LAKE VOSTOK AEROGEOPHYSICAL SURVEY DATA DISTRIBUTION, 26 OCT 2001 University of Texas Institute for Geophysics John A. and Katherine G. Jackson School of Geosciences The University of Texas at Austin The accompanying files are our results from the aerogeophysical surveys we conducted over Lake Vostok during 2000/2001. This work was supported by NSF/OPP grant #9911617 to UTIG. These files include profiles and maps of surface elevation, ice thickness, bed elevation, and gravity. The kinematic carrier phase GPS solutions used in the reduction of these data are also included. The first publication of any maps should list J. Holt, D. Morse, T. Richter, S. Kempf, M. Peters, and D. Blankenship as authors, in that order. Other publications using these data should suitably acknowledge these same participants as well as UTIG staff and NSF/OPP award #991167. FILE FORMAT: The surface elevation, ice thickness, bed elevation, and gravity data files have four fields on each line. The first field is UTC (not GPS) time in ztim format, e.g. "(1998, 350, 533726669)". The fields are: "(year, julian day, 10^-4 seconds)". The next two fields are easting and northing positions in meters using the "LVS" projection. The LVS projection parameters are: 4 # Lambert Conformal Conic 6378137 # Semi-major Axis (A) 6356752.3141 # Semi-minor Axis (B) -76 # First Standard Parallel (SPU) -78 # Second Standard Parallel (SPL) 105 # Center Meridian (BLON) -79 # Projection Origin (BLAT) 0 # False Easting (SHFTX) 0 # False Northing (SHFTY) 25 # Rotation (ROT) The final field is either the surface elevation, ice thickness, free air gravity, or height above the geoid. The units are meters or mgals. REGISTRATION: The positions are interpolated to the time of the observation, except for the gravity profiles. The gravity profiles are interpolated to match the positions (1 Hz or .5 Hz). All positions are WGS-84 and ITRF97. LASER/GPS REDUCTION: We correct aircraft elevations for long term drift by minimizing the laser surface elevation crossover discrepancies. The following corrections have been applied: LVS/CCx/X01a/POS_SJBb (2000, 359, 269112341) -0.235 (2000, 359, 288815566) 0.258 LVS/CCx/X02a/POS_SJBg (2001, 1, 802520107) 0.264 (2001, 1, 824565488) -0.565 LVS/CCx/X03a/POS_SJBk (2001, 2, 741238162) 0.262 (2001, 2, 761244597) -0.054 LVS/CCx/X05a/POS_SJBt (2001, 1, 834583727) 0.339 (2001, 1, 853634527) -0.220 LVS/CCx/X06a/POS_SJBh (2001, 2, 771673106) 0.301 (2001, 2, 792892120) -0.233 LVS/CCx/X08a/POS_SJBD (2000, 363, 190120978) 0.022 (2000, 363, 199041688) 0.026 LVS/CCx/X08b/POS_SJBt (2001, 2, 164143) 0.053 (2001, 2, 21605549) 0.502 LVS/CCx/X09a/POS_SJBr (2000, 362, 163641706) 0.177 (2000, 362, 184201028) -0.207 LVS/CCx/X09c/POS_SJBd (2001, 2, 802629723) 0.302 (2001, 2, 822267802) -0.453 LVS/CCx/X11a/POS_SJBr (2000, 363, 161818689) 0.086 (2000, 363, 181225321) -0.236 LVS/CCx/X12b/POS_SJBC (2000, 362, 132549308) -0.026 (2000, 362, 153230519) 0.058 LVS/CCx/X12c/POS_SJBp (2001, 2, 833027346) 0.569 (2001, 2, 853997466) -1.044 LVS/CCx/X14a/POS_SJBD (2000, 363, 130162206) 0.015 (2000, 363, 151572471) -0.051 LVS/CCx/X15a/POS_SJBr (2000, 362, 100233558) -0.062 (2000, 362, 121868409) 0.064 LVS/CCx/X16a/POS_SJBj (2000, 359, 190216177) -0.063 (2000, 359, 211635937) 0.159 LVS/CCx/X17a/POS_SJBd (2000, 363, 98311783) 0.015 (2000, 363, 118471152) -0.054 LVS/CCx/X18a/POS_SJBn (2000, 364, 139127442) -0.084 (2000, 364, 160790240) 0.040 LVS/CCx/X19a/POS_SJB2 (2000, 355, 54460433) -0.879 (2000, 355, 70238519) -0.214 LVS/CCx/X20a/POS_SJBj (2000, 362, 571179957) 0.034 (2000, 362, 591970494) -0.148 LVS/CCx/X21a/POS_SJBm (2000, 364, 170821144) 0.126 (2000, 364, 190267163) -0.211 LVS/CCx/X22a/POS_SJBe (2000, 358, 797659554) -0.180 (2000, 358, 818738347) -0.060 LVS/CCx/X23a/POS_SJBa (2000, 362, 538415749) -0.190 (2000, 362, 560443405) 0.104 LVS/CCx/X24a/POS_SJB2 (2000, 355, 19915737) -1.174 (2000, 355, 42600126) -0.060 LVS/CCx/X25a/POS_SJBb (2001, 2, 192542013) 0.285 (2001, 2, 213252908) -0.413 LVS/CCx/X26a/POS_SJB2 (2001, 3, 183735427) -0.047 (2001, 3, 204179211) -0.067 LVS/CCx/X27a/POS_SJBl (2000, 358, 764377711) 0.063 (2000, 358, 784612100) -0.141 LVS/CCx/X28a/POS_SJBa (2001, 2, 160542421) 0.316 (2001, 2, 181238219) 0.142 LVS/CCx/X29b/POS_SJBe (2001, 3, 153651898) 0.185 (2001, 3, 174194394) 0.167 LVS/CCx/X30a/POS_SJBe (2000, 359, 532144035) -0.017 (2000, 359, 552601103) 0.105 LVS/CCx/X31a/POS_SJBf (2001, 2, 128953230) -0.074 (2001, 2, 149972487) 0.392 LVS/CCx/X32a/POS_SJB0 (2001, 3, 113395294) -0.462 (2001, 3, 133803334) 0.667 LVS/CCx/X33a/POS_SJBC (2000, 359, 563621607) -0.149 (2000, 359, 584181724) 0.207 LVS/CCx/X34a/POS_SJBe (2001, 1, 675076822) 0.305 (2001, 1, 696448051) -0.193 LVS/CCx/X35a/POS_SJBs (2001, 4, 789364296) 0.374 (2001, 4, 809105009) -0.079 LVS/CCx/X36a/POS_SJBx (2000, 361, 789949343) -0.062 (2000, 361, 811342591) -0.089 LVS/CCx/X37a/POS_SJBa (2001, 1, 643342495) -0.377 (2001, 1, 664309513) 0.738 LVS/CCx/X38a/POS_SJBk (2001, 4, 757539944) 0.290 (2001, 4, 779116279) 0.009 LVS/CCx/X39a/POS_SJBy (2000, 361, 584055338) -0.254 (2000, 361, 604341348) 0.175 LVS/CCx/X40a/POS_SJBb (2001, 4, 594047674) -0.037 (2001, 4, 616969394) 0.018 LVS/CCx/X41a/POS_SJBd (2000, 361, 755919450) 0.137 (2000, 361, 776237628) -0.054 LVS/CCx/X42a/POS_SJBu (2000, 361, 131619438) 0.056 (2000, 361, 152644906) -0.070 LVS/CCx/X43a/POS_SJBf (2001, 4, 563871194) 0.013 (2001, 4, 583633071) 0.225 LVS/CCx/X44a/POS_SJBa (2001, 5, 779992321) -0.004 (2001, 5, 789124172) 0.258 LVS/CCx/X45a/POS_SJBa (2001, 5, 798939925) 0.577 (2001, 5, 808109484) -0.598 LVS/CCy/Y01a/POS_SJBw (2000, 361, 523612537) -0.041 (2000, 361, 566240051) -0.012 LVS/CCy/Y02a/POS_SJBg (2001, 4, 525497949) 0.268 (2001, 4, 547534213) -0.224 LVS/CCy/Y02b/POS_SJBt (2001, 1, 600361011) 0.146 (2001, 1, 624602529) -0.032 LVS/CCy/Y03a/POS_SJBA (2000, 359, 229419157) 0.023 (2000, 359, 254502813) -0.210 LVS/CCy/Y03b/POS_SJBd (2000, 361, 168980385) -0.035 (2000, 361, 193333438) -0.092 LVS/CCy/Y04a/POS_SJBs (2001, 6, 730634364) 0.278 (2001, 6, 773399224) 0.094 LVS/CCy/Y05a/POS_SJBu (2000, 355, 193174089) -0.230 (2000, 355, 235238585) 0.006 LVS/CCy/Y07a/POS_SJBr (2000, 355, 247001267) -0.053 (2000, 355, 295011495) -0.029 LVS/CCy/Y09a/POS_SJBB (2000, 359, 602660081) -0.338 (2000, 359, 627953984) 0.434 LVS/CCy/Y09b/POS_SJBj (2000, 362, 755643456) -0.154 (2000, 362, 797132375) 0.272 LVS/CCy/Y11a/POS_SJBr (2000, 360, 806751406) -0.006 (2000, 360, 848261451) -0.041 LVS/CCy/Y12a/POS_SJBg (2001, 6, 667266234) 0.158 (2001, 6, 709254769) 0.141 LVS/CCy/Y13a/POS_SJBi (2000, 361, 90828390) -0.076 (2000, 361, 112360187) 0.109 LVS/CCy/Y13b/POS_SJBh (2000, 364, 99180068) 0.156 (2000, 364, 123326281) -0.303 LVS/CCy/Y14a/POS_SJBf (2000, 362, 833385796) -0.050 (2000, 362, 861883439) 0.095 LVS/CCy/Y15a/POS_SJBD (2000, 360, 746737504) -0.115 (2000, 360, 787874626) 0.252 All other transects (those outside CC) have no such corrections and are of lower quality. RADAR REDUCTION: Radar ranges were determined using a manually guided, automatic signal tracking algorithm that detects the first arrival of returning energy (see Blankenship and others, 2001). For the radar surface elevation map, we have corrected the radar ranges to the laser values. This map has larger crossover errors than the laser surface, but better coverage. The bed elevation map was obtained by subtraction of the laser surface and ice thickness grids. GRAVITY REDUCTION: The free air gravity data was processed using the algorithms described in Childers (1996), with the following notes: 1. The low pass filter used on both the gravimeter and derived accelerations is the "FFT Filter" of (cosine taper applied to the signal's FFT) described by Childers (1996). Filter parameters were set so that the filter attenuates the signal to zero at 0.006 Hz and the transition width is 0.006 Hz. 2. Corrections for gravimeter platform tilt (Swain, 1996) were implemented as in Childers (1996). 3. The formula for theoretical gravity (latitude correction) used in the processing is a truncated version of the series for the gravity formula of the Geodetic Reference System 1980 (GRS80). (theo_g = 978032.67715 * (1 + 0.0052790414 * sin_lat.^2 + 0.0000232718 * sin_lat.^4). 4. The gravity data time stamps were advanced 4.9 seconds in processing to correct for output delays in the gravimeter. This time was determined to best match gravimeter accelerations to the GPS derived accelerations. MISSING PROFILES: The following transects have not been reduced for the reason given: LVS/CCx/X04a/f_las_srfelv - laser malfunction LVS/CCx/X07a/f_las_srfelv - laser malfunction LVS/CCx/X10a/f_las_srfelv - laser malfunction LVS/CCx/X13a/f_las_srfelv - laser malfunction LVS/CCx/X29a - short transect, reflown as LVS/CCx/X29a LVS/CCx/X08a/f_grvfld - aborted in flight LVS/CCy/Y09a/f_grvfld - reflown as LVS/CCy/Y09b LVS/ECx/X37b/f_grvfld - unusable due to aircraft motion In addition, we have excluded the following gravity profiles from the final grid based on their comparatively large crossover discrepancies: LVS/CCx/X24a/POS_SJB2 LVS/CCx/X19a/POS_SJB2 LVS/CCy/Y02b/POS_SJBt LVS/CCy/Y03a/POS_SJBA LVS/CCy/Y02a/POS_SJBg LVS/CCy/Y13a/POS_SJBi CROSSOVER ANALYSES: The RMS of the x vs. y deviations for the laser surface elevation is 0.107 m. The RMS of the x vs. y deviations for the radar surface elevation is 3.6 m. The RMS of the x vs. y deviations for the ice thickness is 39.83 m. The RMS of the x vs. y deviations for the gravity field is 6.461 mgal. GRIDDING: All grids are made from the provided profiles. The grid spacing is .6 km. A tensioned surface (.35) is fit through the data, then a 7.5 km guasian filter as implemented in GMT is applied. REFERENCES: Blankenship, D.D., D.L Morse, C.A. Finn, R.E. Bell , M.E. Peters, S.D. Kempf, S.M. Hodge, M. Studinger, J.C. Behrendt, and J.M. Brozena. Geological controls on the initiation of rapid basal motion for West Antarctic ice streams: A geophysical perspective including new airborne radar sounding and laser altimetry results. In Alley, R.B. and R.A. Bindschadler eds., The West Antarctic Ice Sheet: Behavior and Environment, American Geophysical Union, p. 105-121, 2001. Childers, V.A., Gravimetry as a geophysical tool: airborne gravimetry and studies of lithospheric faulting and flexure. Doctoral Thesis, Columbia University, 1996. Swain, C.J., Horizontal accleration corrections in airborne gravimetry. Geophysics, 61, 273-276, 1996.