage could easily be measured.Boltwood Cloud Sensor===================This is a commercial cloud sensor unit manufactured by diffraction limited.

已有研究表明，利用新一代热电堆（Thermopile）探测器可实现遥感云检测。该检测方法的核心原理为：多云天空的温度高于晴朗天空。理想的云检测系统还需考虑相对湿度与大气压力的影响，但即便忽略这些因素，仍可获得良好的检测性能。

AAD热电堆探测器
热电堆探测器用于远程测量天空温度。本设计选用的TPS 534型热电堆探测器配备了5.5μm长通（标准）红外（IR）滤光片，可对理想黑体源实现精准的远程温度测量。当被测场景温度高于探测器自身温度时，TPS 534热电堆探测器输出正电压；当被测场景温度低于探测器自身温度时，则输出负电压。因此，需对探测器自身温度进行补偿。TPS 534热电堆探测器内置负温度系数（NTC）热敏电阻，可用于温度补偿。本云探测器设计采用了一种极为简易的模拟式温度补偿方案。模拟温度补偿系统的主要缺陷在于：NTC热敏电阻的温度响应具有极强的非线性，仅能通过线性化电阻网络进行部分校正。该系统的另一核心缺陷为：需通过反复试错对系统增益与电压电平进行精准调校，方可确保其在目标工作温度范围内正常运行。

本云探测器的设计工作温度范围为-30℃至+25℃。超出该范围的工作环境可能导致内部信号饱和，进而引发温度补偿性能异常。通过直接安装于热电堆探测器的圆柱形遮光罩组件，可将云探测器的光学视场角限制为30°全角。理论上，通过调整圆柱形遮光罩组件的尺寸，可实现最大80°的视场角。

本云探测器可向数据记录硬件提供三路±10V的输出电压信号：
- 未补偿传感器输出信号：未施加任何模拟温度补偿的热电堆探测器输出信号。其输出电压与仪器视场内检测到的云量呈正比关系。
- 补偿后传感器输出信号：施加了模拟温度补偿的热电堆探测器输出信号。其输出电压与仪器视场内检测到的云量呈正比关系。
- 温度输出信号：用于对热电堆探测器输出信号进行模拟温度补偿的线性化NTC热敏电阻输出信号。其输出电压与热电堆探测器的温度呈正比关系。该输出电压未经过校准，但可通过实测建立输出电压与温度的对应关系。

博尔特伍德云传感器
该产品为由Diffraction Limited公司生产的商用云传感器设备。