IMOS - Satellite Remote Sensing - Satellite Altimetry Calibration and Validation Sub-Facility

Satellite-based altimeters provide fundamental observations of sea surface height that continue to underpin our understanding of the ocean’s role in the Earth’s climate system. Understanding changes in mean sea level at global to regional scales is critical for understanding the response of the ocean to a warming climate – both through the thermal expansion of the ocean and the melting of mountain glaciers and polar ice caps. Sea surface height also provides a lens into ocean dynamic processes at regional to local scales. As with all scientific observations, validation of instrumentation is vital to ensure that measurements are accurate and reliable.

The IMOS Satellite Altimeter Calibration and Validation Sub-Facility maintains a suite of instrumentation primarily in Bass Strait, providing the only southern hemisphere in situ calibration and validation site that has operated since the launch of the TOPEX/Poseidon mission in 1992. The facility uses Global Navigation Satellite Systems (GNSS) equipped buoys on the ocean surface as well as an array of sub-surface moored oceanographic instrumentation that includes temperature, pressure and salinity sensors and advanced 5-beam acoustic doppler current profilers (ADCPs). Data from this infrastructure is combined to derive a sustained Sea Surface Height (SSH) record that can be directly compared to altimeter measurements. These data provide important contributions to Ocean Surface Topography Science Team (OSTST) and other mission-specific validation teams including those associated with the Sentinel-6 Michael Freilich, Sentinel-3A and 3B, and SWOT missions. For validation of nadir altimeters, the key metric of interest to mission science teams the altimeter absolute bias, the difference between altimeter and in situ measurements of SSH in an absolute reference frame. Analysis of the absolute bias record over time helps ensure data produced from satellite altimeters are accurate and precise on a global scale.

In addition to the primary site located in Bass Strait, the sub-facility operates some sensors opportunistically at other sites including at the Southern Ocean Flux Station (SOFS) in the Southern Ocean, and at Davies Reef and Yongala in and adjacent to Great Barrier Reef. Data made available from the sub-facility includes:

Bass Strait (various locations corresponding to different altimeter comparison points)
• Bottom pressure, temperature and salinity (P, T, S)
• Water current (U, V)
• Significant Wave Height (SWH)
• Sea Surface Height (SSH)
• Note different temporal extents and sampling rates are provided on a site-by-site basis deploying on deployments and variable of choice.

Southern Ocean
• Sea Surface Height
• Significant Wave Height
• Note two different sampling rates are provided. The temporal extent depends on the SOFS deployment.

Davies Reef and Yongala
• Bottom pressure, temperature and salinity (P, T, S)
• Sea Surface Height
• Note different temporal extents and sampling rates are provided on a site-by-site basis deploying on deployments and variable of choice.

星载高度计（satellite-based altimeters）可提供海面高度的基础观测数据，持续支撑我们对海洋在地球气候系统中作用的认知。理解全球至区域尺度的平均海平面变化，对于认识海洋对气候变暖的响应至关重要——这一响应既包括海洋热膨胀，也涵盖山地冰川与极地冰盖的消融。海面高度同时也是探究区域至局地尺度海洋动力过程的窗口。与所有科学观测一样，仪器校准与验证对保障观测数据的准确性与可靠性至关重要。

IMOS卫星高度计校准与验证子设施（IMOS Satellite Altimeter Calibration and Validation Sub-Facility）主要在巴斯海峡（Bass Strait）部署了一套观测仪器，是自1992年TOPEX/Poseidon任务发射以来，南半球唯一持续运行的原位校准与验证站点。该设施依托海面搭载全球导航卫星系统（GNSS）的浮标，以及一套包含温度、压力、盐度传感器与先进五波束声学多普勒流速剖面仪（ADCPs）的水下锚定海洋观测仪器阵列开展工作。通过整合该观测基础设施获取的数据，可生成连续的海面高度（SSH）序列，用于与卫星高度计观测结果直接比对。这些数据为海洋表面地形科学团队（OSTST）以及其他任务专属验证团队提供了重要支撑，包括服务于Sentinel-6 Michael Freilich、Sentinel-3A、Sentinel-3B以及SWOT任务的验证团队。对于天底观测高度计的验证而言，任务科学团队关注的核心指标为高度计绝对偏差——即绝对参考框架下，卫星高度计与原位观测的海面高度之差。对绝对偏差序列的长期分析，有助于保障卫星高度计生成的全球观测数据具备准确性与精密度。

除巴斯海峡的主站点外，该子设施还在其他站点临时部署部分传感器，包括南大洋通量站（SOFS）以及大堡礁海域及周边的戴维斯礁（Davies Reef）与永加拉礁（Yongala）。该子设施对外公开的数据包括：

巴斯海峡（对应不同高度计比对点的多个测点）
• 底压、温度与盐度（P、T、S）
• 海流（U、V分量）
• 有效波高（SWH）
• 海面高度（SSH）
• 注：各站点的时间跨度与采样率因部署方案与观测变量而异。

南大洋站点
• 海面高度
• 有效波高
• 注：提供两种不同的采样率，时间跨度取决于南大洋通量站的部署周期。

戴维斯礁与永加拉礁站点
• 底压、温度与盐度（P、T、S）
• 海面高度
• 注：各站点的时间跨度与采样率因部署方案与观测变量而异。