Phase compensation of MARSIS subsurface sounding data and estimation of ionospheric properties: New insights from SHARAD results
Phase compensation of MARSIS subsurface sounding data and estimation of ionospheric properties: New insights from SHARAD results
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MARSIS 地下探测数据的相位补偿和电离层特性的估计：SHARAD 结果的新见解
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发表时间：
2016
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通讯作者：
T. Watters
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作者：
B. Campbell;T. Watters
火星地下和电离层探测高级雷达（MARSIS）和浅层雷达（SHARAD）仪器的地下雷达探测观测受到电离层相位畸变的影响，导致图像模糊和延迟偏移。基于SHARAD图像校正的经验，我们建议MARSIS雷达图中的电离层模糊可以用沿航迹沿着平滑变化的二次相位误差模型进行补偿。这种方法产生了用于地质解释的聚焦良好的雷达图，并允许分析用于从先前MARSIS研究中的相位畸变项导出总电子含量（TEC）的模型的有效性范围。二次项似乎是一个很好的代理TEC在太阳天顶角>65°的MARSIS波段4（5 MHz）和>75°的波段3（4 MHz）。从2007年到2014年，MARSIS和SHARAD导出的TEC值的比较揭示了季节行为和日冕物质抛射导致的电离层活动特征的相关性。我们还提出了SHARAD和MARSIS的证据，一个持续的区域异常的雷达散射南阿尔西亚山。这些回波以前被认为是由电子密度变化引起的雷达信号折射引起的。有没有强有力的签名，但是，在二次图像补偿项与异常散射，这表明无论是负责折射信号路径的电子密度变化主要发生在偏离航天器轨道的区域，或者这些密度变化有一个最小的影响综合相位失真的subspacer足迹。我们建议观察和分析，以更好地限制这种回声的机制和时间。
Subsurface radar sounding observations by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) and Shallow Radar (SHARAD) instruments are affected by ionospheric phase distortions that lead to image blurring and delay offsets. Based on experience with SHARAD image correction, we propose that ionospheric blurring in MARSIS radargrams may be compensated with a model of smoothly varying quadratic phase errors along the track. This method yields well‐focused radargrams for geologic interpretation and allows analysis of the validity range for models used to derive total electron content (TEC) from phase distortion terms in previous MARSIS studies. The quadratic term appears to be a good proxy for TEC at solar zenith angles >65° for MARSIS Band 4 (5 MHz) and >75° for Band 3 (4 MHz). Comparison of MARSIS‐ and SHARAD‐derived TEC values from 2007 to 2014 reveals correlations in seasonal behavior and in the characterization of ionospheric activity due to coronal mass ejections. We also present SHARAD and MARSIS evidence for a persistent region of anomalous radar scattering south of Arsia Mons. These echoes have been previously suggested to arise from refraction of the radar signal by electron density variations. There are no strong signatures, however, in the quadratic image compensation term correlated with the anomalous scattering, suggesting either that electron density variations responsible for refracted signal paths occur primarily in regions offset from the spacecraft track or that these density changes have a minimal impact on the integrated phase distortion of the subspacecraft footprint. We suggest observations and analyses to better constrain the mechanism and timing of such echoes.