Differential atmospheric dispersion, due to the wavelength-dependent index of refraction of the atmosphere, affects ground-based observations. To correct this effect, the usage of an atmospheric dispersion corrector (ADC) is fundamental. Insufficient or wrong correction of the atmospheric dispersion produces a spectrally elongated shape instead of a circular white one for the observed target. The commissioning tests of ADCs with on-sky observations are not an easy task. In fact, the residual dispersion is expected to be of a few tens of milliarcsec, with the object for a seeing limited telescope being almost 1 arc sec. A procedure was developed, based on ellipse fitting of several cuts from the guiding camera images, to determine the levels of oblongness in an object image caused by atmospheric dispersion. The characterization of the data allows for the validation of the ADC alignment by determining the dispersion direction and minimizing the ellipticity. The ellipse fit method was tested on ESPRESSO using the guiding camera images. The procedure was tested and demonstrated using simulated data that mimics the expected images using real sky dispersion models and real sensor characteristics. The accuracy of the method is highly dependent on the observational conditions and on the ratio between expected elongation (dispersion) and image size, but it is expected that the method can be more sensitive than traditional ADC on-sky alignment methods.

中文翻译：

---

大气色散校正器天空调试测试的简单概念

由于大气折射率的波长相关指数，不同的大气色散会影响地面观测。为了纠正这种影响，使用大气色散校正器 (ADC) 是基础。对大气色散的不充分或错误校正会产生光谱拉长的形状，而不是观察目标的圆形白色形状。使用空中观测对 ADC 进行调试测试并非易事。事实上，残余色散预计为几十毫弧秒，而一个视距有限的望远镜的目标几乎是 1 弧秒。开发了一种程序，基于对引导相机图像的多个切割进行椭圆拟合，以确定大气扩散引起的物体图像中的椭圆度水平。数据表征允许通过确定色散方向和最小化椭圆度来验证 ADC 对齐。使用引导相机图像在 ESPRESSO 上测试椭圆拟合方法。该程序使用模拟数据进行测试和演示，模拟数据使用真实天空色散模型和真实传感器特性模拟预期图像。该方法的准确性高度依赖于观测条件以及预期伸长率（色散）与图像尺寸之间的比率，但预计该方法可以比传统的 ADC 天空对准方法更灵敏。该程序使用模拟数据进行测试和演示，模拟数据使用真实天空色散模型和真实传感器特性模拟预期图像。该方法的准确性高度依赖于观测条件以及预期伸长率（色散）与图像尺寸之间的比率，但预计该方法可以比传统的 ADC 天空对准方法更灵敏。该程序使用模拟数据进行测试和演示，模拟数据使用真实天空色散模型和真实传感器特性模拟预期图像。该方法的准确性高度依赖于观测条件以及预期伸长率（色散）与图像尺寸之间的比率，但预计该方法可以比传统的 ADC 天空对准方法更灵敏。