Department of Geophysics, Stanford University, Stanford, CA 94305;
Department of Electrical Engineering, Stanford University, Stanford, CA 94305.
Proc Natl Acad Sci U S A. 2019 Sep 17;116(38):18867-18873. doi: 10.1073/pnas.1821646116. Epub 2019 Sep 3.
Airborne radar sounding can measure conditions within and beneath polar ice sheets. In Antarctica, most digital radar-sounding data have been collected in the last 2 decades, limiting our ability to understand processes that govern longer-term ice-sheet behavior. Here, we demonstrate how analog radar data collected over 40 y ago in Antarctica can be combined with modern records to quantify multidecadal changes. Specifically, we digitize over 400,000 line kilometers of exploratory Antarctic radar data originally recorded on 35-mm optical film between 1971 and 1979. We leverage the increased geometric and radiometric resolution of our digitization process to show how these data can be used to identify and investigate hydrologic, geologic, and topographic features beneath and within the ice sheet. To highlight their scientific potential, we compare the digitized data with contemporary radar measurements to reveal that the remnant eastern ice shelf of Thwaites Glacier in West Antarctica had thinned between 10 and 33% between 1978 and 2009. We also release the collection of scanned radargrams in their entirety in a persistent public archive along with updated geolocation data for a subset of the data that reduces the mean positioning error from 5 to 2.5 km. Together, these data represent a unique and renewed extensive, multidecadal historical baseline, critical for observing and modeling ice-sheet change on societally relevant timescales.
航空雷达探测可以测量极地冰盖内部和下方的情况。在南极洲,大多数数字雷达探测数据都是在过去 20 年中收集的,这限制了我们理解控制冰盖长期行为的过程的能力。在这里,我们展示了如何将 40 多年前在南极洲收集的模拟雷达数据与现代记录相结合,以量化数十年的变化。具体来说,我们对 1971 年至 1979 年间在 35 毫米光学胶卷上记录的超过 40 万公里的探索性南极雷达数据进行了数字化处理。我们利用数字化过程中增加的几何和辐射分辨率,展示了如何利用这些数据来识别和研究冰盖下方和内部的水文、地质和地形特征。为了突出它们的科学潜力,我们将数字化数据与当代雷达测量结果进行了比较,结果表明,南极洲西部思韦茨冰川残余的东冰架在 1978 年至 2009 年间变薄了 10%至 33%。我们还在一个持久的公共档案中完整地发布了扫描雷达图的集合,并为部分数据更新了地理定位数据,这将平均定位误差从 5 公里减少到 2.5 公里。这些数据共同构成了一个独特而又重新出现的广泛的、数十年的历史基线,对于在与社会相关的时间尺度上观察和模拟冰盖变化至关重要。