José Uribe

Airborne radar sounder for temperate ice: initial results from Patagonia

We describe the development of a low-frequency airborne radar specifically designed for the sounding of temperate ice. The system operates at a central frequency of 1MHz and consists of an impulse transmitter with an output voltage up to 5000V and a digital receiver with a maximum gain of 80dB. The radar was deployed on board a CASA 212 aircraft, which also carries a laser altimeter, an inertial navigation system, a digital camera and a GPS receiver. A description of the radar system is provided, as well as preliminary results obtained at Glaciar Tyndall, Campo de Hielo Sur (Southern Patagonia Icefield), where an ice depth of 670m was reached.

Subglacial Lake CECs: Discovery and in situ survey of a privileged research site in West Antarctica

We report the discovery and on-the-ground radar mapping of a subglacial lake in Antarctica, that we have named Lake CECs (Centro de Estudios Cientificos) in honor of the institute we belong to. It is located in the central part of the West Antarctic Ice Sheet, right underneath the Institute Ice Stream and Minnesota Glacier ice divide, and has not experienced surface elevation changes during the last 10 years. The ratio between the area of the subglacial lake and that of its feeding basin is larger than those for either subglacial lakes Ellsworth or Whillans, and it has a depth comparable to that of Ellsworth and greater than that of Whillans. Its ice thickness is ∼600 m less than that over Ellsworth. The lake is very likely a system with long water residence time. The recent finding of microbial life in Lake Whillans emphasizes the potential of Subglacial Lake CECs for biological exploration.

50 MHz helicopter-borne radar data for determination of glacier thermal regime in the central Chilean Andes

Abstract Despite their importance as freshwater reservoirs for downstream river systems, few glaciers in central Chile have been comprehensively surveyed. This study presents ground-penetrating radar (GPR) and field-based observations for characterizing the englacial and basal conditions of Glaciar Olivares Alfa (33°110 S, 70°130 W), central Chilean Andes. Using a 50 MHz radar mounted onto a helicopter platform, data were collected covering large portions of the glacier accumulation and ablation zones. The radar data revealed boundaries of a temperate-ice layer at the base of the eastern body of Glaciar Olivares Alfa which appears to be covered by colder ice that extends throughout large parts of the glacier. The thickness of the temperate ice layer is highly variable across the glacier, being on average 40% of the total ice thickness. Radar data analyses reveal regions of cold ice at the bottom/base of the glacier and also patterns of highly saturated sediments beneath the glacier. Using GPR data, this study represents the most exhaustive analysis of glacier ice structure performed in the central Chilean Andes. The results will enable improved estimations of the glacier’s mass balance and ice dynamics, helping us to understand its further development and its impact on water availability.

Ice thickness surveys of the Southern Patagonian Ice Field using a low frequency ice penetrating radar system

An airborne low frequency radar system used to survey the ice thickness of the northern part of the Southern Patagonian Ice Field (SPI) is presented. The radar is an impulse system operating at a central frequency of 20 MHz. The system is controlled and operated from a helicopter cabin connected with an optical fibre cable to the antennas that are fixed to an aluminium structure weighting 350 kg that is hanging 40–50 m below the helicopter. At the antenna, there is a high-power transmitter working at a 5 kHz PRF, and a radar receiver. Also, there is a dual frequency GPS for the real-time positioning of the measurements. The survey took place in August 2015 and October 2016 while flying more than 400 kilometres of Glaciares Jorge Montt, OHiggins and the high plateau of the SPI. The system performance was adequate to survey most of the ice thicknesses, including the steep slopes and inaccessible crevassed areas. The maximum ice thickness penetration yielded 581 m of temperate ice. Several bottom reflections were obscure by englacial water and/or surface crevasses.

High resolution FM-CW radar for internal layers mapping in cold ice

A wideband ground penetrating radar was developed in order to detect internal layers in firn and shallow ice, with high resolution. Mapping of near-surface layers improves traditional snow accumulation measurements, extending the spatial and temporal coverage. This system is a frequency-modulated continuous wave (FM-CW) radar, with a transmit signal range from 203 MHz to 1019 MHz and with a power of ∼250 mW. During two over-snow field campaigns in West Antarctica plateau (January and December 2014), this radar mapped near-surface internal layers to a depth of ∼170 m, with a resolution of ∼0.15 m in ice. Future improvement includes the addition of an ultra-wideband microwave snow radar, in order to map internal layers in snow column to a depth of 10 m, with a very high resolution.

Mapping of permafrost surface and active layer properties using GPR: A comparison of frequency dependencies

Ground penetrating radar (GPR) was used to detect internal features and conditions in the active layer of Zackenberg valley in North-East Greenland. For about 16 years there has been a monitoring programme that registers the physical and biological processes in the ecosystem. We aim to improve the monitoring accuracy of the active layer development and estimated soil water content. We used two different GPR frequencies to study their performance in High-Arctic cryoturbated soils. Here we present the analysis of the signal received by quantifying the power of the signal that is reflected from the top of the permafrost and from the internal features in the unfrozen soil. These results will be further used to determine the distribution of dielectric heterogeneities to support water content estimated from the same profiles. Comparing results from 400 and 800 MHz, we found that although both frequencies are suitable to measure thickness and to detect features in the active layer, the 400 MHz gives a better impression of the influence of the dielectric contrast effect from top of the permafrost zone which can be used to quantify the soil water content.