LAKE VOSTOK AEROGEOPHYSICAL SURVEY SUPPLEMENTAL GRAVITY DATA DISTRIBUTION 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 supplemental gravity results from the aerogeophysical surveys we conducted over Lake Vostok during 2000/2001. This work was supported by NSF/OPP grant #9911617 to UTIG. The files include profiles and maps of the gravity field over Lake Vostok, Antarctica. The kinematic carrier-phase GPS solutions used in the reduction of these data are also included. Use of these data in any publication should reference the following and acknowledge UTIG field personnel and NSF grant # 9911617 to UTIG: Richter, T.G., J.W. Holt, and D.D. Blankenship, Airborne Gravimetry Over The Antarctic Ice Sheet, in KIS 2001: Proceedings of the International Symposium on Kinematic Systems in Geodesy, Geomatics and Navigation, Banff, Canada, p. 576-585, 2001. Richter, T., J. Holt, D. Morse, S. Kempf, D. Blankenship and M. Peters, Airborne Gravimetry over Lake Vostok, East Antarctica, in preparation. Holt, J., D. Morse, T. Richter, S. Kempf, M. Peters, and D. Blankenship, Radioglaciology and Airborne Geophysics over subglacial Lake Vostok and Adjacent Highlands, East Antarctica, in preparation. Richter, T.G., S.D. Kempf, J.W. Holt, D.L. Morse, and D.D. Blankenship, Airborne Gravimetry and Laser Altimetry over Lake Vostok, East Antarctica, submitted to Spring Meeting of the American Geophysical Union, 2002. The first publication showing maps resulting from this survey should include in the author list J. Holt, D. Morse, T. Richter, S. Kempf, M. Peters, and D. Blankenship in that order. FILE FORMAT: The 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)" represents "1998-12-16 14:49:32.66". 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 final field is gravity, in units of mgals. 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) REGISTRATION: Values for free air gravity were calculated every 250 meters along the survey lines measured according to the projection for the survey. All positions are WGS-84 and ITRF97. GRAVITY REDUCTION: The free air gravity data was processed using some of the algorithms described in Childers (1996), with the following exceptions and notes: 1. The filtering scheme is different than described in Childers (1996) and subsequent related literature. At an intermediate reduction stage the GPS-derived accelerations were processed through an RC filter to match them to the spectral characteristics of the gravity meter data. For final filtering a moving average filter with a triweight kernel and width of 15 km was used (kernel equation w = 35*((1-d^2)^3)/32 ). The total filter frequency response can described as having attenuation starting at zero Hz with infinite attenuation at about 0.01 Hz, with the half power (0.707 amplitude) point at about 0.0035 Hz. This results in slight "under filtering," leaving some low-amplitude, high-frequency noise. Filtering inherent to the gridding process removes most of this. 2. Corrections for gravimeter platform tilt as described in Childers (1996) were not implemented; instead a first order correction for platform tilt was made by subtracting a constant fraction of the horizontal acceleration from the gravity signal. This was found empirically to be a better correction for platform tilt for this data set. 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 tie was made to the Bldg 57 marker (lat/long: -77 50.82', 166 40.92') at McMurdo station, using the value of 982,973.04 as the absolute g at Bldg 57. 5. Other minor corrections are described in Richter et al., in prep. GRAVITY PRODUCTS: There are three gravity products: unedited, edited, and leveled. The unedited products are in the directory p_grvfld and called ztim_allgrvfld. The edited products are in the same directory and called ztim_bestgrvfld. The leveled products are in the f_grvfld directory and call ztim_grvfld. Lines outside of the main grid are not leveled. GRAVITY EDITS: The following transects form the gravity data set. The range indicated in the second column shows the portion of each transect used in the gridded product. Editing was performed based on examination of intermediate data products generated during reduction or on analysis of crossovers in the grid. Profile Section(s) Used for LVS Grid (km along x coordinate) LVS/CCx/X01a/POS_SJBb all (-5 to 165) LVS/CCx/X02a/POS_SJBg all LVS/CCx/X03a/POS_SJBk all LVS/CCx/X04a/POS_SJBr -5 to 135 LVS/CCx/X05a/POS_SJBt all LVS/CCx/X06a/POS_SJBh -5 to 147 LVS/CCx/X07a/POS_SJBw all LVS/CCx/X08b/POS_SJBt all LVS/CCx/X09a/POS_SJBr 7 to 115 LVS/CCx/X09c/POS_SJBd 115 to 165 LVS/CCx/X10a/POS_SJBr -5 to 135 LVS/CCx/X11a/POS_SJBr 20 to 165 LVS/CCx/X12b/POS_SJBC -5 to 165 LVS/CCx/X12c/POS_SJBa none LVS/CCx/X13a/POS_SJBx 28 to 165 LVS/CCx/X14a/POS_SJBD all LVS/CCx/X15a/POS_SJBr 8 to 170 LVS/CCx/X16a/POS_SJBj all LVS/CCx/X17a/POS_SJBd all LVS/CCx/X18a/POS_SJBn -5 to 62, 73 to 150 LVS/CCx/X20a/POS_SJBj all LVS/CCx/X21a/POS_SJBm all LVS/CCx/X22a/POS_SJBy -5 to 147 LVS/CCx/X23a/POS_SJBa all LVS/CCx/X25a/POS_SJBb all LVS/CCx/X26a/POS_SJBk -5 to 147 LVS/CCx/X27a/POS_SJBl all LVS/CCx/X28a/POS_SJBa all LVS/CCx/X29b/POS_SJBe 10 to 165 LVS/CCx/X30a/POS_SJBe all LVS/CCx/X31a/POS_SJBf 18 to 165 LVS/CCx/X32a/POS_SJBv all LVS/CCx/X33a/POS_SJBC all LVS/CCx/X34a/POS_SJBz all LVS/CCx/X35a/POS_SJBs all LVS/CCx/X36a/POS_SJBx -5 to 60, 75 to 165 LVS/CCx/X37a/POS_SJBa all LVS/CCx/X38a/POS_SJBk all LVS/CCx/X39a/POS_SJBy all LVS/CCx/X40a/POS_SJBb -5 to 158 LVS/CCx/X41a/POS_SJBd all LVS/CCx/X42a/POS_SJBu all LVS/CCx/X43a/POS_SJBf 22 to 165 LVS/CCx/X44a/POS_SJBo -5 to 70, 85 to 147 LVS/CCx/X45a/POS_SJBa 0 to 80, 105 to 165 LVS/CCy/Y01a/POS_SJBw all (-5 to 335) LVS/CCy/Y02a/POS_SJBg 158 to 335 LVS/CCy/Y02b/POS_SJBt 22 to 158 LVS/CCy/Y03a/POS_SJBA -5 to 172 LVS/CCy/Y03b/POS_SJBd 172 to 335 LVS/CCy/Y04a/POS_SJBs all LVS/CCy/Y05a/POS_SJBu 15 to 335 LVS/CCy/Y07a/POS_SJBr all LVS/CCy/Y09a/POS_SJBr none LVS/CCy/Y09b/POS_SJBj all LVS/CCy/Y11a/POS_SJBr -5 to 275 LVS/CCy/Y12a/POS_SJBg -5 to 210, 225 to 335 LVS/CCy/Y13a/POS_SJBi 160 to 335 LVS/CCy/Y13b/POS_SJBh -5 to 160 LVS/CCy/Y14a/POS_SJBf -5 to 245, 269 to 286, 295 to 326 LVS/CCy/Y15a/POS_SJBD all LVS/ECx/X10a/POS_SJBt 140 to 165 LVS/ECx/X10b/POS_SJBv none LVS/ECx/X19a/POS_SJBa none LVS/ECx/X19b/POS_SJBt none LVS/ECx/X28a/POS_SJB0 none LVS/ECx/X28b/POS_SJBn none LVS/ECx/X37a/POS_SJBv none LVS/ECx/X37b/POS_SJBn none LVS/WCx/X10a/POS_SJBx none LVS/WCx/X10b/POS_SJBt none LVS/WCx/X19a/POS_SJBw none LVS/WCx/X19b/POS_SJBz none LVS/WCx/X28a/POS_SJBs none LVS/WCx/X28b/POS_SJBk none LVS/WCx/X37a/POS_SJBk none LVS/WCx/X37b/POS_SJBp none LVS/NCy/Y05a/POS_SJBw none LVS/NCy/Y05b/POS_SJBh none LVS/NCy/Y11a/POS_SJBw 275 to 335 LVS/NCy/Y11b/POS_SJBn none LVS/SCy/Y05a/POS_SJBt -5 to 15 LVS/SCy/Y05b/POS_SJBk none LVS/SCy/Y11a/POS_SJBs none LVS/SCy/Y11b/POS_SJBs none Linear corrections have been applied to minimize the crossover discrepancies. The intercepts are as follows: [Transect] [time_1] [shift_1] [time_2] [shift_2 – shift_1] LVS/CCx/X45a/POS_SJBa (2001, 5, 798943649) 0.396 (2001, 5, 820350278) -0.987 LVS/CCx/X44a/POS_SJBo (2001, 5, 769371447) 0.480 (2001, 5, 789120000) 1.524 LVS/CCx/X43a/POS_SJBf (2001, 4, 566694430) 0.176 (2001, 4, 583629000) -0.634 LVS/CCx/X42a/POS_SJBu (2000, 361, 131623243) 1.983 (2000, 361, 152640526) -2.730 LVS/CCx/X41a/POS_SJBd (2000, 361, 755921795) 0.468 (2000, 361, 776232078) -2.697 LVS/CCx/X40a/POS_SJBb (2001, 4, 594051739) 0.262 (2001, 4, 616964923) -1.358 LVS/CCx/X39a/POS_SJBy (2000, 361, 584057432) -1.053 (2000, 361, 604337105) 2.492 LVS/CCx/X38a/POS_SJBk (2001, 4, 757545278) -4.344 (2001, 4, 779115972) 4.329 LVS/CCx/X37a/POS_SJBa (2001, 1, 643341528) -1.788 (2001, 1, 664304805) 2.357 LVS/CCx/X36a/POS_SJBx (2000, 361, 789955811) 0.605 (2000, 361, 811337083) -0.844 LVS/CCx/X35a/POS_SJBs (2001, 4, 789368375) 2.071 (2001, 4, 809101026) -1.754 LVS/CCx/X34a/POS_SJBz (2001, 1, 675081486) 2.996 (2001, 1, 696444865) -1.715 LVS/CCx/X33a/POS_SJBC (2000, 359, 563623816) 0.054 (2000, 359, 584176053) 0.352 LVS/CCx/X32a/POS_SJBv (2001, 3, 113399342) 2.909 (2001, 3, 133800641) -0.718 LVS/CCx/X31a/POS_SJBf (2001, 2, 132051096) -0.528 (2001, 2, 149966667) -0.124 LVS/CCx/X30a/POS_SJBe (2000, 359, 532147792) 0.437 (2000, 359, 552597632) 0.396 LVS/CCx/X29b/POS_SJBe (2001, 3, 155149067) -0.715 (2001, 3, 174188987) -0.826 LVS/CCx/X28a/POS_SJBa (2001, 2, 160546301) 0.680 (2001, 2, 181235190) -0.621 LVS/CCx/X27a/POS_SJBl (2000, 358, 764379487) -0.254 (2000, 358, 784606753) 0.901 LVS/CCx/X26a/POS_SJBk (2001, 3, 185221316) 0.565 (2001, 3, 204175128) 0.105 LVS/CCx/X25a/POS_SJBb (2001, 2, 192544533) 0.807 (2001, 2, 213247436) -3.177 LVS/CCx/X23a/POS_SJBa (2000, 362, 538420290) -1.252 (2000, 362, 560439589) 0.446 LVS/CCx/X22a/POS_SJBy (2000, 358, 799156757) 1.526 (2000, 358, 818734595) -1.841 LVS/CCx/X21a/POS_SJBm (2000, 364, 170825185) 1.982 (2000, 364, 190260741) 0.604 LVS/CCx/X20a/POS_SJBj (2000, 362, 571183600) 1.182 (2000, 362, 591968481) -0.838 LVS/CCx/X18a/POS_SJBn (2000, 364, 140695857) 1.354 (2000, 364, 160786486) -0.325 LVS/CCx/X17a/POS_SJBd (2000, 363, 98315658) 1.305 (2000, 363, 118468354) -0.957 LVS/CCx/X16a/POS_SJBj (2000, 359, 190220411) 1.308 (2000, 359, 211630676) -0.801 LVS/CCx/X15a/POS_SJBr (2000, 362, 101799722) 0.257 (2000, 362, 121862297) -1.979 LVS/CCx/X14a/POS_SJBD (2000, 363, 130165270) 0.948 (2000, 363, 151568784) -0.254 LVS/CCx/X13a/POS_SJBx (2000, 358, 111650769) 0.167 (2000, 358, 127157683) -1.246 LVS/CCx/X12b/POS_SJBC (2000, 362, 132553421) -1.829 (2000, 362, 153226923) 0.268 LVS/CCx/X11a/POS_SJBr (2000, 363, 164617125) 3.532 (2000, 363, 181221341) -2.804 LVS/CCx/X10a/POS_SJBr (2000, 358, 141002703) 0.048 (2000, 358, 159308684) -1.006 LVS/CCx/X09c/POS_SJBd (2001, 2, 818028642) 0.114 (2001, 2, 822264177) 0.658 LVS/CCx/X09a/POS_SJBr (2000, 362, 165144211) -1.719 (2000, 362, 178420385) 0.975 LVS/CCx/X08b/POS_SJBt (2001, 2, 168286) 0.757 (2001, 2, 21601974) 0.143 LVS/CCx/X07a/POS_SJBw (2000, 358, 169389875) 1.098 (2000, 358, 188628780) -0.357 LVS/CCx/X06a/POS_SJBh (2001, 2, 773168947) 1.061 (2001, 2, 792888400) 0.048 LVS/CCx/X05a/POS_SJBt (2001, 1, 834585125) -0.636 (2001, 1, 853630000) 1.666 LVS/CCx/X04a/POS_SJBr (2000, 358, 201618784) 0.941 (2000, 358, 219632237) -1.054 LVS/CCx/X03a/POS_SJBk (2001, 2, 741242500) 0.260 (2001, 2, 761240250) -0.822 LVS/CCx/X02a/POS_SJBg (2001, 1, 802523623) -0.392 (2001, 1, 824562027) 0.634 LVS/CCx/X01a/POS_SJBb (2000, 359, 269115500) 2.417 (2000, 359, 288813210) -2.134 LVS/NCy/Y11a/POS_SJBw (2000, 363, 756693947) 0.289 (2000, 363, 763713243) 0.021 LVS/CCy/Y03b/POS_SJBd (2000, 361, 168978947) -0.544 (2000, 361, 188478442) 0.174 LVS/CCy/Y13a/POS_SJBi (2000, 361, 92810658) -1.706 (2000, 361, 114295513) 1.898 LVS/CCy/Y02a/POS_SJBg (2001, 4, 526449494) -1.834 (2001, 4, 547532152) 2.740 LVS/CCy/Y02b/POS_SJBt (2001, 1, 603369211) -1.773 (2001, 1, 621540811) 1.066 LVS/CCy/Y05a/POS_SJBu (2000, 355, 195116410) -1.732 (2000, 355, 235237692) 1.877 LVS/SCy/Y05a/POS_SJBt (2000, 364, 717967500) 2.008 (2000, 364, 719929872) -0.434 LVS/CCy/Y15a/POS_SJBD (2000, 360, 746734324) 0.635 (2000, 360, 789823553) -2.869 LVS/CCy/Y14a/POS_SJBf (2000, 362, 816743117) 0.239 (2000, 362, 861885797) -0.166 LVS/CCy/Y13b/POS_SJBh (2000, 364, 99179865) 0.639 (2000, 364, 120364211) -0.521 LVS/CCy/Y12a/POS_SJBg (2001, 6, 667264324) -0.014 (2001, 6, 711170513) 1.109 LVS/CCy/Y11a/POS_SJBr (2000, 360, 812777432) -1.123 (2000, 360, 848261026) 0.497 LVS/CCy/Y09b/POS_SJBj (2000, 362, 755642597) -0.736 (2000, 362, 798107143) 1.852 LVS/CCy/Y07a/POS_SJBr (2000, 355, 247001515) -2.362 (2000, 355, 295009706) 0.232 LVS/CCy/Y04a/POS_SJBs (2001, 6, 730636447) 1.060 (2001, 6, 773397051) -0.118 LVS/CCy/Y03a/POS_SJBA (2000, 359, 231507500) -0.232 (2000, 359, 254501806) 0.044 LVS/CCy/Y01a/POS_SJBw (2000, 361, 523610921) -0.775 (2000, 361, 566239487) 1.237 UNUSED PROFILES: The following gravity transects have not been reduced for the reason given: LVS/CCx/X29a - short transect, reflown as LVS/CCx/X29b LVS/CCx/X12c - redundant with and not as good as X12b LVS/CCx/X19a - GIPSY solution only, not good enough LVS/CCx/X24a - GIPSY solution only, not good enough LVS/CCy/Y09a - redundant with and not as good as Y09b CROSSOVER ANALYSES: Within the grid (CC block), the RMS crossover discrepancies for each version of the gravity data set are: unedited gravity field: 33.993 mgal edited gravity field: 2.126 mgal leveled gravity field: 1.306 mgal GRIDDING: The grid is made from the included leveled profiles. The grid spacing is 0.6 km. A tensioned surface (.35) is fit through the data, then a 7.5 km gaussian filter as implemented in GMT is applied. REFERENCES: Childers, V.A., Gravimetry as a geophysical tool: airborne gravimetry and studies of lithospheric faulting and flexure. Doctoral Thesis, Columbia University, 1996.