Archive of Boomer Seismic Reflection Data, collected on USGS Cruise 99ASR01, Lake Okeechobee, Florida, 29 June - 30 June, 1999.

Seismic reflection profiles are acquired by means of an acoustic source (usually generated electronically), and a hydrophone or hydrophone array. Both elements are typically towed in the water behind a survey vessel. The sound source emits a short acoustic pulse, which propagates through the water and sediment columns. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), and detected at the hydrophone. This process is repeated at intervals ranging between 100 ms and 1 s depending on the source type. In this way a two-dimensional image of the geologic structure beneath the ship track is constructed. Seismic data are stored in SEG-Y format, which is a standard digital format that can be read and manipulated by most seismic-processing software packages. The SEG-Y file format includes a 3200-byte descriptive header that contains detailed information regarding the data acquisition and processing parameters. All data presented here are stored in SEG-Y, Integer, Motorola format. The SEG-Y formatted trace data files have a .tra extension. Additional recording parameters for each seismic data file can also be found in the .par file associated with each .tra file. However, the .par files and the cent_rmc.pln file are only needed to replay the data with Triton Elics Delph Seismic software. The seismic energy source employed here was a boomer transducer towed on a sled at the lake surface providing 200 joules per shot. The reflected energy was received by an Innovative Transducer Inc. (ITI) solid core streamer and recorded by PC-based Triton Elics Delph Seismic acquisition software. The ITI streamer contains 10 hydrophones evenly spaced over 6 meters, however only data received by elements 5-8 where summed, resulting in a higher signal to noise ratio for the data. The streamer was positioned parallel to the boomer sled and laterally separated from it by 7 m. The sled was towed 20 m behind the Global Positioning System (GPS) antennae. The sample frequency of the data was 16000 Hz and the total record length was 200 ms for tracklines oke699_1 to oke699_7 and 300 ms for tracklines oke699_8 to oke69911. The fire rate was every 0.5 s, which resulted in a shot spacing of about 1 m based on survey speeds of 3.5-4 knots. GPS navigation was provided by a Trimble Centurian P-Code receiver directly fed to the acquisition system. The shotpoint navigation provided in this report has not been corrected to reflect the 20 m offset of the source to the GPS antenna. The horizontal accuracy of the navigation data was within 31m. The navigation data are stored as flat ASCII files. The raw navigation files were generated by the Delph Seismic Software for each trackline and provide the following information for each unique position fix, all separated by commas: shotpoint number, longitude, latitude, heading, speed, date, and Greenwich Mean Time(GMT). The edited navigation file contains all the unique fixes for each trackline with spurious points removed. A separate file containing edited navigation for every 500th shotpoint interval is also provided. Both the edited navigation and the 500th shotpoint navigation files contain six fields separated by commas: shotpoint number, date, GMT, longitude, latitude, and the trackline number. This navigation data can be used to plot trackline maps of the seismic profiles at any scale or map projection desired. The trackline map provided on this disc is a Mercator projection and was created with ESRI's GIS software ArcView 3.2. The map was then exported to Adobe Illustrator and saved as a GIF image. This GIF image is viewable with your WWW browser.