用GMRT观测金星的偏振和亮度温度
Polarisation and Brightness Temperature Observations of Venus with the GMRT
摘要：
在2015年7月25日和9月6日期间，金星在1297.67 MHz（23 cm），607.67 MHz（49 cm）和233.67 MHz（1.28 m）的频率下被巨型米波射电望远镜（GMRT）观测到，当时它接近它的下合。由这些观测结果得到的金星亮温（Tb）值分别为622{ \pm }43 K和554{ \pm }38 K（频率分别为1297.67和607.67 MHz），与以前的观测结果一致。试图在233.67 MHz下导出Tb，证实了321 K的上限，该上限明显低于先前报道的相同频率下的426 K的上限。我们还提出了金星表面的介电常数（ε）值估计使用程度的偏振图的金星，来自GMRT偏振观测和理论计算。在607.67 MHz和1297.67 MHz下，金星表面的ε估计为~4.5，接近于基于雷达的观测（包括麦哲伦在2.38 GHz（12.6 cm）下的观测）报告的ε值4至4.5。
英文摘要：
Venus was observed at frequencies of 1297.67 MHz (23 cm), 607.67 MHz (49 cm) and 233.67 MHz (1.28 m) with the Giant Metrewave Radio Telescope (GMRT) during the period of 25th July and 6th September 2015 when it was close to its inferior conjunction. Values of the brightness temperature (Tb) of Venus from these observations were derived as 622{\pm}43 K, 554{\pm}38 K for 1297.67 and 607.67 MHz frequencies, respectively, are in agreement with the previous observations. The attempt to derive the Tb at 233.67 MHz affirms an upper limit of 321 K which is significantly lower than the previously reported upper limit of 426 K at the same frequency. We also present the dielectric constant (ε) values of the Venus surface estimated using the degree of polarisation maps of Venus, derived from the GMRT polarisation observations and theoretical calculations. The ε of the Venus surface was estimated to be ~4.5 at both the 607.67 MHz and 1297.67 MHz, close to the reported values of ε of 4 to 4.5 from the radar-based observations including the Magellan observations at 2.38 GHz (12.6 cm).
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