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BACKGROUND

This archive consists of two-dimensional marine seismic reflection profile data collected in canals in the Miami, Florida area. This data was acquired in November and December of 2001 and January and February of 2002 using a 4.9-meter (16-foot) jonboat. These data are available in a variety of formats, including binary, ASCII, HTML, shapefiles, and GIF images. Binary data are in SEG-Y format and may be downloaded for further processing or display. Reference maps and GIF images of the profiles may be viewed with your web browser. All GIS information provided is compatible with Environmental Systems Research Institute (ESRI) software. A reconnaissance test line (02ASR02-02b02) was collected northwest of the survey area during Field Activity 02ASR02 for possible use in a future project. It is archived here for organizational purposes only.

Purpose:
Marine seismic reflection data is used to image and map sedimentary and structural features of the seafloor and subsurface. These data are useful in mapping stratigraphy and in assessing other submarine geologic characteristics and features. These data were collected as part of a larger Aquifer Storage and Recovery and Leaky Coastal Margins project done in cooperation with the South Florida Water Management District.

Supplemental Information:
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 milliseconds and 1 second depending on the source type. In this way, a two-dimensional image of the geologic structure beneath the ship track is constructed.

Seismic data were stored in SEG-Y format (Barry et al., 1975), 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 is stored in SEG-Y, Integer, Motorola format. The SEG-Y data files are too large to fit on one CD-ROM, so they have been distributed onto two CD-ROMs, with the SEG-Y data files for Field Activities 01ASR01 and 01ASR02 on Disc 1 and the SEG-Y data files for Field Activities 02ASR01 and 02ASR02 on Disc 2. The SEG-Y formatted trace data files are located in the SEGY folder located at the top level of these CD-ROMs and 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 UTM_401_1.pln file are only needed to replay the data with Triton Elics Delph Seismic software. Note: The web version of this archive does not contain the SEG-Y Trace files. These files are very large and would require extremely long download times. To obtain the complete CD-ROM archive, contact USGS Information at (888) ASK-USGS.

For Field Activity 01ASR01, the seismic source employed consisted of a boomer transducer towed on a sled at the sea surface providing 100 joules per shot. The reflected energy was received by an SN Technologies NexGen solid core streamer and recorded by PC-based Triton Elics Delph Seismic acquisition software. The streamer contains 10 hydrophones evenly spaced every 2 meters. Only data received by elements 7 and 8 were summed for line 01b01 and for line 01b02 through shot number 2,819. Afterward, only data received by elements 8 and 9 were summed. The streamer was positioned parallel to the boomer sled and laterally separated from it by approximately 3 meters. The sled was towed approximately 5 meters behind the GPS antenna. The sample frequency of the data was 12 kilohertz, and the total record length was 100 milliseconds. The fire rate was every 0.5 seconds, which resulted in a shot spacing of about 0.64 meters.

For Field Activity 01ASR02, the seismic source employed consisted of a boomer transducer towed on a sled at the sea surface providing 280 joules per shot. The reflected energy was received by an SN Technologies NexGen solid core streamer and recorded by PC-based Triton Elics Delph Seismic acquisition software. The streamer contains 10 hydrophones evenly spaced every 2 meters. Only data received by elements 8 and 9 were summed for line 01b01 through shot number 8,903.  Afterward, data received by element 10 was also summed. The streamer was positioned parallel to the boomer sled and laterally separated from it by approximately 3 meters. The sled was towed approximately 5 meters behind the GPS antenna. The sample frequency of the data was 24 kilohertz, and the total record length was 100 milliseconds. The fire rate was every 0.5 seconds, which resulted in a shot spacing of about 0.64 meters.

For Field Activity 02ASR01, the seismic source employed consisted of a boomer transducer towed on a sled at the sea surface providing 280 joules per shot. The reflected energy was received by an SN Technologies NexGen solid core streamer and recorded by PC-based Triton Elics Delph Seismic acquisition software. The streamer contains 10 hydrophones evenly spaced every 2 meters. Only data received by elements 8, 9, and 10 were summed for line 02b01 and for line 02b02 through shot number 1,748. Only data received by elements 5, 6, and 7 were summed for line 02b02 between shot numbers 1,750 and 2,828. For the rest of line 02b02 and for all other lines, only data received by elements 4, 5, and 6 were summed. The streamer was positioned parallel to the boomer sled and laterally separated from it by approximately 3 meters. The sled was towed approximately 5 meters behind the GPS antenna. The sample frequency of the data was 12 kilohertz for line 02b01 and 24 kilohertz for all other lines. The total record length was 100 milliseconds. The fire rate was every 0.5 seconds, which resulted in a shot spacing with a range of about 0.46 to 0.64 meters.

For Field Activity 02ASR02, the seismic source employed consisted of a boomer transducer towed on a sled at the sea surface providing 280 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 streamer contains 10 hydrophones evenly spaced about every 0.6 meters (2 feet). However, only data received by elements 3 and 4 were summed. The streamer was positioned parallel to the boomer sled and laterally separated from it by approximately 3.5 meters. The sled was towed approximately 5.5 meters behind the GPS antenna through shot number 8,230 of line 02b01, approximately 7.5 meters behind the antenna for the rest of line 02b01, and about 6 meters behind the antenna for line 02b02. The sample frequency of the data was 24 kilohertz, and the total record length was 100 milliseconds. The fire rate was every 0.5 seconds, which resulted in a shot spacing with a range of about 0.46 to 0.64 meters.

Differential GPS navigation was fed to the acquisition system every second by a WAAS/Beacon DGPS receiver. The accuracy of this receiver is to within 5 meters. However, the data required some editing to remove spurious fixes. These edited results were used to generate the trackline maps presented here. The navigation data has not been corrected to reflect the offset between the source and the GPS antenna. Position fixes for every 500 shots and for the start of line are also provided as an aide for registering of the data after plotting. All navigation data presented in this archive is stored as flat ASCII text files in the NAV folder located at the top level of these CD-ROMs. Edited navigation files are stored in the EDITNAV subfolder of the NAV folder, unedited navigation files are stored in the RAWNAV subfolder, and 500-shot interval files are stored in the SHOTNAV subfolder.

The trackline maps provided in this archive are in geographic projection. They were created using ESRI's GIS software ArcView 3.2, exported to Adobe Illustrator for further editing, and saved as GIF images. These GIF images are viewable with your web browser and can be found in the MAPS folder located at the top level of these CD-ROMs. The arc project and shapefiles used to create the maps are available in the ARC subfolder of the SOFTWARE folder located at the top level of Disc 2. The project is compatible with ArcView 3.x (UNIX or Windows) and ArcGIS 8.1 (Windows). The shapefiles can be viewed using the public domain software ArcExplorer 2.0 (Windows) and 4.0 (Windows, UNIX, Linux), which can be downloaded from the ESRI website at http://www.esri.com/software/arcexplorer/.

Field Activity Collection System (FACS) logs are available in both html and Rich Text format. They can be found in the FACS folder located at the top level of these CD-ROMs. Scanned GIF images of the original FACS logbooks are also provided. They can be found in the LOGBOOKS folder located at the top level of these CD-ROMs.

Also included on these CD-ROMs are Seismic Unix (SU) scripts that allow the user to strip off navigation fixes from the SEG-Y headers, along with a fix for every 500 shots. The seismic data is then converted to SU format, filtered, and gained, and GIF-formatted images of the profiles are produced. These images can then be displayed using a variety of shareware programs such as ImageMagick (UNIX or Linux) or a web browser.

A reconnaissance test line (02ASR02-02b02) was collected during Field Activity 02ASR02 for possible use in a future project. It is archived here for organizational purposes only.

DISC CONTENTS

INDEX.HTM:  a home page for viewing this report using a WWW browser

README.RTF:  a Rich Text formatted version of this page

DISCLAIM.RTF: the USGS disclaimer for this report in Rich Text format

METADATA.RTF: formal FGDC metadata for the seismic reflection data and for the associated shotpoint navigation maps in Rich Text format

FACS Folder: contains the 01ASR01, 01ASR02, 02ASR01, and 02ASR02 subfolders, each of which contains the Field Activity Collection System logs that document the field activity overview, crew, equipment, and operations in Rich Text format

LOGBOOKS Folder: contains the 01ASR01, 01ASR02, 02ASR01, and 02ASR02 subfolders, each of which contains scanned GIF images of the observer's original handwritten FACS logbook

HTML Folder: contains all HTML documents used in this report and GIF images used by the HTML hyperlinks

MAPS Folder: contains GIF images of the trackline maps

NAV Folder: contains the EDITNAV, RAWNAV, and SHOTNAV subfolders

EDITNAV Subfolder: contains edited navigation files extracted from the SEG-Y headers in ASCII text format by Field Activity ID

RAWNAV Subfolder: contains the 01ASR01, 01ASR02, 02ASR01, and 02ASR02 subfolders, each of which contains the raw navigation for each line extracted by Delph Seismic in ASCII text format

• 01ASR01 Subfolder
• 01ASR02 Subfolder
• 02ASR01 Subfolder
• 02ASR02 Subfolder