Radar Profiles and GPS Surveys, Black Rapids Glacier, Alaska ---AUTHOR(S): Howard Conway Department of Earth and Space Sciences University of Washington Johnson Hall Rm-070, Box 351310 4000 15th Avenue NE Seattle, WA 98195-1310 Phone: (206) 543-1190 Fax: (206) 543-0489 conway@ ess.washington.edu Charles Raymond Emeritus Professor Department of Earth and Space Sciences University of Washington Johnson Hall Rm-070, Box 351310 4000 15th Avenue NE Seattle, WA 98195-1310 Phone: (206) 543-1190 Fax: (206) 543-0489 Kenichi Matsuoka Norwegian Polar Institute Fram Centre NO-9296 Troms¿ Phone: +47 77 75 05 00 Fax: +47 77 75 05 01 kenichi.matsuoka@npolar.no ---FUNDING SOURCE AND GRANT NUMBER: Data collection on Black Rapids Glacier was funded by NSF grant 93-16807. Additional interpretation of these data was funded by NSF grant 05-20541: Collaborative Research: Polarimetric Characteristics of Radio-wave Scattering from Water Pathways within Glaciers Deduced by Laboratory Experiments and Computer Simulations. ---DATA SET OVERVIEW: I. Black Rapids Glacier, in the Alaska Range, USA is approximately 40 km long and 2.3 km wide (1_locationmap). II. Radio echo-sounding profiles collected across the upper section of the glacier from mid-May to mid-July, 1993 (2_radar profiles) were used to define the spatial pattern of ice thickness. Km-XX denotes distance from the top of the glacier III. Ice thickness data were collected using a low-frequency (2-5MHz) monopulse radar system (Gades, 1998). Reflections were stacked and bandpass filtered to reduce environmental noise. Two-way travel times were calculated by accounting for the geometry of the system. Ice-thickness data were estimated using a 2-D migration procedure and assuming a spatially-constant wave speed of 168 m ms-1. Uncertainty depth comes from uncertainty in wave speed (±2 m ms-1 or 1.2% of the ice thickness) and uncertainty in picking the two-way travel time (±0.015 ms or ±3 m). Uncertainty for 600 m thick ice is about ±11 m. Radar profiles were located between survey poles set on the glacier and positioned by GPS. Positions between poles were interpolated using a calibrated bicycle wheel odometer (for distance) and a pressure transducer (for elevation changes). Radar profiles include: 3_longKm14-Km18; longitudinal profile that starts at Km-14 and ends at Km-18. 4_crossKm14; 5MHz cross profile at km-14 on June 3, 1993; profile looking down glacier. Thick white line shows approximate depth calculated using 2-d migration and wave speed of 168 m ms-1. 5_crossKm16; 5Mhz cross profile at km-16 on June 24, 1993; profile looking down glacier (north to the left). Thick white line shows approximate depth calculated using 2-d migration and wave speed of 168 m ms-1. 6_crossKm18; 5MHz cross profile at km-18 on May 23, 1993; profile looking down glacier. Thick white line shows approximate depth calculated using 2-d migration and wave speed of 168 m ms-1. IV. Surface topography was determined primarily from kinematic GPS surveys supplemented by the pressure record from the radar profiles. These data were assimilated with USGS 1966, 1:63,350 Mt Hayes B-6 and Mt Hayes C-5 Quadrangles. Our maps were constructed using 1927 North American Datum (horizontal locations), and the National Geodetic Vertical Datum 1929 (vertical positions). Maps: The Generic Mapping Tool (GMT) package (Wessel and Smith, 1995) was used to interpolate surface elevation (7_surfacemap). Contour intervals are 25 m. Ice thickness (8_icethickness) data to a grid 2 sec longitude by 20 sec latitude. Contour intervals are 100 m. Ice thickness data are dense (spacing ~15 m) along the transverse radar profiles, but sparse (spacing ~1000m) along the direction of ice flow. From Km-14 to Km-20, ice thickness data are more dense in the north-south direction and less dense in the east-west direction (2_radar profiles). The opposite is true for the upper section of the glacier; contours in the upper section of the glacier are less accurate near the edges. Bed topography (9_bedmap) was calculated by subtracting the ice thickness from surface topography. Contour intervals are 100 m. Basal hydraulic potential (10_hydraulicpotential) was calculated from the bed topography and the surface topography. Contour intervals are 1 bar. V. Additional information about the measurements is given in the 1998 PhD thesis of Anthony Gades (11_GadesPhD1998). Additional information about interpretation of basal reflectivity is given in a paper that is in review with Journal of Glaciology (12_Gades and others2011). ---INSTRUMENT DESCRIPTION: Radio Echo Sounder: 2 MHz center frequency, resistively-loaded dipole antennae, _ 1 Kv balanced impulse transmitters (Weertman, 1993) and commercial calibrated digital-recording Tektronix 222 oscilloscopes with no pre-amplifiers for receiving and recording. Global Positioning System (GPS) receivers, a calibrated bicycle wheel odometer (for distance) and a pressure transducer (for elevation changes). ---DATA COLLECTION and PROCESSING: -Description of data collection -Description of derived parameters and processing techniques used -Description of quality control procedures -Data intercomparisons, if applicable ---DATA FORMAT: -PDF radar profiles and cross tracks, location map, surface map, ice thickness figure, bedmap figure, hydraulic potential figure ---DATA REMARKS: See: 12_Gades and others2011.pdf Radio echo probing of Black Rapids Glacier, Alaska during onset of melting and spring speedup Anthony M. GADES, Charles F. RAYMOND, Howard CONWAY REVISION: October 15, 2011 ---REFERENCES: B. E. Barrett, T. Murray, R. Clark and K. Matsuoka. "Distribution and character of water in a surge-type glacier, revealed by multi-frequency and multi-polarization ground-penetrating radar," Journal of Geophysical Research, Earth Surface, v.113, 2008, p. F04011. K. Matsuoka and H.P. Marshall. "Laboratory/numerical Experiments of Radar Scattering: Towards Interpreting the Shape of Subsurface Targets (INVITED TALK)," Eos Trans. AGU Fall Meet. Suppl., v.88, 2007. Matsuoka, Thrsteinsson, Bjornsson, and Waddington. "Anisotropic radio-wave scattering from englacial water regimes, Myrdalsjokull, Iceland," Jorunal of Glaciology, v.53, 2007, p. 473.