DIMM中计算公式的分析及验证实验

差分像运动监测仪（DIMM）是目前被广泛应用的大气相干长度测量仪，其传统计算公式中对接收子孔的要求限制了仪器的小型化。通过理论分析与数值计算，文中明确了计算公式中的物理意义，并提出采用新的计算公式能够降低对仪器几何结构的限制。用两个紧挨着的6 cm子孔替换原来标准DIMM中的子孔面罩，得到小型化DIMM测试原型，利用该小型化DIMM原型与一台标准DIMM放在一起同时观测相同的恒星开展大气相干长度测量对比实验。对于小型DIMM，实验结果显示，采用传统计算公式得到的纵向大气相干长度明显大于横向，而采用新计算公式得到的纵向与横向大气相干长度统计上更相一致。验证了文中关于DIMM中计算公式的论述。

Analysis of formulae in DIMM and the verified experiment

The Differential Image Motion Monitor (DIMM) is a widely used instrument for measuring atmospheric coherence length. The miniaturization of the instrument is limited by the requirement of receiving sub-aperture in the traditional formulae. Through theoretical analysis and numerical calculation, the physical meaning of formulae was clarified, and the new calculation formulae were proposed to reduce the limitation on the geometrical structure of the instrument. A miniaturized DIMM test prototype was obtained by replacing the mask in the original standard DIMM with two adjacent 6 cm sub-aperture mask. The miniaturized DIMM prototype was used together with a standard DIMM to simultaneously observe the same star for the comparison experiment of atmospheric coherence length measurement. For miniaturized DIMM, the experimental results show that the longitudinal atmospheric coherence length obtained by the traditional formulae is significantly larger than the transverse, and the longitudinal and transverse atmospheric coherence length obtained by the new formulae is more statistically consistent. Thus, the discussion on the calculation formula in DIMM is verified.