END OF SEASON FIELD REPORTS
2005-06 End of Season Field Reports
ITR/SI+AP: A Mobile Sensor Web for Polar Ice Sheet Measurements (I-188)
NSF-OPP and NASA supported
PIs: Sivaprasad Gogineni (lead), Arvin Agah, Christopher Allen, David Braaten, Costas Tsatsoulis, Victor Frost, and Glenn Prescott (University of Kansas), Ken Jezek (Ohio State University) and C. Lingle ( University of Alaska, Fairbanks)
High Resolution Ice Thickness and Plane Wave Mapping of Near-Surface Layers (I-346)
PIs: Pannirselvam Kanagaratnam (lead) and David Braaten (University of Kansas)
|Eric L. Akers (KU)||Pannirselvam Kanagaratnam (KU)|
|Torry L. Akins (KU)||Claude M. Laird (KU)|
|David A. Braaten (KU)||Jerome E. Mitchell (ECSU)|
|Allan J. delaney (CRREL)||Abdul Jabbar Mohammed (KU)|
|Prasad Gogineni (KU)||Joel C. Plummer (KU)|
|Jennifer F. Holvoet (KU)||Richard S. Stansbury (KU)|
1) Map deep snow layers and basal topography with a SAR (Synthetic Aperture Radar)/radar depth sounder with a vertical resolution of 5 m or better to characterize internal layering in deep ice and obtain ice thickness.
2) Map near-surface annual layers with an accumulation radar system to a depth of about 150 m with 10-cm vertical resolution to characterize spatial variability and longer-term accumulation rates.
3) Map near-surface snow and ice layers to a depth of about 10 m with about 3-cm vertical resolution using a plane wave radar system to characterize spatial variability and recent accumulation rates.
In an effort to characterize the history of the ice sheet in the vicinity of the planned West Antarctic Ice Sheet (WAIS) deep ice core and the WAIS Divide, to detail past glacial deformation from the deep internal layering, and to determine basal conditions (whether the bed is wet or frozen), a set of radars were deployed to map an 9-km x 25-km area. The radars deployed include: (1) a wideband, SAR/radar depth sounder that generates a linearly-swept FM chirp in the 120- to 300-MHz band for measuring ice thickness with fine resolution (< 1 m vertical) and mapping deep internal layers and basal topography; (2) an ultra - wideband accumulation radar that operates at frequencies from 0.5 to 2.0 GHz for mapping near-surface firn and ice layers with fine resolution of about 10 cm from the surface to about 100 m depth, and (3) a wideband plane wave radar operating over a frequency range of 12 - 18 GHz to detect near-surface internal firn layers with 3-cm resolution from the surface to a depth of about 10 m.
An advance group of five researchers (Akers, Akins, Kanagaratnam, Laird, and Mohammed) and cargo arrived on site on December 19, 2005, after considerable delays, due mostly to poor weather at WAIS and the backlog of flights that resulted. Telephone and internet connections were established, first via ground antennas and Iridium satellite, followed by setup of our differential GPS system for accurate logging of antenna positions. Starting December 20, 2005, three radar sleds were assembled, one for the plane wave radar and two for the SAR/radar depth sounder - one for the transmitter array and the other for the receiver antenna array. The radars were then assembled and tested, starting with a series of calibration procedures. The SAR was first deployed on December 24, 2005, and tested in bistatic mode along a straight line, stopping every 200 m, on a precisely marked 4-km flagged route set up previously using the GPS system. Unfortunately, due to the higher ice loss and/or weaker bedrock scattering in this region, SAR operation was not possible, and some adjustments to the radar were required. Because of this, the radar was operated in a narrowband mode to optimize antenna and transmit amplifier performance as well as to increase the pulse-width limited bedrock echo return power. The resulting 20-MHz bandwidth limited the vertical resolution to about 5 m. The in-situ modifications were successful and allowed mapping of the deep internal layers and bedrock topography. On December 28, the plane-wave radar was tested around the deep core site and was found to be working well.
The rest of our team arrived on December 29, allowing us to work in three groups. One group focused on the plane-wave radar operation and accompanying snow pit studies, a second group ran the modified SAR/depth sounder and accumulation radars and a third group monitored our data downloads, GPS and communications systems and worked on outreach activities from our base in the science hut. The plane-wave radar/snow pit studies were conducted between December 30, 2005, and January 8, 2006. Four snow pits were excavated to a 2-m depth at different sites in the vicinity of WAIS field camp, including at one of the shallow core sites drilled by Sowers' group. Visual stratigraphy was recorded in the 4 pits, a series of fixed-volume firn samples were collected and temperature measurements were made at regular intervals down the pit walls. The firn samples were weighed to determine density vs. depth profiles. The plane wave radar system, pulled by a Skidoo, mapped around all four pit sites so that the density measurements can be used to improve the accuracy of the layer depths provided by the radar. The mapping by the depth sounder and accumulation radars was done from December 31, 2005 - January 7, 2006. These systems were housed in a PistenBully, with the transmitter and receiver sleds pulled behind, and driven along 9 parallel lines spaced 1 km apart in an 8-km x 30-km rectangular grid. The grid was centered on the future site of the deep ice core near one end and overlapped the WAIS Divide near the other. On January 8, the two radars were used to map a 2-km x 2-km fine mesh grid centered on the deep core drill site. Grid lines were spaced every 200 m. Work was completed on January 9, 2006, when the accumulation radar was used to map near-surface snow and ice layers along two lines (20 km each) spaced roughly 200 m apart out across the WAIS Divide to an ice core drill site on the 2000/2001 ITASE traverse and back.
We wish to thank all the WAIS field camp staff, and especially Camp Manager Dave Zastrow and Mechanic Dave Anderson, for their phenomenal support. They were always willing to help out, even on Sundays and holidays. Thanks also go to Keith DePew and the Science Cargo staff, to Andy Young.