EAGLE/ICECAP II RADARGRAMS

These radargrams were collected as part of the ICECAP (International Collaborative Exploration of the Cryosphere through Airborne Profiling) collaboration in 2015/16 (ICP7) and 2016/17 (ICP8). These data were in part funded by the US National Science Foundation (grant PLR-1543452 to UTIG), Antarctic Gateway, ACE-CRC the G. Unger Vetlesen Foundation, and supported by the Australian Antarctic Division through project AAS-4346.These data collection represents georeferenced, time registered instrument measurements (L1B data) converted to SI units, and is of most interest to users who wish to reprocess the data. Users interested in geophysical observables should used the derived Level 2 dataset. The data format are netCDF3 files, following the formats used for NASA/AAD/UTIG's ICECAP/OIB project at NASA's NSIDC DAAC. Metadata fields can be accessed using the open source ncdump tool, or c, python or matlab modules. See https://www.loc.gov/preservation/digital/formats/fdd/fdd000330.shtml for resources on NetCDF-3, and https://nsidc.org/data/IR2HI1B/versions/1 for a description of the similar OIB dataset.RADAR Ice penetrating radar provides the geometry of the ice shelves and outlet glaciers, and provides constraints on properties at the base of the ice (e.g. subglacial waters, sub ice shelf melting)ER2HI1B        georeferenced radar echo data; 4 Hz NetCDF Data Acquisition ParametersA 1-μsec transmitted chirp was used for both surface and bed. Two 14-bit digitizer channels with offset receiver gain were used to record returned echoes over 64 μsec, accommodating 120 dB of dynamic range, including accurate representations of power of the surface and bed echoes.Bandwidth: 52.5-67.5 MHzTx power: 5700 WWaveform: 1 μsec FM chirp generation, analog down-conversion to 10 MHz centerSampling: 12-bit ADC at 50 MHz samplingRecord window: 64.74 μsecAcquisition: two gain channels separated by 47 dBDynamic Range: 120 dBMonostatic Rx/TxData rate: 2.2 MB/secMaximum Doppler frequency: 36 HzPulse Repetition Frequency: 6250 HzOnboard stacking: 32xProcessing ApproachUnfocused Synthetic aperture radar (SAR) processing was done (internally referred to as pik1). This is a quick form of processing with no dependencies on other instruments. The first 10 recorded stacks are coherently summed resulting in a 20 Hz sample rate. Then, a narrow band notch filter is applied at 10 MHz to remove local oscillator (LO) leakage. The pulse is compressed using frequency domain convolution of over-scaled synthetic chirp waveform. This results in gains of 83 dB from overscaled chirp, 11.7 dB from range compression, and -3 dB from Hanning window. These are converted to magnitude and five of these stacks are incoherently summed resulting in the final 4 Hz sample rate.Error SourcesFor this Level 1B product, errors in power may be due to transmitter or receiver malfunctions. Elevated background noise may occur with areas of strong surface scattering (for example crevasses) or Radio Frequency (RF) noise from anthropogenic sources (for example radio calls from the aircraft or other radar systems).

本数据集为冰圈机载剖面探测国际合作研究（International Collaborative Exploration of the Cryosphere through Airborne Profiling，简称ICECAP）项目的采集成果，数据获取时间覆盖2015/2016年度（ICP7）与2016/2017年度（ICP8）。本数据集部分经费由美国国家科学基金会（向德克萨斯大学海洋研究所UTIG拨付的PLR-1543452号项目）、Antarctic Gateway、ACE-CRC以及G·昂格·韦尔滕森基金会提供，并由澳大利亚南极局通过AAS-4346号项目予以支持。

本数据集为经地理配准、时间同步的仪器测量数据（L1B数据），已转换为国际单位制，主要面向希望对数据进行二次处理的用户。若需获取地球物理可观测值，请使用衍生的Level 2数据集。本数据集采用netCDF3格式，遵循美国国家航空航天局（NASA）/澳大利亚南极局（AAD）/UTIG的ICECAP/OIB项目在美国国家冰雪数据中心分布式主动存档中心（NSIDC DAAC）所采用的格式规范。可通过开源工具ncdump，或C、Python、Matlab模块读取元数据字段。如需了解NetCDF-3格式的相关资源，请访问https://www.loc.gov/preservation/digital/formats/fdd/fdd000330.shtml；如需了解类似的OIB数据集的说明文档，请访问https://nsidc.org/data/IR2HI1B/versions/1。

冰穿透雷达可获取冰架与出口冰川的几何形态，并可为冰底属性（如冰下水体、冰架底部融化情况）提供约束依据。
ER2HI1B：地理配准雷达回波数据；4Hz NetCDF格式

数据采集参数：
本次采集采用1微秒的发射线性调频脉冲（chirp），用于地表与冰底信号探测。系统配备两路带有偏移接收增益的14位数字化仪通道，可在64微秒的记录窗口内捕获回波信号，动态范围达120dB，能够准确反映地表与冰底回波的功率特征。
- 带宽：52.5~67.5 MHz
- 发射功率：5700 W
- 波形：1微秒调频线性调频脉冲生成，经模拟下变频至10 MHz中心频率
- 采样：采用12位模数转换器（ADC），采样率50 MHz
- 记录窗口：64.74 微秒
- 采集配置：两路增益差为47dB的增益通道
- 动态范围：120 dB
- 收发配置：单站收发（Monostatic Rx/Tx）
- 数据速率：2.2 MB/秒
- 最大多普勒频率：36 Hz
- 脉冲重复频率：6250 Hz
- 板载堆叠：32倍

处理方法：
本次采用非聚焦合成孔径雷达（Synthetic Aperture Radar，SAR）处理流程（内部代号为pik1），该处理方式无需依赖其他仪器，属于快速处理方案。首先将前10个记录的堆叠数据进行相干求和，得到20 Hz的采样率；随后在10 MHz处施加窄带陷波滤波器，以消除本地振荡器（Local Oscillator，LO）泄漏。通过对过缩放的合成线性调频脉冲波形进行频域卷积实现脉冲压缩，该过程可获得83 dB的过缩放增益、11.7 dB的距离压缩增益，以及汉宁窗带来的-3 dB增益。将处理结果转换为幅值形式后，对其中5个堆叠数据进行非相干求和，最终得到4 Hz的采样率。

误差来源：
对于本Level 1B产品，功率误差可能源于发射机或接收机故障。背景噪声升高可能出现在强地表散射区域（如冰裂缝），或来自人为源的射频（Radio Frequency，RF）干扰（如航空器无线电通话或其他雷达系统的信号）。