Krietemeyer Andreas, van der Marel Hans, van de Giesen Nick, Ten Veldhuis Marie-Claire
Faculty of Civil Engineering, Delft University of Technology, 2628 CN Delft, The Netherlands.
R&D Department of Seismology and Acoustics, Royal Netherlands Meteorological Institute (KNMI), Utrechtseweg 297, 3731 GA De Bilt, The Netherlands.
Sensors (Basel). 2022 Mar 15;22(6):2267. doi: 10.3390/s22062267.
Low-cost dual-frequency receivers and antennas have created opportunities for a wide range of new applications, in regions and disciplines where traditional GNSS equipment is unaffordable. However, the major drawback of using low-cost antenna equipment is that antenna phase patterns are typically poorly defined. Therefore, the noise in tropospheric zenith delay and coordinate time series is increased and systematic errors may occur. Here, we present a field calibration method that fully relies on low-cost solutions. It does not require costly software, uses low-cost equipment (~500 Euros), requires limited specialist expertise, and takes complex processing steps into the cloud. The application is more than just a relative antenna calibration: it is also a means to assess the quality and performance of the antenna, whether this is at a calibration site or directly in the field. We cover PCV calibrations, important for deformation monitoring, GNSS meteorology and positioning, and the computation of PCOs when the absolute position is of interest. The method is made available as an online web service. The performance of the calibration method is presented for a range of antennas of different quality and price in combination with a low-cost dual-frequency receiver. Carrier phase residuals of the low-cost antennas are reduced by 11-34% on L1 and 19-39% on L2, depending on the antenna type and ground plane used. For the cheapest antenna, when using a circular ground plane, the L1 residual is reduced from 3.85 mm before to 3.41 mm after calibration, and for L2 from 5.34 mm to 4.3 mm. The calibration reduces the Median Absolute Deviations (MADs) of the low-cost antennas in the vertical direction using Post Processed Kinematic (PPK) by 20-24%. For the cheapest antenna, the MAD is reduced from 5.6 to 3.8 mm, comparable to a geodetic-grade antenna (3.5 mm MAD). The calibration also has a positive impact on the Precise Point Positioning (PPP) results, delivering more precise results and reducing height biases.
低成本双频接收机和天线为一系列新应用创造了机会，这些应用分布在传统全球导航卫星系统（GNSS）设备价格高昂的地区和学科领域。然而，使用低成本天线设备的主要缺点是天线相位方向图通常定义不明确。因此，对流层天顶延迟和坐标时间序列中的噪声会增加，并且可能会出现系统误差。在此，我们提出一种完全依赖低成本解决方案的现场校准方法。它不需要昂贵的软件，使用低成本设备（约500欧元），所需的专业知识有限，并将复杂的处理步骤转移到云端。该应用不仅仅是一种相对天线校准：它还是一种评估天线质量和性能的手段，无论这是在校准场地还是直接在野外进行评估。我们涵盖了对形变监测、GNSS气象学和定位以及在关注绝对位置时计算天线相位中心偏移（PCO）很重要的相位中心偏差（PCV）校准。该方法以在线网络服务的形式提供。结合低成本双频接收机，针对一系列不同质量和价格的天线展示了校准方法的性能。根据天线类型和使用的地面平面，低成本天线的载波相位残差在L1频段降低了11% - 34%，在L2频段降低了19% - 39%。对于最便宜的天线，使用圆形地面平面时，L1残差从校准前的3.85毫米降至校准后的3.41毫米，L2残差从5.34毫米降至4.3毫米。该校准使用后处理动态（PPK）方法在垂直方向上降低了低成本天线的中位数绝对偏差（MAD）20% - 24%。对于最便宜的天线，MAD从5.6毫米降至3.8毫米，与大地测量级天线（MAD为3.5毫米）相当。该校准对精密单点定位（PPP）结果也有积极影响，能提供更精确的结果并减少高度偏差。
