Comparison of realtime nav and post processed nav SIOSEIS has a new (October 2000) geometry option, type 9, that computes the shot to shot distance or DFLS (distance from last shot) on each shot using the latitude and longitude in the SEG-Y trace header. (32 bit integer, words 19 and 20 are the x and y coordinates, which are also the seconds of arc longitude and latitude scaled by the scalar in SEG-Y 16 bit integer word 36). SIOSEIS process SEGDIN honors the LDEO "nav block" which is written in the SEG-D extended header. When using the LDEO "shooting by distance" algorithm, the time and position of the next shot are predicted. On the Blake Ridge cruise, the Fugro differential Trimble 4000 was used for the GPS position. While the Fugro was sampling every second, the LDEO system only save every tenth (10th) fix. Ten GPS samples (or the tenth?) sample was somehow used to determine the ship's speed and the Furuno's course was used to PREDICT when the next shot would be 37.5 meters from the previous. The predicted time was then used to issue a command to fire the guns and trigger the Syntron recording system. A new undocumented change was made sometime before the Blake cruise where a GPS clock was added to the Syntron recording system. While this clock is part of the Syntron, it is not used by the Syntron and is mearly a replacement of "Joe's" true-time clock. This clock is the "official shot time". The Syntron cpu clock is used in the SEG-D header, but is ignored by SIOSEIS. SEGDIN uses "Joe's" clock in the SEG-Y trace header. The SEG-Y shot time was checked against the LDEO post processed shot time and is identical. SIOSEIS process SEGDIN honors the LDEO "nav block" which is written in the SEG-D extended header. The position is converted to seconds of arc and scaled (multiplied) by 10. to preserve resolution. Geom type 9 computes the distance from last shot (DFLS) using these predicted positions. LDEO produces a daily file with the shot point number, shot time, and ship's GPS antenna position for each shot. The algorithm used to compute these locations is documented on the Ewing web page. A much longer time period is used to calculate the shot point (GPS antenna) with some "future" positions included. ******************************************************************* ************** RECOMMENDATION *********************** ******************************************************************* TS.N FILES SHOULD BE USED FOR POST-PROCESSING NAVIGATION AND BINNING. Both type 6 and type 9 geometry honor the differences of distance in latitude and longitude according to Nathaniel Bowditch's "American Practical Navigator", Vol II., 1981, page 5. The SIOSEIS DFLS (distance from last shot) variable was computed and compared on one 3490 tape with 120 shots (~.5 hours). DFLS is a 2-D variable. It is a radius of a circle. DFLS = SQRT(delta_lat**2 + delta_long**2) geom type 6 geom type 9 (ts.n file) (nav block) shot 157247 dfls 37.5265 37.8069 shot 157248 dfls 37.3292 37.2644 shot 157249 dfls 37.3292 37.5041 shot 157250 dfls 37.4823 37.5041 shot 157251 dfls 37.4823 37.5041 shot 157252 dfls 37.5265 37.2644 shot 157253 dfls 37.5501 37.8069 shot 157254 dfls 37.3966 37.3809 shot 157255 dfls 37.2431 37.3809 shot 157256 dfls 37.5924 37.2644 shot 157257 dfls 37.3966 37.2644 shot 157258 dfls 37.3550 37.6917 shot 157259 dfls 37.5501 37.5831 shot 157260 dfls 37.3966 37.0798 shot 157261 dfls 37.5087 37.8069 shot 157262 dfls 37.4285 37.0516 shot 157263 dfls 37.5826 37.4813 shot 157264 dfls 37.6221 37.9287 shot 157265 dfls 37.4285 37.2644 shot 157266 dfls 37.4682 37.6917 shot 157267 dfls 37.3550 37.4813 shot 157268 dfls 37.6624 37.6917 shot 157269 dfls 37.3143 37.1546 shot 157270 dfls 37.7037 37.7701 shot 157271 dfls 37.2857 37.0798 shot 157272 dfls 37.5924 38.2331 shot 157273 dfls 37.2857 37.2644 shot 157274 dfls 37.4390 36.8374 shot 157275 dfls 37.5924 37.8069 shot 157276 dfls 37.5924 37.5041 shot 157277 dfls 37.5924 37.3809 shot 157278 dfls 37.5501 37.8069 shot 157279 dfls 37.4823 37.5831 shot 157280 dfls 37.2857 37.0798 shot 157281 dfls 37.4823 37.9287 shot 157282 dfls 37.4390 36.9552 shot 157283 dfls 37.6355 37.6917 shot 157284 dfls 37.3735 37.6917 shot 157285 dfls 37.4823 37.5041 shot 157286 dfls 37.4823 37.6338 shot 157287 dfls 37.3292 36.9552 shot 157288 dfls 37.7458 37.8069 shot 157289 dfls 37.3966 37.4813 shot 157290 dfls 37.5924 37.5041 shot 157291 dfls 37.3966 37.5041 shot 157292 dfls 37.5265 37.3809 shot 157293 dfls 37.6795 37.6917 shot 157294 dfls 37.2660 37.2644 shot 157295 dfls 37.5265 37.6338 shot 157296 dfls 37.6174 37.3489 shot 157297 dfls 37.5117 37.8013 shot 157298 dfls 37.5595 37.7701 shot 157299 dfls 37.3593 37.2644 shot 157300 dfls 37.7117 37.5041 shot 157301 dfls 37.5265 37.9287 shot 157302 dfls 37.3735 37.0798 shot 157303 dfls 37.6795 37.3809 shot 157304 dfls 37.5715 38.2331 shot 157305 dfls 37.4187 37.0798 shot 157306 dfls 37.9122 37.9287 shot 157307 dfls 37.6641 37.3489 shot 157308 dfls 37.7117 38.0570 shot 157309 dfls 37.4073 37.3489 shot 157310 dfls 37.7079 37.7701 shot 157311 dfls 37.7079 37.2111 shot 157312 dfls 37.6576 38.0570 shot 157313 dfls 37.2024 37.4933 shot 157314 dfls 37.3541 37.2266 shot 157315 dfls 37.6576 37.2111 shot 157316 dfls 38.2083 37.9287 shot 157317 dfls 37.3541 37.6338 shot 157318 dfls 38.3781 37.2266 shot 157319 dfls 37.5563 37.4933 shot 157320 dfls 37.4048 37.6338 shot 157321 dfls 37.5058 37.6338 shot 157322 dfls 37.5563 37.3489 shot 157323 dfls 37.1019 37.6441 shot 157324 dfls 37.2533 36.9280 shot 157325 dfls 37.3051 37.3489 shot 157326 dfls 37.4563 37.6338 shot 157327 dfls 37.3051 37.2266 shot 157328 dfls 37.3577 37.2266 shot 157329 dfls 37.4111 37.6441 shot 157330 dfls 37.5619 37.3489 shot 157331 dfls 37.5619 37.3489 shot 157332 dfls 37.3702 37.9129 shot 157333 dfls 37.4263 37.2266 shot 157334 dfls 37.3702 37.5508 shot 157335 dfls 37.4263 36.9703 shot 157336 dfls 37.5058 37.7701 shot 157337 dfls 37.3042 37.3489 shot 157338 dfls 37.4073 37.0798 shot 157339 dfls 37.4561 37.9287 shot 157340 dfls 37.4561 36.9280 shot 157341 dfls 37.4561 37.6338 shot 157342 dfls 37.6081 37.6338 shot 157343 dfls 37.4561 37.2111 shot 157344 dfls 37.6081 37.6441 shot 157345 dfls 37.6081 37.6338 shot 157346 dfls 37.4561 37.5041 shot 157347 dfls 37.6576 37.6338 shot 157348 dfls 37.4561 37.4933 shot 157349 dfls 37.7079 37.7701 shot 157350 dfls 37.3541 37.3489 shot 157351 dfls 37.7079 37.5041 shot 157352 dfls 37.3541 37.4933 shot 157353 dfls 37.4073 37.6441 shot 157354 dfls 37.5117 37.2111 shot 157355 dfls 37.5117 37.3809 shot 157356 dfls 37.7117 38.0570 shot 157357 dfls 37.4648 37.0798 shot 157358 dfls 37.5715 38.0570 shot 157359 dfls 37.5715 37.6338 shot 157360 dfls 37.4648 37.3809 shot 157361 dfls 37.4187 36.9552 shot 157362 dfls 37.6641 38.0570 shot 157363 dfls 37.4648 37.0798 shot 157364 dfls 37.6641 37.6338 shot 157365 dfls 37.6641 38.0570Return to EW0008 example. 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